Summer 1995 (v7n3)
Reflective mulches repel aphids and protect cucurbitaceous crops from virus diseases.
James J. Stapleton, Charles G. Summers, Roger A. Duncan and Albert S. Newton
Adapted from Plant Protection Quarterly 5(1):4-5. 1995
Introduction
Virus diseases carried by aphids can hinder the production of cucurbits (e.g., melons, squash, cucumbers) in California. Aphid feeding causes some direct damage to the plant, but the loss due to disease is far greater. Numerous studies have shown that reflective mulches covering the soil can repel aphids and delay or reduce the incidence of non-persistent virus diseases in susceptible vegetable crops. The lack of suitable materials for mulching impeded adoption of this practice in California up until a few years ago.
A number of silver polyethylene mulches are now commercially available and have been used with some success. This film must be removed and properly disposed of in order to prepare the ground for the following crop. Another material being explored, but not yet commercially available, is water-soluble, biodegradable synthetic latex spray mulch. This product can be applied more economically than polyethylene films, and can simply be incorporated into the soil after harvest. This report details field experiments to compare the effects of reflective spray mulch and plastic film products in repelling aphids, delaying the onset of virus disease, and increasing yield of zucchini squash and cantaloupes.
Materials and Methods
Replicated field experiments were conducted for two years (1993 and 1994) near Fresno, California from August to October, and compared silver-painted spray mulch (Styrofan, BASF Corp.) with several silver and white pigmented plastic film mulches. Experimental sites were pre-irrigated, fertilized and treated with pre-plant herbicides according to standard practices for the area. Treatments consisted of 5-6 replications, 3.1 x 7.6 meters. Plots were separated by fallow areas 3.1 meters wide. Each plot was three beds wide. The center bed was used as the data row, with a guard row on either side. Treatments in the 1993 zucchini experiment included two silver polyethylene films, white polyethylene film, silver nylon film and silver nylon net mulch, silver-painted spray mulch and white spray mulch, no mulch with two applications of the insecticide diazinon to plant foliage, and a non-mulched control.
Planting holes were made in the mulches, and zucchini squash (Cucurbita pepo var. melopepo vv. sunre 7918) was seeded on August 3. After emergence, the crop was raised according to standard cultural practices. Plants were rated for appearance of first foliar symptoms of virus disease infection at the first squash harvest, and one and two weeks following the first harvest. Plants were picked 12 times, about every other day. Squash were rated for marketability (size and presence or absence of virus symptoms) and yield. Procedures for the 1994 cantaloupe experiment were similar, except that treatments included complete bed coverage (1.7 meters) with silver polyethylene mulch; complete, 75 percent, 50 percent, and 25 percent bed coverage with silver spray mulch; and the nontreated control. Melons were harvested three times.
Results and Discussion
1993 Squash. Cotton/melon aphid (Aphis gossypii) were found on squash plants shortly after emergence. On the date of first squash harvest, foliar virus symptoms were visible on more than 95 percent of the plants grown on bare soil, with or without insecticide sprays. White-colored spray or plastic mulches gave moderate (36-42%) relief from virus infection , while only seven to 17 percent of plants grown on silver-colored spray or plastic mulches exhibited symptoms (figure 1). Suppression of foliar virus symptoms was not documented after the fourth picking. Multiple infection by zucchini yellows mosaic (ZuYMV), watermelon mosaic-2 (WaMV), and cucumber mosaic (CMV) viruses occurred in the field. Infection by watermelon mosaic-1 or squash mosaic viruses was not detected, and cucurbit aphid-borne yellows virus (CABYV) was not tested.
All mulch treatments allowed significant (P < 0.05), 3- to 5- fold increases in cumulative, marketable yield of squash, as compared to the non-mulched controls. The silver spray mulch was as effective as silver polyethylene (figure 2). Early infection of control plants drastically reduced their ability to produce fruit, and the plants were essentially nonproductive.
1994 Cantaloupe Melon. As in the squash experiment, aphid populations and virus pressure were high from the time the plants emerged. Non-mulched plants were nearly 100 percent infected with CMV, WaMV, and ZuYMV prior to the first harvest. Mulched plots did not approach 100 percent infection until six weeks later. All mulch treatments gave large increases in yield, ranging from 4-fold (25 percent bed coverage) to 25-fold (polyethylene 100 percent bed coverage). The mulch treatments gave early protection to the emerging and developing squash plants, allowing production of a marketable crop which otherwise would not have been possible.
Conclusions
The results of this work, conducted under conditions of severe aphid and virus pressure, indicated that sprayable mulches can be as effective as plastic film mulches in reducing disease losses. Additional studies to refine biological and economic considerations of using spray mulch for virus suppression in vegetable crops are currently underway.
For more information write to: James Stapleton, UC Kearney Ag Center, 9240 S. Riverbend Ave., Parlier, CA 93648.
(DEC.526)
Contributed by James Stapleton
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