UC IPM Funded Projects: Project Description

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Control of curly top virus using trap crops and repellents against the vector, beet leafhopper. (03XA004)

Program

Exotic Pests and Diseases Research Program

Principal
investigator

G.P. Walker, Entomology, UC Riverside

Host/habitat

Sugarbeets

Pest

Curly Top Virus; Beet Leafhopper Circulifer tenellus

Disciplines

Entomology, Plant Pathology

Review
panel

Agricultural Systems

Start year (duration)

2003 (Three Years)

Objectives

Determine the relative attractiveness of different plant ages of sugar beets and tomatoes to spring-migrating beet leafhoppers.

Evaluate the effectiveness of trap crops and repellents to deter migrating beet leafhoppers from settling and feeding on tomatoes.

Determine the spatial dynamics of the initial arrival of spring-migrant beet leafhoppers in commercial tomato fields and their subsequent within-field dispersal.

Determine the repellency of imidacloprid and kaolin to beet leafhopper and the effect of kaolin on beet leafhopper probing behavior.

Examine flight behavior as leafhoppers approach potential hosts and initiate landing.

Project
Summary

The use of trap crops and repellents will be examined for their potential use in preventing inoculation of tomato fields with curly top virus by the insect vector, beet leafhopper. Both the virus and vector are exotic pests, native to the Old World. Sugar beets are a preferred host of beet leafhopper and will be tested for their suitability as a trap crop. Several repellents will be tested to determine their effectiveness at deterring migrating beet leafhoppers from settling in tomato fields: silver reflective plastic mulch, white plastic mulch, green plastic mulch, and spray coverage of kaolin. Tests will be conducted in both experimental plots and commercial fields. The spatial distribution of vector leafhoppers landing tomato fields will be examined to determine if only the upwind end of the field needs protection. Finally, flight behavior of the vector will be examined to gain insights on how to design improved trap-crop and repellent strategies.

Third-year
progress

Plastic mulches were demonstrated to provide several benefits for growing tomatoes on the west side of the Central Valley. Plants recovered from transplant shock more rapidly when planted into plastic mulch (reflective silver or dark green). In field tests, there were reduced numbers of beet leafhoppers on the silver reflective plastic mulch treatment. Plants in plastic mulch (both reflective silver and dark green) also grew larger and produced heavier yields. This added benefit is very important to make the use of plastic mulches economically viable. The kaolin-based insect repellent Surround did not result in lower numbers of beet leafhopper in field tests, and in laboratory tests, it did not demonstrate any repellency. We did not detect consistent differences in leafhopper numbers among different planting dates of tomatoes or sugar beets. As expected, the leafhoppers reproduced, creating nymphal populations in sugar beets but not in tomatoes. In large commercial tomato fields, migrating leafhoppers were distributed throughout the field rather than concentrated on the field margins. This means that control measures need to be applied over the entire field rather than only on the windward edge of the field.

Second-year
progress

Plastic mulches were demonstrated to provide several benefits for growing processing tomatoes on the west side of the Central Valley. Plants recovered from transplant shock more rapidly when planted into plastic mulch (reflective silver or dark green). Rapid growth early in plant development is considered important in escaping infection by curly top virus. Unfortunately, beet leafhopper populations and curly top virus incidence were low in 2004 so we were unable to detect if the rapid early growth we observed reduces incidence of virus infection. However, we did observe reduced numbers of beet leafhoppers on the silver reflective plastic mulch treatment. Plants in plastic mulch (reflective silver and dark green) also grew larger and produced heavier yields.

The kaolin-based insect repellent Surround did not result in lower numbers of beet leafhopper, although the overall low population of beet leafhoppers made differences difficult to detect. We did not detect consistent differences in leafhopper numbers among different planting dates of tomatoes or sugar beets. As expected, the leafhoppers reproduced, creating nymphal populations in sugar beets but not in tomatoes. In large commercial tomato fields, migrating leafhoppers were distributed throughout the field rather than concentrated on the field margins. This means that control measures need to be applied over the entire field rather than only on the windward edge of the field.

First-year
progress

This project consists primarily of field experiments, and data collection will not begin until the Spring migration of the leafhoppers begins. Based on weather conditions, Spring migration should begin next week (week of April 5, 2004). Therefore, there is no data yet to summarize. We have completed the set up our field plots for three experiments at West Hills Community College in Coalinga. These field plots include four different planting times for sugar beet, four different direct-seeding and two different transplant times for tomato, and two different transplant times for each of four repellents (three colors of plastic mulch and kaolin) and untreated controls. We will begin sampling leafhoppers the week of April 5, 2004. We also have arranged with our UC Cooperative Extension Collaborator for four commercial fields to conduct the experiment of Objective 4. We will also begin sampling leafhoppers for this experiment the week of April 5, 2004.

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