Biofumigants in Commercial Onion Production to Enhance Soil Nutrient Availability, Soil Quality, and Control of Weed, Nematode, and Disease Pests

Final Report for SW01-023

Project Type: Research and Education
Funds awarded in 2001: $134,317.00
Projected End Date: 12/31/2005
Matching Non-Federal Funds: $54,912.00
Region: Western
State: Utah
Principal Investigator:
Brad Geary
Brigham Young University
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Project Information

Abstract:

Biofumigant treatments (Idagold, mustard; Sunrise, canola; Colonel, oilradish) did not increase P and N concentrations in onions, but mineralization of N increased on an infrequent basis. Fumigation, metam sodium, stunted early and late season onion growth at low soil P, biofumigant treatments had little effect on early or late season development. Stands and yields were reduced by biofumigants in some years. Biofumigant treatments had little affect on pink root and are not recommended for control. Metam sodium treatments had the greatest affect on pink root and is recommended, but it sunted early growth and tended to reduce stands and lowered Mycorrhizae colonization. Metam sodium controlled the most weeds but was not acceptable, Colonel and Sunrise volunteered. The high-input herbicide program was the best, followed by the low input program; both were better than an untreated check.

Project Objectives:

The objectives of this work are:
1. Evaluate a mustard and oilradish cultivar for the ability to reduce onion production problems, and compare them to soil fumigated with Metam Sodium and not fumigated.

2. Evaluate summer-fall bio-fumigant crop effects on both P and N availability to subsequent onions.

3. Evaluate and compare soil properties such as cation exchange capacity, infiltration and permeability rates, water-holding capacity and bulk density.

4. Determine if a bio-fumigant crop positively or negatively impacts root populations of mycorrhizae and Phoma terrestris.

5. Determine if the use of bio-fumigant crops in onion production has potential to reduce the use of synthetic fumigants and herbicides applied for weed control by reducing weed germination and growth.

6. Evaluate the effects of fallow, Metam Sodium, a mustard and oilradish cultivar on nematode population and subsequent nematode damage to onions.

7. Disseminate information by conducting research on grower farms, presenting data at field days, workshops and annual growers meetings.

Introduction:

The main objective of this project is to improve phosphorus and nitrogen availability to commercially grown onions in high lime, calcareous soils by using bio-fumigants instead of the synthetic fumigant Metam Sodium, while maintaining the benefits of fumigation. Mustard and oilradish cultivars have been suggested as substitutes for commercial fumigants in controlling soil-borne pests (weeds, insects, diseases, nematodes) affecting the yield and/or quality of crops. Using a general bio-fumigant crop prior to onions has considerable appeal in that it may be significantly cheaper than commercial fumigants, as well as provide other soil quality benefits like nutrient recycling or conservation.

Onions, in the Treasure Valley of Idaho and eastern Oregon, are a high value crop that requires significant inputs (fertilizers and pesticides) to grow a high yielding, quality crop suitable for local and foreign markets. Use of synthetic fertilizers, fumigants, insecticides, herbicides and fungicides continually pose a wide range of problematic issues related to the environment, human health and economic profitability. Bio-fumigant crops in commercial onion production have potential for reducing chemical soil inputs and increasing nutrient recycling by increasing biological activity.

Phosphorus availability is sometimes marginal in the highly calcareous soils of the Treasure Valley, and stunted onions have occurred when the commercial fumigant Metam Sodium was used. However, the stunting was ameliorated when P was applied. Reduced beneficial mycorrhizal infection of onions with synthetic fumigation has been implicated, but it is not known if bio-fumigant crops will be as limiting to mycorrhizal root infections on onions. Much of the N mineralization following a previous wheat crop occurs during the bulbing period for onions, the period of maximum N utilization, and is therefore used effectively by the plant. Bio-fumigants themselves have potential for releasing significant N for onions during bulbing if the N release is sufficiently delayed until bulb initiation in June.

Along with nutrient recycling and availability, pesticidal activities of the Brassica species on weeds, nematodes and soil-borne pathogens will be collected by observing: 1) weed emergence, growth and biomass, 2) nematode counts during the year, and 3) pathogen root infections. Soil physical characteristics will also be observed by taking soil samples before and after treatments have been applied. Through small plot research in known high lime, calcareous soils and through on-farm demonstrations, this work will examine the impact of a mustard and oilradish cultivar as bio-fumigants by observing: 1) effects on phosphorus and nitrogen availability, 2) soil physical properties, 3) impact on populations of mycorrhizae and Phoma terrestris, 4) weed control, 5) nematode control, and 6) crop yields and costs of production in commercially grown onion fields.

All results will be disseminated to farmers in the Treasure Valley to encourage the use of bio-fumigants and better-integrated pest management practices. Data will be presented to growers twice annually through field days sponsored by the University of Idaho and Oregon State University. Data will also be presented at workshops and the annual Idaho Eastern Oregon Onion Grower meeting.

