Fruit Rots

Black Rot (Guignardia bidwellii): This is probably the most damaging grape disease in New England. Most loss is caused by damage to the berries, though leaves, tendrils and new shoots are also damaged. The fruit is susceptible from fruit set until veraison; resistance increases as fruits transition from pea-size to veraison.

This disease is caused by a fungus that overwinters in mummified berries and stem lesions. Mummies on the soil surface release spores when rain soaks them in the spring. There is a continuous production of spores throughout the spring and summer. These are carried to new plants by wind. The duration of leaf wetness required for infection to occur varies with temperature (see Table 53). Young tissue is infected in less than 12 hours between 60–90˚F. Spores germinate and produce mycelium resulting in symptoms in 8 to 25 days, depending on the weather. New leaves and half-grown berries are most susceptible. Secondary infections occur when new spores are produced on the current year’s infections. Secondary spores are produced into August, and are spread by splashing rain.

On leaves, infections appear as yellowish-tan spots in late spring. These roughly circular spots enlarge and become reddish-brown with a dark outline. Lesions are roughly circular in shape. Shoots develop sunken, elliptical black lesions, up to 2 cm in length. On the berry, symptoms do not appear until the fruit is half grown. Lesions start as a small whitish dot and quickly engulf the whole berry. The infected area develops a reddish brown color. The berry wrinkles and blackens completely within a few days. These fruit become mummies that are very hard and stony, and supply inoculum for the following year.

Management: Sanitation is very important. Destroy all mummies and canes with lesions. Remove infected tendrils from vines. Plant grapes in locations having good air circulation, taking advantage of prevailing winds and sun. Black rot is more likely to occur near woodland borders than in full sun, and it occurs much more severely in wet years than in dry ones. Protectant fungicides offer good control if applied initially when the shoots are 10-16 cm long and continued until the berries contain approximately 5% sugar. Strobilurins (Abound, Elite, Flint, Sovran, Nova and others) are excellent eradicant and protectant materials. See pest management schedule for recommended materials and timing. Varietal resistance is another control option (see Table 59). 

Bitter Rot (Greeneria uvicola): Bitter rot, while most common in southern grape regions, may infect grapes in New England. If 10% of the berries in a wine pressing are infected with bitter rot, the wine can be undrinkable. Bitter rot may be easily confused with black rot. Infected berries first develop brownish, water-soaked lesions. The bitter rot fungus infects ripe grapes, and unlike the black rot fungus, does not infect green berries. Bitter rot susceptibility increases at veraison. Lesions often have concentric rings in white-fruited varieties. Berries turn brown but retain their shape. Within 3-4 days, black pustules erupt on the berry. If overripe berries become infected, they are not easily detected, because pustules do not form. These berries are the most bitter, and the most likely to be mistakenly harvested.

Warm, humid weather at the time berries ripen favors the disease. The fungus grows rapidly, and berries can rot in 5 to 7 days. Wounding promotes fungal growth.

Management: Promote good air circulation for good drying in the vineyard. Fungicides used for the control of other diseases usually will also control bitter rot. If conditions are right for infection, late season sprays should not be omitted. Most varieties have some degree of resistance to the fungus.

Botrytis Bunch Rot (Botrytis cinerea): Botrytis rot can cause serious losses in susceptible varieties. While some rot is acceptable in wine grapes, and may even be desirable, the disease can get out of control. The fungus that causes the disease is present in grape mummies, debris on the vineyard floor and in organic matter around the planting. Spores are released in moist, cool weather in spring, and then throughout the growing season. These first spores infect blossoms at the end of bloom. A second infection occurs at berry maturity. The fungus uses senescing or dead material as a base to spread into healthy tissue. Botrytis-infected berries are at first soft and watery. The berries usually become covered with gray, fuzzy fungal mycelium within a few days. Rotted berries shrivel, then drop to the ground to eventually become mummies.

