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Grape Index
Chapter 18. Weed Control and Air Pollution
Control of weeds in young vineyards, is necessary weeds compete with vines for water and nutrients and interfere with harvesting of mature vines. Herbicides can be used for strip weed control. A weedfree strip down the row can eliminate the need for close cultivation in vines (Lange et al., 1974). A mowed cover crop between rows used with a weedfree strip in the vine row improve water penetration in some soils. Savings in cost are also possible by using herbicides for weed control in vineyards. The reader should obtain a current issue of Crop Weed Control Recommendations, published by the University of California for the latest suggestions (Agamalian et al., 1972).

Control of Annual Weeds

Several herbicides used to control annual weeds are discussed below.

Aromatic Weed Oils

Young weeds 1-2 in. (2.54-3.81 cm) high are most sensitive to emulsions of these oils. Repeat applications may be required to keep weeds under control since oils usually cause only contact damage. Vine trunks should not be sprayed.

Diuron (Karmex) and Simazine (Princep)

Although these chemicals are structurally unrelated, their herbicidal properties in vineyards are similar. They are applied as wettable powders containing 80 percent active ingredients. These herbicides are applied to the soil surface and must be leached into the soil by irrigation or rainfall to be effective. Excessive

irrigation in light soil must be avoided, however, or the chemicals may be leached into the rootzone of young vines and out of the rootzones of weed seedlings (Lange et al., 1974).

Diuron is more effective than simazine on crabgrass and barnyardgrass, while simazine is more effective on wild oats and groundsel. Both chemicals are not toxic to weed seeds until they germinate, when they attack the young seedlings that absorb the herbicides through their roots. Most annual weeds will be destroyed or repressed if the herbicides are applied and leached into the soil before the seeds germinate.

Low rates of these chemicals in soil are effective against germinating weed seedlings from three months to a year or more, depending on the amount used. Both herbicides are decomposed by soil microorganisms, and they break down more rapidly in warm, moist soils. Diuron simazine are generally ineffective in controlling well-established annual or perennial weeds.

Higher rates of herbicides are required on clay soils and those with high levels of organic matter, usually typical of rainy areas. When diuron and simazine are leached into the soil, most is adsorbed on clay particles and organic matter and this portion is unavailable for absorption by seedling roots. Although diuron generally provides goods selective weed control, it is less safe than simazine, especially in light coarse-textured soils low in organic matter.

Diuron and simazine should be applied as a band treatment in the vine row from December 1 to March 1 on bearing vines three or more years old with trunk diameters of 1½ in. (3.81 cm) or more. The rate per acre is based on the area sprayed rather than on the area of the entire vineyard.

Injury to grapevines from excessive applications of simazine or diuron is first indicated by chlorotic leaves, which eventually turn brown on the margins. With extreme injury, leaves eventually die; later, new leaves develop (Lange et al., 1974).

Prior to the first application of the herbicides, soil in the vine row should be tilled into an even ridge sloping slightly upward to the vines. This ridge should not be disturbed by additional seasonal cultivation in the middle of the row.

Napropamide (Devrinol)

This is an extremely safe herbicides in vineyards when applied preemergence and incorporated by rainfall or sprinkler. It controls many of the same weeds an nitralin and is particularly effective on grasses and on some weeds resistant to nitralin and trifluralin, such as sowthistle and yellow nutsedge. Napropamide gives poor control of weeds in the tomato family.

Napropamide can also be applied to soil surfaces in young, established vineyards. Four pounds per acre (4.48 kg per hectare) is required when applied after application. If the proper amount of water is used, good residual control will persits throughout the summer. If there is a delay of 10 days or more before leaching the chemicals into the soil, weed control may be poor.

Paraquat*

This is most effective against young weeds. It is water-soluble and must be applied to weed foliage, which it kills on contact. It is not translocated in grapevines. It may be combined in the spray mixture with a preemergence herbicide to control weeds, and an additional application after preemergence treatment is unnecessary.

