PESTS : Silver Paint Discourages Aphids
Entomologist Charles Summers says silver-colored spray paint applied to the soil in a planting bed seems to deter some insect and disease problems in vegetables.
Summers and another University of California expert, plant pathologist James Stapleton, began trying a water-based silver spray paint last year to discourage aphids on squash.
“When an aphid is flying along looking for a place to land, it cues in on reflections coming off of plant surfaces,” Summers reports in a recent edition of California Agriculture, published by the university. “If they see a reflection of the sky, the aphids don’t land.”
The idea behind keeping aphids from landing is they transmit viruses that stunt plant growth, reducing yield and causing deformed, discolored, unmarketable vegetables. Peppers and melons are as susceptible as squash.
Summers and Stapleton, both based at the Kearney Agriculture Center, applied the silver spray as a ground mulch in one of eight treatment methods for zucchini.
They reported that plants grown on beds treated with the spray-on silver paint produced 3,973 pounds of good-quality zucchini per acre.
Untreated control beds averaged 867 pounds per acre, but by the end of the season 90% of the zucchini was so virus-damaged a harvest was pointless. The experiments covered 12 harvests.
“The treatment works,” Summers says. “The silver-spray mulch repels aphids and delays the onset of virus infection by 10 days to two weeks.”
Summers and Stapleton also reported side benefits: The plants need less water because evaporation from the soil surface is reduced, and the crust formed on the spray-painted surface suppresses weeds.
Silver or white plastic also would help control aphids, they say, but must be gathered and disposed of at the end of the growing season while the water-based paint is simply incorporated into the soil without harmful effects.
Aluminum foil also would work but is too expensive in commercial operations.
In a related story, Michael J. Costello and Miguel A. Altieri describe how they used a living mulch of low-growing grasses and legumes as an alternative to pesticides in suppressing aphids in broccoli fields.
They found such a mulch does not reduce crop yields if properly maintained and that lower-intensity light reflected from broccoli grown with a living mulch is less attractive to aphids.
“In addition to replacing pesticides, living mulches smother weed growth, protect the soil from wind and water erosion, enhance soil fertility and structure and reduce soil compaction from heavy equipment,” they say. “They can play a role in conventional as well as organic agriculture.”
Altieri is an associate professor at UC Berkeley, and Costello is a postdoctoral researcher there.
They said lack of specialized equipment is the main limitation to commercial application of living mulches at this time. Their experiments were conducted at the Rural Development Center in the Salinas Valley.
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California Agriculture is published by the University of California’s division of agriculture and natural resources, 300 Lakeside Drive, 6th Floor, Oakland, CA 94612-3560.