Management: Good air circulation and vineyard sanitation are helpful. Leaf removal around the clusters has shown excellent control of the disease in California. White-fruited varieties (particularly Riesling and Seyval) are highly susceptible. Protective fungicides should be used when wet weather occurs near bloom and berry ripening. See pest management schedule for recommended materials and timing. Fungicides should be used thoughtfully to avoid promoting resistance by the fungus.

Ripe Rot (Colletotrichum acutatum, C. gloeosporioides, Glomerella cingulata): Ripe rot is a disease affecting grapes at or near harvest time which has largely been confined to the southeastern U.S. but has caused problems in recent years in southern New England. Rotted berries turn uniformly dark-brown over part or all of the berry and sometimes have pink or orange spore masses on the surface. As infected fruit mature, lesions appear as slightly sunken or flattened rotted areas. As lesions expand, the entire grape eventually rots, and may drop or become shriveled or mummified as it decays. Ripe rot infections can occur at any stage of fruit development, but fruit that is infected in when unripe does not rot until it begins to ripen. In these berries the fungus remains in a latent state until conditions allow it to further develop in the tissue. Once infected grapes begin to rot and produce spores in the vineyard, the disease can spread rapidly to other uninfected fruit, within the same bunch or neighboring bunches. The most devastating losses occur on susceptible cultivars during warm rainy harvest seasons. Generally, darker-skinned cultivars are more resistant while white cultivars are more susceptible.

Management: Before spring arrives, remove or disk into the soil all overwintered mummies left on the trellis and ground from the previous season. Good canopy management practices are essential for control of ripe rot. Shoot thinning, leaf removal, pruning, cluster thinning and shoot positioning are all cultural practices that open the vine canopy to increase airflow and light, reduce the amount of moisture trapped within the canopy, and allow better penetration and coverage by fungicides. Timely harvesting of all ripe grapes is recommended, to prevent overripe fruit with fungal sporulation from hanging on the vines too long. Where the disease is a problem, fungicide applications are critical during the period between bloom and pre-harvest. Captan and Pristine are the best fungicide choices for control of the disease.

Foliage and Cane Diseases

Downy Mildew (Plasmopara viticola): This disease causes damage primarily by attacking the vine, though all parts of the plant are susceptible to injury. The optimum conditions for the disease are cool to moderate temperatures, and wet weather. The disease is caused by a fungus that requires living tissue as a host. In spring, spores of the fungus come from dead tissue on the ground. Free water is required for infection, and infections may occur during high humidity throughout the season. Splashing water or handling wet plants may readily spread the spores. The spores grow into cottony masses, producing many new spores which can spread the infection. As tissue dies, it falls to the ground where the fungus overwinters. Severe epidemics can defoliate the vine.

On leaves, new infections are difficult to see. They appear first as generally angular, pale-yellow spots delimited by veins which later become brown. On the underside of the leaf the cotton-like ‘downy’ growth appears. Fruit infection occurs at two times. First, when the berries are the size of small peas, infections will cause berries to turn light brown and soft. Berries will shatter easily. Sometimes the downy growth covers the berries. During the heat of the summer, little fruit infection occurs. The second infections occur in the late summer or early autumn. These berries do not turn soft or develop downy growth, but turn dull green, then purplish-brown. Shoots and tendrils develop water-soaked lesions, become stunted and distorted, and may die.

Management: Remove debris from the vineyard floor. Maximize air circulation to improve drying. European grapes are generally more susceptible than American grapes. The most serious epidemics occur when a wet winter is followed by a wet spring and a warm summer with frequent precipitation. Fungicides should be applied when disease pressure is high. Apply just before bloom; 7-10 days later; 10-14 days later; 3 weeks later. See pest management schedule for recommended materials and timing.

Powdery Mildew (Uncinula necator): Powdery mildew causes losses by infecting leaves and berries. It is primarily a problem on European grape varieties, although American varieties may be damaged. It may be confused with downy mildew (see above). Losses are not generally heavy from the disease, but can build up over several years.

