Off-season Plant-parasitic Nematode Management for Vegetables through Biofumigant Cover Crops

View the project final report

Commodities

• Agronomic: mustard, radish (oilseed, daikon, forage), rye
• Vegetables: cabbages, tomatoes

Practices

• Crop Production: cover crops
• Pest Management: biofumigation

Georgia has an important role in the national vegetable production with a farm gate value of $1.14 billion. The state is a leading producer of fresh market vegetables including cucurbits, brassicas, bell peppers, onions, sweet corn and tomato. Among the important vegetables for the state, cabbage and tomato are those grown as a double crop on the same land. For example, cabbage is typically planted between January 15 and March 15 and harvested 80-85 days later, while tomato is planted between March 15 and May 1 and harvested 70-90 days later. Nevertheless, the annual reiteration of this cabbage-tomato rotation is considered a poor production system, once there is a high risk of increasing plant-parasititc nematodes which considerably reduce marketable yields.

The humid and hot environmental conditions along with numerous rainfall and mild winters in southern Georgia favor the establishment and development of PPNs. Hence, nematodes are a major limiting factor in vegetable production areas of southern Georgia. PPNs can infect a broad range of vegetables by feeding on or inside the roots and establishing a parasitic association with host plants that cause disruption in water and nutrient uptake. Symptoms caused by PPNs are commonly observed in the roots and above-ground parts of plants as nutrient deficiencies, stunted growth, or poor yield. The intensive and continuous cultivation in southern Georgia, like the cabbage and tomato rotation, make PPNs a constraint in vegetable production.

Currently there are several species of PPNs that cause direct damage on vegetables. A survey for Georgia vegetable fields consisting of 278 samples collected during the spring and summer growing seasons of 2018 found root-knot, stubby root, ring, spiral, root-lesion, lance and reniform nematodes respectively in 67 percent, 47 percent, 36 percent, 34 percent, 23 percent, 16 percent and 5 percent of sampled fields. Among these nematodes, the root-knot nematode is an immense challenge for growers due to its capability to infect a wide range of vegetable crops. In Georgia, root-knot nematode are widely dispersed in major vegetable producing regions where they cause serious yield loss particularly in small-scale farms that may not have the resources necessary to utilize fumigants.

For decades, one of the main approaches to control root-knot nematode has been the application of fumigants to disinfest soil prior to planting. In recent year and after the phase-out of methyl bromide, which provided a high level of root-knot nematode control, there has been an increase in the number of vegetable growers that have problems with root-knot nematode. Indeed, root-knot nematode is an important yield-limiting pest in both small and large-scale farms, however the problem is often more severe for small-scale and organic growers who are economically limited to employ applicators to treat the soil or do not use fumigation treatment.

The phase-out of methyl bromide has caused a void in vegetable production that is forcing growers to use new fumigants and non-fumigant nematicides to control nematodes. However, new regulations regarding application of fumigants (buffer zones, specialized equipment and safety equipment, and special licenses), difficulty of application, and high costs of fumigants are compelling growers to use sustainable and environmentally friendly, yet effective options for PPN control. Non-fumigant nematicides, although are easier to apply and tend to be less expensive, are not as broad-spectrum as fumigants and are generally less effective on the first crop of double-cropping systems. One approach for management of PPNs and reduction of their damage to vegetables is the use of biofumigant cover crops in the rotation.

In the southeastern U.S., despite long growing seasons, the practice of growing 2 to 3 crops on the same agricultural land often creates a narrow window for growers to use cover crops. Major cover crops used in Georgia are winter annuals, however, vegetable growers may use effective Brassica cover crops in rotation with cash crops for managing PPNs. To qualify as an effective winter cover crop, Brassica crops should have a better control PPNs than rye, a commong winter cover crop, to have a place in root-knot nematode management. Brassica crops, due to their ability to produce generic biocides, are particularly useful for suppressing root-knot nematode and improving soil health. Cover crops should be a poor host for certain root-knot nematodes species to qualify as a suitable cover crop. Oilseed radish and white mustard are cool season cover crops and poor hosts to certain root-knot nematode species and have shown to lower population densities in the soil. Research conducted in Georgia reported an increase in root-knot species in the rhizosphere of some Brassica species, but incorporation of the crop residues into soil suppressed the nematode. Management of nematodes in a winter cover crop-vegetable cropping system should be enhanced by gaining more information on nematode population changes as influenced by nematode-resistant Brassica crops and the use of an effective non-fumigant nematicide. We hypothesize that oilseed radish and white mustard as biofumigant crops can suppress root-knot nematode populations and help retain nematodes in their rhizosphere that in turn increases the efficacy of nematicides applied in the upper layers of the soil profile. It is expected that these nematode-resistant cover crops can open new opportunities for managing root-knot nematode in vegetable crops.

The objectives are this project are:

• To determine the effects of oilseed radish, white mustard and rye on PPNs, and subsequent damages caused by root-knot nematode to cabbage and tomato when planted after cover crops;
• To evaluate the effects of selected cover crops on beneficial nematode communities;
• To compare the efficacy of biofumigant cover crops and 1,3-Dichloropropene on populations of parasitic and beneficial nematodes.