Final Report for SW05-091
The yield and quality of a potato crop are the result of complex interactions amongst crop nutrition, cultural practices, and pest damage. In this project we developed a participatory process to share knowledge, experience, and farmer innovation; to illuminate new strategies for farmer-identified problems in whole farm systems; and to enhance their adoption and adaptation. This project piloted a participatory approach to learning and adaptation of novel farming systems strategies, evaluate the effects of soil and crop management on tuber insect pests and diseases, weeds, nitrogen availability, and profitability, and extended project findings to a larger audience of farmers
1. Pilot a participatory approach to learning and adaptation of novel farming systems strategies.
2. Evaluate the effects of soil management on tuber insect pests and diseases, weeds, nitrogen availability, and profitability.
3. Extend project findings to a larger audience of farmers.
Potatoes are an important crop for diversified organic farmers in western OR/WA; little is known about organic potato yields in this region, but potato yields have been reported to be lower than conventional in other regions (Varis et al 1996). It is not clear which factors are responsible for relatively low yield of organic potatoes; in some cases low yields were attributed to insect pest damage (Seamans et al, 2003) or diseases (Varis et al, 1996), but in other cases the primary cause of low yield was unknown. The yield and quality of a potato crop is the result of complex interactions amongst nutrition, pests, germplasm, and cultural practices; these interactions vary by region and farm.
In western Oregon and Washington, tuber and western flea beetle and wireworms significantly impact tuber quality, reducing the viability of potato production in this region. The most important disease is late blight, due to the very wet spring and fall weather and the lack of organic control strategies other than copper fungicides, which most diversified organic farmers in this region do not wish to apply. Another potential yield reducing variable is N supply during critical yield determining periods in crop development; organic systems in some cases do not provide enough demand, reducing yield (Gaskell et al, 2000). In this project, we endeavored to work on improving organic potato production through an integrated suite of on-farm and participatory research and education activities focused on pest and nutrient management, along with best cultural management, in organic potato production.
PEST MANAGEMENT: Early on in the first year of the project, after a number of discussions with the participant growers, regional potato experts, and some preliminary sampling on project farms, it was determined that the most likely insect pest groups were flea beetles and wireworms (click beetles as adults). We discussed disease management issues with the farmer group, and determined that late blight was the primary challenge for the group. We decided to begin by learning from outcomes of the European BlightMOP project (http://www.ncl.ac.uk/tcoa/producers/research/blightmop/), which led us to learn about and evaluate late blight resistant germplasm, cultural practices, and copper fungicides.
A concern for the small organic farm is the need to make fertilizer decisions for a range of crops in a system that relies on large amounts of organic matter contributions where fertilizer recommendations have not been calibrated. Fertilizer guides are typically made for certain crops in specific locations and extrapolating the results to fit different scenarios is not advised. However, knowing the soil N contribution to crop N uptake could improve recommendations by creating a baseline for applying additional fertilizer.
Organic farms generally supply large amounts of organic matter to their soils through composts and cover cropping. Over time, these additions increase the size of the active pool of soil organic matter (Marriott and Wander, 2006) and could change the amount of N from mineralization that should be budgeted for. Estimating the contribution of soil N to these systems could lead to more efficient use of N, minimizing risks to the environment and lowering production costs (Jarvis et al., 1996; Rice and Havlin, 1994). Increased information on the contribution of soil N to the crop could be useful to these growers since their nutrient management programs are driven by soil N mineralization. If soil N mineralization is high the amount of fertilizer that is recommended could be in excess.
Specific information relating N mineralization from soil to organic agriculture is not available. Extension bulletin PNW 513 Nitrogen Uptake and Utilization by Pacific Northwest Crops (Sullivan et al., 1999) estimates that the soil N supply from mineralization in the Willamette Valley, OR commonly ranges from 50 to 130 kg N ha-1 depending on soil type and crop management practices. A common recommendation states that N mineralization estimates can be made by assuming that approximately 2% of the total organic N in the surface foot of soil is mineralized annually (Brady and Weil, 1999; Schepers and Mosier, 1991) and that the uncertainty associated with this estimate is 25 to 50% (Schepers and Mosier, 1991). This estimate could double with irrigation bringing favorable moisture conditions, or a history of adding crop residues that increase the soil organic matter content and enlarge the pool of readily decomposable plant material compared with the more recalcitrant pool of soil organic matter (Schepers and Mosier, 1991). A situation likely encountered on the study farms.
One of the best field-based approaches to estimating N mineralization is using a recently unfertilized crop as a bioassay of N mineralization (Schepers and Meisinger, 1994). Field methods capture the variability of field conditions including farming management practices, soil moisture and temperature, and the rooting depth of the crop. Potatoes have been used as a field bioassay of soil N supply (Zebarth, 2005b).
Fertilizer trials generally include a nutrient control plot were the contribution of N by the soil is estimated in absence of fertilizer N applications. Usually in these plots, P and K are added to assume no other plant growth limitations. In Canada, Zebarth (2005a) observed in ‘Russet Burbank’ potato a N uptake of 91, 60, and 73 kg ha-1 in 2000, 2001, and 2002. Riley (2000) on sandy soils in Norway, observed N uptake values of 46 kg ha-1 by ‘Rutt’ potato, an early maturing cultivar. Trehan (2006), in India, observed a N uptake of 122 kg ha-1 as an average of 11 cultivars of potato following a green manure crop of Sesbania sp., and 51 kg ha-1 without the green manure crop. Lorenz (1944 and 1947), in California, observed N uptake values of 71 and 67 kg ha-1 in 1942 and 1945 for ‘White Rose’ potato. Dyson and Watson (1971) at the Rothamsted experiment station in England found that ‘King Edward’ potato contained a total of 50 and 90 kg N ha-1 in 1963 and 1964. Millard and Marshall (1986) found that ‘Maris Piper’ potato contained 80 and 60 kg N ha-1 in 1983 and 1984 in 100 days after emergence. Vos (1997) growing ‘Prominent’ and ‘Vebeca’ potatoes in the Netherlands, found an average of 110, 55, 55, 75, and 55 kg N ha-1 in years 1988, 1989, 1990, 1992, and 1993. Overall, the amount of N taken up by the potato plant in N control plots is variable from year to year probably due to climatic and environmental conditions affecting N mineralization and losses of N from the system.
Recommendations for fertilizer N rates to obtain optimal potato yields vary. The Extension Service publication Potato Nutrient Management for Central Washington (Lang et al., 1999) gives fertilizer N recommendations based on yield goals and residual soil test N which includes NO3-N and NH4-N. With a soil test N value of 0, they recommendation applying 220, 280, 340, and 390 kg N ha-1 to achieve yields of 45, 60, 70, and 80 Mg ha-1 respectively. For every 10 ppm increase in soil test N the N application rate decreases by 20 % from the 0 ppm value.
