Ecological Management of Potato Cropping Systems (ANE93.018)

Final Report for LNE93-036

Project Type: Research and Education
Funds awarded in 1993: $11,870.00
Projected End Date: 12/31/1996
Matching Federal Funds: $377,971.00
Matching Non-Federal Funds: $138,838.00
Region: Northeast
State: Maine
Project Leader:
Gregory A. Porter
University of Maine
Expand All

Project Information


[Note to online version: The report for this project includes tables and appendices that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact Northeast SARE at (802)-656-0471 or]

This project compares several alternative management strategies with conventional potato management strategies. In one set of experiments, a conventional soil management system is compared to several utilizing organic soil amendments [an oat, pea, vetch, green manure crop; and/or a soil amendment (waste potato compost and beef manure)]. The crop rotation treatments did not affect soil physical properties or yields. The soil amendment treatment improved soil organic matter content, soil structure, and levels of several key soil nutrients. Moisture content of the soil was increased by amendments, particularly under irrigation. With fertilizer rates held constant, crop growth was enhanced by the soil amendments. The amendment treatments significantly improved potato yields by 8.6, 8.2, and 3.4 t / ha from 1993-95. Yields responded significantly to soil amendment in both irrigated and non-irrigated systems with the highest yields in each year obtained when both inputs were used, yet short-term economic performance of the amendments was negative. Economic performance would be enhanced if the amendment rates were optimized, fertility management was adjusted for those applied in the amendments, and if yield benefits occur several years after application ceases. In the related potato cropping systems study, a similar soil amendment system also significantly increased potato yields during 1994 (4.0 t / ha, 12%) and 1995 (5.5 t / ha, 30%), while two-year average N fertilization rates were decreased by 65%, P2O5 by 50% and K2O by 75%.


Comparing pest management strategies, three biological control agents were studied singly and in combination to determine their effectiveness for control of the Colorado potato beetle (CPB). This study has demonstrated that CPB can be successfully managed with the combination of biological agents which include releases of the predator, Perillus bioculatus, and foliar applications of the pathogens, Bacillus thurengiensis, and Beauveria bassiana. The combination of all three agents results in greater season long reduction in CPB populations than any one agent alone. This biological management program was more successful in reducing CPB populations than a conventional insecticide based-management program, and a reduced-input management program. In addition, the biological management program appears to have carry over effects between years which are not seen in the other two programs. It is hypothesized that residual levels of B. bassiana in the soil and CPB population, may be responsible for reduced adult populations in the spring following treatment. This carry over effect could greatly enhance the economic viability of biological control programs for this pest.

Project Objectives:

Objective 1. Determine the effect of green manure, compost and manure use on soil physical properties, nitrate leaching, and potato plant growth, water status and yield.

Objective 2. Determine the impact of two microbial pathogens (Bacillus thuringiensis and Beauveria bassiana) and two insect predators (Perillus bioculatus and Coleomegilla maculata), singularly and in combination, on mortality of Colorado potato beetle.


Materials and methods:

Site Information

This project is being conducted primarily at the University of Maine's Aroostook Farm agricultural research center at Presque Isle, Maine. The study location is in the center of the major potato producing region in the eastern United States. Potato is the primary cash crop in the area with additional production of small grains, cool-season vegetables, small grains, and livestock. Agriculture in the area features heavy specialization for potato production and is very dependent on chemical fertilizers and pesticides. Few farmers use organic soil amendments, green manure cover crops, or biological pest control measures. The topography of the experimental site is gently rolling and typical of the area. The soil type is a Caribou loam (fine loamy, mixed, frigid, Typic Haplorthods). This soil type is well drained and comprises the predominant soil type used for potato production in Maine. The commercial potato farms to be used in this study are within a 30-mile radius of the research farm and feature similar topography and soils.

Objective 1. An experiment conducted at Aroostook Research Farm, Presque Isle, ME from 1993 to 1995 examined the effects of soil management practices as an alternative to supplemental irrigation for enhancing yield of potatoes (cv. 'Superior'). Soil management treatments compared soil amendment (unamended vs. soil amended annually with 44 t / ha manure and 10 t / ha compost) and crop rotation practices (1:1 rotation with oats versus 1:1 rotation with green manure). Amendments were initially applied during 1992. Non-irrigated production was compared with two rates of supplemental irrigation. Supplemental irrigation began after tuber initiation and was scheduled based on gypsum blocks buried 23 and 46 cm below the surface of the potato row. The experiment was a split-plot, randomized complete block design with four replications per treatment. Mainplots (0.05 ha each) consisted of the three water management treatments. Subplots (0.012 ha each) were assigned to amendment and crop rotation treatments in a 2 x 2 factorial combination. A summary of the project results is presented below, additional details on methodology and results are presented in Attachment #1.

Objective 2. An interdisciplinary study of the potato agroecosystem was initiated at the University of Maine in 1991 with the objective of developing an understanding of the ecosystem ecology, and based on this, develop a sustainable potato production system in northern Maine. The insect pest management treatments being compared include: (1) conventional (CONV), which relies on synthetic insecticides and economic thresholds recommended by the Maine Cooperative Extension Service; (2) reduced input (RI), which relies on the same materials as the CONV, but double the pest thresholds; and (3) biological (BIO), which relies on biological and bio-rational materials for pest suppression.

