Reflective Mulch Fights
Pests in Vegetable Fields

By Lisa Lieberman
California Correspondent

In the same way that humans shy away from ultraviolet (UV) light because they know it’s bad for them, it seems that silver leaf white flies and aphids don’t much care for UV rays either.

Scientists have found that aphids and white flies - pests that afflict most California vegetable crops - are ultra sensitive to UV rays and tend to stay away from them. So as a deterrent to these pests, more growers have been using plastic reflective mulches in vegetable fields instead of pesticides to fight these pests.

UV rays work well against aphids and white flies, since theses pests use visual cues when they search for food. But unlike humans, they don’t sense shapes, but see wavelengths of light.

“When they approach a field of (vegetables), they are perceiving green wavelengths coming at them,” said Charles Summers, an entomologist with the University of California Kearney Agriculture Center, Parlier, Calif.

Plastic reflective materials are comprised of plastic sheets with thin layers of chemically bonded aluminum ions. They are spread throughout vegetable fields in six feet widths and varying lengths before planting.

The plastic reflective mulches act like a mirror and reflect UV light as well as other types of light into the atmosphere, Summers said.

The plastic mulches seem to work especially well in zucchini, squash, cucumber, cantaloupe, broccoli and sweet corn crops. The plastic mulches can be used in conjunction with conventional pesticides to fight aphids and white flies.

But the reflective mulches tend to keep pests out of the fields, alleviating the need for using pesticides, Summers said.

“By using reflective mulches we can virtually control aphids and white flies without insecticides,” Summers said.

The reflective mulches cost about $150 to $200 per acre to apply Summers said.

Some pests, especially, aphids, transmit different types of viruses, including the watermelon mosaic, cucumber mosaic and zucchini yellow mosaic viruses to vegetables.

While it takes several minutes for insecticides to kill aphids in the fields, it only takes several seconds for an aphid to transmit a virus, which can cause a problem long after the pest is dead.

Once the virus is in the field, similar to Pierce’s disease in grapes, there’s not much a grower can do to get rid of it, Summers said.

The best cure for a virus is prevention. And that means keeping the pests out of the field in the first place, Summers said.

Researchers have discovered possible beneficial uses of wheat straw as a reflective mulches in vegetable row crops.

The wheat straw, which cost about $50 per acre to apply, seems to have similar properties in reflecting UV rays as the reflective plastic mulches, Summers said.

In addition to being cheaper to apply than plastic mulches, the wheat straw can also be disked into the soil at the end of the growing season.

The main disadvantage of the plastic mulch is that, as with any other plastic, it has to be picked up and disposed of at the end of the growing season. And that takes additional labor, Summers said.

Whether growers use plastic reflective mulches or wheat straw mulches, both techniques also have several other advantages, Summers said. The mulches help reduce weeds and conserve water.

Since the mulches tend to reflect more light up from the ground, this creates more light penetration in the plants themselves, and hastens photosynthesis. This helps increase plants’ canopy sizes, which can ultimately result in healthier plants and larger sized vegetables.