Petiole sampling can provide a grower with an in-season method to ascertain whether or not to supply addition N fertilizer to obtain desired yields, as top dressing with N fertilizer has been shown to maintain petiole nitrate (petiole N) during tuber bulking (Gardner and Jones, 1975). Petiole nitrate values generally start high at the beginning of the season and decline with growth (Gardner and Jones, 1975; Lewis and Love, 1994; Meyer and Marcum, 1998; Wescott et al., 1991), therefore sampling petioles more than once during the growing season is recommended (Gardner and Jones, 1975). A monitoring program is suggested due the variability in values from one site to the next and in order to measure the actual effects of soil N availability during growth (Wescott et al., 1991).
On-farm N monitoring was conducted by this project to assist organic farmers in making fertilization decisions. Specifically, monitoring was conducted to: (i) Evaluate the balance between N supplied and N utilized by a potato crop under a variety of organic management regimes, (ii) determine the most reliable methods for assessing crop N status within our organic farming systems, (iii) develop typical system values (N inputs and N outputs) for organic potato production under our growing conditions and grower management goals.
A. INSECT PEST MANAGEMENT:
First year insect management objectives:
1. Determine the main pest species present and their phenologies
2. Develop sampling and diagnostic methods
3. Assess extent of tuber damage by these species
4. Recommend and discuss management approach
- diagnosis/management fact sheets
- develop hypotheses and activities for year 2
Second year insect management objectives:
1. Multi-farm experiments looking at the effects of mulching, hilling and nematodes on reducing flea beetle damage to tubers
5 Produce a diagnosis/management fact sheet for flea beetles
6 Produce a handbook for wireworm management
7 Investigate where flea beetle overwintering sources are and observe how quickly they move to and build up in the potato fields
8 Continue to monitor for the presence of the 2 extra-evil wireworm species
9 Assess insect damage differences among varieties
10 Look at the effect of planting date on flea beetle tuber damage
First year methods:
Five farms were intensively sampled for the incidence, arrival/movement patterns, and damage levels of the species in these two pest groups throughout the course of the potato growing season in this year.
Second year methods:
After discussing the 2006 season data during the December 2006 project meeting, the growers voted on priorities for insect potato pest management for the 2007 growing season. The strategies they were most interested to investigate in on-farm experiments were entomopathogenic nematodes, and covering the base of the potato plants with soil or a mulch to prevent oviposition. It was also agreed that we would monitor tuber flea beetle overwintering sources and how far and how quickly they move to potato fields that were planted on different dates. They were also interested in differences in insect damage among various available varieties, and so these differences were assessed for flea beetle and wireworm damage.
Insect Management: Materials and Methods
Experiments with replicated blocks of treatments were performed at 5 of the project farms. Finely chopped barley straw mulch and nematodes were tested at SHF, GTF, 47th and PF, chopped leaf mulch was tested at SHF and GTF, and extra high hilling at the base of the plants was tested at WGF.
Mulching and high hilling was completed within a week after the first overwintering tuber flea beetles were seen, so that the base of the plants would be covered by the time these beetles had mated and were ready to lay eggs for the next generation. Mulches were at least 3” high at the base of the plants, and the extra high hills were twice as high as the normal hills, covering much of the base of the plants. Mulches were applied with a compost spreader at SHF and GTF, and by hand at PF and 47th.
Two species of nematodes (Steinernema carpocapsae and Heterhabditis bacteriophora) purchased from Biologic Company were applied by watering can at a rate of 45.3 million infective juveniles per acre on two occasions starting at least one month after planting (so that we could see if the they could affect at least partially-established flea beetle larval populations). Soil samples from nematode plots and a nearby control plot were taken on two occasions at the end of the season, and used for a bioassay with sentinel waxworm larvae in the lab to see if nematode-treated plots contained viable nematodes.
Plots were 150 square feet in size, replicated four times, and replicated control plots of the same size were set up as well. Plots were placed on the edges of the fields to maximize the chance for flea beetle infestation, and flea beetle adults were monitored in each plot on a weekly basis to keep track of the potential for differential flea beetle pressure in each plot/treatment.
Tuber damage was assessed once at 90 DAP (days after planting) and once at 105 DAP, covering most of the normal range of harvest dates, and allowing a comparison of the potential effect of additional damage in control plots if tubers are left in the ground longer. Tubers were rated for tuber flea beetle damage.
In addition to the experiments, the timing of emergence of tuber flea beetles from potential overwintering sources on each farm was monitored by sweeping and yellow sticky traps in winter/early spring potato fields, patches of solanaceous weeds, and cull piles/volunteers.
B. LATE BLIGHT (LB) MANAGEMENT
1. Teach farmers LB diagnostic techniques and encourage them to adopt LB best cultural management strategies (destroy culls, keep foliage dry, irrigate in early morning, etc)
2. Identify LB resistant potato cultivars and evaluate their productivity and marketability in western OR/WA on-farm environmental conditions and markets
3. Evaluate efficacy of copper fungicides and other materials for LB management
Diagnostics and cultural management. We gave presentations on LB diagnosis, disease cycle, and cultural and chemical management strategies at every winter meeting. Farm fields were scouted for LB and any other diseases. We visited farms with a history of LB problems during the growing season to demonstrate LB diagnosis and identify practices that might be contributing to LB disease development.
Resistant varieties: We identified and obtained seed for available LB resistant potato germplasm. Ospud identified 3 commercially available LB resistant cultivars in 2006: Island Sunshine (IS), Jacqueline Lee (JL), and Defender. Ozette, a PNW Slow Food potato clone, is also reported to be resistant to foliar LB (Vales/Yilma OSU potato LB clonal evaluations). These were grown in non-replicated trials on 5 cooperating farms in 2006 as well as in inoculated replicated trials at the OSU research farm. Project farmers grew Jacqueline Lee and Ozette in variety trials in 2007.
Materials for LB management: Most Ospud farmers in western WA and northwestern OR have experienced late blight epidemics. In 2006 Ospud emphasized cultural management strategies and identified and trialed LB resistant clones. However, farmers west of the Cascades can experience epidemics in spring or fall despite practicing best cultural management and growing resistant clones. For this reason, Ospud farmers requested an LB spray trial in 2007. Requested materials included coppers, oxidizers, compost teas, and biologicals.