In 1992, the combination of Bacillus thurengiensis (Bt) and Beauveria bassiana (applied as a tank mix) for larvae, and rotenone for adults was utilized for CPB control in the BIO system. Seasonal densities of small larvae were higher in the BIO plots than in CONV, but no differences were observed in large larval densities. Predators which target the egg stage may add significantly to a biological management program for CPB in relatively cool environments such as northern Maine, therefore, studies were conducted during 1993-94 to evaluate augmentative releases of Perillus bioculatus in the Potato Ecosystem Study. This research consisted of (1) a small-plot experiments in which releases of the predator were assessed alone and in combination with other biological management tactics, and (2) a large, system-level study in which P. bioculatus was used as one component of the BIO pest management program which was compared to CONV and RI programs. A summary of the project methods and results is presented below, additional details on methodology and results are presented in Attachment #1.

Small Plot Tests: Evaluation of Augmentative Releases of P. bioculatus in Combination with Bt and B. bassiana.

General Methods. In 1993, a study was conducted at the University of Maine's Aroostook Research Farm in Presque Isle, ME, to examine the impact of predator releases (P. bioculatus and C. maculata), and foliar applications of the insect pathogens, Beauveria bassiana and Bacillus thurengiensis (Bt), on the survival of the Colorado potato beetle (CPB). All P. bioculatus were produced at the USDA ARS Laboratory in Yakima, WA, and shipped as nymphs for release. The following treatments were randomly assigned to plots in a randomized complete block experiment: (1) Bt alone, (2) B. bassiana alone, (3) P. bioculatus alone, (4) Bt and B. bassiana, (5) Bt and P. bioculatus, (6) B. bassiana and P. bioculatus, (7) Bt, B. bassiana, and P. bioculatus, and (8) control with no releases or applications. Two cages within each plot received the same treatments as the uncaged portion of the plot, and C. maculata releases were randomly assigned to one of the two cages, with the other acting as a control (no C. maculata release).

In 1994, the previous year's study was replicated at the University of Maine's Aroostook Research Farm in Presque Isle, ME, plus the University of Maine Sustainable Agriculture Research Farm in Old Town, ME. C. maculata were not released in 1994. CPB life stages, pest and predator densities, CPB adult emergence, and percent defoliation were studied at all sites. In addition, 15 randomly selected larvae per plot were collected 36 hours post spray in each of the plots receiving Bt or B. bassiana treatments, and the control. The larvae were fed fresh foliage in the laboratory every other day, and monitored daily for death and sporulation.

Two additional experiments were conducted at the 1994 Old Town site: (1) a comparison of full rate of Bt with 2 rate Bt, both with and without P. bioculatus, and (2) a comparison of four sprays of B. bassiana applied at weekly intervals over 4 weeks, with four sprays of B. bassiana applied over 2 weeks with 48 hrs between applications one and two, and application three and four.

Systems Study. A System Level Comparison of Pest Management Programs.

General Methods. In both 1993 and 1994, the combination of CPB biological control agents (P. bioculatus, Bt, and B. bassiana) was used as part of an integrated biological management strategy for pests in an on going Potato Ecosystem study at the University of Maine Aroostook Farm Potato Center in Presque Isle, Maine. A general description of this project is provided in the introduction. P. bioculatus releases were initiated in the BIO plots with the onset of CPB oviposition. Nymphs were released at a density of one per plant on three occasions between July 20 and August 12 in 1993, and July 6 and 20 in 1994 . CPB life stages were sampled on 50 to 30 plants per plot each week throughout the growing season. Seasonal densities of eggs, small larvae, and large larvae and incidence of adults were calculated and compared between pest management treatments using ANOVAs.

Research results and discussion:

Objective 1. The soil amendment treatments increased soil organic matter, aggregation, and fertility after a single season. After three years of application, the soil amendment treatment had significantly increased soil organic matter content (3.74 vs. 4.94%), cation exchange capacity (5.7 vs. 7.2 meq 100/ gm ), and the soil test levels of phosphorus (37.4 vs. 42.5 kg / ha), potassium (298 vs. 551 kg / ha), calcium (1366 vs. 1906 kg / ha), magnesium (429 vs. 524 kg / ha), and zinc (0.91 vs. 1.28 kg / ha). Nitrate-N concentrations in the surface soil during 1995 were increased due to amendment application. Soil amendments significantly decreased soil bulk density (1.24 vs. 1.14 g cm-3) and increased water stable aggregate content of the soil (37.9 vs. 43.4%). Average size of the soil aggregates was increased. Gravimetric moisture sampling revealed that the amendment program increased soil moisture levels throughout much of the growing season by about 10% and that plots receiving both soil amendment treatment and supplemental irrigation had particularly high soil moisture content. We were not able to detect any effects of the soil amendment treatments on water infiltration rates (unamended range 4.6 to 48.0 cm / h; amended range 3.6 to 71.7 cm / h) or laboratory-measured, soil-moisture-retention characteristics. The green manure crop rotation significantly increased nitrate-N levels within the soil, but had no other significant effects on soil properties. While the observed soil fertility increases due to amendment applications are generally desirable for crop production, environmental degradation could occur if these nutrients move off site due to runoff or leaching.

Runoff collectors were established on selected experimental plots during 1994 and 1995. Samples collected during 1995 indicated that irrigation treatments significantly increased runoff volume by 85%, but had no effect on sediment movement. Amendment application did not significantly affect runoff volume or sediment movement. Based on the changes in soil physical properties described above, the RUSLE was used to evaluate the potential for the soil amendments to decrease soil erosion. The seasonally adjusted soil erodability factor (Kf) was projected to drop from 0.243 to between 0.198 and 0.216, depending on the assumptions used. Averaged over a two-year crop rotation, the estimated soil erosion on a Caribou loam soil in Maine (91 m slope @5%) would drop from 5.10 to between 4.14 and 4.55 Mg / ha / year.