The fungal pathogen overwinters in specialized structures on or in living tissue. In spring, spores are released that attack new tissue. Unlike other grape diseases, rain and free moisture are not important to the spread of powdery mildew. Warm conditions with high relative humidity favor this disease. Wind carries newly produced spores from infected areas into new locations. Infected leaves have the appearance of being coated with a white powder. Severely infected leaves curl and defoliation may occur. Leaves of American varieties like Niagara and Concord are very susceptible. Young fruit and blossoms may be misshapen by infections; mature fruit is immune.

Management: Cultural practices can help reduce disease incidence. Planting in sites with good air circulation and sun exposure and the use of appropriate training systems which allow for good air movement are highly advisable.Use fungicides where infections are known to occur. Copper and lime sulfur dormant applications provide good early season control. However, there are label restrictions. Check with your state Extension Specialist for recommendations. Because some varieties are sensitive to sulfur, this material should always be applied at cooler temperatures (<85˚F). Strobilurin (group 11) fungicides are also effective, but care should be taken to avoid selecting for resistance by the fungus. See pest management schedule for recommended materials and timing.

Eutypa Dieback (Eutypa armeniacae): This disease also has been known as “dead arm.” It causes limbs to die back and forms cankers. Recently, it was shown to occur in conjunction with Phomopsis, causing the dead arm symptoms. Cankers are frequently found around old pruning cuts. They are usually under the bark, and show only as a flattened area on the surface. The cankers run lengthwise along the limb. Infections occur on pruning cuts in early spring. Over several years, the infection increases, causing new leaves to emerge small and yellowed. New shoot growth has shortened internodes, leaves are small and cupped and all growth is chlorotic. After about 5 years, the bark sloughs off, and eventually, the cane dies. This is seldom seen in vineyards younger than 8 years old.

Management: Infected material should be removed; in some cases it may be necessary to remove the whole plant. Make cuts well below cankers. Destroy all prunings. Prune directly after a rain to minimize risk for infection, as the atmospheric spore load has been washed out temporarily. Prune late in the dormant season to promote rapid healing of wounds. Multiple trunk systems are recommended with renewal on an 8- to 10-year cycle. This helps minimize risk of losses due to both Eutypa dieback and crown gall. All commercial varieties are susceptible.

Phomopsis cane and leaf spot (Phomopsis viticola): This is a fungal disease that causes reddish-brown lesions on canes, leaf spots and fruit rot. Small black spots at the base of developing shoots are the first sign of infection. These areas may crack, and late in the season may appear bleached. Leaf infections appear as small, dark lesions with yellow margins. Usually the lower leaves are affected first. While berry infections are rare, and symptoms are similar to those of black rot. The fungus overwinters in lesions in wood. In spring, spores are released and spread by rain. Cool, wet weather promotes the spread of the disease.

Management: Prune and destroy infected canes. Late dormant fungicide applications help to kill the overwintering fungal fruiting bodies on the surface of the vine. Two applications of Captan (at 1” and at 6” shoots) provide good management under normal conditions. Protectant fungicides (especially Abound and Mancozeb) are helpful at preventing infection, especially in cultivars less susceptible to the fungus. See pest management schedule for recommended materials and timing. Concord, Catawba, Chelois, Delaware, Niagara, and Rougeon are the most susceptible varieties.

Anthracnose (Elsinoe ampelina): This disease, like several of the others discussed, is worst during warm, humid, and rainy growing seasons. It reduces the quantity and quality of the berries. Circular “birds-eye” lesions are produced on the leaves with brown to black angular-shaped margins. If infection is severe, numerous lesions may coalesce, making large areas of the leaf necrotic. Often lesions will be concentrated on the veins. Necrotic tissue may drop out, leaving a “shot hole.” Youngest leaves are the most susceptible.