Treatments (4 applications on 8/30, 9/3, 9/10 and 9/17/07; except for #9: 5 applications on 8/21, 8/29, 9/1, 9/5, 9/12)
1. Cuprofix (copper sulfate: Cerexagri-Nisso)1, 3 lbs/A,
2. Kocide 3000 (copper hydroxide: DuPont)2, 1.75 lbs/A,
3. Nordox 75 WG (copper oxide: Monterey Chemical)3, 2.5 lbs/A
4. Oxidate (hydrogen dioxide and peroxyacetic acid: BioSafe), 6 gals/A
5. Sonata (QST 713 Bacillus subtilis: Agraquest), 3 qts /A
6. Horsetail tea (horsetail: BD Institute4), 300 units/A
7. Maria Thun barrel compost tea (compost: BD Institute4), 600 units/A
8. Water control (applied same dates as 1-7), 600 gals/A
9. Wilt Farm tea (compost tea: Wilt Farm5), 600 gals/A
1Cuprofix is not currently OMRI or WSDA listed for use on certified organic farms
2Kocide 3000 was OMRI-listed in October 2006 but may no longer be listed.
3Nordox is currently listed by OMRI and WSDA for use on certified organic farms. It is regulated, and must be used in a manner that minimizes accumulation of copper in the soil [205.601(i)(1)]
4Josephine Porter Institute for Applied Biodynamics, PO Box 133, Woolwine, VA 24185 276-930-2463 www.jpbiodynamics.org. Materials were applied as recommended by JPI.
5Wilt Farms, Hwy 99W, Corvallis, OR. 541 752-0460. Tea was applied as received from Wilt Farm on dates that Wilt Farm produced tea. On two of the application dates, tea was stored overnight and applied the following day.
Treatments were applied with a hand-pump backpack sprayer. Spray volume was extremely high, approximately 600 gallons per acre, to ensure coverage of all foliar surfaces (including the undersides of leaves where Phytophthora infestans sporulates), using this low efficiency backpack sprayer.
Field trial design:
The randomized complete block experiment (9 treatments, 4 blocks) was conducted at the Lewis Brown Horticulture Farm in Corvallis, Oregon. Plots consisted of 3, 15-ft rows of Yukon Gold potatoes planted on 12” in-row and 34” between-row spacing. Potatoes were planted on a conventionally managed field. A conventional aphicide was applied at planting but no other pest management materials were applied other than the treatments. Plots were separated by a 10 ft no-plant gap in the row direction. Contiguous plots were separated by a continuous buffer row of potatoes that also served as an inoculation row. Potatoes were planted on June 19 to ensure that the potatoes matured during the fall when shorter days, dew, and rain increase the likelihood of a LB epidemic. Establishment in this field was poor; approximately 20% of the seed did not sprout. Sprouted seed was transplanted from extra rows and the 10 ft between-plot border rows to replace the unsprouted seed; after transplanting, plot stands were close to 100%.
Inoculation: Late blight did not occur in this field naturally. A natural late blight epidemic did occur at Persephone Farm. Diseased, sporulating foliage was collected from the Persephone field in the morning on August 28 and stored in plastic bags in a cooler during the day. The Lewis Brown trial was irrigated in the afternoon to wet the foliage. Approximately 2 stems per 15 ft inoculation row were distributed in inoculation rows in the field trial just before sunset.
Disease evaluation: The central 12-ft section of the center row of each plot was evaluated for disease severity. This 12-ft row section was evaluated as three 4-ft sections, resulting in three disease ratings per plot. These ratings were averaged to generate one mean disease severity rating per plot. Disease severity was evaluated on a 10 point scale: 1 = 0% necrosis, 2 = 0.1-2.5% (mean = 1.25), 3 = 2.5 – 10% (mean = 6.25), 4 = 10-25% (mean = 17.5), 5 = 25-50% (mean = 37.5), 6 = 50-75% (mean = 62.5), 7 = 75-90% (mean = 82.5), 8 = 90-97.5% (mean = 93.75), 9 = 97.5-99.9% (mean = 98.75). 10 = 100%. Area under disease progression curve (AUDPC) was calculated for the period 9/12/07 – 9/23/07. Analysis of variance and mean separation by the LSD procedure were performed using SAS statistical software.
C. NITROGEN MANAGEMENT
1. Evaluate the balance between N supplied and N utilized by a potato crop under a variety of organic management regimes.
a. Measure the timing and quantity of plant-available N supply for organically-grown potato (N mineralized from soil organic matter, N applied in irrigation water)
b. Measure timing and amount of plant growth and N uptake (tuber yield, tuber + vine N uptake, petiole nitrate-N, soil nitrate-N
2. Determine the most reliable methods for assessing crop N status within an organic farming system
3. Develop typical system values (N inputs and N outputs) for planning crop N budgets
Materials and Methods (McQueen, 2008)
This research was conducted using a collaborative grower-scientist approach. Growers brought their questions and concerns to the scientists who implemented practical on-farm monitoring to look for answers. Researchers monitored crop N uptake, yield, soil nitrate-N, and petiole nitrate-N in grower fertilized fields. These measurements were also performed in zero-N plots (no current season inputs) to provide an estimate of N contribution from N mineralization. Aerobic soil incubations were also used to provide an estimate of N mineralization.
Crop N uptake in grower fertilized fields
Plots were located within the potato field where farmer cultural and fertilization practices were not altered. These on-farm plots were approximately 30 m long and a minimum of 4 rows wide with no replications. Sampling took place from the inside 2 rows of the plots. At each sampling event, 3 adjacent plants were removed from 3 locations within the plot, totaling 9 plants. The plants were separated into tubers and shoots which were weighed and then dried at 55°C; the roots were discarded. Following drying, the plants were ground in a stainless steel Wiley Mill through a 2mm screen and analyzed for total C and N with a LECO Total CNS elemental analyzer (LECO Corp., Las Vegas, NV; Nelson and Sommers, 1996). Biomass, N uptake, and tuber yield were averaged at each sampling date and the means of the three samples were used for calculations with the standard error of the mean used for an estimate of variability. The results determined per plant were multiplied by a constant plant per hectare basis for comparative purposes. The in-row spacing was similar at most locations, 20 to 30 cm between plants, and although row spacing varied from approximately 1 to 2 m, vines did not generally cover the inter-row area wider than 1 m, therefore, a plant population of 36 360 per hectare was used to estimate a between-row spacing of 0.9 m and an in-row spacing of 0.3 m. Nitrogen uptake was determined by multiplying the dry biomass by its N concentration (Eq. 1).
uptake N kg ha-1 = dry biomass kg ha-1 x N% 
Equation 2 is an example of converting the N uptake on a per plant basis to a per hectare basis
kg N plant-1 x 36 360 plants ha-1 = kg N ha-1 
Due to the observational nature of this study, statistical analyses were not performed. Samples were not taken from a random population and plots on farms were not replicated; in addition, samples taken within a farm are not considered independent of one another.
Crop N uptake in zero N plots
Zero-N plots of at least four rows wide and 15 m long were marked and no current season amendments, such as composts or chicken litter, were added. The zero-N plots were not replicated within the field. Calculations performed were the same as reported for the crop N uptake in grower fertilized fields.