Young seedling weeds that germinate in the winter while vines are dormant can be controlled by applying paraquat. A wetting agent (surfactant) should be added to the paraquat at 1 qt/100 gal (1 liter/400 liters) of spray solution. Paraquat should not be applied to green grape shoots and green trunks of young vines. It is tightly bound to the soil and is only slowly available to microorganisms which can degrade the unbound paraquat. In the soil paraquat has almost no phytotoxicity, except in sandy soils when applied at very high rates.

Trifluralin (Treflon) and Nitralin (Planavin)

These herbicides are chemically similar and are insoluble in water. Both are unstable on the soil surface. The rate of surface breakdown is greater with trifluralin. The chemicals must be incorporated into the soil immediately following application. Nitralin is less volatile and can be incorporated by rainfall or sprinkler irrigation. Trifluralin must either be applied by subsurface layering or tilled in within hours after application. Both chemicals can be used with greater safety on sandy soils than either diuron or simazine.

Trifluralin, nitralin, and napropamide inhibit the growing points of roots and shoots on contact, and are very effective for control of grass species. Neither roots or shoots of susceptible plants will grow through soil containing these chemicals, and plants die because roots cannot contact soil moisture. However, in heavy soil that cracks, chemicals-free shoots can grow through these cracks. When incorporated into the soil, these chemicals can persist from a few months to a year or more. They are degraded by microbial and nonmicrobial means.

Incorporation of ½ lb per acre (0.56 kg per hectare) may be used for short-term control of annual weeds on sandy soils, but 1 lb per acre (1.12 kg per hectare) or more should be used on sandy loam and heavy soils. Since incorporation of the herbicides is difficult in established vineyards, the treatments are of most value in new vineyards immediately prior to planting.

Control of Perennial Weeds
Field Bindweed (Convolvulus arvensis)

Repeated discing between the vine rows can keep binweed under control, but it does not control the weeds around the vines. Although the row plow or repeated applications of weed oil can partially control bindweed, some injury to young grapevines may result. Paraquat is much safer than oil if kept off foliage and can be sprayed repeatedly in the same manner as weed in the row, ½ - 1lb of paraquat per acre (0.56-1.12 kg per hectare) with a surfactant is effective (Lange et al., 1974).

The amine form of 2,4-D can be used to control field bindweed in vineyards. However, care should be taken to keep 2,4-D off the grape foliage, since leaf malformation and injury to developing clusters can result. It is safer to apply 2,4-D to bindweed after the normal grape berry shatter following bloom than at earlier stages. Lifting the trailing shoots of vines that might otherwise be sprayed helps to minimize damage. Spray drift can be reduced by using a hooded boom equipped with low-pressure flooding nozzles that deliver coarse droplets. Bouncing of the boom can result in drift, so tractor speed should be adjusted to the terrain. Speeds should not exceed 2 or 3 miles per hr. The 2,4-D should be applied only on days relatively free of wind, using 1½ lb of 2,4-D in 60-80 gal of water per acre (1.68 kg of 2,4-D in 561-748 liters per hectare). This method is often not feasible because it is difficult to obtain a permit to use 2,4-D from the county agricultural commissioner after March, and for successful control 2,4-D sprays are usually required during the summer months.

A safe and effective method for bindweed control is now possible with the application of trifluralin by subsurface layering. The herbicide is applied by means of a spray blade or row plow at a soil depth of 4-6 in. (10.2-15.2 cm) (Fig. 18-1). The layer of trifluralin destroys the growing tips of the weed shoots when they contact the chemical.

No phytotoxic effects on bearing vines has been observed from the use of layered trifluralin. Annual weed control has been effective in addition to bindweed control in the treated areas. However, some weed species such as those in the cabbage family (mustard, shepherd?s purse, London rocket) are resistant to layered trifluralin.