Lesions on the stems and shoots may also be numerous; coalescing lesions will split open the tissue into the pith. Margins will be raised and purplish to brown in color. Lesions on the rachis and pedicels of the fruit cluster are like the stem lesions. If infections are numerous, berries may drop off entirely, or they may develop cracking. Spores are released from overwintering lesions on stems or berries and are dispersed by rainfall. Spores are infectious over a wide temperature range, but need water in order to penetrate susceptible tissue. Hail injury may especially favor infection by this fungus.

Management: Do not plant highly susceptible varieties in heavy soils with poor drainage. Dormant fungicide applications help to reduce the inoculum of the pathogen. Protectant sprays beginning when shoots are 5-10 cm long and continuing at 2-week intervals are recommended. A fungicide should be applied 24 hours after hail injury.

Root and Trunk or Crown Diseases

Crown Gall (Agrobacterium vitis): Crown gall is a bacterial disease that infects more than 2,000 species of plants (including grapes). Crown gall of grape is a major problem in cold climate regions. The disease affects all grape cultivars. Vines with galls at their crowns or on their major roots grow poorly and have reduced yields. Severe economic losses result in vineyards where a high percentage of vines become galled within a few years of planting.

Wounds are necessary for infection to occur. Observations suggest that freeze injury and mechanically-caused wounds are highly conducive to infection. The disease is particularly severe following winters that result in freeze injury on cold-sensitive cultivars, such as those of Vitis vinifera. Crown gall is characterized by galls or overgrowths that usually form at the base of the trunk. Aerial galls may form as high as 3 feet or more up the trunk. Galls generally do not form on roots. 

Early in the disease development, galls are small, more or less spherical, white or flesh-colored, and soft. Because they originate in a wound, the galls at first cannot be distinguished from callus. However, they usually develop more rapidly than callus tissue. As galls age, they become dark brown, knotty, and rough. The bacterium can survive in the soil for many years even in the absence of grapevines.

Management: Control procedures include: (1) planting only nursery stock that is free of any obvious galls on crowns or roots: (2) not planting into a field where crown gall has occurred previously, unless a non-host crop, such as strawberries or most vegetables, is grown for two or more years before replanting; and (3) minimizing winter injury to root and crown systems.

In addition to be above procedures, a nonpathogenic bacterium, Agrobacterium radiobacter strain K-84, is commercially available for biological control of grown gall. The biocontrol agent may be applied to roots of healthy plants when they are first set out. After planting, the control becomes established in the soil around the root zone and prevents crown gall bacterium from entering this region. However, the biocontrol agent will not cure plants that were already infected before its application.

Fruit Pests

Grape Berry Moth (Paralibesia viteana): The grape berry moth (GBM) is about 3/8 - 1/4” long and has a broad gray band across the middle of its wings. The larva is grayish-green and about 3/8” long when full grown. Larvae are found in the blossoms, young fruit clusters, and newly-formed berries; later they are found in green and ripening berries. Larvae feeding in the green and ripening berries cause most losses. Infested green berries will be seen to have a maroon coloration on one side, especially where the berry comes closest to or contacts a nearby berry in the same cluster. Such coloration indicates that a larva has fed on one berry, burrowed into another, and connected them with webbing. Ripening berries infested with larvae are detected by the wrinkled, shrunken appearance of the fruit.

Management: Remove wild grape plants from areas adjoining the vineyard. Till between rows to bury overwintering larvae. Pheromone traps are available to monitor onset of activity and pressure. Traps should be placed in the vineyard prior to the onset of GBM activity, usually around bloom. Threshold numbers for these traps have not been verified for New England, but they are useful to determine the onset of GBM activity.