The samples for soil nitrate-N determination were collected before and during the growing season. From the preplant samples, a whole field sample (mixture of the 3 field composite samples) was submitted for nutrient analysis. Samples taken in the farmer fertilized field consisted of three composite samples of 10-15 cores each. Samples from the zero-N plots consisted of a single composite sample. Sampling was conducted with a 2.5 cm diameter probe to a depth of 30 cm in the potato hill. Because of the soil movement accompanying hilling operations, soil sampling to 30 cm within hills is equivalent to sampling to a depth of 15 cm inches deep across a flat field.
Petiole samples were taken at the time of plant sampling to help monitor the relative N status of the plants. A sample consisted of twenty first fully mature leaves, one per plant, stripped of the blades and placed in a paper bag. The petioles were dried at 50°C and submitted for analysis to a commercial plant tissue testing laboratory for nitrate-N by a nitrate combination electrode (Hanna Instruments, Ann Arbor, MI).
Aerobic soil incubations
Soil was collected for laboratory incubations in spring prior to planting and again in the summer. Approximately 500 g soil on a dry weight basis was added to Ziploc bags and then incubated at 22 C for 9 weeks. Soil was subsampled at three week intervals, extracted with 2M KCl, and analyzed for nitrate-nitrogen.
OBJECTIVE ONE. Pilot a participatory approach to learning and adaptation of novel farming systems approaches.
Before the first meeting, growers were sent a potato production survey in which they described their production system from seed sourcing to market. Group participants received surveys before the meeting. During the first and second meetings in December 2005, farmers and the project team collaboratively 1) identified and prioritized the issues reducing potato production profitability, 2) identified and discussed any known solutions, 3) generated hypotheses to be tested during the first growing season in on-farm trials, and 4) identified who would participate in on-farm trials. Staff met monthly from December through August to plan, trouble-shoot and discuss project activities, and bi-weekly from August through December to interpret data and plan the December 2006 meeting. Before each December meeting, draft agendas were drafted by staff for grower review; the agenda for the December meeting was finalized after incorporating grower input. On-farm reports (whole group and farm-specific) were sent to each participant before the meeting. At the meeting, staff presented research reports with considerable interaction from farmers and staff. One farmer presented his potato enterprise budget and the group discussed the production surveys in the context of the enterprise budgets. In the final morning session, farmers and staff prioritized research issues for summer 2007 and evaluated the year’s work and the meeting process. Staff then drafted research and extension activities to address those priorities with farmer input when needed; these proposals were presented to the group at the second winter meeting in February 2007.
Two farmer meetings were held in 2007: a one-day meeting in February before the growing season and a final two-day meeting in December.
The goals of the February meeting were to evaluate the first year’s field data and to review the budget and make future decisions regarding project direction and field trials. During the meeting, Jeff McMorran, OSU Extension Seed Certification Specialist, gave a presentation on potato seed certification and seed handling in response to interest voiced by project farmers. Additionally, Al Mosley, OSU Emeritus Potato Specialist who is very popular with this group of farmers, provided a lively question and answer period.
Researchers presented a comprehensive range of options for 2007 field trials in areas farmers had previously identified as important. These areas included variety trials, a late blight spray trials, nitrogen management, and flea beetle and wireworm management. Budget ramifications for each option were also included and considered. From the range of options the farmers were able to pick which trials they would like conducted on their farms in 2007. The following is a list of these decisions:
• Seven farms chose to test fourteen varieties of potatoes.
• Five farmers requested a late blight spray trial to evaluate organically approved materials. Seven farms chose to repeat the zero nitrogen trials on their farms.
• farmers requested research on flea beetle management. Five farms chose to test hilling and mulching, and 3 farms chose to evaluate nematode applications for biological control of flea beetles.
The group discussed enterprise budgets and case studies. Farmers shared their existing potato enterprise budgets at a previous meeting. The pros and cons of enterprise budget formats were discussed with researchers; the group concluded that OSU staff would help farmers take appropriate data if interested.
The project budget was discussed and priorities were set for the remaining funds.
The meeting was ended with a brief, general, oral evaluation of the meeting in which growers expressed satisfaction at the format and outcomes of the meeting. Farmers reiterated the value of “the whole production approach” of the farmer presentations by project farmers at past meetings and expressed a strong desire to present the OSPUD Project at future conferences.
The December 17-19th meeting was the project’s final farmer meeting. The objectives of the meeting were to present the results of the 2007 field trials, evaluate the value and outcomes of the project, determine a schedule for farmer outreach, and discuss possibilities for further group collaboration and research.
The meeting also included a potato variety tasting and an open forum with Jeff McMorran, Al Mosley, and Oscar Gutbrod, OSU potato specialists, brought back by popular demand to discuss seed certification and quality.
For the field trial presentations, each researcher partnered with a farmer for their presentation. The researcher presented his or her results, and the farmer presented his or her interpretations of the work and its meaning to his/her farming operation.
The farmers created an outreach schedule and some farmers volunteered to present at each event (4 local conferences, 1 national conference, 2 farmer meetings).
Farmers were given draft copies of three of the Extension documents created from this project: What’s Wrong with my Potato Tubers, Flea Beetle Management for Organic Potatoes, and Estimating Nitrogen Mineralization in Organic Potato Production and comments were solicited.
Project farmers brainstormed and prioritized suggestions for a future group projects similar to OSPUD. They identified important elements of OSPUD that they would like to see in future collaborations, including a focus on a particular crop as well as participatory and multidisciplinary approaches to solving the problems associated with that crop. Farmers decided that they would like to focus on either Alliums or Brassicas in the next project. Regardless of the crop, they would like to conduct variety trials and tastings, and maintain a strong focus on organic soil management. The farmers agreed to take these ideas back to their farmer-to-farmer exchange meeting this winter. They would discuss and evolve these project ideas with this larger group of organic vegetable farmers, identify which crop family to focus the project on, and recruit additional farmers to bring into the project. OSU staff will then work with this larger group of farmers to develop the next integrated participatory crop-focused project.
OBJECTIVE TWO: 2. Evaluate the effects of soil management on tuber insect pests and diseases, weeds, nitrogen availability, and profitability.
A. INSECT PEST MANAGEMENT
Flea Beetles – First year
The three flea beetle species in the Willamette Valley that are capable of inflicting economic damage on tubers are the tuber flea beetle (Epitrix tuberis), the tobacco flea beetle (E. hirtipennis), and the western potato flea beetle (E. subcritina). The first two of these species were found in the potato fields on five of the sampled farms, and the third species was present in very low numbers at a few of the farms. Tuber flea beetle numbers were about twice as high as those of tobacco flea beetles.