Onions (Allium cepa L.) grown in the Treasure Valley of Oregon and Idaho are worth about 112 million dollars annually (Idaho Agricultural Statistics). They are grown on approximately 20,000 acres and account for approximately one-third of the total onion storage crop in the U.S. annually. Maximum economic returns are based on yield, bulbs greater than three inches in diameter and bulb uniformity. In order to ensure optimum size, quality standards and maximize economic returns, onion growers apply fertilizers, fumigants and pesticides to help plant growth and bulb development.

In order to decrease the number of weed, pathogen and nematode problems, onions planted in the spring are commonly fumigated the previous fall with the commercial fumigant Metam Sodium. However, adverse affects of this fumigant on nutrient availability to onions, particularly phosphorus (P), have been measured locally in highly calcareous soil. Reduced beneficial mycorrhizal infection of onions with the fumigation has been implicated. Onions are known to be especially dependent on mycorrhizal associations for accessing soil P when P availability is otherwise limited (Krikun et al., 1990; Afek et al., 1990; Ojala et al. 1982; Nelson and Safir, 1982). The effects of bio-fumigants on beneficial mycorrhizae and subsequent infection of onions have not been examined. Some bio-fumigants high in glucosinolates can release compounds similar to the active ingredients of commercial fumigants such as Metam Sodium. But the quantities, activities and dynamics of the release of these compounds during growth, and from incorporated bio-fumigant tissues, can be expected to differ from those associated with commercial Metam Sodium applications.

Weed control is currently one of the greatest expenses for onion producers. Suppression of weed germination and emergence by bio-fumigants can reduce weed competition (Al-Khatib et al. 1997) and has the potential to reduce fumigant and herbicide use for weed control. Currently, onion growers rely on multiple herbicide applications for acceptable weed control, which in other crops here in Idaho has led to tolerant weed species (Eberlein et al., 1992). Reducing the amount of chemicals applied to control weeds lessens the risk of ground water contamination, which is a serious concern in the Treasure Valley of Idaho because of high water tables.

To maintain good yields with high quality produce, soil fumigation is often used to control soil pathogens. One pathogen that significantly influences onion production is Phoma terrestris E. M. Hans., commonly referred to as pink root. Although fumigation has been shown to increase yields and decrease P. terrestris (Hartz et al., 1989) populations, there are growing concerns about the environmental hazards of chemical fumigants. Bio-fumigants, such as mustard and oilradish, have been proposed as alternatives to chemical fumigants in controlling soil-borne pests. Research has shown that green tissue of Brassica species can decrease the population densities of some fungal pathogens (Mayton et al., 1996), and it is anticipated that pink root populations can be decreased with incorporation of a green manure in the fall.

Nematodes also pose a serious problem to onions because fields that are cropped repeatedly to onions have experienced significant losses due to the lesion nematode Pratylenchus spp. This is evidenced by the increase in the number of root and soil samples containing high populations of lesion nematodes submitted to the University of Idaho Nematode Diagnostic Laboratory at Parma. Additional evidence is provided by the high percentage of acreage of several crops that is fumigated for nematode management. If nematode counts (based on soil sampling) are high enough to warrant inclusion of a nematicide, treatment is generally done preceding the planting of onion during the second year of the cycle. This application is costly and requires careful management because of health and environmental concerns. Under the current system growers risk unforeseen losses because nematode populations are some times not detected during sampling.

Integration of the suitable antagonistic crops such as mustard and oilradish would reduce the rapid build-up of nematode populations and reduce the risk of high populations, which result in yield loss. New bio-fumigant varieties contain specific alleleochemicals that inhibit a variety of soil-borne pests. The substitution of plant derived allelochemicals for synthetic organic pesticide decreases the potential for environmental contamination, thereby reducing associated negative impacts on human health. Growers have expressed willingness and interest in evaluating these tactics that reduce reliance on chemical nematicides.

Using a general bio-fumigant crop prior to onions has considerable appeal in that it may be significantly cheaper than commercial fumigants, as well as provide other soil quality benefits including increased soil organic matter, increased water holding capacity, nutrient recycling or conservation, weed control and pathogen suppression. The green manure value of these bio-fumigant crops is often touted as part of the justification for their consideration. They unquestionably take up nutrients for a period of time during their growth, affording some protection against loss of these nutrients due to leaching or runoff. Ideally, nutrients in them are then recycled with incorporation of the plant into the soil and are available to the next crop.

The effects of commercial fumigants on nutrient cycling have been reported (Ellis, 1995; Khaliq, 1998; McCallister, 1997). However, the effects of bio-fumigants on the dynamics of nutrient cycling in general are seldom evaluated. This is particularly the case for minor acreage crops such as onions. Nitrogen release from incorporated bio-fumigants is of interest for onions in that it is commonly the nutrient most limiting to onion growth and more of this nutrient is applied than others in onion production. Furthermore, nitrogen management practices of onions in the production area of Idaho and eastern Oregon have been implicated in the nitrate contamination of shallow aquifers (Bruck, 1986).