June through August rainfall for 1993-95 totaled 27, 23, and 16 cm, respectively. Irrigation increased yields by 3.14, 7.84, and 12.1 t / ha over the three respective years. Amendments significantly increased total yields in all three years of the study (8.62, 8.18, and 3.36 t / ha, respectively). US#1 yields were also increased (3.25, 7.84, and 2.69 t / ha, respectively). The rotation crop treatments did not significantly affect yields or US#1 yields. The higher N rate increased yields during 1993 (1.57 t / ha), but decreased yields during 1994 (2.46 t / ha). Contrary to expectations, total and US#1 yields at the lower N rate (134 kg N / ha) were not higher in the green manure rotation than the oat rotation. The 1993 results indicate that the green manure rotation crop as managed in this study was not able to greatly enhance productivity via N delivery to the subsequent crop. During 1994, 134 kg N / ha provided sufficient N to maximize yields even when oats were the previous crop. In parallel studies we have shown that the green manure crop can decrease the N fertilizer requirement by 67 to 134 kg / ha (33 to 66%). There were no significant interactions among irrigation, rotation crop, or soil amendment treatments.

During 1993, total yields in the non-irrigated, amended treatments were higher than those in the best irrigated, unamended treatment; however, the amended treatments were not able to maintain this advantage during the drier 1994 and 1995 growing seasons. Yields in the non-irrigated, amended treatments were 92 and 82% those of the irrigated, unamended treatments. In comparison, yields in the non-irrigated, unamended treatments were only 72 and 69% those of the unamended, irrigation treatments. From this, the yield enhancing effects of the soil amendment treatment make it an attractive alternative to supplemental irrigation; however, the soil amendment program was not able to entirely compensate for the dry conditions experienced during 1994 and 1995. It is noteworthy that yields were consistently higher for the irrigated, amended treatments than the irrigated, unamended by an average of 7.06 t / ha or 19%. Only the irrigated and amended treatments consistently reached or exceeded our target yield potential of 41 t / ha, suggesting that the soil structural and nutrient supply improvements provided by the amendments can be beneficial even in irrigated systems. It is not possible to determine how much of the response was due to nutrient supply and how much was due to changes in soil physical properties.

Irrigation increased potato top growth from mid-season onward during 1994 and 1995. The soil amendment treatments enhanced early growth of the potato crop and increased the size of the plant canopy. As was expected, irrigation resulted in leaf water potential (LWP) measurements that were closer to zero than those obtained for non-irrigated plots. Soil amendment treatments did not significantly affect LWP at any sample date; however, they did result in lower stomatal resistance and increased transpiration rates on several sample dates. These results indicate that the soil amendment treatments did improve crop water status; however, the extent to which they did so is difficult to establish because of the temporal changes in water supply over the season and the expectation that the larger crop canopy in the amended treatments would deplete soil water more rapidly than the smaller, unamended crop canopy.

Irrigation increased tuber size during two of the three study years, while the soil amendment treatment increased tuber size only during 1994. There were no treatment effects on incidence of scabby, sunburned, misshapen and growth-cracked tubers. Tuber decay incidence was very high during 1993, but relatively little tuber decay occurred during 1994 and 1995. Supplemental irrigation dramatically increased the incidence of tuber rot during 1993 (17.2 vs. 41.3%) and also increased rot incidence during 1994 (0.1 vs. 1.1%). Soil amendment also tended to increase the incidence of tuber rot (1993: 25.7 vs. 29.7%; 1994: 0.4 vs. 0.7%; 1995: 0.3 vs. 1.0%), possibly because it results in increased soil moisture levels throughout much of the growing season. Soil amendment did not dramatically affect the incidence of hollow heart in these experiments, but it decreased specific gravity in two of three growing seasons (1993: 1.078 vs. 1.075; 1995: 1.076 vs. 1.071). Crop rotation did not generally affect tuber quality in this study.

Supplemental irrigation is a proven tool for enhancing potato yields in Maine, yet it is an expensive technology that is not readily accessible to all growers and cannot be readily used on all farms. Soil amendment application is a promising tool for improving soil quality and enhancing potato yields in Maine; however, application can initially be costly and refinement of the amendment programs will be needed to accurately assess the economic impact of this approach. The current soil amendment system was designed to rapidly build soil organic matter and was not designed to optimize the rate of amendment application. It is likely that amendment rates and frequencies of application were much higher than were necessary for obtaining the yield increases observed in this work. In this experiment, we did not lower fertilizer rates to compensate for the nutrients present in the amendments. Other experiments have clearly indicated that fertilizer cost savings can be achieved when these amendments are utilized. For example, a similar soil amendment system in a related potato cropping systems study significantly increased potato yields during 1994 (4.0 t / ha, 12%) and 1995 (5.5 t / ha, 30%), while two-year average N fertilization rates were decreased by 65%, P2O5 by 50% and K2O by 75%. In addition to the nutrient responses that could not be addressed within this study, it is extremely likely that the positive effects of the amendments on soil properties and crop yields will last for several seasons after amendment applications have ceased. The potential of soil amendments should be studied over a much longer time period before any conclusions are drawn as to their true feasibility for Maine producers. Potential impacts on plant diseases and tuber decay should also receive more attention.

Objective 2

Small Plot Tests: Evaluation of Augmentative Releases of P. bioculatus in Combination with Bt and B. bassiana.

