Sunspots on a Granny Smith apple can mean the difference between the lowest price for juice or the more lucrative fresh fruit market. As for nuts, last year buyers paid on average 3-cents a pound more for sunscreen-protected nuts than untreated ones, said Lagrutta.
Climate change and drought in Australia and California's Central Valley have meant challenging growing conditions for farmers that are affecting the quality, yields and price of produce. Sunscreens alleviate at least one worry for farmers, who lose money with each fruit or vegetable that develops sun damage.
"Under climate change, heat stress will become a bigger issue for plants, especially when it creates new heat-released disease," said Eric Wood, a professor of civil and environmental engineering at Princeton University.
Plants react to sun stress like humans. They perspire — a process called transpiration — which means the more temperatures rise, the more water they need. As drought grips several of the world's key growing regions, scientists are looking at ways to conserve by helping plants use less.
Liquefied clay has been used for years, but now a California company is finding positive results with an SPF 45 product made of multicrystaline calcium carbonate crystals that are engineered to specifically deflect ultraviolet and infrared light from the plants and trees on which it is sprayed. The product keeps out the bad light, but lets in the good photosynthesis rays that aid ripening.
The sunscreen has been tested in Australia and Chile, where UV rays affect production, and is in the second year of field tests in California.
Tests show its immediate impact is increasing yields by diminishing stress and heat-related defects, but the company that makes it hopes the product also can play a role in water and energy conservation by increasing a plant's water efficiency.
The sunshield, Purshade, made by Purfresh Inc., recently lured 20 U.S. and international farm product researchers and advisers to a walnut grove near Visalia, Calif.
The product also is being tested on tomatoes, grapes, kiwis and lychees in Australia, said Kerrie Mackay, who works for a company that sells crop protection products in Queensland, which she says is in 140-year drought.
"Sunburning is a big problem for us," she said, watching Lagrutta compare the telltale yellowing on one block of walnuts with a uniformly green plot sprayed with Purfresh. "We have some of the highest UV intensity in the world. With drought and climate change, finding ways to use water more efficiently is always important to us."
Amador County's Shenandoah Valley in the arid Sierra Nevada foothills is far from the temperate Napa Valley, but Dick Cooper of Cooper Vineyards has been growing 100 acres of premium wine grapes since the 1980s by using vine canopies to shade bunches.
In dry years, like this one, vine vigor is slow and exposed bunches of his pinot grigio shrivel into something resembling an olive pit, he said.
For the second year, he sprayed Purshade sunscreen on several of his blocks of white grape varietals to help protect them. He says that during the crush the calcium carbonate crystals drop to the bottom of the fermentation tanks with the rest of the sediment that comes in with grapes, so taste isn't affected.
"I'm not an expert on anything, but I'm always interested in trying anything," he said. "When my vines don't put up enough canopy, I like to give them a little help."