Much of the N mineralization following a previous wheat crop occurs during the bulbing period for onions, the period of maximum N utilization, and is therefore used effectively by the plant. It is not clear what effect bio-fumigants would have on decomposition of previous crop residues and the associated N mineralization. Fall and pre-plant applied N is typically used less effectively than side-dressed N or pre-plant slow release N sources designed to provide N more in sync with dynamics of N uptake into onions (Brown et al., 1988). Brassica bio-fumigants themselves have potential for releasing significant N for onion during bulbing if the N release is sufficiently delayed until bulb initiation in June.

Glucosinolates and glucosinolate degradation products have been shown to be effective germination inhibitors of some weed and crop seeds (Al-Khatib et al. 1997; Bialy et al. 1990; Boydston and Hang 1995; Brown and Morra 1995, 1996; Krishnan et al. 1998). Brassica green manure crops have been evaluated for weed suppression in greenhouse studies and in various crops. Krishnan et al. demonstrated that three Brassica species; brown mustard (B. juncea), rapeseed (B. napus), white mustard (B. hirta) inhibited germination and reduced fresh weight of kochia, shepherds-purse, and green foxtail in the greenhouse. Redroot pigweed germination was reduced by rapeseed and white mustard, but not by brown mustard, and velvetleaf germination was only reduced by white mustard (Krishnan et al.1998). In soybeans, brown and white mustard reduced weed biomass 49% six weeks after emergence at one location, but did not reduce biomass at another location (Krishnan et al.1998). In green pea, weed suppression with white mustard and rapeseed was 25 and 30% at 60 days after pea planting compared to peas planted following wheat. However, at the end of the season weed pressure was not different (Al-Khatib et al.) In potatoes, spring incorporation of fall-planted rapeseed reduced weed density 85 and 73% and weed biomass 96 and 50% in 1992 and 1993, respectively (Boydston and Hang 1995).

Yield and quality losses of onion due to nematodes remain a serious problem in Idaho. Development of management procedures for reducing nematode populations is an industry priority. In particular, lesion nematode Pratylenchus spp. is one of the major constraints in the production and productivity of the onion. Current management methods combine cultural practices and chemical control to keep nematode populations below economic thresholds. Inclusion of nematode antagonistic crops in the rotational system is one of the economically viable, environmentally safe options for the lesion nematode management.

Research from our previous greenhouse studies at the Parma Research and Extension Center has revealed that oilradish, mustard, rapeseed and sudan grass are the potential crops for the mangement of nematodes in potato, sugarbeet and onion cultivation (Araji and Hafez, 2000). Recent studies indicated that rapeseed is effective in reducing the population of M.chitwoodi and increases the fresh weight of tomato plants (Hafez and Sundararaj, 1999a). Experiments conducted in microplots and the field confirmed that rapeseed ‘Humus’ and oilradish ‘Raphanus sativus’ reduced the population of M. chitwoodi and P. penetrans and increased potato tuber yield (106-185%) and quality under Idaho conditions (Al-Rehiayani and Hafez, 1999). Further, it was confirmed that addition of the bacterium, Bacillus megaterium, along with rapeseed ‘Humus’ or oilradish increased yield and quality of potato tuber and suppressed population of both the nematode species under greenhouse and field-microplot conditions (Al-Rehiayani et al., 1999). It was also found that addition of prophos along with rapeseed considerably increased the number 1 potatoes (Hafez and Sundararaj, 2000a). Studies on the efficacy of green manure crops along with mocap, vydate and cultural practices on potato indicated that maximum tuber yield was from rape seed plots (Hafez and Sundararaj, 2000b). Sugarbeet yield was also significantly increased when mustard ‘Metex’ was planted as a preceding crop (Hafez and Sundararaj, 1999b). Mustard cultivars differ with respect to their potential of sugarbeet cyst nematode management (Hafez and Sundararaj, 1998). Higher efficacy may be obtained from identification of resistant rotational crops that serve as poor hosts for the lesion nematode species on onion. Utilization of such resistant cultivars release compounds harmful to the nematode, reducing the nematode survival, thereby reducing nematode damage and increasing yield.

Cooperators

Click linked name(s) to expand
  • Brad Brown
  • Ernie Chandler
  • Saad Hafez
  • Terry McGonigle
  • Larry Nelson
  • Corey Ransom

Research

Materials and methods:

Objective 1
The experimental design for this work was a split-plot design with fallow, Metam Sodium, Mustard cultivar and a oilradish cultivar as the main plots. The sub-plots consisted of nitrogen added, phosphorus added, nitrogen and phosphorus added and no fertilizer. The experiment was replicated six times. During years 1, 2 and 3 the work was conducted on the University of Idaho research farm near Parma, Idaho in a field with high lime soils and low phosphorus levels. In year 3, a five acre section of land, in two separate onion grower’s fields, one bio-fumigant crop used prior to an onion crop. Yields and quality data were collected at all locations during all three years.

Objective 2
Fall planted winter barley or spring wheat was grown as a previous crop on plots previously receiving variable P rates and the grain harvested at maturity. Four subsequent interim treatments consisting of two non-planted controls and two bio-fumigants was seeded after the cereal stubble was disked and incorporated. One of the two non-planted controls was fumigated with Metam Sodium at a rate of 35 gal/A in mid November. All interim treated plots were fall bedded on 22” rows as per the usual practice for onions in the area. Onions were uniformly planted and grown the following spring with the exception of selected treatments, which received sufficient and insufficient N.