The 1993 CPB data from outside the cages indicate that there were significantly fewer CPB adults and fourth instar CPB in the Bt treatments than the remaining treatments. Fourth instar densities were significantly lower in all treatments compared to the check with densities lowest in the Bt plots (0.05 / plant), and lower densities in the B. bassiana plots (1.26 / plant) than in the P. bioculatus plots (1.38 / plant). There were no treatment effects on egg mass or first instar larval densities, and no interactions between any of the natural enemy treatments. Densities of CPB second and third instar larvae were reduced by the Bt treatments, but no other significant differences were observed between B. bassiana or P. bioculatus treatments and the control.

Analysis of the 1993 cage data revealed no impact of C. maculata releases on total emergence of adult CPB; however, Bt, B. bassiana, and P. bioculatus significantly reduced the number of emerging adults. The lowest mean emergence was observed in plots with all three mortality agents, however, P. bioculatus alone resulted in significantly higher adult emergence than the remaining non control treatments. There were no differences in the densities of emerging adults between Bt treatments and B. bassiana treatments. These results indicate that considerable additional mortality occurred during the pupal stage in the soil in the B. bassiana treatments.

The 1994 results of the small plot study at both sites were similar to the 1993 results; however, several treatment effects were detected earlier in the population than during the previous year. Egg mass densities were significantly reduced in the Bt plots at the Presque Isle site. P. bioculatus reduced small larva densities at the Old Town site (1.67 + 0.48 first instars in the predator versus 4.26 + 1.11 in the non predator plots). Predators significantly reduced densities of second, third, and fourth instars in Presque Isle, whereas in 1993, P. bioculatus effects were not detected until the fourth instar stage. Bt effects were also detected in second (p=0.03) and third (p=0.01) instar densities in Old Town, and all instars at the Presque Isle site. In all cases, densities of CPB larvae were lower in all Bt plots versus non Bt plots. B. bassiana treatments significantly reduced fourth instar densities in Presque Isle, but not at the Old Town site. Interactions between treatments were detected for only egg mass densities at the Presque Isle site. Bt treatments without predators appeared to have little effect on egg mass densities at this site, however, Bt in combination with P. bioculatus resulted in fewer egg masses than P. bioculatus applied by itself.

Defoliation ratings ranged from 0.3% for plots with the combination of all three biological control agents at both sites to 54.3% and 27.6% in the controls in Old Town and Presque Isle, respectively . Defoliation ratings in all biological treatments were significantly less than the control, but not different from each other in Old Town. However, the B. bassiana alone treatment did result in more defoliation than the other treatments in Presque Isle. In Old Town, the B. bassiana plots did not have significant reductions in CPB larval densities, but resulted in only 6.2% defoliation. Large larvae were observed on the foliage, but most were infected and caused little feeding damage.

Emergence of summer adults at both sites was significantly reduced by all biological agents, compared to the control. There were no significant differences between the treatments receiving some form of CPB control, but the lowest mean emergence at the Presque Isle site was observed with the combination of three agents. In addition, 42% of the adults emerging in B. bassiana treatments at the Old Town site died within 10 days of emergence, whereas, only 15% of those in non B. bassiana plots died over the same period. There was no difference in post emergent mortality of adults at the Presque Isle site; however, there was a significant B. bassiana effect on the number of collected larvae that died post spray at both sites. In Old Town, 61% of those collected from B. bassiana plots died compared with 42% from Bt, 44% from the B. bassiana + Bt, and 21% of the control. In Presque Isle, 90% of those collected from B. bassiana plots died compared with 53% from Bt, 95% from the B. bassiana + Bt, and 19% of the control.

Comparisons of half and full rates of Bt with and without P. bioculatus, did not result in any significant differences in CPB densities between treatments. However, mean densities of large larvae were consistently lower in the Bt + P. bioculatus plots compared with the other treatments, with no difference between the full Bt rate with P. bioculatus and the half Bt rate with P. bioculatus. Emergence of summer adults was significantly greater in the control plots than all other treatments, but half rate Bt did not differ from the full rate of Bt. Again, percent defoliation was low in all of the treatments and was significantly less than that observed in the controls.

Comparisons of consecutive applications of B. bassiana compared with applications applied at weekly intervals showed no significant differences between treatments in the densities of immature life stages of the CPB. The trends in the means showed lower emergence and defoliation in the B. bassiana treatments than the controls, but no difference between application strategies. Emergence averaged 8.0 + 3.5 for controls versus 1.3 + 0.9 for weekly B. bassiana applications, and 2.0 + 1.5 for consecutive B. bassiana applications. Defoliation averaged 54.3 + 25.7% for controls versus 6.2 + 2.2% for weekly B. bassiana applications, and 4.3 + 0.8% for consecutive B. bassiana applications.)

Systems Study. A System Level Comparison of Pest Management Programs

In 1993, CPB densities exceeded the threshold an average of three times during the growing season in CONV, once in RI, and once in BIO. As a result, the CONV plots received three treatments with Asana7, the RI plots received one application of Asana7, and the BIO plots received one application of Bt and B. bassiana in combination. The incidence of CPB adults was significantly lower in BIO than RI, and the seasonal densities of eggs, small and large larvae were all lower in BIO than CONV and RI. As might be expected given the higher thresholds, there were more small and large larvae in RI than in CONV. All of these strategies successfully reduced CPB populations below economic thresholds. There were no significant differences in yields between pest management treatments.

In 1994, CPB densities exceeded thresholds an average of three times in CONV, twice in RI, and 2.75 times in BIO. The CONV and RI plots were again treated with Asana7. The BIO plots received two applications of Bt and B. bassiana for larvae, and three out of four blocks were treated with rotenone for summer adults. In 1994, densities of all CPB lifestages were significantly lower in BIO compared with both RI and CONV. In this on going study, CPB populations have been declining in the BIO relative to the other treatments since 1992. The proportion of adults in the plots prior to the applications of any foliar treatments or predator releases has been lower in the BIO plots compared with the other treatments.