Brown marmorated stink bug (BMSB) (Halyomorpha halys): Adult BMSB are approximately 3/4 inch long and are shades of brown on both the upper and lower body surfaces. They have the typical “shield” shape of other stink bugs, almost as wide as they are long. To distinguish them from other stink bugs, look for lighter bands on the antennae and darker bands on the membranous, overlapping part at the rear of the front pair of wings. Masses of 20-30 eggs are laid on underside of leaves. The 5 nymphal stages range in size from 1/8 - 1/2 inch. Nymphs and adult BMSB feed on many hosts including small fruits, tree fruits, vegetables, ornamentals, and seeded crops such as corn and soybeans. BMSB feeds by puncturing the fruit with piercing/sucking mouthparts, and injecting saliva which allows the insect to suck up the plant material through its mouthparts. Fruit tissue at the point of entry and just below into the flesh, then dies and the rest of the fruit grows around it. This leaves a sunken area on the skin at the point of entry, and browning, dead tissue in the flesh.

BMSB has become a serious insect pest throughout much of the mid-Atlantic states and southern New York. As of 2020, BMSB has not caused economic damage to farms in New England. It is unknown at this time whether there will be one or two generations per year.

Management: Monitor for the presence of BMSB using suitable traps (see appendices for sources).  If found, see pest managment table for recommended materials and rates.

Spotted wing Drosophila (SWD) (Drosophila suzukii): SWD are invasive vinegar flies (fruit flies) that can attack unripened fruit. Female SWD cut into intact fruit with their serrated ovipositor to lay eggs under the skin. This allows larvae of SWD to be present during ripening, leading to a risk of detection in ripe fruit after harvest. During egg-laying and larval feeding, sour rot and fungal diseases can also be introduced, further affecting fruit quality. There is a greater risk of fruit contamination at harvest from SWD compared with native species that lay eggs only in already-damaged and rotting fruit.

Management: SWD do not appear to severely threaten grapes at this time. Thin-skinned grapes may be more damaged than thick-skinned grapes and red grapes may be more damaged than green grapes. If SWD have damaged grapes in previous years, apply insecticides when grapes begin to turn color through harvest. Choose insecticides based on efficacy and preharvest interval. Most insecticides will be made more effective by adding sugar to stimulate SWD feeding.

Foliage and Cane Pests

Grape flea beetle (Altica chalybea): This is a metallic blue beetle about 3/16 - 1/4” long that jumps when disturbed. It is found on swelling buds during the spring. The flea beetles overwinter as adults and emerge during April. They chew holes in the ends and sides of buds that are beginning to swell. Such damage destroys the capacity of a bud to develop a primary or secondary shoot. Once the buds have grown to a length of 1/2” or more, the beetles cannot cause significant injury.

Management: See pest management table for recommended materials and timing.

Grape Phylloxera (Phylloxera vitifoliae): The presence of this soft-bodied insect ( about 1/16” or less in length) is indicated by galls or knob-like protrusions on the underside of leaves. It is found primarily on leaves of Vitis vinifera varieties, especially after bloom. The damage results from new leaves remaining curled and unproductive on the vine.

Management: Plant resistant rootstocks. Remove infected leaves. Spray applications should be made immediately after bloom and again 10 days later. See pest management table for recommended materials and timing.

Grape Leafhopper (Erythroneura comes) and Potato Leafhopper (Empoasca fabae): These soft-bodied, elongated insects about 1/8” long, walk quickly when disturbed and hop when touched. The grape leafhoppers are yellow and white or red and white. The potato leafhopper is light green and has a distinctive side-ways walk. Leafhoppers appear primarily in mid-summer and are found on the underside of leaves, especially young ones. Feeding activity causes white blotches on leaves, leaf curling, and eventual leaf drop.

Management: Sample by examining 25-50 leaves per block.  When populations of leafhoppers build up to 3 or more per leaf, apply an insecticide. See pest management table for recommended materials and timing.