Mineralized N as nitrate was measured periodically from recovered buried bags placed in the soil to the first foot. Nitrogen and P uptake in onions were measured at bulb initiation and maturity. Onion yield and grade were measured at maturity.

Objective 3
Soil physical property samples were collected prior to Brassica seeding but following wheat stubble incorporation. The samples provided a composite analysis of the treatment areas. All samples were taken to a depth of 12 inches and were studied in a lab by U of Idaho researchers. The following spring samples were collected from all plots in three replications. Soil physical property analysis were done all three years at the highly calcareous soil location near Parma, ID.

Objective 4
All treatment plots were tested for pathogen populations of P. terrestris root infection ratings. Soil population counts were taken in July following incorporation of wheat stubble and again in April. Three times during the growing season onion tissue samples were collected, dried, ground and plated on PDA to count colony forming units within the plants. All plots were harvested in September when yield and quality data were collected.

Beneficial mycorrhizae was quantified by detecting fungal infection in onion roots once every year during the end of July. Root infection sites were identified using the procedure of Speidel and Wollum, (1980).

Objective 5
Weed plots were established in a separate location than the plots in the highly calcareous soil. Methods of bio-fumigant management and fumigant application followed the same procedure at both locations. Treatments in the weed control trial were arranged in a split-plot design with herbicide input level as the main-plot and level of fumigation as the sub-plots. Herbicide programs will include no herbicides, reduced herbicides, and a conventional herbicide treatment. The sub-plots included no fumigation, commercial fumigation, a mustard and an oilradish cultivar as green manures. Weed emergence and growth were monitored in permanent quadrats by taking weed counts and visual evaluations weekly. Weed biomass and onion yield were determined at the end of the season.

Objective 6
Nematode population density was estimated before planting the bio-fumigants in July-August, before incorporation and fumigation, after incorporation and fumigation and after onion harvest. Eight weeks after planting the bio-fumigants, they were incorporated into the soil. In the following spring, onions were planted in the field at the rate 120,000 seeds/A. Responses of the individual treatments were recorded by counting the nematode population in the soil and root at harvest. Onion yield and size was recorded.

Objective 7
During the third year of the study, five acres of onions at two different locations, within two grower’s commercial fields had one of the bio-fumigants fall incorporated. Weed emergence and growth data, along with P. terrestris counts in the soil and plant tissue, were collected throughout the year and compared to an adjoining five acres within the same field. Yield and quality data were collected at the end of the year and onions grown in the bio-fumigant section were compared to onions grown in the standard commercial onion production area.

Information collected from this work was disseminated through two field days each year; one at the University of Idaho Experiment Station and the other at the Oregon State Malheur Experiment Station. The information was also be presented at workshops and at the annual Idaho Eastern Oregon Onion Meeting. Peer reviewed journal articles are being prepared and will be published within the next year.

Research results and discussion:

Objective 1 – Evaluate a mustard and oilradish cultivar for the ability to reduce onion production problems, and compare them to soil fumigated with Metam Sodium and not fumigated.

Evaluation and comparison of the biofumigants, fallow and chemical fumigant on onion production is best described in objectives 2 – 7 and will not be repeated here in objective 1.

Objective 2 – Evaluate summer-fall biofumigant crop effects on both P and N availability to subsequent onions.

The biofumigants, especially the oilseed radish (Colonel) tended to have higher P and N concentrations when no P was previously applied as compared to the highest P rates, probably due to greater biomass and nutrient dilution with adequate P. “Colonel” had significantly higher P and N concentrations than “Idagold” at higher P rates, but “Idagold” tended to have higher total P and N content due to greater biomass (Table 1). Mineralized N increased as the growing season progressed over all years and net N mineralization tended to be higher with higher available P in most years (Table 2). Increased biomass with previously applied P at 225 lbs/A did not significantly affect mineralized N when compared to the same fumigation treatment. The biofumigants “Idagold” and “Colonel” tended to release more N before onions were planted and in some years during the onion season than the fallow or fumigated plots (Tables 2 and 6). Onion stands were largely unaffected by biofumigants in 2004 or available P as compared to the fallow treatment. Stands were generally highest where the soil was fall fumigated using Metam sodium. Early season onion growth was stunted by the previous fall fumigation and nutrient contents were reduced. Onion plant P concentrations in June and frequently in August were significantly higher with previously applied P. Biofumigants did not affect early season onion growth or nutrient concentrations. Previously applied P did not affect dry biomass of onions near maturity nor N and P content, except for the fumigated treatment where previous P increased plant P concentrations. Marketable yield was significantly reduced with fall fumigation at the lowest P rate in all years.

Wheat was grown in successive years after biofumigation to determine the long term effects on the soil and nutrient availability. Initially Colonel had increased yields and protein content but as the third year of wheat was harvested the differences were not significant (Table 7). None of the treatments tested had an immediate or lasting influence on grain heading, maturation, number of heads, kernels per head or 200 kernel weight (Table 8). Idagold and colonel increased K uptake in wheat the year after onions and biofumigants had been in the test plots. The increase in K remained two years after for the biofumigant Idagold (Table 9). Sulfur uptake was influenced the same as K and Ca and Mg had increased uptake levels the first year following onions but the effects were not significant by the second year of wheat (Table 9). Wheat flag leaf P and SPAD were not influence by the biofumigant treatments (Table 10).

