Agricultural pest management
Special Weed Problems
(Reviewed 6/06, updated 5/08)
Most of these special weed problems can be minimized through an active preplant weed management program.
Bermudagrass is a vigorous spring- and summer-growing perennial. It grows from seed but its extensive system of rhizomes and stolons can also be spread during cultivation. In vineyards, it is very competitive for moisture and nutrients. Seedlings are controlled with preemergent herbicides. If bermudagrass develops in a vineyard or in localized areas, immediately spot treat it with a postemergent herbicide such as glyphosate (Roundup).
Blackberries (Himalayan and California) are vigorous perennial vines that are often found around vineyard margins and sometimes around grapevines. They 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 aren't stressed. A re-treatment may be required on large clumps if regrowth occurs. If blackberry is growing into a vine, separate the berry vine from the grapevine before treating so the herbicide will not get into the grapevine.
Dallisgrass is a common perennial weed found in vineyards. It can be highly competitive in newly planted vineyards; in established vineyards it competes 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 with preemergent herbicides. It has a clumpy growth habit that gives it a bunchgrass appearance. Treatment with glyphosate has been successful in controlling dallisgrass infestations.
Field bindweed is a vigorous perennial weed that either grows from seed, which can survive for up to 30 years in the soil, or from stolons, rhizomes, or extensive roots. Because of the seed's longevity in the soil, it is critical to destroy plants before they can produce seed. The plants may spread from stem or root sections that are cut during cultivations, however cultivation controls seedlings. Iffield bindweed appears 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 can act as a biennial. Each plant can produce over 40,000 seeds, which are disseminated by wind. 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. Glyphosate-resistant populations of hairy fleabane in the U.S. and worldwide are less prevalent than those of horseweed. Do not use repeated applications of low rates of glyphosate (Roundup, Touchdown), especially to plants taller than 6 inches, or resistance to this herbicide may develop.
Horseweed, also referred to as marestail, is typically a summer annual weed. However, when seed germinates in late summer, it can act like a biennial. More than 200,000 seed are produced by a single plant and disseminated by wind 1/4 mile or more. Horseweed hosts the glassy-winged sharpshooter (a carrier of Pierce's Disease). Frequent mechanical tillage offers good control as long as the plants are less than the rosette stage of growth. Flaming or mowing does not provide adequate control. Soil-residual herbicides, including simazine (Princep), isoxaben (Gallery), and flumioxazin (Chateau), provide good control at high label rates. Glufosinate (Rely) and 2, 4-D provide the best control on emerged plants from the seedling to rosette stage. Control in California with glyphosate (Roundup, Touchdown) is variable. Horseweed is known to develop resistance to glyphosate 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. Severe setback of a young vineyard can occur under these conditions. Postemergent 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.
LITTLE MALLOW (CHEESEWEED)
Little mallow is an annual or biennial plant that is sometimes not controlled with preemergent herbicides. Plants larger than 4 to 6 inches won't be controlled well with glyphosate. 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. One or two buds germinate to form new plants; however, if destroyed by cultivation or an herbicide, then a new bud is activated. In established vineyards, if nutsedge develops, spot treat it with glyphosate.
UC IPM Pest Management Guidelines: Grape
A. Shrestha, UC IPM Program, Kearney Agricultural Center, Parlier