Grapes and Herbicide Damage

Weed Types

• Weeds common to backyard gardens where grapevines grow include both perennials and annuals. Clover, crabgrass, purslane and spurge are annual weeds often controlled with herbicides sprayed directly on the soil. Herbicide chemicals may soak into the soil near grapevines and cause damage through the root system of the vines. Perennial weeds include bermudagrass, dandelion and nutsedge. Sprays for perennial weeds should be targeted directly onto the plant to avoid herbicide drift to grapevines.

Symptoms of Herbicide Damage

• Herbicide damage symptoms vary but often include slight leaf yellowing, malformation of leaves, reduced vine branch development, reduced grape size and yield, and possible vine death. Symptoms typically worsen with growth in the spring and summer. If you use herbicides near grapevines, the most effective to do so is during the vine's dormancy period in winter. Glyphosate (Roundup) herbicides cause leaf curl and severely reduced grape size and production. Dicamba herbicides produces leaf wilt, grape cluster reduction and twisted vine growth. Symptoms such as yellowing leaves and reduced fruit production are often mistaken for disease.

Weed Control

• Weed control in the garden is essential because harmful insect pests and disease develop easily in weedy areas. Both handpicking and use of a string trimmer are recommended by the University of California Integrated Pest Management Program. Placing a 3- to 4-inch layer of mulch around the base of the grapevine is also an effective weed-control technique. Weed seeds cannot germinate and grow if they do not receive sunlight. Organic mature compost is sometimes used as mulch material because the composting process itself kills weed seeds.

Additional Weed-Control Methods

• Grapevines are often grown to the side of a lawn turf area. Weeds may easily encroach on the nearby landscape. Mowing regularly with a high blade cuts off weed seed heads and prevents weeds from spreading. Spurge and wood sorrel spread low to the ground and must be handpicked or controlled by other methods. Cultivating soil around grapevines is also an effective weed-control technique. Care should be taken to avoid deep cultivation, which may damage grapevine roots.