Tender young grapevines, raised at plant nurseries and destined for backyard or commercial vineyards, need to be kept free of certain kinds of microscopic worms called nematodes. That's why — before planting the vines — nursery managers typically fumigate planting beds with the chemical methyl bromide.
For the past six years, however, Agricultural Research Service plant pathologist Sally M. Schneider and colleagues have been testing an array of compounds that might prove to be effective, affordable, environmentally acceptable alternatives to methyl bromide.
Why the need for alternatives? Most uses of methyl bromide are being phased out because of concerns that this chemical damages Earth's protective ozone layer.
In recent experiments at L.E. Cooke Co., a commercial nursery in Visalia, Calif., Schneider and co-researchers explored the power of alternative chemicals to zap root-knot nematodes. These nearly transparent worms feast on plant roots, causing the plant to form small knots, or galls, that interfere with roots' ability to take up water and nutrients.
The researchers found that nematode control in nursery beds fumigated with either of three experimental treatments was about the same as that in nursery beds treated with methyl bromide and tarped. The experimental treatments were chloropicrin, iodomethane (a compound available for experimental use only) plus chloropicrin, or 1,3-dichloropropene plus chloropicrin (Telone C35), then covered with a plastic tarp for 16 days.
What's more, the young grapevines — a half-dozen different kinds of popular wine, fresh-market and raisin varieties — were nematode-free, when scrutinized at harvest nine months later. And, the plants were generally of the same high quality as those from nursery beds treated with methyl bromide.
Some of the alternative chemicals are already being used to protect other crops. But the grapevine study is likely the first to extensively investigate those compounds for protecting grapevines in a busy commercial nursery.
Schneider and collaborators Thomas J. Trout, an agricultural engineer and research leader, and plant pathologist James S. Gerik are with the ARS San Joaquin Valley Agricultural Sciences Center in Parlier, Calif., near Fresno. ARS is the U.S. Department of Agriculture's chief scientific research agency.