Most of these special weed problems can be minimized through an active preplant weed management program.
Bermudagrass is a vigorous perennial weed that grows in the spring and summer. Bermudagrass is propagated by seed and an extensive rhizome and stolon system that is often spread during cultivation. It competes aggressively with grapevines for moisture and nutrients. Seedlings can be controlled with preemergence herbicides. Immediately spot treat any developing areas of bermudagrass in a vineyard with a postemergence herbicide such as sethoxydim (Poast) or glyphosate (Roundup). Glyphosate at high rates provides better control of bermudagrass than sethoxydim, however, sethoxydim is safer to use around grapes. Do not allow any herbicide to drift onto the grapevines.
Blackberries (Himalayan and California) are vigorous perennial plants often found around vineyard margins and occasionally around grapevines. They can interfere with all cultural operations, especially pruning and harvest. For best control, spot treat with glyphosate at the flower stage or after fruiting when there is good soil moisture and the plants are not water stressed. If regrowth appears, especially on large clumps, re-treatment may be required. If blackberry is growing into a vine, separate the berry stem from the grapevine before treating to reduce the chance of herbicide contacting the grapevine.
Dallisgrass is a common perennial weed found in vineyards. It has a clumpy growth habit that gives it a bunchgrass appearance. It can be highly competitive in newly planted and in established vineyards, where it competes with grapevines for soil moisture and nutrients. Dallisgrass seedlings germinate in spring and summer and form new plants on short rhizomes that developed from the original root system. Dallisgrass seedlings can be controlled with cultivation or preemergence herbicides. Treatment with glyphosate has been successful for control of dallisgrass infestations.
Field bindweed is a vigorous perennial weed that grows from rhizomes, an extensive sprouting root system, or seeds. Seeds can survive for up to 30 years in the soil, therefore it is critical to control these plants before they can produce seed. Seedlings of field bindweed are controlled with cultivation, but mature plants may spread from stem or root fragments created by tillage operations. If field bindweed is present in or around the vineyard, spot treat with high label rates of glyphosate.
Hairy fleabane, also called flax-leaf fleabane, is a summer annual that reproduces by seed. If emergence occurs in late summer, it may act like a biennial. Each plant can produce over 40,000 wind-disseminated seeds. Hairy fleabane is often found growing in the same location as horseweed, a related species. Frequent tillage or soil disturbance can significantly reduce the population. Soil-residual herbicides, such as simazine (Princep) and rimsulfuron (Matrix), can provide good control before the plants emerge. Once plants have emerged, applications of glufosinate (Rely), 2, 4-D, or combinations of these two herbicides can provide good control of seedlings. Grapevines are very sensitive to 2,4-D; only use this material when vines are dormant. In both, the US and worldwide, glyphosate-resistant hairy fleabane is less prevalent than glyphosate-resistant horseweed. Do not use repeated applications of low rates of glyphosate (Roundup, Touchdown), especially when plants are taller than 6 inches, or resistance to this herbicide may develop.
Horseweed, also referred to as marestail, is typically a summer annual weed. However, plants that germinate from seed in late summer, often act like a biennial. More than 200,000 seed are produced by a single plant and can be disseminated by wind more than a 1/4 mile. Horseweed hosts the glassy-winged sharpshooter (a carrier of Pierce's Disease). Frequent mechanical tillage offers good control if done before plant growth reaches the rosette stage. Flaming or mowing does not provide adequate control of horseweed. Soil-residual herbicides, including simazine (Princep), isoxaben (Gallery, Trellis), rimsulfuron (Matrix), and flumioxazin (Chateau), provide good control at high label rates. Glufosinate (Rely) and 2, 4-D provide the best control of emerged plants from the seedling to the rosette stage. Control in California with glyphosate (Roundup, Touchdown) is variable. Horseweed is known to develop resistance to glyhosate where repeated applications are used.
Johnsongrass is a perennial weed that spreads from seed or from an extensive system of underground rhizomes. It grows vigorously in spring and summer when it overtops newly planted vines and competes for light, moisture, and nutrients. Under these conditions, severe setback of a young vineyard can occur. Postemergence application of fluazifop or clethodim can be used around newly planted vines. If johnsongrass develops in or around vines in an established vineyard, spot treat it with glyphosate to prevent the spread of its rhizomes. Do not allow herbicide to drift onto grapevines. Always read and follow all label instructions.
LITTLE MALLOW (CHEESEWEED)
Little mallow is an annual or biennial plant that occasionally is not controlled with preemergence herbicides. Glyphosate may provide inconsistent control of plants larger than 4 to 6 inches. Mature plants are tall and woody with a large taproot that can be removed with a shovel or with cultivation. Oxyfluorfen effectively controls seedlings and young plants.
Yellow nutsedge is a perennial weed that reproduces from underground tubers that survive for 2 to 5 years in the soil. The tubers are easily spread by cultivation equipment. Each tuber contains several buds that are capable of producing plants. If the tuber is not killed by cultivation or sprayed with an herbicide, one or two buds germinate to form new plants. If nutsedge develops in established vineyards, spot treat with glyphosate.