Managing Garlic Bloat Nematode Using Bio-Fumigant Cover Crops
During spring 2011 all three cooperating farms were sampled to establish baseline levels of garlic bloat nematode present in the soil. At this time the experimental design was established for each farm (diagrams attached), and cover crop seed was ordered in preparation of summer planting. The results of this testing on each cooperating farm were negative for GBN. Each farm was re-sampled more extensively to determine if an error had been made in sampling or transport that had killed any nematodes present. The second set of samples also came back negative for GBN.
This unexpected result may have been an anomaly, or it may have indicated that our climate, with its wet falls, does not allow GBN to enter its overwintering stage. This spring we will again sample at the cooperating farms, which each had GBN present in their seed for a second year. If the results again come back negative, this will be a strong indicator that GBN persists exclusively on the seed, rather than in the soil. If this is the case, I would like to transition to using cover crops before the garlic is planted, to see if residue can suppress nematodes present in the seed without suppressing the growth of garlic.
Our two objectives were 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. It appeared that GBN was not able to survive in the soil through the winter, based on our sampling results. We will verify this result next year with our spring sampling on fields that had infested garlic in 2011. In order to expand our monitoring of GBN in these fields, we will also sow onion seeds, which show symptoms of GBN very quickly.
Because our objective of using biofumigant cover crops to control GBN in the soil was nullified this year, we looked for other ways to use biofumigant cover crops to suppress GBN. A secondary use of these cover crops that has been proposed is as a pre-plant treatment for infested garlic seed. If we are not able to recover GBN in the soil again this spring, we will examine use of biofumigant cover crops in this capacity.
April 2011: Establish tentative two year cover cropping and rotation plans with grower cooperators and order year one seed. This was accomplished according to plan.
May 2011: Collect baseline data on nematode populations and soil health from all sites and plant mustard cover crops. Deliver all year one seed to cooperators. The mustard cover crops were planted and seed was delivered. Sorghum was not planted, because the results indicating that GBN was not present had been received by this point.
June -July 2011: Plant vegetable crops as appropriate and plant sorghum sudangrass cover crop (end of July). Flail mow mustard cover crop and incorporate. After biofumigation period, retest GBN populations in the soil. This step was not completed because there were no GBN present in the soil.
September 10-15: Mow and incorporate sorghum-sudangrass cover crop. Roll soil lightly to improve biofumigation. After two weeks, a winter non-host cover crop may be sown. This step was not completed because there were no GBN present in the soil.
Late August 2011: Test vegetable and sorghum-sudangrass fields for GBN in the soil. This step was not completed because there were no GBN present in the soil.
October 2011: Test fall mustard field for GBN in the soil prior to garlic planting. This step was not completed because there were no GBN present in the soil.
November 2011- January 2012: Compile results from assessments, make recommendations for growers for 2012. Update growers and Extension staff about progress during winter meetings. We have discussed the results of this trial at the Cornell Ag. Agents Inservice (20 attendees) and at the New England Vegetable and Fruit Conference in New Hampshire (225 attendees). Results will also be discussed at three garlic schools in New York this winter (100+ attendees expected)
Impacts and Contributions/Outcomes
because the results were unexpected and are not yet conclusive, we have not disseminated this information as reliable yet. However, interest in the persistence of GBN in the soil is quite high. If GBN does not persist in the soil, this will be extremely beneficial for growers, particularly those who grow predominantly garlic.
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