Jonhson Grass (Sorghum halepense) and Bermuda Grass (Cynodon dactylon)

Repeated discing of the middle of the rows can control Jonhson grass or Bermuda grass, but hand labor, row plowing, or herbicides are required to control them in the vine row. Dalapon is partially effective and may control both grasses if applied monthly at low rates(4lb dalapon/100 gal of water containing 8-16 oz of a surfactant or wetting agent per acre). This is equivalent to 4.48 kg dalapon per 935 liters of water containing 420-560 surfactant.

Fig. 18-1. Generalized drawing of back view of a spray blade. In front of the spray nozzle, a shank lifts a layer of soil so nozzles can wet the underlying soil surface. (Redwarn from Lange, 1972).

Dalapon spray should be kept from contacting grapevines as much as possible, and any spray runoff prevented from soaking into the soil. It should be applied soon after an irrigation to allow as much time as possible between the application and the next irrigation. Dalapon is very soluble and can be leached into the soil, absorbed by grape roots, and translocated to the leaves. Injury is expressed by marginal chlorosis and cupping of the leaves, shoot stunting, and clusters with shot berries. Spot applications on Bermuda grass and Johnson rather than spraying the entire vine row can minimize injury.

Incorporation of trifluralin during the dormant season at labeled rates for bindweed also helps control Johnson grass and Bermuda grass. The vine rows should first be plowed to move the soil and rhizomes into the center of the rows, and then the soil should be sprayed with trifluralin. Discing or trilling should follow, as this breaks up the rhizomes and incorporates the herbicide. Although the roots and rhizome pieces in the treated soil do not develop normally and some die, most have a normal appearance after the first year. A second treatment is usually necessary the second year for adequate control. Although neither Johnson grass nor Bermuda grass is eliminated by this treatment, repeated annual use can greatly reduce weed stands with no hazard to vine growth.

Glyphosate (Roundup)

This is a very potent and promising translocated herbicide or the control of perennial weeds in vineyards and other perennial crops (Lange et al., 1975). However, the compound is not yet recommended because there is more plant damage in direct foliar applications or through drift than that caused by other translocated herbicides such as 2,4-D, even though fewer immediates symptoms result.

Glyphosate translocates rapidly in most plants, moves farther into the unsprayed portions of vines and trees than do other translocated herbicides, and slowly kills plant tissues. If foliage is treated rapid wilting results, followed after several days by yellowing and/or dying. Regrowth in woody and some perennial weeds is usually severely stunded.

Nonbearing Vineyards

Trifluralin or nitralin incorporated as a preplant treatment 1-2 in. (2.54-5.08 cm) deep can be used to control annual weeds in new plantings. Lower rates should be used for sandy soils than for heavier ones. Grape rooting or cutting should be planted so that the base is below the treated soil, to insure good root development. Treated soil should not be used to fill in around roots.

These herbicides can also be incorporated around young established vines as they are relatively nontoxic to the vines. High rates can greatly reduce branching of roots of a grape cutting in that part of the soil where the herbicides were incorporated. Nitralin can also be applied to the soil surface and incorporated by sprinkler irrigation or rainfall in young plantings.

Application of Herbicides

Preemergence herbicides should be applied before rainfall. Before spraying, remove trash from vineyards. It is desirable to prune the vines before spraying. Diuron and simazine are usually applied in the dormant season. Uniform soil coverage in the area to be treated is necessary. Some drift of simazine, diuron, nitralin, or trifluralin onto the vines has not caused injury.

Paraquat and dalapon are usually applied in the growing season, and drift must be minimized. Droplets of paraquat cause necrotic spots on leaves and fruit, and drift of dalapon can cause chlorotic leaves with marginal burn.

2,4-D is usually applied in the growing season and great care must be exercised to minimize drift. Sensitivity of grapes to 2,4-D decreases with age of the shoots; therefore, where 2,4-D permits can be obtained, it is best to delay spraying until 2 weeks after flowering to minimize the effects of accidental drift.