Japanese Beetle (Popillia japonica) and Rose Chafer (Macrodactulus subspinosus): These clumsy, large beetles can feed heavily on the foliage of many different plants. Japanese beetles are a shiny copper color, almost round in shape with legs that tend to stick out. They will play dead when disturbed, dropping to the ground. Rose chafers are very similar behaviorally but dull green in color and more oval in shape. They can be found on both leaves and fruit. The feeding damage to leaves results in skeletonizing of the leaves with only the veins left; injured fruit is unsalable. Japanese beetles are about 1/2” long and copper-colored, with metallic green markings. They feed on grape foliage, skeletonizing the leaves during the mid and late summer. The larvae, or grubs, live in the soil, feeding on roots of grasses.

Management: The beetles can be controlled with sprays of labeled insecticides. Traps are also available which use a sex and/or feeding attractant to capture the adults in a can or plastic bag, but such traps may not provide adequate control. Place traps near, but not in the planting, as traps within a planting may suffer increased localized damage from beetles which are attracted, but do not fall into the trap. See pest management table for recommended materials and timing.

Two-spotted spider mite (Tetranychus urticae): Spider mites are very small (1/50”), insect-like creatures that feed on grape foliage, sucking out plant juices and causing a white stippling or bronzing of the leaves. Under heavy infestations, leaves will turn brown and be covered in a fine webbing. Adults may also move onto the fruit, reducing consumer appeal by their presence. 

Management: There have been some reports that soaking sprays of water applied at relatively high pressure may temporarily suppress mite populations. Foliar applications of broad-spectrum insecticides such as diazinon and Danitol may suppress populations of spider mites, but these materials may also reduce populations of natural predators which feed on the spider mites. Several companies now commercially produce predatory mites which feed on spider mites. These predators can be released in grape plantings and may provide some control of spider mites, but research is needed to determine appropriate release rates and timing. It is important, however, to encourage natural enemies of spider mites by reducing the use of pesticides which may harm natural enemies. See pest management table for recommended materials and timing.

Grapevine Aphid (Aphis illinoisensis): These aphids are dark brown and about 1/32 - 1/16” in length. They appear on young shoots and leaves during summer months. When abundant, aphids prevent proper extension of shoots, expansion of leaves, and development of fruit.

Management: When present, an overhead irrigation system can be used to reduce aphid numbers on the vines. This is not a “tested” method but has been recommended anecdotally. Similarly, spraying with water at high pressure can have the same result: washing the aphids off the vine.

Grape Tumid Gallmaker (Janetiella brevicauda): The grape tumid gallmaker (GTM) is a tiny midge (a type of fly) that lays eggs on developing leaves, stems and fruit clusters, causing large galls that can interfere with fruit development and yield.  There are several generations during the season, but the first generation in the spring is the most problematic. The larvae are well protected within the galls making them difficult to kill with contact insecticides.  The adults only live one day, making it difficult to time insecticide applications. 

Management: Pesticide applications for GTG are not economically prudent unless the infestation is heavy or the vineyard has a history of tumid gall problems. Treatment should be timed to kill adults of the overwintered generation as they emerge. Since adults are difficult to detect, it may be most feasible to base control measures on the first sign of larval entrance into vine tissues or on the first indication of gall formation. Systemic insecticides timing application is not as critical, but should be applied as early as possible after sufficient foliage is present (10” stage). Growers might also consider burying the pupae by mounding soil up under the vines early in the season (late April). This form of cultural control might prevent adults from reaching the soil surface.

Vertebrate Pests

Birds: Birds are a major pest problem in grapes. Left unchecked, they can destroy enough of the crop to ruin the profitability of a vineyard. The loss of chemical deterrents has made bird control a more difficult task in recent times, but effective means are still available.

Netting is the most effective way to keep birds out of the vineyard. Although initial costs can be high, most netting will last for many years if cared for properly. Netting should be hung over some sort of support structure built around the vineyard. Usually posts are set nine feet above the ground around the perimeter of the vineyard, and wire is run from pole to pole to form a grid over the planting. The netting is hung over this grid when the fruit begins to turn color. Some temporary nine foot poles may be placed within the vineyard at intersections of the grid to keep the netting from drooping. Bury the edges of the netting or anchor it to the ground to keep birds from crawling underneath. Remove the netting when the harvest is complete, and store in a cool, dry place.