Objective 3 – Evaluate and compare soil properties.

Soil quality measurements were made in the weed free treatment of the study. The addition of plant dry matter contributes to the organic matter in the soil. Organic matter is a principle component of soil structure and contributes to water holding capacity and porosity. The organic matter was measured in each treatment to determine the contribution that the addition of green manure made to the soil. Bulk density measurements were made early in the season when the onions were 25 cm tall. The bulk density was measured on the surface 15 cm of soil using the standard core sample method. Aggregate stability was also measured using a dry sieves method. Soil aggregates were collected from the surface of the soil sieved to determine the number of aggregates at each size. Each of the samples was then sieved again to determine the difference among the sieved weights.

The addition of the green manure did not significantly influence soil bulk density or organic matter (Table 11) as was also the case in 2004. Soil nitrogen levels at 7-30 cm depth were significantly lower in the biofumigant treatments than the fallow treatment. Likely due to the extraction of nitrogen by the biofumigant plants and the majority of nitrogen deposited in the 0-7 cm depth with the plant biomass. Colonel had significantly more phosphorus at the 0-7 cm depth than the metam sodium or fallow treatments. There were no significant differences in phosphors levels among the treatments at the 7-30 cm depth. Potassium levels were significantly higher for Colonel and Idagold than Metam Sodium or Fallow at 0-7 cm. Sunrise had significantly higher potassium than all other treatments at 7-30 cm depth, suggesting that biofumigants had a benefit in increasing soil potassium. Cation exchange capacities did not differ significantly among the Fallow, Metam Sodium and the biofumigant treatments (Table 11).

Continuous green manure applications may indeed increase %OM over time. Nutrient recycling appears to occur with incorporation of the plant biomass back into the soil. Both of which, are and will be beneficial to the soil and onion production if the practices continue. However, it may take many years for the soil organic matter to increase and other beneficial soil properties to be observed.

Objective 4 – Determine if a biofumigant crop positively or negatively impacts root populations of Mycorrhizae and Phoma terrestris (pink root).

Mycorrhizae counts were collected by taking a core of soil 6 inches deep by 2.5 inch diameter with the onion at the center. Each sample was washed on a 500 micrometer sieve to remove soil. Then the roots were washed again on a 25 micrometer sieve. The onion roots were then placed in 70% ethanol. The root density / gram of soil was calculated and the Mycorrhizae were stained and counted according to vesicular colonization and hyphal colonization. Mycorrhizae sampling dates will be given when the mycorrhizae analysis is completed.

Mycorrhizae colonization of onion roots

2002

Metam sodium treatment had significantly less arbuscule colonization than the fallow, “Idagold,” and “Colonel” on the May 2 sampling date. Significant differences remained among the metam sodium and “Idagold,” and “Colonel” treatments for the May 16 sampling date. “Sunrise” had significantly less colonization than “Idagold,” and “Colonel,” and “Idagold” in the May 2 and May 16 sampling periods, respectively. In general arbuscular colonization percentages increased early and then decreased as the onions matured until there were no differences among treatments. Metam sodium clearly reduced colonization, but “Sunrise” appears to have some negative influences on beneficial Mycorrhizae.

Hyphal colonization follows the pattern of arbuscular colonization in that metam sodium had significantly less colonization than the fallow, “Idagold,” and “Colonel” on the May 2 sampling date. Significant differences remained among the metam sodium and “Idagold,” and “Colonel” treatments for May 16. Hyphal colonization increased early in the growing season and then plateau. Metam sodium and “Sunrise” reduced the colonization of Mycorrhizae in onion roots.

Metam sodium significantly reduced colonization on May 2 and May 16 when compared to all other treatments. The percent of arbuscular colonization followed the patterns from field E4 where the percentage increased and then either plateau or decreased as the onions developed.

Metam sodium significantly reduced colonization on May 2 and May 16 when compared to all other treatments. The percent of hyphal colonization followed the patterns from field E4 but the colonization was higher than in E4.

2003
High Lime Plots 2003
All data for high lime plots were analyzed as a split-plot experiment in five blocked replicates with fertilizer as the main plot factor at three levels: check, N, and NP, where N was applied at 225 lb N ac1 and P was applied at 225 lb P2O5 ac1. Fumigation was the split-plot factor at four levels: fallow, Vapam, Idagold, and Colonel.
Vapam significantly (Table 10) reduced root length and mycorrhizal colonization (Table 11).Vapam fumigation also reduced shoot P concentration and shoot dry mass at various harvests, and the combination of these effects significantly (Table 12) reduced shoot P content at the last two harvests (Table 13). Fertilizer effects and interactions between fumigation and fertilization were rare (Tables 10 and 12), indicating that the compensation for lack of mycorrhizae in onion offered by P fertilizer was only partial. For example, shoot P content in the Vapam treatment on the 6 June was 106 g P shoot1 in the check and 205 g P shoot1 in the NP treatment, compared to between 288 and 347 g P shoot1 in the fallow and biofumigant treatments given NP fertilization. The significant interaction between fumigation and fertilization for shoot P content at the third harvest did not show any meaningful pattern in relation to treatments and was likely generated as a chance event, which is prone to happen one time in twenty for the 5% probability level.
These results show that chemical fumigation reduces mycorrhizae of onion and that P fertilizer is only partly effective to offset this effect in the early season. Further, the biofumigant treatments do not inhibit the growth of mycorrhizae and are associated with early season growth and P nutrition of onion that was essentially indistinguishable from that of the fallow treatment.

