Managing Garlic Bloat Nematode Using Bio-Fumigant Cover Crops

View the project final report

• 2011 annual report
• 2012 annual report

Commodities

• Vegetables: garlic

Practices

• Crop Production: crop rotation, cover crops
• Education and Training: on-farm/ranch research
• Pest Management: biological control
• Production Systems: general crop production
• Soil Management: soil microbiology

Garlic Bloat Nematode (Ditylenchus dicapsci) was confirmed in sixteen counties throughout New York as well as in Massachusetts and in Vermont in 2010. Garlic Bloat Nematode (GBN) reduces yield and quality of food grade garlic by stunting and yellowing the plants, damaging roots and the basal plate, and increasing secondary infection by fusarium and soft rot pathogens. Damage in 2010 ranged from minor to 80% stand loss. Additionally, infested garlic should not be sold as seed, which is a primary market for many growers. Garlic is a staple of fresh market growers throughout the northeast, and is a primary crop for growers in each state. Cornell Cooperative Extension, in cooperation with the Garlic Seed Foundation, implemented broad outreach efforts during the 2010 growing season to reduce further spread of GBN to currently uninfested farms, but many farms are already infested with GBN. In order to assist farms which are infested with GBN, we will develop best practices to eliminate the nematode from the soil. The majority of garlic growers in New York are using organic practices to grow garlic, so we will focus on organically approved methods. Our two objectives are to determine the effectiveness of two bio-fumigant cover crops, Sorghum-Sudangrass and Mustard at eliminating GBN from the soil; and to determine how long GBN survives in the soil when a host plant is not present. These two objectives will be met through on-farm trials tailored to our three farmer cooperators’ needs and abilities.

Our two objectives are to determine the effectiveness of two biofumigant cover crops, Sorghum-Sudangrass and Mustard at suppressing GBN in the soil; and to determine how long GBN survives in the soil when a host plant is not present. These two objectives will be met through the use of on-farm trials tailored to each farm’s needs and abilities.

Cover Crop Trial: The two cover crops that we are interested in are high dhurrin Sorghum-Sudangrass (var. Trudan 8 or a similar substitute) and a high glucosinolate mustard (var. Pacific Gold or similar substitute). Sorghum-Sudangrass has been shown to be an effective control for northern root knot nematode (Abawi, 1998), but little research exists on its use as a control for garlic bloat nematode. Soil will be tested for nematode populations and overall soil health prior to cover crop planting. Mustard is often used as a biofumigant (Bjorkman and Shale, 2010) but again, no conclusive research about its effect specifically on GBN currently exists.

Each selected cover crop will be evaluated on a minimum of one farm and compared to a non-host crop treatment with no biofumigant activity (Check). Ideally, each crop will be grown on at least two sites. Prior to planting the cover crops, baseline data will be collected on nematode populations and general soil health. Four composite soil samples per treatment will be collected from each establish site for nematode analysis. One soil sample per treatment will also be collected before tillage practices and send for soil health analysis using the Cornell soil health protocol (http://soilhealth.cals.cornell.edu). Cover crops will then be planted and maintained by the grower, and will be flail mowed or chopped and incorporated in a timely manner to ensure maximum biofumigation (see timeline). Two to four weeks after cover crops have been incorporated, the soil will again be tested for GBN populations. If the soil still contains GBN, the same site will have the same treatment repeated again in 2012. If the test does not detect GBN, clean garlic seed will be planted in the test plots to assure that the soil is truly nematode free.

Establishing a timeline for nematode eradication from soils by growing non-host plants:
In order to determine the amount of time needed to eliminate GBN in soils lacking a host crop to the nematode in our temperate climate, a rotation of non-host crops will be adopted on all farms, either as a dedicated trial or as our control sample for the biofumigant trial. Soil will be tested for nematode populations and overall soil health prior to planting the first non-host crop. Nematode levels will be monitored in the fall 2011, in the spring of 2012, and in the fall of 2012, or until nematode populations have reached an undetectable level. On dedicated sites the trial will be broken into four replications; on sites paired with biofumigants the trial will also be broken into four replications.

Reducing GBN Populations: Growers who are not producing garlic for seed may consider eliminating GBN to be a secondary goal to keeping production levels maximized. We will work with one grower to use both mustard and sorghum-sudangrass in a rotation with garlic. This grower will plant cover crops in July after the garlic has been harvested, and will then replant clean garlic seed into the same field in the fall. We will test the soil while the garlic is still in the field during the spring of 2011, and after the cover crop has been incorporated in the early fall. We will then test the garlic to see if it has become infested. We will repeat this procedure twice, in 2011 and in 2012.

While this management strategy is not a best practice, we recognize that a number of producers who do not have enough land for a longer rotation and will be planting garlic back on the same land either year after year or biannually. This treatment will allow us to determine if following garlic with a biofumigant cover crop suppresses nematode populations enough to create an environment where food grade garlic can be effectively produced.