Flea beetle populations increased at the edges of the potato fields more rapidly than at the inner areas of the fields. This indicates that flea beetles initially came from overwintering sites outside of the potato fields, and gradually spread into the inside of the fields from the edges. The ‘edge’ area of the field was defined as potato plants within 5 meters of the outside edge of the field.
The extent of tuber damage in each of the five fields relative to flea beetle populations and the timing of their arrival was also assessed. Three of the fields showed the expected higher or lower amount of damage with higher or lower flea beetle populations respectively, but two of the fields showed the opposite trend, with high populations yet comparatively little tuber damage. There are many possible management and/or biological factors in these fields that could cause the large flea beetle populations to not reach their typical damage potential, and this also shows that the beetle population levels are not always reliable predictors of damage in a field.
Since tubers are more susceptible to damage from increasing numbers of flea beetle larvae as the season progresses, the time of arrival of the beetle adults to a field in the spring could also be an indicator of the extent of damage in a given field. The timing of arrival of flea beetle adults also turned out to not be a reliable predictor of tuber damage, but the sampling at the beginning of spring may not have been intensive enough to catch the first individuals. The plan for year 2 was to increase the intensity of flea beetle sampling in the early spring to confirm the actual timing of arrival, as well as to provide biofix information for predictive tuber and tobacco flea beetle degree day phenology models that are being developed.
Sampling and diagnostic methods for flea beetles were tested and developed, and these have been summarized in an identification and monitoring worksheet for use in the field. Sweep netting of potato plants was more efficient than simple visual observation for assessing beetle numbers in the crop field. Yellow sticky traps yielded some information on flea beetle numbers, but they were not as efficient as sweep netting, and are probably more useful for assessing the timing arrival of the first flea beetles rather than population levels. Since flea beetle populations were shown to increase initially at field edges, monitoring efficiency can be increased by focusing on these parts of the field. A flea beetle damage rating system was also developed to quantify damage for the consistent diagnosis of flea beetle damage.
Wireworms – First year
Since wireworms have a 4-5 year life cycle, fields that were planted to potatoes in the 2005 season were also sampled in addition to the 2006 potato fields at each of the 5 farms. Adult beetles of the wireworms were sampled with pitfall traps, white sticky traps and pheromone ground traps for two invasive species from Europe (Agriotes lineatus and A. obscurus) which have a reputation for causing more consistent damage to tubers and other crops than the other local wireworm species. Wireworm larvae were sampled with underground bait traps of germinating grain.
Several different species of wireworms were obtained at the 5 farms, but efforts for species-level identification and confirmation focused on the two invasive species due to their economic importance in British Columbia and Washington State over the past several decades. In 2005 the known distribution of these two species in Oregon consisted of only a few nurseries and ports near the Columbia River which were reported in a survey by the Oregon Department of Agriculture (ODA). One of the project farms in this same area near the Columbia River had A. lineatus adults in the pheromone traps. Another farm about 15 miles south of this area also had A. lineatus in the pheromone traps, and this was a new county record of this invasive species that was reported to the ODA.
Although species-level identity of the other wireworm species was not confirmed in most cases, the extent of overall wireworm damage relative to overall wireworm and adult numbers in a given field was recorded. As for the flea beetles, numbers of wireworms were not always associated with the extent of wireworm damage in a given field. Wireworm damage in general was not as prevalent as flea beetle damage among project participants.
Pitfall traps and white sticky traps trapped very few wireworm adults, but the pheromone traps and larval bait traps were useful for wireworm monitoring and should be continued in project fields where wireworms are a concern. As was done for the flea beetles, a wireworm damage rating system was developed for consistent diagnoses, and discussions with the growers provided them with information about how to tell that damage apart from the damage of other insect and other tuber skin problems.
Flea beetles – Second year
GTF and SHF farms had relatively moderate to heavy levels of flea beetle damage overall, and both the straw and leaf mulch plots, and the nematode-treated plots, had appreciably less total flea beetle damage (ranging from 15-45% relative reductions in damage), as well as appreciably less damage in the FB3, ‘high damage’, category (ranging from 41-81% relative reductions in damage). PF and 47th farms had relatively low flea beetle damage overall, and no appreciable differences were seen among treatments and the control for total flea beetle damage as well as within flea beetle damage categories. No appreciable differences were seen in the amount of flea beetle damage between high hill plots and control plots at WGF, but flea beetle adult pressure in the high hill plots was three times higher than that for the control plots. All soil samples from nematode-treated plots contained viable nematodes.
Tuber flea beetles were generally not found any earlier in cull piles or in patches of solanaceous weeds compared to the winter/early spring potato fields present at two of the farms, so they may have been overwintering among sheltered locations throughout the farm. One other interesting observation is that the two farms that had relatively high flea beetle damage (GTF and SHF), were the same two farms that had winter/early spring potato fields within a few hundred feet of the main potato field. Tuber flea beetles tended to arrive to the edges of the potato fields 2-3 weeks after planting in general.
B. LATE BLIGHT MANAGEMENT
Resistant varieties: Ospud identified 3 commercially available LB resistant cultivars in 2006: Island Sunshine (IS), Jacqueline Lee (JL), and Defender. These were grown in non-replicated trials on 5 cooperating farms in 2006 as well as in inoculated replicated trials at the OSU research farm. Defender was highly resistant to foliar LB and IS and JL were somewhat to moderately resistant in on-farm and research station trials in 2006. Ozette, a PNW Slow Food potato clone, is also reported to be resistant to foliar LB (Vales/Yilma OSU potato LB clonal evaluations). Project farmers grew Jacqueline Lee and Ozette in variety trials in 2007 and they were productive, marketable, and performed well in taste evaluations; most farmers intend to grow these clones if high quality organic seed is available. In addition, at least two project farmers plan to grow Defender in the future.
Materials for LB management: The three copper products (Cuprofix, Nordox 75WP, and Kocide 3000), applied at the highest labeled rate, reduced AUDPC by 88% with no significant difference amongst copper products. In epidemics initiated early in tuber bulking, this level of disease control would likely increase potato yield. A locally produced compost tea, although applied on dates different from those of all other treatments, reduced disease severity compared to the control (applied on different dates) by 60% and 28% at the 2nd and 3rd evaluation dates, respectively. Oxidate significantly reduced disease severity by 42% at the 2nd evaluation date but not on any other date. No other treatments (Sonata, horsetail tea, Maria Thun barrel compost tea) significantly reduced disease severity.
C. NITROGEN MANAGEMENT
Nitrogen Objective 1: Evaluate the balance between N supplied and N utilized by a potato crop under a variety of organic management regimes.