Visual scare devices have variable effectiveness on birds. Scarecrows, balloons, kites, or stuffed owls may work on certain bird species in certain areas, but none seem to have widespread dependability. When using scarecrows, “scare eye” balloons, stuffed owls, or snakes, put them in the vineyard only when the fruit begins to ripen, and move them regularly, at least once a day. Six scare-eye balloons per acre are recommended. Take them out of the field as soon as harvest is over. This will reduce the chance of birds becoming accustomed to the devices, and increase the longevity of their effectiveness. Kites and helium-filled balloons positioned high above the planting with a silhouette of a hawk hanging from them have provided good results in some areas.

Noise deterrents, such as propane cannons, alarms and recorded distress calls seem to have the least effect on birds in vineyards, but may greatly annoy neighbors. A combination of noise and visuals may be effective, however. Several operations have hired people to regularly drive motorcycles and/or ATVs through the vineyard when the fruit is ripe, and this seems to keep birds away quite well. Be sure to make drivers aware of where pickers are however, to avoid possible accidents.

Bird Shield™, a repellent formulated from methyl anthranilate, is currently being registered for use on blueberries, cherries, and grapes. Methyl anthranilate is commonly used as a grape flavoring in human food preparations. Bird avoidance is based on odor quality and irritation. To humans, this chemical has a grape-like or fruit odor and a slightly bitter, pungent taste. Unfortunately, efficacy data do not support recommending this material at this time.

For a complete discussion of bird control in fruit crops, see Bird Damage Prevention for Northern New England Fruit Growers by Dr. Alan Eaton of the University of New Hampshire.

The primary goal of weed management is to optimize yields by minimizing competition between the weeds and the crop. Weeds reduce yields by competing with the crop for water, light, and nutrients. Weeds also harbor insects and diseases and encourage vertebrate pests. Timely cultivation, wise use of herbicides, and never permitting weeds to go to seed are integral parts of a good weed management system. Many of the weeds found in these fields are difficult-to-control perennial weeds that are not common in annual crop culture. New plantings usually have fewer perennial weed problems than older plantings. Annual and biennial weeds can also exist in these fields. Fields should be scouted at least twice a year (spring and fall) to determine specific weed problems. The selection of a weed management tool should be based on specific weeds present in each field. Most annual weeds can be reduced with mulches that are free of weed seeds and placed thickly, but perennial weed may require additional management. Several herbicides are labeled for use in this crop. A list of herbicides and their recommended uses is presented in Table 58 below.

Herbicides can be broadcast or applied as a directed spray to the base of the crop. With a band treatment, only 1 to 2 feet on either side of the rows is treated. The area between the crop rows is usually maintained with a mowed cover of sod, clover, weeds, or a combination of these. This cover is used primarily for erosion control and to improve trafficability in the field. With banding, less herbicide is needed in each acre. For example, a 3 foot band (1.5 feet on either side of the row) where rows are spaced 9 feet apart will require only one third the amount of herbicide normally required for a broadcast treatment.

Weeds can develop resistance to herbicides. The Weed Science Society of America (WSSA) developed a grouping system based on the mode of action of different herbicides. WSSA Group numbers can be used as a tool to choose herbicides in different mode of action groups so mixtures or rotations of active ingredients can be planned to better manage weeds and reduce the potential for resistant species.

Cultivation and mulching are sometimes used as weed management tools. All cultivations should be timely and shallow to minimize crop root injury, to minimize loss of soil moisture, and to avoid repositioning new weed seeds to the soil surface. Mulches that are free of weed seeds and placed thickly enough can be very effective at reducing or eliminating most annual weeds from the crop row. They are seldom effective on perennial weeds. If mulches are used in combination with herbicides, use the lowest recommended herbicide rate to avoid crop injury.