Agricultural pest management
Integrated Weed Management
(Reviewed 6/06, updated 10/08)
Weed control in vineyards enhances the establishment of newly planted vines and improvesthe growth and yield of established vines. Growers have many weed management tools available to achieve these objectives; however, the methods of using these tools vary from year to year and from vineyard to vineyard.
Weed management is part of an overall vineyard management system; plants on the vineyard floor can influence other pests such as insects, mites, nematodes, and diseases. A weed management program should start before new vines are planted. The more difficult-to-control weeds (particularly perennials) are easier to manage before vines are planted. Weeds reduce vine growth and yields by competing for water, nutrients, and sunlight. Competition is most severe during the first 4 years of the vine's life or where root growth is limited. Weeds around the grapevine trunk not only compete directly with vine growth, but provide a good habitat for field mice or voles, which can girdle and kill young vines. Gophers are most prevalent in nontilled vineyards and are common where broadleaf weeds, such as field bindweed and perennial clovers, predominate. These animals feed on the roots and weaken or kill young vines. Dry weed growth is a fire hazard. For optimum yields and vine health, control weed growth, especially in the area next to the base of young vines.
After about the third year, the effect of competition from weeds is somewhat lessened as vines become established, and shading from the vineyard canopy reduces weed growth. In older vineyards, however, weed growth can interfere with cultural practices and harvest. For example, tall weeds can disrupt the application pattern of water from low-volume spray emitters. Frequent cultivation near vines can injure vine roots or the base of the vine trunk. Vine trunk injuries can encourage crown gall or collar rot infections.
Integrated weed management practices vary considerably from vineyard to vineyard. Location in the state, climatic conditions, soils, irrigation practices, topography, and grower preferences significantly influence vineyard floor management decisions and the tools used. Weeds are commonly controlled either chemically or mechanically in a 2- to 5-foot-wide strip in the vine row. The area between vine rows may be chemically treated, mechanically mowed, or tilled. Alternatively, mulches, subsurface irrigation, and flamers can also be used to control weeds in vineyards. Often several weed management techniques are used in a vineyard depending upon weed species, age of vines, soil conditions, and grower preference.
Soil characteristics are important to weed management. Soil texture and organic matter influence which weed species are present, the number and timing of cultivations required, and the activity and residual effects of herbicides. Annual species, such as puncturevine, crabgrass, horseweed, and Panicum spp., or perennials like johnsongrass, nutsedge, and bermudagrass are more prevalent on light-textured soil whereas perennials such as curly dock, field bindweed, and dallisgrass are more common on heavier-textured soils. Less preemergent herbicide is required for weed control on sandy, light soils, but residual control may be shorter than on clay or clay loam soils. Use low rates of herbicide on sandy soils or those low in organic matter. Clay soils are slower to dry for effective cultivation than sandy loam soils; thus, more frequent cultivation is practiced on lighter soils than heavy soils.
The irrigation method, amount of water applied, and pattern of rainfall affects weed growth as well as the frequency and timing of cultivation and the selection of chemicals and their residual activities. Frequent wetting of the soil promotes more rapid herbicide degradation in the soil. Herbicide degradation is generally faster in moist, warm soils than in dry, cold soils. Degradation is also more rapidunder drip emitters or micro-sprinklers than under furrow irrigation. The first irrigation following an herbicide application is the most critical in terms of how far the herbicide is moved into the soil; subsequent irrigation is less important to the movement of the herbicide.
When properly used, herbicides registered for use in vineyards can control most weed species. In most situations, combinations or sequential applications of herbicides will be required to provide effective, economical control. Before using any herbicide, identify the weed species to be controlled, then read and follow product label directions carefully.
Herbicides are traditionally discussed as two groups: those that are active against germinating weed seeds (preemergent herbicides) and those that are active on growing plants (postemergent herbicides). Some herbicides have both pre- and postemergent activity. Herbicides vary in their ability to control different weed species. Check the SUSCEPTIBILITY OF WEEDS TO HERBICIDE CONTROL tables and consult product labels for specific weed control activity. Herbicides can be combined for controlling a broader spectrum of weeds.