2004

Low lime plots did not have consistent significant differences among the treatments and the arbuscular mycorrhizae infections. High lime plots had significantly more mycorrhizae than the metam sodium treated plots. Phosphorus levels tended to decrease mycorrhizal colonization.

High lime plots.

Mycorrhizae results
Vapam significantly reduced root length and mycorrhizal colonization.Vapam fumigation also reduced shoot P concentration and shoot dry mass at various harvests, and the combination of these effects significantly reduced shoot P content at the last two harvests. Fertilizer effects and interactions between fumigation and fertilization were rare, indicating that the compensation for lack of mycorrhizae in onion offered by P fertilizer was only partial.
These results show that chemical fumigation reduces mycorrhizae of onion and that P fertilizer is only partly effective to offset this effect in the early season. Further, the biofumigant treatments do not inhibit the growth of mycorrhizae and are associated with early season growth and P nutrition of onion that was essentially indistinguishable from that of the fallow treatment.

Pink Root
Pink root samples were collected on June 2 and July 26, and were estimated by placing the onions in 6 classes based on the infection of the roots. Class 1 was 0%, 2 = 1-3%, 3 = 4-6%, 4 = 7-10%, 5 = 10-15% and 6 = 16-30%. In low lime plots (field M6), pink root severity was not significantly different among the treatments (Table 21). Idagold and Metam Sodium had significantly less disease severity than the Colonel and Sunrise treatments. However, Idagold and Metam Sodium were not significantly different from the fallow treatment. In the high lime field, the Metam Sodium (fumigated) treatment was significantly lower than the other treatments. Idagold and Colonel were not significantly different from the fallow treatment (Table 4).

Objective 5 – Determine if the use of biofumigant crops in onion production has potential to reduce the use of synthetic fumigants and herbicides applied for weed control by reducing weed germination and growth.

Methods
Weed control programs included a weedy check, low herbicide inputs, high herbicide inputs, and a weed free check. The low input herbicide program consisted of Buctril (0.19 lb ai/acre) plus Goal (0.094 lb ai/acre) applied to 2-leaf onions on May 23, 2002, May 16, 2003, and May 3, 2004, Buctril (0.25 lb ai/acre) plus Goal (0.125 lb ai/acre) plus Poast (0.19 lb ai/acre) applied to 3 to 4-leaf onions on May 31, 2002, May 27, 2003 and May 20, 2004 and Goal (0.25 lb ai/acre) applied to 4 to 6-leaf onions on June 12, 2002, June 9, 2003 and June 3, 2004. The high input herbicide treatment was the same as the low input but included a preemergence application of Roundup (0.375 lb ai/acre) and Prowl (1.0 lb ai/acre) on April 2, 2002, April 7, 2003, March 26, 2004, and the addition of Prowl (0.5 lb ai/acre) to the last postemergence application on June 12, 2002, June 9, 2003, and June 3, 2004. Herbicide applications were made with a CO2-pressurized backpack sprayer calibrated to deliver 40 gpa at 30 psi pressure in 2002 and 2004. In 2003, herbicides were applied with a 4-wheeler mounted sprayer calibrated to deliver 30 gpa of water at 30 psi. Plots were 6 rows wide by 25 feet long. Weed control was evaluated using weed counts, visual weed control ratings, and weed biomass samples. Weed counts were taken from 10 feet of rows 2 and 4 in each plot on May 6, June 3, June 11, June 25, and July 24, 2002, May 13, June 8, and June 23, 2003, and April 20 and June 1, 2004. On July 29, 2002, July 11, 2003, and July 20, 2004, weed control was evaluated visually. Weed biomass samples were harvested from 5 feet of one row of each plot, separated by species, dried, and weighed on July 29, 2002, July 16, 2003, and July 19, 2004. Following sampling, weeds were removed from all plots to allow for harvesting in September. Onion stand was determined for each plot by counting the number of onions in 10 feet of rows 2 and 4. Onion yield was determined by harvesting 25 feet of the center 4 rows of each plot. In 2003, a reduction in onion stands in the first replication that was unrelated to treatment, required the first replication to be removed from the analysis of onion stand and yield data.
Weed Control
In 2002, the oilradish and mustard volunteered averaging 1.0 and 0.25 plants/yd2, respectively. In 2003, the oilradish volunteered producing a significant number of plants (35 plants/yd2). The mustard also volunteered but not in significant numbers. In 2004 the oilradish (Colonel) again volunteered. The hot mustard did not volunteer in any year. In each year volunteer biofumigants were removed by hand. Without the use of hand labor, the biofumigants would not have been effectively controlled by herbicide applications and would have been as competitive with the onion crop as many of the weeds. There were few effects of fumigant treatments on visual weed control (Table 9) or weed biomass (Table 10). In 2002, Vapam and the oil radish had higher redroot pigweed control than the fallow treatment, Vapam and the hot mustard greater common lambsquarters control than the fallow treatment, and Vapam provided greater annual grass control than all other treatments except for the mustard. The high input herbicide program provided increased control of all species in two out of three years, although differences were significant for each species for different years. Redroot pigweed and common lambsquarters biomass data was combined across all three years for. Hairy nightshade, kochia, and total weed biomass were combined across 2002 and 2004. Annual grass biomass could not be combined across years. In all years weed biomass was reduced by the high input herbicide treatment compared to the untreated check. In most cases, the low input herbicide treatment also reduced weed biomass compared to the untreated check. The exceptions were in 2003 where kochia, annual grass, and total weed biomass in the low input herbicide plots was equal to those in the untreated plots.