Cooperating Farms

In 1996, attempts were made to implement the biological management program for the Colorado potato beetle on two commercial farms: Wood Prairie Farm in Bridgewater, ME, and Gorenson Farm in Dresden Mills, ME.

At Wood Prairie Farm, a field of potatoes was divided into 6 sections for comparing different combinations of foliar formulations of Bt (Novodor 3%7 provided by Abbott Laboratories, Chicago, IL), and B. bassiana (Mycotrol7, provided by Mycotech Bioproducts, Butte, MT), with and without releases of the predatory stinkbugs, P. bioculatus. The planned foliar treatments included: full rate of Bt alone, full rate of Bt with B. bassiana, and 2 rate Bt with B. bassiana. Three releases of stinkbug predators were made at a rate of one nymph per plant on June 26, July 3, and July 10. CPB densities in all sections (with and without predators) never reached levels requiring foliar applications. Over the season there were no significant differences in CPB densities between sections with and without releases of the predators, although there was a trend for both fewer small and large larvae in areas where the predators were released. CPB populations will be monitored in 1997 to see if there is any evidence of a carry-over effect from the B. bassiana applications.

At Gorenson Farm, two fields of potatoes were divided into two sections. One section received foliar applications of Bt and the other section received foliar applications of Bt with B. bassiana. No predators were available for release at this site. Four foliar applications were made on all sections between June 25 and July 22. In field #1, relative densities of CPB larvae were higher in the Bt plus B. bassiana treatment section than the Bt alone section. However, in field #2, the opposite was true. In field #1, the section treated with Bt alone was planted and harvested early (starting in mid-July), and there was considerable migration of larvae from this area to the adjacent section which was treated with Bt plus B. bassiana.

Participation Summary


Educational approach:

Presentations conducted during this study are listed below. Abstracts from the presentations are attached where available.

Grower presentations (Objective #1):
Tour and discussion of research plots with potato industry representatives. G.A. Porter and J.C. McBurnie. (August 1993)
Tour and discussion of research plots with potato industry representatives and congressional staff. G.A. Porter and J.C. McBurnie. (August 1994)
Maine Potato Conference Annual Meeting in Caribou, Maine. McBurnie, J.C. and G.A. Porter. (January 1994)
Presentation of research results to Aroostook Water & Soil Management Board, Presque Isle, ME. G.A. Porter (March 1995)
Tour and discussion of research with potato industry reps. G.A. Porter (August 1995)
Presentation of research results to technical and field staff of McCain Foods Ltd., Florenceville, New Brunswick, Canada. G.A. Porter (November 1995)
Maine Potato Conference 10th Annual Meeting in Caribou, Maine. Porter, G.A. and J.C. McBurnie. (January 1995)
Maine Potato Conference 10th Annual Meeting in Caribou, Maine. McBurnie, J.C. and G.A. Porter (January 1995)
Maine Potato Conference 11th Annual Meeting in Caribou, Maine. G.A. Porter (January 1996)
Maine Plant Food Education Society Annual Meeting in Bangor, Maine. G.A. Porter (January 1996)
McCain Foods Grower Conference, Perth Andover, New Brunswick, Canada (March 1996)

Grower presentations (Objective #2):
Maine Potato Conference 9th Annual Meeting in Caribou, Maine. E. Groden (January 1994)
University of Maine Small Farm Field Day, Old Town, Maine. Groden, E. (August 1994)
Maine Farmer-to-Farmer Conference, Bar Harbor, Maine. E. Groden (November 1994)
University of Maine Small Farm Field Day, Old Town, Maine. Groden, E. (August 1995)
Maine Farmer-to-Farmer Conference, Bar Harbor, Maine. Liebman, M. (November 1995)
Maine Potato Conference 11th Annual Meeting in Caribou, Maine. Liebman, M. (January 1996)
Maine Potato Board Research Presentation, Orono, ME. E. Groden (November 1996)

Scientific presentations (Objective #1):
78th Annual Meeting of the Potato Association of America in Calgary, Alberta, Canada. G.B. Opena, L. Zhang, and G.A. Porter (July 1994)
86th Annual Meeting of the Agronomy Society of America in Seattle, WA. G.A. Porter et al. (November 1994)
Northeast Potato Technology Forum in Fredericton, New Brunswick, Canada. G.A. Porter. (March 1994)
Northeast Potato Technology Forum in Fredericton, New Brunswick, Canada. G.A. Porter. (March 1995)
SARE/ACE Symposium in Newark, New Jersey. G.A. Porter (January 1995)
Agricultural Science & Technology Workshop (Potato Irrigation, Soil, and Water Management Program) in Truro, Nova Scotia, Canada. J.C. McBurnie (April 1995)
Am.Water Resources Assoc. Meeting in Salt Lake City, Utah. J.C. McBurnie (April 1995)
79th Annual Meeting of the Potato Association of America in Bangor, ME. Opena, G.B., L. Zhang, G.A. Porter. (August 1995)
79th Annual Meeting of the Potato Association of America in Bangor, ME. Porter, G.A. et al. (August 1995)