Preemergent herbicides are active in the soil against germinating weed seedlings. These herbicides are applied to bare soil and are leached into the soil with rain or irrigation where they affect germinating weed seeds. If herbicides remain on the soil surface without incorporation, some will degrade rapidly from sunlight. Weeds that emerge while the herbicide is on the surface, before it is activated by rain or irrigation, will not be controlled. Also, large weed seeds, such as wild oat, may germinate in the soil below the herbicide zone and still be able to emerge.
Postemergent herbicides are applied to control weeds already growing in the vineyard. They can be combined with preemergent herbicides or applied as spot treatments during the growing season. In newly planted vineyards, selectivepostemergent herbicides are available for the control of most annual and perennial grasses, but not broadleaf weeds. Young vines need to be protected from contact by some postemergent sprays. Be sure to check and follow individual label instructions.
In most vineyards, herbicides are used only on a narrow strip of soil centered on the vineyard row; thus, the area treated with herbicides in these vineyards is 15 to 30% of the total vineyard area.
Application equipment must be accurately calibrated to apply the proper amount of herbicide to the soil and young growing weeds. For safe application and to minimize drift, spray equipment should be equipped with a short boom that has low pressure (LP), flat fan nozzles. Off center (OC) nozzles are often used on the end of the boom to apply chemicals in the vineyard row. Some herbicides require special use precautions as indicated in the table below. Always read and follow the entire product label before using any pesticide.
For treatment of small areas, especially for perennial weeds, a backpack sprayer or low-volume controlled droplet applicator can be used. Extreme care needs to be exercised to avoid drift of herbicides (such as glyphosate-Roundup and Touchdown, oxyfluorfen-Goal, or paraquat-Gramoxone) to vine leaves or green stems.
Many different species of summer and winter annual and perennial weeds are found infesting California vineyards. Weeds vary from area to area and year to year; even within a vineyard. To determine the best control practices, conduct weed surveys at least twice each year: once in late winter and again in late spring or summer to determine the spectrum of weeds present. These surveys are the basis for weed management decisions about herbicide choice or cultivation equipment and practices.
Spring weed survey
A survey in late spring or summer can help in determining the spectrum of weeds present and decision-making on herbicide choice or cultivation practices.
Keep records of your weed surveys (example form— ) so that you can track weed population information from year to year to better understand ongoing weed control problems such as resistance.
Winter weed survey
By surveying weeds in late winter and keeping track of your observations (example form— ), you can identify any species that escaped control from earlier management and know what perennials are present. If herbicides were used, surveying identifies whether you need to change to a different herbicide.
Keep survey records so that you can track weed population information from year to year to better understand ongoing weed control problems such as resistance.
How to survey your fields for spring and winter weeds:
Information collected over a period of years tells you how weed populations may be changing and how effective your management operations have been. This way you can return and see how well your weed management actions are working.
WEED MANAGEMENT BEFORE PLANTING
Control annual and perennial weeds before planting a vineyard to reduce the competition from weeds during vineyard establishment. It is especially important to control established stands of perennial weeds before grapevines are planted in order to reduce theircompetition in the new vineyard and to avoid potential injury to young vines from herbicides. Perennial weeds that can be especially troublesome are field bindweed, johnsongrass, dallisgrass, bermudagrass, and nutsedge.
An especiallyeffective method of weed control before planting vines is to cultivate, then irrigate to germinate new weeds, and cultivate again to destroy seedling weeds. Frequent cultivation lowers weed seed populations in the soil, thus reducing weed growth. At least two cycles of cultivation, irrigation, followed by a shallow cultivation are needed for a marked reduction in weed seedlings. Unfortunately, this method is not effective on established perennial weeds.
A method of control for perennial grasses such as bermudagrass and johnsongrass is to cultivate the soil when it is very dry. Cultivation cuts the rhizomes into small pieces so they can dry. The soil is reworked frequently using spring tooth harrows to pull new rhizomes to the surface and dry them out as well. If the soil is irrigated or rain occurs before total control of the perennial plant is achieved, the rhizome pieces will begin to grow and the effectiveness of this practice is reduced. By the same token, working the soil when wet can increase the population of perennial weeds, because each piece of cut rhizome can root and develop into a new plant.
Field bindweed growth can be reduced for 1 to 2 years by deep plowing or with a reclamation blade (a large V-shaped blade) to cut the roots 16 to 18 inchesdeep in dry soil. Populations of nutsedge can be reduced by deep plowing with large moldboard plows to bury the nutlets to a depth of at least 12 inches.