The median soil N mineralization rate (soil samples collected midseason; incubated at 22oC in laboratory) was 0.7 ppm N per day across 12 farms studied. The N-supplying capacity of the soils is estimated at 100 to 140 lb/acre for 2000 degree days (base 0°C) assuming a sample depth of 6 inches and soil bulk densities of 1.0 to 1.3 g cm-3. The uptake of N by the potato in zero-N plots at harvest ranged from 74 to 212 lb N/acre with a median of 138 lb N/acre in 2006 (six farms), and 66 to 276 lb N/acre with a median 169 lb N/acre in 2007 (seven farms). This indicates a high amount of N mineralization was taking place on many of the participating farms.
On-farm N monitoring results showed a wide range of N availability that appeared to be primarily related to long-term management practices (years in organic production, typical rates of N inputs from fertilizer, compost and cover crops). The rate of current season compost application had little effect on N availability. Several farms had consistently high soil and plant N, illustrating an oversupply of N relative to plant needs. Over-application of rapidly-available N sources (e.g. fish, feather meal) during the current season appeared to be the main reason for N oversupply. Several other farms had consistently low soil and plant N, suggesting that N deficiency limited tuber yields. One farmer was surprised to learn irrigation water (well water with N = 15 ppm) was an important N source at his farm. Substantial amounts of crop N uptake in the absence of current season N inputs (zero N plots) demonstrated that mineralization of N from soil organic matter was a major source of N at these farms.
Nitrogen Objective 2:
Determine the most reliable methods for assessing crop N status within an organic farming system
Based on monitoring data from the two years, we recommend the following methods for assessing N sufficiency on our organic farms:
1. Vine + tuber N uptake by an unfertilized potato crop is the best measure of N mineralized from soil organic matter. This measurement incorporates site-specific factors, and is a low technology method that has credence with organic growers (Sullivan and McQueen, 2008).
2. Soil nitrate-N and petiole nitrate-N samples collected at 45, 60, and 75 days after planting. Soil nitrate values are easier to interpret than petiole values, as soil nitrate values are not strongly affected by cultivar.
3. Nitrate analysis of irrigation water. We had one farm with very low soil nitrate, low petiole nitrate, but good yields. At this farm, irrigation water (15 ppm nitrate-N) was a very important N source.
Nitrogen Objective 3: Develop typical system values (N inputs and N outputs) for planning crop N budgets
From our monitoring data, we developed typical system values that can be used in planning crop N budgets and in modeling of the N cycle for organic potato crops:
1. A typical crop N uptake value is 200 lb N/acre (for yields ranging from 15 to 30 ton/acre).
2. Median N uptake by an unfertilized potato crop was approximately 150 lb N per acre from typical western Oregon soils.
3. The typical rate of crop N uptake for unfertilized potato crops during tuber growth was 2 lb N per acre per day
4. Median net mineralized N in laboratory incubations (0.7 ppm N per day in 9-wk incubations at 22oC) was approximately equivalent to seasonal crop N uptake (150 lb N/acre) measured in the field (taking into account incubation time and temperature).
Objective 3. Extend project findings to a larger audience of farmers
(see NINE: Outreach)
Brady, N.C., and R.R. Weil. 1999. The nature and properties of soils. 12th ed. Prentice-Hall, Inc., Upper Saddle River, NJ.
Dyson, P.W., and D.J. Watson. 1971. An analysis of the effects of nutrient supply on the growth of potato crops. Ann. Appl. Biol. 69:47-63.
Gaskell,M.J., Mitchell, J., R. Smith et al, 2000. Soil fertility management for organic crops. University of CA. Div of Ag and Natl Res. Pub 7249. http://anrcatalo.ucdavis.edu.
Gardner, B.R., and J.P. Jones. 1975. Petiole analysis and the nitrogen fertilization of russet burbank potatoes. Am. Potato J. 52:195-200.
Jarvis, S.C., E.A. Stockdale, M.A. Sheperd, and D.S. Powlson. 1996. Nitrogen mineralization in temperate agricultural soils: processes and measurement Adv. Agron., Vol. 57. Academic Press.
Lang, N.S., R.G. Stevens, W.L. Pan, and S. Victory. 1999. Potato nutrient management for central Washington. EB1871. Washington State University Cooperative Extension.
Lewis, R.J., and S.L. Love. 1994. Potato genotypes differ in petiole nitrate-nitrogen concentrations over time. Hortscience 29:175-179.
Lorenz, O.A. 1944. Studies on potato nutrition II. Nutrient uptake at various stages of growth by Kern County potatoes. Proc. Am. Soc. Hort. Sci. 44:389-394.
Lorenz, O.A. 1947. Studies on potato nutrition III. Chemical composition and uptake of nutrients by Kern County potatoes. Am. Potato J. 24:281-293.
Marriott, E.E., and M.M. Wander. 2006. Total and labile soil organic matter in organic and conventional farming systems. Soil Sci Soc Am J 70:950-959.
McQueen, J.P.G. 2007. Estimating the Dry Matter Production, Nitrogen Requirements, and Yield of Organic Farm-Grown Potatoes. M.S. Thesis. Oregon State University, OR. http://ir.library.oregonstate.edu/dspace/bitstream/1957/6245/1/mcqueenj_MSthesis.pdf
Meyer, R.D., and D.B. Marcum. 1998. Potato yield, petiole nitrogen, and soil nitrogen response to water and nitrogen. Agron J 90:420-429.
Millard, P., and B. Marshall. 1986. Growth, nitrogen uptake and partitioning within the potato (Solanum tuberosum L.) crop, in relation to nitrogen application. J. agric. Sci., Camb. 107:421-429.
Nelson, D., and L.E. Sommers. 1996. Total carbon, organic carbon, and organic matter, In D. L. Sparks, ed. Methods of soil analysis: Part 3 - Chemical methods, Vol. No. 5. SSSA and ASA, Madison, WI.
Rice, C.W., and J.L. Havlin. 1994. Integrating mineralizable nitrogen indices into fertilizer nitrogen recommendations, In J. L. Havlin and J. S. Jacobsen, eds. Soil testing: prospects for improving nutrient recommendations, 40 ed. Soil Science Society of America, Inc., Madison, WI.
Riley, H. 2000. Level and timing of nitrogen fertilizer application to early and semi-early potatoes (Solanum tuberosum L.) grown with irrigation on light soils in Norway. Acta Agric. Scand. Sect. B Soil Plant Sci. 50:122-134.
Schepers, J.S., and A.R. Mosier. 1991. Accounting for nitrogen in nonequilibrium soil-crop systems, In R. F. Follett, et al., eds. Managing nitrogen for groundwater quality and farm profitability. Soil Science Society of America, Inc., Madison, WI.
Schepers, J.S., and J.J. Meisinger. 1994. Field indicators of nitrogen mineralization, In J. L. Havlin and J. S. Jacobsen, eds. Soil testing: prospects for improving nutrient recommendations, Vol. 40. Soil Science Society of America, Inc., Madison, WI.