Scientific presentations (Objective #2):
Annual Meeting of the Northeastern Branch of the Entomological Society of America, Newport, RI. E. Groden (March 1994)
USDA-ARS Biological Control Laboratory, Weslaco, TX. E. Groden. (March 1994)
USDA-ARS Potato Pest Researchers Meeting in Calgary, Alberta, Canada. E. Groden et al. (July 1994)
VI International Colloqium on Invertebrate Pathology in Montpelier, France. E. Groden et al. (September 1994)
University of Maine, Department of Plant Biology, Orono, ME. E. Groden (October 1994)
Society for Invertebrate Pathology 28th Annual Meeting, Ithaca, NY. E. Groden (July 1995)
Society for Invertebrate Pathology 28th Annual Meeting, Ithaca, NY. Fernandez, S. and E.Groden (July 1995)
79th Annual Meeting of the Potato Association of America, Bangor, ME. Groden, E. et al. (August 1995).
Canadian Entomological Society Meeting. Fredericton, New Brunswick. E. Groden and J. Zhang. (October, 1996)

Publications and Press Releases:
“Soil Management and Supplemental Irrigation Effects on ‘Superior’ potatoes: I. Soil Properties, Yield, and Quality.” Porter, G.A., G.B. Opena, J.C. McBurnie, W.B. Bradbury, and J.A. Sisson. In preparation: Agron. J.
“Soil Management and Supplemental Irrigation Effects on ‘Superior’ potatoes: II. Growth and Dry Matter Partitioning,” Opena, G.B., G.A. Porter, and L. Zhang. In prep.: Agron. J.
“Soil Management and Supplemental Irrigation Effects on ‘Superior’ potatoes:III. Root Growth.,” Opena, G.B. and G.A. Porter. In preparation: Agron. J.
“Evaluation of Integrated Biological Control Program for the Colorado Potato Beetle (Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae).” Groden, E., F.A. Drummond, J. Zhang, S. Fernandez, and D. Brever. In preparation: Biol. Control
“Crop water management through soil improvement,” McBurnie, J.C., G.A. Porter, and W.B. Bradbury. Proceedings of the American Water Resources Assoc. 1995. pp477-484.
“Growth and yield of Superior potatoes as affected by soil management and supplemental irrigation,” Opena, G.B. M.S. thesis, University of Maine. Orono. August 1995.
“Study shows that soil management is important” Maine Potato News, Presque Isle, ME (November 1995)
“Soil and Water Management Project Final Technical Report” submitted to the Aroostook Water and Soil Management Board, Presque Isle, ME (November 1995)
“Irrigation experiments at science farm prove successful in fighting droughts” Presque Isle Star Herald Newspaper, Presque Isle, ME (September 1995)
“Irrigation trials show increase in potato production” University of Maine Department of Public Affairs, Orono, ME (September 1995)
“Potato Eco-project converts skeptics” Maine Potato News (August 1995)
“Potato Eco-project converts skeptics” New England Farmer (August 1995)

No milestones

Project Outcomes

Impacts of Results/Outcomes

Objective 1: The results from this objective indicate that cull potato compost and manure applications to a potato soil can increase yields (10 to 30%) relative to a conventional soil management system. This soil management approach increases soil water holding capacity, enhances soil physical properties, and improves yield, but we have shown that it cannot enhance yields during dry growing seasons to the same extent that is possible through use of supplemental irrigation. Our data indicate that yield improvements in response to soil management take place even when supplemental irrigation is utilized. Short-term economic analysis indicates that the soil amendment program as used in this series of experiments is not economically viable for conventional potato growers in Maine. This is partly because the experimental systems used higher amendment loading rates than would likely be justified on a commercial farm. The amendments are expensive to purchase and apply in northern Maine under current conditions. Also, the data available only allow us to use yield benefit during the year after amendment application as our measure of crop performance in the amended system. It is extremely likely that these positive benefits will be observed for several seasons after soil organic matter has been increased; therefore, the economic viability will be very different when viewed on a more long-term basis. If adopted, this technology could enhance productivity and stabilize yields for potato growers in the northeast, while also improving soil quality and reducing the risk of soil erosion. Work within a related cropping systems study indicates that the combination of manure, compost, and the legume rotation crop used here can result in these yield increases while allowing average nitrogen fertilization rates to be reduced by 65%, phosphate by 50% and potash by 75%. We were not able to test the potential for reducing fertilizer rates in the present study. Land spreading of composts and manures has additional value as a waste disposal technique. The Maine potato industry for example produces more than 90,000 metric tons of cull potatoes each year that could be composted. Observed changes in soil physical properties suggest that soil erosion may potentially be reduced by the amendment treatments.

We hypothesize that the changes in soil quality which resulted from our amendment programs will persist in the soil for several cropping cycles after soil amendment application ceases and that the subsequent benefits to crop yield (and reduced fertilizer use and soil erosion) will result in the soil amendment applications being economically viable for Maine potato producers in the long-term.

Objective 2: The results from the biological control study thus far indicate that use of an integrated biological control program for the Colorado potato beetle will not reduce yields of potatoes, and will result in lower densities of the pest. The amount and toxicity of materials used is less in the biological system compared with the conventional pest management program. In 1993, three applications of the broad spectrum insecticide, ASANA7 were required to maintain the pest below economic thresholds, while one application of the combination of the pathogens (Bt and B. bassiana) was utilized in the biological management program. Most importantly, the biological control programs tested within this object have carry-over effects on CPB populations and therefore reduce the costs associated with CPB infestations in subsequent growing seasons.