Seedlings of perennials can be controlled with repeated cultivation.
Soil solarization is a nonpesticidalmethod of controlling soil-borne pests by placing clear plastic sheets on moist soil during periods of high ambient temperature. The plastic sheets allow the sun's radiant energy to be trapped inthe soil, heating the upper levels. Solarization during the hot summer months can increase soil temperature (108-131°F at a depth of 2 inches) to levels that kill many disease-causing organisms (pathogens), nematodes, and weed seedlings. It leaves no toxic residues and can be easily used on a small or large scale. Soil solarization also improves soil structure and increases the availability of nitrogen (N) and other essential plant nutrients. (For additional information see Soil Solarization, U.C. Publications, 21377.)
Weed seedlings and established annual weeds can be controlled either with preemergent or postemergent herbicides before planting. Before planting a vineyard, use a preemergent herbicide in conjunction with a rotation crop, and make sure the residual period of the herbicide isnot long enough to preclude planting the vines. Postemergent herbicides generally have a short soil residual and are safer to use before planting vines. Many growers prefer to use preemergent herbicides only after the vines have been planted to avoid possible exposure to herbicides that may be in the backfill soil.
WEED MANAGEMENT IN NEW VINEYARDS
Grapevines are most sensitive to weed or cover crop competition during the first few years of growth and where soil depth is limited. Weedy vineyards may require several more years to become economically productive than weed-free vineyards. Regardless of the method used to control weeds, be careful not to injure vines with chemicals, or to mechanically damage the vine trunk or roots. As grapevines become established, competition from weeds is lessened as shade from the vine canopy reduces weed growth.
Some growers prefer to manage weeds without herbicides for the first year or two after planting. This usually requires hoeing, cultivating, or using weed knives (less than 2 inches deep) around vines several times during spring and summer as well as cultivating or mowing between vine rows. This is best accomplished when weeds are still in the seedling stage; it becomes more difficult when weeds are allowed to get large. Hand tools are generally used close to the vine to minimize injury, particularly when the vines are young. Mechanical cultivators available for use in the vine row include: weed knives, spyder cultivators, and rotary tillers. Rotary tillers such as a Weed Badger, Kimco, or Clements Hoe are most effective if used on loose soil that is not rocky. Hand-held mechanical flails (Weed Eaters) may be used, but can injure vine trunks. Disks or mowers can be used between the rows. Mechanical control of weeds must be done repeatedly when weeds are immature. The equipment should be set to cut shallowly, to minimize damage to vine roots. As weeds mature, they are difficult to control, may clog equipment, and produce seed. When using any mechanical equipment around vines, be careful not to injure the grapevine feeder roots or trunk.
Planted cover crops can also be used to reduce weed populations between vine rows. With cover crops, the species selected and management will differ from one area of the state to another. Be sure to select a cover crop that will not become competitive with the young vines. Cultivation in preparation for planting a winter annual cover crop will also reduce weed growth. To preserve surface cover, mow the cover crop to the correct height recommended for that crop.
Weeds in the vine row can also be controlled using mulches. Organic mulches (cereal straw, green waste, composted wood chips) or synthetic mulches of polyethylene, polypropylene, or polyester can be used around young vines. Always apply mulches when the soil surface is free of weeds. Mulches prevent the growth of weed seedlings by blocking light and preventing it from reaching the soil surface. They create more uniform moisture conditions, which in turn promotes young vine growth. However, mulches may also provide a good habitat for gophers, voles, field mice, and snakes or be a source of new weed seed that came with the mulch. Mulches do not control perennial weed growth unless alllight can be excluded. Some woven fabric mulches offer excellent weed control for several years, but the initial cost of purchase and installation is high.
To control weeds with herbicides after grapevines are planted and before bearing, applya preemergent herbicide (e.g., oryzalin, napropamide, or oxyfluorfen) to either a square or circle around each vine (at least 3-6 feet across) or as a band down the vine row. Herbicides can also be applied to control weeds after they emerge. Selective herbicides are available for annual grass control and suppression of perennial grasses (e.g., sethoxydim, fluazifop, and clethodim), but to be effective they require the addition of an adjuvant (either a nonionic surfactant or a nonphytotoxic oil). These materials do not control nutsedge or broadleaf weeds and clethodim is the only one that will control annual bluegrass. Paraquat can be used to control weeds near young vines protected with shields or wraps. The nonselective herbicide glyphosate can control broadleaf weeds after emergence, but it should be used only around mature vines with brown bark and should not be allowed to contact leaves or green shoots.
