Novel Rotation Crops as Alternatives to Fumigant Nematicide Treatment in Deciduous Tree Fruit Production

Novel Rotation Crops as Alternatives to Fumigant Nematicide Treatment in Deciduous Tree Fruit Production

Summary

This project will continue the evaluation of the feasibility of seven (7) alternative rotation crops as substitutes for soil fumigants used to control dagger nematode (Xiphinema spp.) prior to replanting tree fruit orchards.
Replicated field plots will be established at orchard replant sites in Pennsylvania and West Virginia. Treatments will consist of plantings of canola, corn, fescue cultivars with and without an Acremonium endophyte, marigolds, oats, and wheat. Dagger nematode population densities will be determined at planting and periodically during two growing seasons to determine the effectiveness of these crops for suppression of nematode population densities. Soil sampling and laboratory assays will also assess the impacts of these crops on nontarget soil organisms such as earthworms, and nematode predators and parasites.
Greenhouse and laboratory experiments will be conducted to evaluate whether suppression is due to the host suitability of the crop or to the development of a soil microflora antagonistic to nematodes.
Economic analyses will determine the production costs, market potential and feasibility of integrating each of the alternate crops into existing production systems. Additionally, the costs and benefits to subsequently replanted orchard trees associated with nematode suppression will be estimated for each rotation crop and for soil fumigation.
This information will be incorporated into a slide and video program for growers and crop consultants. Findings will also be integrated into Expert Systems IPM programs and regional Extension publications to assure rapid dissemination.

Objectives

(1) Evaluate the effectiveness of seven (7) alternate crops for suppression of dagger nematodes in orchard replant sites.

Dagger nematodes, Xiphinema americanum and Xiphinema rivesi, are major risk factors associated with production of deciduous tree fruits in the northeast and throughout the United States. Other widely distributed nematodes of concern to fruit growers include root lesion nematodes, Pratylenchus spp.; ring nematodes, Criconemella spp.; and root knot nematodes, Meloidogyne spp. All of these nematodes may cause serious yield losses when present in high numbers; however, because of the potential of dagger nematodes to serve as vectors of lethal virus diseases, nematode control strategies in fruit orchards are driven by the need to suppress dagger nematode population densities to the lowest possible level.

Current nematode control recommendations involve application of chemical nematicides and fumigants prior to replanting orchards. Two years of rotation crops are recommended to improve soil fertility and structure, control perennial weeds and eradicate other pests. The most frequently used rotation crops, corn and soybeans, help achieve these goals and provide an economic return to growers during the rotation years. However, both of these crops serve as excellent hosts for nematodes, increasing their population density, and thereby, increasing the need for chemical nematicide applications.

(2) Quantify the impact of alternate crops on dagger nematode reproduction, tomato ringspot virus transmission, soil microflora associated with nematode biocontrol, and other nontarget soil organisms.

To properly utilize rotation crops to suppress nematode populations, their mode of action must be understood. These crops may be nematode-resistant hosts or be toxic to nematodes. If so, their use as an orchard cover crop may be needed to extend nematode control throughout the life of the orchard.

A competing hypothesis suggests that these crops induce a soil microflora that contains naturally occurring nematode biocontrol agents. As such these cover crops could induce biological soil suppressiveness to provide a long residual effect after the orchard is established. Virtually no information is available to evaluate these phenomena; however, a new technique developed at West Virginia University has the potential to provide quantitative data to evaluate the significance of this mechanism.

Tomato ringspot virus, vectored by dagger nematodes, has a broad host range, thus alternate rotation crops should be evaluated for their virus host status. Crops that serve as virus reservoirs would be inadvisable for fruit orchard rotations.

Other soil organisms may also be impacted by these crops and have long term effects on the subsequent orchard crop. Specifically earthworm populations, known to be negatively affected by chemical nematicides, may also be impacted by nematode suppressive crops. Because of their importance in improving soil structure, earthworm populations provide an important bio-indicator of the impacts of rotation crops.

(3) Assess the economic implications of integrating alternate crop production into existing orchard practices.

The economic feasibility of producing alternate rotation crops within existing orchard operations is a key factor in their widespread acceptance and implementation. Additional costs of crop rotation such as labor, machinery, and delays in fruit tree planting must be calculated against reduced pesticide costs and any returns from the rotation crop. For a complete economic analysis, efficacy of crop rotation versus fumigation must be incorporated into a yield loss function that assesses both reduced yields and increased tree mortality associated with nematodes.

(4) Disseminate research results via Extension and regional Extension Farm programs.

Five major horticultural stations are located within 50 miles of research sites and frequent interactions with Extension specialists will serve to maximize dissemination and utilization of our research. Regional and national dissemination occurs via meetings with the Northeast Nematology Research Project, the Cumberland-Shenandoah Fruit Workers Conference, the Stone Fruit Decline Workshop, and national professional society meetings. Growers and crop consultants in the region readily adopt new production recommendations, especially when economic benefits complement improved environmental protection. As such, relatively simple educational materials, e.g., slide shows and video programs, will reach a wide audience through existing extension programs. These materials will also enhance dissemination of findings nationwide.

Results

Researchers found that some crops may provide environmentally sound and economical tactics for controlling soil-borne disease that affect the tree fruit industry. Two rotation crops, marigold and canola, effectively suppressed dagger nematodes. Canola, a brassica species, was easier to establish, more successfully competed with weeds and seemed to be resistant to tomato ringspot virus.

Other brassica species have shown similar characteristics, but more research is needed to identify the best cultivars. No rotation was as effective as soil fumigation, although brassicas and marigolds were as effective after two years as post-plant nematicides in most experiments.

Some rotation crops - wheat, oats and fescue - gave inconclusive results, while others - sunflower, sudan grass and alfalfa - were good hosts for dagger nematodes.

Fruit growers have expressed interest in this work and researchers anticipate that an effective crop rotation program for dagger nematode control would be readily accepted.