The pesticides most likely to be reduced with the use of a biological control program for the Colorado potato beetle include the following insecticides (common name, most common trade name, and rate per acre used per application; number of applications per growing season varies from 8-10 in Southern Maine to 2-4 in Northern Maine):
Azinphosmethyl (Guthion 3F7) - 1 pt/A
Carbaryl (Sevin 4F7) - 0.5 - 1 qt/A
Carbofuran (Furadan 4F7): 1-2 pts./A
Cryolite (Kryocide7): 10-12 lbs/A
Endosulfan (Thiodan 3EC7): 0.67-1.33 qts./A
Esfenvalerate (Asana XL.66EC7): 9.6 oz/A
Oxamyl (Vydate L7): 1-4 pts/A
Imidacloprid (Admire 2F7): 1 pt/A
Imidacloprid (Provado 1.6F7): 3.75 oz/A
Phosmet (Imidan 70WP7): 1.33 lbs/A

Although there may be concern about the use of these compounds due to regulations regarding food safety tolerances and health effects, the more immediate threat to growers is their decreased effectiveness due to insecticide resistance. Colorado potato beetle has demonstrated a tremendous capacity to develop resistance to all major classes of insecticides. Resistance has been increasing in Maine and the Northeast.

We hypothesize that use of the biological management program will continue to have a suppressive effect on CPB populations in subsequent cropping cycles as the amount of B. bassiana builds in the population and in the soil.

Economic Analysis

Objective 1--Economic Results: The economic results take the form of partial budgets. Care has been taken to make the input prices and field operation costs used in the analysis reflect prevailing commercial conditions in Aroostook County, Maine at the time period of the study (see Attachment #1 for a summary of compost, manure, spreading, and irrigation costs used in this study). Unfortunately, the assumed prices for manure ($6.21 / ton) and compost ($18.18 / ton) do not represent true market prices because a market for these inputs has not yet developed in this area. As more suppliers enter the market, competitive forces would cause the prices to be bid down. Therefore, the comparisons are constructed first using the actual prices paid for these inputs (Price 1) and then, again, assuming market prices 35% lower than the current prices (Price 2). A potato price of $6.60 / cwt was assumed for comparison purposes. All comparisons are made on a per-acre basis, assuming a 400-acre farm with 200 acres in potato production each year.

Partial budgeting results for the comparison of the non-irrigated systems with and without amendment are presented in Table 1.1. Partial budgets for the following comparisons are presented in Attachment #1: 1) non-irrigated versus irrigated; 2) reduced irrigation, amended versus moderate irrigation, unamended. Each budget is based on the simple average of the 1994 and 1995 experimental results, since the irrigation system was not set up in time in 1993 to provide full-season irrigation. Yield responses were also averaged two rotation crop treatments, since differences between the rotation crops were not significant. Amendment alone provided an additional 52 cwt / A, but was not profitable (Table 1-1). Due to the high rates of amendments used, additional costs exceeded the short-term yield benefits and the amended system reduced profits by $366.48 / A and $200.84 / A at the two respective amendment prices. Moderate irrigation alone resulted in an additional 94.75 cwt / A yield, additional costs of $228.87 / A per acre, and additional profit of $396.48 / A (see attachment #1 for details). Amendment with reduced irrigation yielded an additional 34.75 cwt / A compared to moderate irrigation without amendment, but this also was not a profitable option (see attachment #1 for details). When compared to the moderate irrigation system, this system reduced profits by $480.33 / A and $244.93 / A at the two respective amendment prices.

In the two cases where amendment is added, it is illustrative to perform a break-even analysis to see what potato prices or amendment costs would have to be for the option to break even from a profitability standpoint. Holding the amendment costs constant at each of the two amendment price assumptions, the potato price would have to be $13.65 and $9.13 / cwt, respectively, for amendment to pay for itself via the observed short-term tuber yield increases. These potato prices are too high to be reasonably expected in Maine, except that the $9 price is within the reasonable range for Maine seed producers. Break-even potato prices for the moderate irrigation, no amendment vs. reduced irrigation, amendment scenario ($20.42 and $13.66 / cwt) are not reasonably achievable.

The break-even average amendment price ($2.49 to 3.39 / ton, assuming a $6.60 / cwt potato price) is between 20 and 30 percent of the average actual amendment price paid per ton.

Conclusions--Objective #1. Based on the experimental results reported in this study, it appears that supplemental irrigation alone may be a profitable investment for producers of 'Superior' potatoes regardless of market outlet. It is important to note that both of the growing seasons represented within the present study (1994 and 1995) were relatively dry and, therefore, that the observed yield response to irrigation was relatively large. With current (and reasonably foreseeable) prices for compost and beef manure, amendment alone and amendment coupled with reduced irrigation are not profitable options for Maine potato producers, according to the results obtained in this study. However, only a few years of data may not tell the whole story when it comes to adoption of a technology that could provide increasing, future benefits. The current soil amendment system was designed to rapidly build soil organic matter and was not designed to optimize the rate of amendment application. It is likely that the amendment rates and frequencies of application were much higher than were necessary for obtaining the observed yield increases. Also, we did not lower fertilizer rates in this experiment to compensate for the nutrients present in the amendments. Our other experiments have clearly indicated that fertilizer cost savings can be achieved when these amendments are utilized. Finally, it is extremely likely that the positive effects of the amendments on soil properties and crop yields will last for several seasons after amendment applications have ceased. The response to the soil amendments should be studied over a much longer time period before any conclusions are drawn as to their true utility for Maine producers.

Objective 2 --Economic Results. Table 2-1 contains the yield, total revenue and revenue less Colorado Potato Beetle (CPB) control costs for each treatment/year combination in the study. Revenue less CPB costs were calculated with and without the costs of the Perillus bioculatus releases, since this agent was found to be expensive and because any suitable population reductions may be achieved without it. Overall, the reduced input and conventional pest management systems are shown to be economically comparable when revenue minus CPB control costs are considered. The biological management system still does not provide enough protection at a sufficiently reasonable cost to be feasible from the producer standpoint. It does, however, result in less environmental damage than the other two systems and, if the value of those damages are considered, the biological pest management system would compare more favorably with the others. It is beyond the scope of this study to quantify the value of the environmental effects.

