The stubby-root nematode (Paratrichodorus minor) and the pin nematode (Paratylenchus hamatus) are pests that attack grapevines. Invisible to the naked eye, nematodes are microscopic, parasitic roundworms that suck tissue fluid from grapevine roots. Depending upon the species, nematode worms either enter the roots or remain on the exterior when feeding. The feeding causes galls, or swollen areas, to form on roots and diminishes grapevine health. Damage includes growth loss and, as a result, a reduction in grape crops. For control, maintain well-aerated soil to decrease the likelihood of infestation. Soil fumigation with pesticides, such as those containing the active ingredient metam sodium for preplant control or fanamiphos for postplant control, are reliable options. The University of California suggests contacting a local, county-extension agent to create a control program tailored to your particular worm problem.
Variegated cutworms (Peridroma saucia) feed on grapevines as well as other host plants, such as potatoes and carnations. As the name implies, the worms, or immature larvae, display a variety of brown- and gray-mottled bodies with yellow dots and dark stripes. Cutworms measure approximately 2 inches in length. With the most prevalent damage appearing on younger grapevines, cutworms feed on fruit and leaves and are known to chew through the base of plants, resulting in collapse. For control, home gardeners should release parasites such as Euplectrus plathypenae, which kill cutworms. Parasites are available in garden-supply stores, catalogs and online. For severe problems, pyrethroid insecticides offer effective control.
Grape leaffolders (Desmia funeralis) are the immature larval form of moths. Though they display translucent bodies, gardeners often mistake them for green worms, as the leaf tissue they consume is visible. Their bodies also display telltale markings of black dots near their second set of legs, which distinguishes them from other similar pests, according to the University of California Integrated Pest Management Online. Grape leaffolder web leaves together, then roll the leaves over into an enclosed area for safe feeding. Severe infestations and repeated seasons of feeding result in a loss of leaf tissue that exposes grapes to sun damage and causes defoliation. For control of these worms, release the parasite Bracon cushmani, which paralyzes leaffolders. Apply the biological spray Bacillus thuringiensis for an organic method of management or the insecticide spinosad for chemical control.