Onion Stand and Yield
While onion stand was not affected by fumigant treatment in 2003, onion stand was significantly reduced by all biofumigant treatments compared to the fallow or Vapam treatments in both 2002 (Table 12) and 2004 (Table 11). Correspondingly, onion yield was not reduced by fumigant treatments in 2003, but was significantly reduced by the three biofumigants in 2002 and 2004. It appeared that onion stand and yield were reduced because of the biofumigants that volunteered. However, the hot mustard did not volunteer in any year and yet onion stand and yield were reduced in the hot mustard plots in 2002 and 2004. This result suggests that the biofumigants are affecting the seed bed in some way that is reducing onion stand. Reductions in onion stand almost always result in reduced onion yields. Herbicide treatment did not affect onion stand in any year. Herbicide treated and handweeded plots yielded greater than untreated plots in all three years. Onion yields were increased with both the low and the high input weed control treatments compared to the untreated plots, and in 2003 onion yields were similar between the herbicide treatments and the handweeded check. In most comparisons in 2002 and in 2004, herbicide treatments yielded lower than the handweeded check. This was likely due to less than complete weed control in herbicide treated plots in 2002 and 2004.

Overall, the use of biofumigants did not positively affect weed control. However, the biofumigants did reduce onion stand and yield in two of the three years. Additionally, the mustard and the oilradish volunteered at varying levels in all three years becoming weeds themselves. Onion growers can not accept the negative affects caused by the biofumigants without any positive affect on weed control or suppression.

Objective 7 – Disseminate information by conducting research on grower’s farms, presenting data at field days, workshops and annual growers meetings.

This research project was presented to growers at three field days, to the Idaho Eastern Oregon Onion Research Committee, and twice at the Annual Onion Grower’s Meeting held in Ontario, Oregon.

Since this is the third and final year of the project, the biofumigants were grown by two commercial onion growers in their fields. The first grower had extremely poor stands of the biofumigant Idagold. The seed was placed in a fertilizer cart and was only supposed to be spread over a three acre area, however, the fertilizer cart with fertilizer and Idagold seed was used on 15 plus acres of land. The Idagold plants were spaced too far apart for significant biomass returns to the soil and the whole field had Idagold in it, so there was no control portion of the field to compare the biofumigants.

The second grower choose to use two biofumigants, Idagold and Colonel, a non-treated section and chemically fumigated the remaining portion of his field. Each biofumigant and non-treated section of the field was approximately 2.5 acres. Biofumigants stands were good but growth varied according to soil fertility levels. Where the field had higher N fertilizer application, the biomass that was produced was significantly greater than other portions of the field which had lower N application levels.

The amount of dry biomass that was worked into the soil in the fall was 1.5 tons / acre for the Idagold biofumigant and 1.6 tons / acre for the Colonel biofumigant. Stand counts, pink root, and nematodes for each of the four treatments within the grower’s field are given in (Table 26). Chemical fumigation had the highest stand counts followed by Idagold. Pink root severity data on onion roots was collected in June and July. Idagold was consistently lower in both sampling periods and was the lowest in June. Nematode counts were about the same except for Colonel (oilradish), which had a lot more pin nematodes than any other treatments.

Whole plant tissue samples from the treatment areas were collected on June 15 and July 28, dried and weighed. Onions samples from the chemical fumigated plot had higher dry weights than the other treatments. Similar results were observed in yield of onion bulbs that were harvested on September 14 (Table 27). More plant material, onion bulbs, was collected from the fumigated plot, nearly 100 cwt more than the next best treatment (control).

Although plate rot data was not recorded, it was observed that onion bulbs from biofumigant treatments and the non-treated areas had much higher rates of plate rot than the onion bulbs grown in the fumigated soil. The fumigated onions also had more onions and larger onions with fewer culls. Plate rot was so severe that the grower did not harvest the onions from the biofumigant treatments and from the non-treated areas, instead he disked them into the soil because the problem was so severe.