Farmer Adoption

Changes in Practice: Better information on the long-term benefits of soil amendment and crop rotation programs will help expand the interest in adopting results from Objective #1. Interest in the use of composts, manures, and green manures to build soil organic matter is increasing (see survey results below), but adoption has not yet taken place on a large scale in Maine. Current availability of composts, manures, and information appear to be limiting factors. Paper mill sludges are more readily available in Maine and application to potato soils is increasing rapidly (1996, 8 applying farms, up to 1500 acres). Permits for application on up to 5000 acres have been issued. Although the use of Bt for Colorado potato beetle management is very common in southern New England, only a few Maine growers currently rely on this material for pest control due to the increased expense and necessity for accurate timing of applications. B. bassiana is currently an experimental use material which may be registered for Colorado potato beetle control by 1996. It was recently registered for rangeland grasshoppers and sweet potato whitefly. Predators are currently reared by USDA for experimental use, and cost effective rearing and application technologies are being investigated.

Operational Recommendations: Growers should be looking for low cost sources of organic matter (manures, sludges, composts) to improve soil quality and yields of the drier fields on their farms. Present data does not justify the amendment rates that we used in our study or the purchase of composts at the price charged to our project. Including the long-term benefits to soil and yields may; however, justify even the costs incurred in our study (more information is needed to prove this). The biological CPB program studied within this project proved to be very effective, especially since B. bassiana offers a mode of action differing from Bt for biological control and attacks the CPB at a stage not normally susceptible to control practices. It should be of immediate value to organic growers and of value to conventional growers as the price of B. bassiana drops and/or as resistance develops to currently effective materials used by conventional growers.

Farmer Evaluations: Response to questionnaires distributed to growers following the 1995 Maine Potato Conference presentations are attached. Eleven of 31 respondents at the 1995 potato conference said that they would change practices as a results of information presented at the meeting and the most common change noted was importing organic matter for soil improvement. Note: a small fraction of growers attending these sessions actually return these questionnaires.

A more in depth survey on adoption of alternative soil management techniques was conducted during 1996. Approximately 1000 survey's were sent to Maine potato industry personnel. Only 35 surveys were returned by growers (35 surveys, 600 Maine growers, 5.8% return rate). Detailed results of the survey and all comments written on the forms are provided as an attachment. Highlights were as follows:

**** Growers gave high scores to recent information provided on the topics of general soil management, use of composts as soil amendments, supplemental irrigation, and general use of rotation crops. A considerable portion of the information provided on the topics of soil amendment use and supplemental irrigation was supported by this SARE/ACE project. Essentially all respondents found that information presented on these topics was of great value. Use of alfalfa rotations, manures as soil amendments, and paper mill sludges as soil amendments received lower scores and 14 to 26% of growers responded that the information on these tools was of little value to them.

**** Most growers (>80%) indicated that they had changed general soil management practices and crop rotations as a result of recent UM Cooperative Extension programs. In the case of soil management, growers indicated that 5120 acres had been affected (Maine produces approximately 80,000 acres of potatoes annually) . In the case of crop rotations the total affected was 2430 acres. Sixty-eight percent of the growers indicated that they planned to change rotation crops and 84% indicated that they plan to increase the length of rotation. The results indicate that growers feel confident that they can improve these practices with the information, technology, and financial resources currently at hand.

**** Smaller percentages of growers had changed practices relating to supplemental irrigation (37%, 1710 acres), composts (29%, 100 acres), manures (43%, 195 acres), and paper mill sludges (9%, 0 acres). Interest in these technologies appears to be increasing; however, as a substantial percentage of growers indicated that they are considering making changes by using supplemental irrigation (74%), composts (41%), manures (50%), and paper mill sludges (22%). Slower adoption of these technologies probably reflects: low availability of soil amendments, costs of adoption, and the continuing need for information of the use and benefits of each technology. Growers appear to be concerned that cull potato composts may spread plant diseases to their fields.

**** Availability of the amendments is likely to be a key factor affecting the adoption of their use. Paper mill sludges are available in the greatest volume in Maine and grower interest in their use has increased dramatically as a result of UM Cooperative Extension efforts. Applications were made on eight farms during 1996, affecting up to 1500 acres. Permits have been obtained to spread these sludges on 12 farms, affecting up to 5000 acres.

**** Many growers provided written comments supporting the need for soil improvement through crop rotation and soil amendment use. Many also felt that supplemental irrigation would fit on a portion of their acreage. A summary of the comments is attached.

Producer Involvement
Number of growers/producers in attendance (1994-96) at:
Conferences: 700
Field Days: 165

Areas needing additional study

The economic analysis (based only on input costs and short-term yield responses) suggests that the soil management techniques are not cost effective in the 'short-term,' but that they could readily be if they have long-term positive effects on yield. Research is needed to determine if measurable increases in productivity occur for several years after amendment application. It is likely that such changes do indeed occur. Also, the present economic analysis (based solely on this set of experiments) did not include benefits obtained from reduced fertilizer applications (we have documented these in other studies), waste disposal, and reduced soil erosion. The latter two benefits are difficult to quantify. Research is needed to assure that cull potato composts do not contain harmful plant pathogens and do not increase plant disease problems in subsequent potato crops (the observed increase in soil moisture content caused by the amendments appears to result in increased tuber rot incidence under certain conditions). The biological control program for CPB has been extremely effective; however, realistic costs of the program need to be established and long-term benefits need further study. Aphid management needs to be enhanced within the biological control program.

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.