Subsurface Layering

For subsurface layering of trifluralin, a spray blade with nozzles spaced 4-6 in. (10.1-15.2 cm) apart at the trailing edge may be used (fig. 18-1). This allows the herbicides to be trapped under the soil which flows over the blade as it is pulled through the soil. The blade is kept 4-6 in. (10.1-15.2 cm) below the soil surface (Lange et al., 1972).

Winter or early springs is the best time for layering of trifluralin. All trash should be removed, and established annual weeds should be killed to reduce interference with blade operation. Apply trifluralin in 40-80 gal of water per acre (374-748 liter per hectare). Shallow discing or other tillage prevents cracking of soil and will help prevent bindweed penetration through the layer of herbicide. This discing must not penetrate the layer of trifluralin or control will be greatly reduced.

Air Pollution

The rapid introduction of new herbicides and pesticides has led to new problems such as volatilization, drift, soil residues, and misapplication. Other types of industrial emissions and waste can also be pollutants and have an adverse effect on grape growth. Solution of these problem is difficult, but permanent damage to atmosphere and soil must be avoided.

2,4-D Type Injury

In many vineyards of the world 2,4-D type injury can be found on occasional leaves whether or not it has been applied locally, since minute amounts of 2,4-D and related compounds can cause leaf malformation (Weaver, 1970). Grapes are exceedingly sensitive to 2,4-D. One drop containing 0.0001 ?g of 2,4-D placed on a young leaf of Tokay grape can later cause formative effects (Kasimatis et al., 1971). Thus 0.8 mg of 2,4-D, when properly placed, could cause a leaf malformation on every vine in the approximately 20,000 acres (8,094 hectares) of Tokay grapes in California.

After spraying with 2,4-D was begun in 1946, it was noted that much drift occurred especially by sprays from airplanes. There was frequent damage to adjoining crops, one of the most sensitive being the grapevine. Drift can occur from airplanes for many miles and also from ground rigs, although these are usually smaller in magnitude. Formative effects from 2,4-D that occur in vineyards early in the season do not ordinarily appear in the following growing season. The effects caused by early sprays of 2,4-D persist, often having formative effects on leaves that develop late in the same season. Vines sprayed with 2,4-D late in the same season may show few no formative effects because the rate of shoot growth at that time is very slow. A few malformed leaves resulting from small amounts of 2,4-D have not been proven to be detrimental, unless drift occurs at critical times such as flowering.

Smog, Ozone, and Oxidant Stipple

In the 1950s injury to grapes was observed in southern California by Los Angeles type (photochemical) smog. Ozone is the main component of the smog which causes the most damage. A ?stipple? of some grape leaves occurs in midsummer and becomes progressively more severe with the season, resulting in a substantial loss of chlorophyll. The primary symptoms consist of small, brown to black, discrete, dotlike lesions, which are easily distinguished from lesions of other grape disorders because the stipples occur only on the upper surface of the leaf. The lesions vary in diameter from about 4/1000 – 20/1000 inch (0.1-05 mm) and are confined to groups of cells bounded by the smallest veins (Richards et al., 1959). Large lesions result from a coalescence of small ones and may measure up to 80/1000 inch (2.0 mm) in diameter. Aggregates of these minute spotlike lesions produce the typical stippled appearance. Reduced chlorophyll and photosynthesis also indirectly reduce berry weights, sugar content, and cane growth (Thompson et al., 1969). Patches of palisade cells die in mature leaves exposed to toxic concentrations of ozone in the air.

Since the discovery of ozone stipple in southern California the injury has spread to other industrial regions of the state. Widespread oxidant stippled browning and premature senescence of leaves (ozone injury) has also been observed in grape growing regions near the Great Lakes (Shaulis et al., 1972). Benomyl sprays have been shown to reduce the severity of oxidant stipple. Since ozone entry into the leaf is governed by the degree of stomatal opening. Low soil moisture and shading can decrease the degree of stippling (Kender and Shaulis, 1973).

As the population increases, air pollution will probably have a greater impact on grape growers in the future.

Continue to Part 5, Chapter 19