The biofumigants tested in this study will not be a viable substitute for chemical fumigation in commercial onion production. Results from small plot research indicated that biofumigants did little in benefiting onion yield and grade. In fact, the yields were consistently lower, which was likely due to the poor onion stands experienced in biofumigant plots. When the study was taken into a commercial onion grower’s field, the problems persisted and new ones became apparent. Stands were again lower in the biofumigant treated areas, and the biofumigants appeared to have increased the incidence and severity of plate rot.

Research conclusions:

The goal of this project was to find an alternative to chemical fumigation of onion fields. It was anticipated that the benefits from nutrient cycling and soil physical properties would help to offset the negative impacts that green manures have on onions. However, the nutrient cycling, soil physical properties, and pest control benefits from biofumigants were not beneficial in a way that would encourage commercial onion growers to use them. The biofumigants actually created more problems, for example, they volunteered and became very competitive weeds, reduced stands and germination, and in a growers field there was an increase in fusarium plate rot. Therefore, the results are not beneficial by increaseing onion yields and pest control and I do not recommend that Colonel, Idagold, and Sunrise be used as biofumigants in commercial onion production.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Geary, B., C. Ransom, M. Thompson, B. Brown, T. McGonigle, S. Hafez and J. Ellsworth. Biofumigant Use In Weed Control. Parma Weeds Tour. June 6, 2002.

McGonigle, T., B. Geary, R. Forster, B. Brown and C. Strausbaugh. Impact of Crop Rotation and Soil Tillage on Rotts and Mycorrhizal Fungi. Molecular Biology and Biotechnological Applications of Mycorrhizal fungi. New Delhi, India. March 23-26, 2003. Abstract

McGonigle, T., B. Geary, R. Forster, B. Brown and C. Strausbaugh. Impact of Crop Rotation and Soil Tillage on Rotts and Mycorrhizal Fungi. Molecular Biology and Biotechnological Applications of Mycorrhizal fungi. New Delhi, India. March 23-26, 2003. Proceedings

McGonigle, T., B. Geary, R. Forster, B. Brown and C. Strausbaugh. Impact of Crop Rotation and Soil Tillage on Rotts and Mycorrhizal Fungi. Molecular Biology and Biotechnological Applications of Mycorrhizal fungi. New Delhi, India. March 23-26, 2003. Oral presentation
Geary, B., C. Ransom, M. Thompson, B. Brown, J. Ellsworth, T. McGonigle and S. Hafez. Use of Biofumigants in Onion Production. Parma Onion Field Day. July 24, 2003.

Brown, B. and B. Geary. Nutrient recycling with biofumigant crops in crops. Parma Onion Field Day. July 24, 2003.

Geary, B., C. Ransom, M. Thompson, B. Brown, J. Ellsworth, T. McGonigle and S. Hafez. Use of Biofumigants for the control of onion pests. 44th Annual Meeting Oregon/Idaho Onion Growers. Feb. 3, 2004.

Beck, D., B. Geary, C. Ransom, R. McGonigle, B. Brown and M. Thornton. Biofumigation with radish and mustard as an alternative to metam sodium for control of pink root and weeds in onions. National Allium conference. Grand Junction, Colorado. 2004. Abstract

Beck, D., B. Geary, C. Ransom, R. McGonigle, B. Brown and M. Thornton. Biofumigation with radish and mustard as an alternative to metam sodium for control of pink root and weeds in onions. National Allium conference. Grand Junction, Colorado. 2004. Oral presentation

Geary, B., D. Beck, C. Ransom, R. McGonigle, B. Brown and M. Thornton. Use of Biofumigants For Pest Control In Onion Production. BYU PAS 694R Seminar speaker. April 9, 2004.

Geary, B. B. Brown, C. Ransom, and S.L. Hafez. Biofumigants in Commercial Onion Production to Control Weed, Nematode and Disease Pests. International Biofumigation Conference. Moscow, Idaho. 2006. Abstract

Geary, B. B. Brown, C. Ransom, and S.L. Hafez. Biofumigants in Commercial Onion Production to Control Weed, Nematode and Disease Pests. International Biofumigation Conference. Moscow, Idaho. 2006. Oral Presentation

Intending to publish 5 peer reviewed articles by April of 2007.

Project Outcomes

Project outcomes:

When the biofumigants were used in commercial onion grower’s fields, they did not perform well. Both fields had volunteer problems and one grower had a very severe fusarium plate rot problem, while his non-biofumigant onions had no fusarium plante rot. The fusarium was so severe that he did not harvest the onions but disked them up because they would not pass the standard grades for marketable onions. Economically this was a loss of approximately $8,000.

Farmer Adoption

No onion farmers are adopting biofumigants into their commericial onion production systems.

Recommendations:

Areas needing additional study

Biofumigants that do not volunteer and become a weed problem.

Chemical components released by biofumigants that inhibit pink root.

Relationship between biofumigants and fusarium plate rot.

Long term effects of nutrient cycling, soil physical properties, and disease control when incorporating biofumigants or green manures into soil on a yearly basis.

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.