COMPARISON OF SPRAYABLE AND FILM MULCHES IN DELAYING THE ONSET OF APHID-TRANSMITTED VIRUS DISEASES IN ZUCCHINI SQUASH

Silver spray mulch and two silver polyethylene film mulches, applied to the planting beds before seeding, were effective in repelling alate aphids and delaying the onset of several virus diseases in spring- and fall-planted zucchini squash (Cucurbita pepo) in California's San Joaquin Valley. Disease symptoms in plants growing over these mulches appeared 7 to 10 days later than in plants growing on unmulched beds. In spring seeded squash, approximately 30% of the plants on unmulched beds were infected with one or more viruses by the first harvest while only 10 to 15% of those grown over the silver mulches showed virus symptoms. In fall-planted trials, 100% of the plants grown on unmulched beds, with and without insecticide applications, were virus-infected by the first harvest; less than 10% of plants grown over silver mulches were diseased at first harvest. Silver-pigmented mulches were generally more effective in repelling aphids and delaying virus onset than were white-pigmented mulches. Marketable fruit yields in the spring planting were approximately 70% higher in plots mulched with silver than the unmulched control. In the fall trial, yields of marketable fruit were 75 and 80% greater in plots mulched with silver polyester film and silver spray, respectively, than those from the unmulched control, either with or without an insecticide application. Although plants grown over the silver mulched plots eventually became infected, they continued to produce a significantly higher percentage of marketable fruit throughout most of the season than did the unmulched controls. Water-soluble, biodegradable silver sprays may be advantageous over polyethylene films because they can be incorporated into the soil at the end of the season, rather than requiring removal and disposal in a landfill.