In conjunction with the use of herbicides in the vine row, mow or cultivate the weeds between the rows. Mowing may be required four to eight times during spring and summer, whenever weeds are 6 to 8 inches high. Cultivation is required when weed seeds germinate following each irrigation.
WEED MANAGEMENT IN ESTABLISHED VINEYARDS
It takes at least 3 years for a vineyard to become established under normal growing conditions. Established vines are more tolerant of many herbicides than newly planted vines, thus increasing the options available for weed control. Generally weeds are controlled between vine rows by discing or mowing, with a basal treatment of herbicide around each vine or with a strip application of herbicide down the vineyard row.
Cultivation can be used in established vineyards to control annual and biennial weeds and seedlings of perennial weeds. Control seedlings of field bindweed, bermudagrass, and johnsongrass before they are 3 weeks old or they may form perennial structures such as rhizomes. Cultivating established perennials in an irrigated vineyard often increases the weed problem. Cultivation also cuts and damages the roots of vines, reducing the ability of the vine to take up nutrients and allowing access to the vine of soil pathogens.
Flaming is a method that can be used to control young weeds in mature vineyards. Use either a single flame that is directed to the base of the vine or several burners on a boom to flame the weeds between the vineyard rows. Flame is only effective on young weeds. Do not use flaming around young vines because it may damage the thin, green bark. Adjust equipment speed for desired weed injury without igniting or damaging the vine trunks. In mature vineyards annual broadleaf weeds can be controlled with flaming but grasses are somewhat tolerant. Never use flaming where there is dry, dead vegetation or where leaves or duff have collected around the base of the vine. Dry vegetation may ignite and cause a fire that can girdle the vines. Flaming may also damage or ignite mulches in the vineyard.
Mulches can also be used for weed control as discussed in the section WEED MANAGEMENT IN NEW VINEYARDS. Because organic mulches degrade, they must be replenished annually. As mulches degrade they become a perfect growth medium for weed species such as common groundsel, prickly lettuce, common sowthistle, and panicle-leaf willowherb.
If using herbicides to control weeds, apply a preemergent herbicide or combinations of herbicides in fall after harvest, or split into two applications (fall and spring), or in winter with a postemergent (foliar) herbicide if weeds are present. It is possible to use postemergent herbicides as new weeds germinate. For greatest safety, direct herbicide sprays only at the soil or at weed foliage, not at the vine leaves, shoots, or 1- to 2-year-old wood. In vineyards where tree rows are mulched or sprayed, often there are fewer weeds to treat, thus a visual weed-seeking sprayer can be used to reduce herbicide use and effects on the environment.
Frequently, two or more herbicides need to be applied to obtain adequate weed control. It is critical to identify the weed species present in the vineyard as described above in the section on Monitoring to determine which herbicide or combinations will providethe most effective control. Combinations may include one or more preemergent herbicide or a mixture of preemergent and postemergent herbicides. Read and follow label directions carefully before combining herbicides.
Cover crops are planted insome vineyards to replace the resident weed vegetation on the vineyard floor. These winter annual cover crops are fall-seeded cereal crops such as wheat, oat, cereal rye, or barley, or for nontilled vineyards 'Blando' bromegrass, 'Zorro' fescue, or subterranean clovers. These are seeded into a prepared seedbed between vine rows in late September through mid-November. Most plants will reseed themselves if mowed in January or early February and then allowed to regrow into April and May. Mowing after the seeds mature ensures seeds for the next season. Keep cover crops away from young vines. Changing cover crop species reduces the potential for buildup of disease pathogens, weeds, rodents, and insect pests. For more information on cover crops, consult UC/ANR Publication 21471, Covercrops for Califomia Agriculture, or UC/ANR Publication 3338, Cover Cropping in Vineyards: A Growers Handbook.
UC IPM Pest Management Guidelines: Grape
A. Shrestha, UC IPM Program, Kearney Agricultural Center, Parlier