Seamans, A., G. Abawi, et al, 2003. Final Report SARE Project LNE01-154. Farm ecosystem and management factors contributing to pest suppression on organic and conventional farms.
Speiser, B., L. Tamm, T. Amsler, J. Lambion, et al, 2006. Improvement of late blight management in organic potato production systems in Europe: field tests with more resistant potato varieties and copper based fungicides. Biol. Agric. Hortic. 23: 393-412.
Sullivan, D.M., J.M. Hart, and N.W. Christensen. 1999. Nitrogen uptake and utilization by pacific northwest crops PNW 513. Oregon State University Extension Service.
Sullivan, D.M., J.P.G. McQueen, and D. Horneck. 2008. EM8949-E. Estimating Nitrogen Mineralization in Organic Potato Production. Oregon State University Extension Service. http://extension.oregonstate.edu/catalog/pdf/em/em8949-e.pdf
Trehan, S.P. 2006. Genetic control of different potato cultivars in the manipulation of nitrogen uptake from green manured soil. Adv Hort Sci 20:199-207.
Varis, E., L. Pietila, and K. Koikkalainen, 1996. Comparion of conventional , integrated and organic potato production in field experiments in Finland. Acta Agric Scandinavicca Section B – Soil and Plant Science 46:41-48.
Vos, J. 1997. The nitrogen response of potato (Solanum tuberosum L.) in the field: nitrogen uptake and yield, harvest index and nitrogen concentration. Potato Research 40:237-248.
Wescott, M.P., V.R. Stewart, and R.E. Lund. 1991. Critical petiole nitrate levels in potato. Agron J 83:844-850.
Zebarth, B.J. 2005a. Pelletized organo-mineral fertilizer product as a nitrogen source for potato production. Canadian Journal of Soil Science 85:387-395.
Zebarth, B.J. 2005b. Estimation of soil nitrogen supply in potato fields using a plant bioassay approach. Canadian Journal of Soil Science 85:377-386.
A. INSECT PEST MANAGEMENT:
- The tuber flea beetle was identified and confirmed as the most important insect pest in Western OR and WA.
- Monitoring and tuber damage assessment methods were developed and methods that growers can use are described in an extension publication
Improved strategies for monitoring beetles and preventing damage to tubers were developed by the project. Specifically:
1. Field placement (early and late season crops on same farm) is important. Beetles move from early spring potato crops to nearby main summer-season potato fields
2. Tuber flea beetle monitoring and corrective management activities should focus on field edges early in the season
3. Mulching potato hills reduced flea beetle damage levels when compared to control plots
4. Adding nematodes reduced flea beetle damage levels when compared to control plots
B. LATE BLIGHT MANAGEMENT: We taught farmers to diagnose LB in the field. We identified at least 3 commercially available potato cultivars with LB resistance and good market quality for organic fresh market production, and these cultivars have been adopted by project farmers. We demonstrated that copper fungicides effectively controlled LB; one large scale farmer in a potato production region is now using copper fungicides to manage LB.
C. NITROGEN MANAGEMENT:
This project has (i)strengthened our knowledge of best methods for N monitoring, and has (ii) developed typical system values that can be used in planning crop N budgets and in modeling of the N cycle for organic potato crops. Overall, we found that soil N mineralization supplied most of the N needed by organic potato crops. This finding will assist growers in reducing expensive, rapidly-available N inputs, and will likely reduce soil nitrate-N available for leaching to groundwater at the end of the growing season.
Grower responses. Many of the collaborating farmers expressed surprise at the nitrogen results. According to the growers, they have placed their emphasis of supplying adequate N through fertilizers without appreciating the amount of N released by the soil in their systems. As a result of our findings, some of the growers intend on reevaluating their N fertilizer regimes to see if they need to reduce an over-supply of N. The growers were pleased to hear that their methods of applying organic sources of N have likely increased the level of N release by the soil through mineralization.
D. PROJECT EVALUATION RESULTS:
In order to measure the OSPUD project’s impact, farmer collaborators were asked about their past and future practices and intentions (see attached survey). At least one third of the farmer collaborators indicated a positive change in the following:
• Ability to diagnose late blight in the field
• Management of late blight through irrigation management
• Growing late blight resistant potato cultivars
• Planting only certified seed, when available
• Adjusting within- and between-row spacing based on seed size & type (cut or whole)
• Storing seed at temperatures favoring rapid emergence
• Warming seed before cutting
• Adjusting preplant application rates of broiler litter or high-N specialty products (seed meals, blood meal, fish fertilizer etc) to reflect their soil N mineralization potential & crop need (↑or ↓ rate)
• Accurately diagnosing flea beetle damage
• Monitoring flea beetle damage in tubers
• Monitoring flea beetle populations in the potato field
• Adjusting rotation to reduce flea beetle populations
• Using cultural methods to manage flea beetle populations
• Accurately diagnosing wireworm damage on potato tubers
• Monitoring tuber wireworm damage
• Adapting rotation to reduce wireworm populations
More than half of the farmer collaborators indicated that they strongly agreed with the following statements:
• They would participate in another research project with OSU.
• They would conduct an on-farm experiment with assistance from OSU
• They would encourage another grower to join in a participatory research project
• They would encourage another grower to participate in a project with OSU
• Being part of the OSPUD project made them a better manager of their potato crop
• Interacting with other farmers helped them better understand their farm
• An important factor in the success of OSPUD was bringing together farmer-derived and science-derived information
• Science-based information is essential to improving organic systems
Additionally more than half of the farmer collaborators indicated that they agreed with the following statements:
• They would conduct an on-farm experiment in cooperation with a group of farmers who are doing same or similar experiments
• Being part of the OSPUD project helped them reduce risks
• Interacting with researchers helped them better understand their farm
When asked about their increase in knowledge, farmer collaborators indicated the OSPUD project had increased their knowledge of potato varieties, flea beetle management, seed quality and handling, and row and plant spacing. Nearly 90% felt their knowledge of nitrogen fertilization, wireworm and late blight management and potato production economics had increased as a result of the project.
More than half the farmer collaborators felt that the knowledge gained about potato varieties, nitrogen fertilization, flea beetle management, seed quality and handling, and row and plant spacing changed their farm practices. The farmers indicated this was a direct result from their participation in the OSPUD project.
Half of the farmer collaborators had participated on a research project with the university and half had collaborated with other farmers in the past. Participants noted that OSPUD differed from these other projects in several ways: (1) more knowledge gained, (2) more collaborative, (3) less responsibility on the growers, (4) broader in scope, (5) longer period of time, (6) wide variety of university resources, (7) more in depth, (8) more solid research, and (9) better organized and planned.
