Project hones vegetable-growing techniques
Multiple grants fund experimentation with organic grafting
By STEVE BROWN
MOUNT VERNON, Wash. -- Verticillium wilt kills about a fourth of Washington state's tomato, eggplant and watermelon crops in most years. Some years it can kill the entire crop.
Researchers at the Northwestern Washington Research and Extension Center are looking at grafting vegetable scions onto resistant rootstock to provide disease control. The practice, long used in Asia, Europe and Canada, can be effective in both conventional and organic operations.
"It's an ancient technology, but relatively new to the U.S.," WSU graduate student Sacha Johnson said.
There are few options available for organic growers, she said, and she's looking for alternatives to fumigation. "And rotation as a tool has its limits, with the 15-year life of Verticillium wilt."
The research, funded entirely by grants, is now in its second year. Grafting has cut losses from 100 percent to 10 percent in two fields, one at the Mount Vernon center and the other at a cooperating grower's field in Eltopia, in Eastern Washington.
"We're also grafting heirloom tomatoes to see if you get more vigorous yield," Johnson said.
She has been developing different techniques for grafting the vegetables, including the design of an inexpensive "healing chamber" for the newly grafted plants. This covered structure allows control of heat, light and humidity for the seven days required for the scion and rootstock to heal together.
"We're troubleshooting for growers to do it on their own," she said.
Another WSU project, this one in conjunction with research in Tennessee and Texas, is investigating the use of biodegradable mulches in production systems that use protective high tunnels.
The high tunnels are passively heated, three-season structures that many growers use to extend the growing season, make use of limited farmland and grow crops organically.
"The goal is a tillable, biodegradable, organically certified mulch," graduate student Jeremy Cowan said.
By using mulch fabric that degrades in the field, he said, farmers will save significant labor and disposal costs, help conserve resources and decrease pollution.
Polyethylene plastic mulches have been commonly used, but they are expensive, nonrenewable and must be removed from the soil and taken to landfills.
An experimental nonwoven polylactic acid mulch and two products made of cornstarch polymer were tested alongside plastic and cellulosic controls.
Carol Miles, horticulturist at Mount Vernon, said neither the polylactic acid nor the polymer products would be allowed in U.S. organic systems because of two issues: the genetically modified corn and the additives used to make the polymer.
One of the European-manufactured cornstarch polymer products "impressed me," she said. "And it was allowed in European Union organic systems. I naively thought it would be allowed in the U.S., but it's not."
In growing plots of tomatoes, strawberries and lettuce -- both in open-field settings and under high tunnels -- the cellulosic and polymer mulches degraded the most; the polylactic acid and plastic degraded the least.