Farmer collaborators described their role in OSPUD as a collaborator by providing directions, information and feedback to university researchers and fellow farmers as well as a facilitator and active member at planning meetings.
Farmers overwhelmingly responded that the most valuable aspect of OSPUD was the relationship building with other growers and researchers, but also included the interaction and collaboration with university specialists, the broad, multi-discipline approach, and detail on a single crop.
The most inspiring aspect of the project for many farmers was (1) the openness of other farmers and willingness of university researchers to work on organics with small growers and (2) the increased confidence in growing potatoes they gained. Also noted was the refining of their nutrient management practices and inspiring them to become more knowledgeable of other crops.
Educational & Outreach Activities
McQueen, J.P.G. 2007. Estimating the Dry Matter Production, Nitrogen Requirements, and Yield of Organic Farm-Grown Potatoes. M.S. Thesis. Oregon State University, OR. http://ir.library.oregonstate.edu/dspace/bitstream/1957/6245/1/mcqueenj_MSthesis.pdf
1. What’s Wrong with my Potato Tubers? Diagnosing tuber abnormalities in western Oregon and Washington, 2008. L. Selman, N. Andrews, A. Stone, and A. Mosley. Oregon State University Extension Publication EM 8948-E.
2. Estimating Nitrogen Mineralization in Organic Potato Production, 2008. D.M. Sullivan, J.P.G. McQueen, and D.A. Horneck. Oregon State University Extension Publication EM 8949-E
3. Flea Beetle Pest Management for Organic Potatoes, 2008. M. Ambrosino and P. Jepson. Oregon State University Extension Publication EM 8947-E.
eOrganic (eXtension for organic agriculture) content:
1. Estimating Nitrogen Mineralization in Organic Potato Production, 2008. D.M. Sullivan, J.P.G. McQueen, and D.A. Horneck. The OSU Extension Publication listed above has been adapated for eXtension. It will be published on eXtension as part of the eOrganic launch in fall 2008.
2. Organic Management of Late Blight of Potatoes and Tomatoes. A. Stone, Oregon State University, and S. Miller, Ohio State University. This unit will be published on eXtension as part of the eOrganic launch in fall 2008.
3. Ospud developed a project workspace on the eOrganic collaborative workspace (eOrganic.info). It is a model for the use of the workspace by participatory research and extension projects.
Outreach programs and events, including field days.
Ospud website: www.ospud.org
Potato evaluation and tasting, November, 2006, Gathering Together Farm, Philomath, OR. In cooperation with the OSU Potato Breeding Program, approximately 50 organic potato farmers, retailers, chefs, processors, and researchers drafted organic potato germplasm selection criteria and evaluated approximately 25 potato cones for appearance, flavor, and texture (steamed, chipped and fried).
Organic Production Conference, North Willamette Research and Extension Center, Portland, OR. January, 2008. Presentation by Jeff Falen, Persephone Farm; Jim Fields, Fields Farm, and Dan Sullivan, Oregon State University, on Ospud results and experiences.
Oregon Tilth conference, February 2008, Salem, OR: presentation by Josh Volk, Sauvie Island Organics; Jeff Falen, Persephone Farm; and Jim Fields, Fields Farm, on Ospud results and experiences.
Oregon Small farms and Direct Marketing Conference, March 2008, Corvallis, OR. John McQueen, Oregon State University. Presentation on Ospud results and experiences.
Washington Tilth Producers Conference, November 2008. Laura Masterson, 47th Ave Farm; Tim Terpstra, Ralph’s Greenhouse, and Gwendolyn Ellen, Oregon State University. Will present information on Ospud experiences and results.
Ecofarm Conference, January 2009. Ospud has submitted a proposal to Eco Farm to present Ospud results and experiences. Josh Volk, Sauvie Island Organics; Alex Stone and John McQueen, Oregon State University.
A. INSECT PEST MANAGEMENT
One of the growers was ask to evaluate the effectiveness and calculate the economic feasibility of the straw mulch method for preventing damage by flea beetle larvae. This was then discussed with project participants at the final meeting. While the cost/benefit of economic feasibility versus effectiveness in reducing flea beetle damage was generally considered favorable, a few of the growers mentioned that the straw mulch method in particular created substantial problems with weed management. It was also discussed that the high hill method of preventing flea beetle damage needs further research since the results from this project for that method were inconclusive.
B. LATE BLIGHT MANAGEMENT
Copper fungicides have been shown to extend the potato production period by 2-4 weeks (Speiser, 2006). This was supported by the results of the Ospud copper fungicide spray trial. We did not take yield data from the trial, but similar work in the EU has shown a 10-40% yield increase in fields protected by copper. Ospud farmers market potatoes at $.80 or $2 per pound (wholesale/retail). Therefore, increased potato crop market value resulting from copper applications to an average 5 T (diseased) potato crop would range from approximately $800/A (5 T yield, 10% increase, $0.80/lb) to $8000/A (5 T yield, 40% increase, $2 per pound). In the 2007 field trial, the Nordox applications cost approximately $50 per acre (2.5 lbs/A/application, 4 applications), not including labor and equipment costs.
C. NITROGEN MANAGEMENT
This project demonstrated that in organic systems, soil organic matter can supply much of the N required for the crop. This project demonstrated a number of tools that can be used to assess site-specific N supply and adjust N input rates accordingly. Several of the farms plan to reduce application rates of N inputs (fish, feather meal, chicken compost). Growers reducing N inputs by 50 lb N per acre will save $50 to $150 per acre (N input cost = $1 to $3 per lb N). Several other farms plan to increase N application rates because of the low plant N and soil N values measured in on-farm monitoring. A 5 T/A increase in yield is likely at these farms with greater N inputs (increase in tuber yield worth $800 to $8000 per acre using same economic assumptions used in “Late Blight Management”, above).
This project also demonstrated the value of measuring N in well water. The N contributed by well water at one farm in this study (approximately 50 lb N/acre) replaces 50 lb N from other sources (value of $50 to $150 per acre at N input cost of $1 to $3 per lb N).
See Impact and Outcomes Section above.
Areas needing additional study
Farmer participants are interested in collaborating on a project in the future; the majority are interested in working on Allium crops, with Brassicas running a close second. The major problems to be addressed in Alliums are downy mildew, weeds, thrips, timing of planting, irrigation, nutrient management, rotational strategies, harvest techniques, storage and variety selection. It was unanimous that all components of OSPUD should be included when developing the next project. The farmers suggested that the next project include more farmers, have more varietal taste tests, and shorter meetings.
The OSU/PNW potato programs continue to evaluate specialty potato germplasm (commercially-available and research clones) for LB resistance; Alex Stone plans to partner with them to identify emerging LB resistant clones with organic market potential.