Spraying Grape Vines for Bugs, Home Guides, SF Gate

Spraying Grape Vines for Bugs

Grape vines are susceptible to several insect pests, which can be controlled with proper management..

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Growing grapes has been popular with California gardeners for hundreds of years. Early varietals brought to the area from Mexico eventually were replaced by European grapes, which were superior for consumption, from eating fresh to making into wines and preserves. California growers today generally prefer European varieties such as Ladyfinger and Perlette, which are well-suited to California’s longer growing season. The first step in controlling pests on grape vines is to know what pests to expect and when to expect them. Proper control measures often can minimize or avoid chemical sprays.

European Grapevine Moths

The blotchy-brown European grapevine moth, which showed up in Napa County in the fall of 2009, is described as a “significant invasive pest” by the U.S. Department of Agriculture. Larvae emerge in three generations, beginning in late May and continuing through September. These pests damage grapevines by forming webs over and feeding on flower clusters, unripe grapes and grape bunches, emptying the grapes and leaving skin and seeds. Control often is targeted at the second generation to avoid re-infestation from untreated vineyards. Reduced-risk pesticides, including growth regulators, spinosyns and Bacillus thuringiensis, are registered for this use in California. Other control measures include removal of contaminated grapes and vines, and breeding-cycle disruption. Quarantines have been used to slow infestations in some areas of California. Because this is a recently introduced pest, research to find the best control is ongoing.

Grape Phylloxera

Grape phylloxera are minute, oval-shaped insects that overwinter on grape roots. They emerge in spring when soil temperatures hit 60 degrees Fahrenheit. They feed on roots, causing stunted or dead vines. Phylloxera are found in heavy clay soils, and do not appear to be a pest in areas with sandy soil. Controlling phylloxera is mostly achieved through planting grape rootstock that is resistant to the pest. Chemical treatments are generally ineffective because they can’t penetrate clay soils, and phylloxera populations rebound quickly, even after a heavy die-off. Sodium tetrathiocarbonate and imidalcloprid, when used in a drip-irrigation system, have shown some effectiveness, according to the University of California-Davis.

Leafhoppers

The slender, splotchy leafhopper is considered a major pest in vineyards from southern California to the San Joaquin Valley. Adult leafhoppers overwinter on grape leaves and in weeds; adults and nymphs feed on grape leaves, leaving empty cells and causing leaves to wither and drop. Feces accumulation on berries is also a problem, especially with table grapes. In most areas of California, vines can tolerate moderate leafhopper infestations; natural predators also help control populations. Chemical control is generally used only in coastal regions and the Central Valley, where infestations can be heavy. Pesticides typically aren’t recommended for use in a backyard garden; cultural controls such as weed and plant-debris removal and natural enemies are usually sufficient to keep leafhoppers under control. Insecticidal soaps are recommended when needed. They are effective only when applied to bugs, so all plant surfaces must be covered, and regular re-application is often necessary.

Grape Mealybugs

Grape mealybugs are small, flat, waxy, pinkish-gray pests active in warm weather. Mealybugs produce “honeydew,” a waxy substance that coats grape bunches and promotes the growth of black, sooty mold. They do not harm vines, according to California’s Statewide Integrated Pest Management Program. Control in the home garden takes advantage of the fact that the young and eggs of these bugs overwinter under the bark of the plant. Remove loose bark in the winter. Natural enemies such as parasitic wasps, mealybug destroyers, lacewings, spiders and minute pirate bugs can do their work on this pest if you don’t kill them with sprays and if you control ants that may interfere with them.

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Pest and Disease Control of Vineyard Grapes

To me disease and pest control is probably the least interesting subject regarding grape growing. Yet if you don’t get this part right you’ll just be spinning your wheels.

Diseases:

Seriously, it does not matter if you have a small backyard project or a larger scale vineyard you will be faced with these less than pleasant elements of nature that you will need to know how to deal with.

But don’t worry, it’s very easy if you put the following disease and pest maintenance plan into action.

Even more, you should consult local agricultural departments and fellow grape growers in all aspects of canopy management, disease and pest control.

Regions vary greatly in disease and pest issues. A major problem in one area may not exist in another. Local knowledge will help you tremendously.

The two most effective means of disease control are good canopy management and preventative fungicides treatments.

You will need to use fungicide on a regular basis and it should be done in a preventative maintenance manner. Waiting until fungus appears is usually too late.

Be sure to visit the educational sites I reference later in the fungus and insect sections. They are chalk full of healthful information. This information is an easy read short and to the point with excellent images. Spend a few minutes to an hour on these sites and you’ll practically be an expert.

Canopy management insures a uniform vine structure. The canopy includes all the stems, leaves and fruit clusters that have grown from your two main canes.

Basically canopy management is the thinning and positioning of leaves, stems and fruit clusters during the summer. Positioning includes spacing shoots and fruit clusters amongst your catch wires so that all have equal exposure to sunlight and air flow.

Removing fruit clusters is an emotional experience but can help produce significantly higher wine quality.

Wine that has been produced from grapes at different stages of ripeness will be inferior to that produced from well managed canopy systems. The more sunshine and air flow that is allowed to penetrate your vines the less likely you will encounter fungus diseases.

Thinning:

  • remove shoots that are growing downward
  • remove shoots from excessive areas of vine density, a general rule of thumb is to have two to four shoots per foot of trellis
  • remove shoots that are not bearing fruit, unless they are being retained for possible cane renewal
  • remove shoots that have emerged from the trunk base, unless they are being retained for possible cane renewal
  • remove excess leaf growth in fruiting zones so that grapes can dry easily and have good sun exposure

Each shoot should contain no more than one grape cluster at an average size of 5-8 ounces. An average size cluster needs approximately ten to fifteen leaves for proper ripening. If your grape clusters are small you can get by with two per shoot. For uniform results all shoots should have approximately the same amount of leaves.

Positioning:

In the growing season use twine to insure a uniform canopy by securing the shoots evenly and upwardly to the catch wires. Again, position all shoots and fruit clusters for equal exposure to sunlight and air flow. Be sure to position fruit clusters so that they are not touching one another.

Fungus:

Powdery Mildew: Grape vines infected with powdery mildew display white powder-like splotches on leaves, stems and grapes. Powdery mildew is experienced worldwide. It can grow well in both wet and dry regions. It can kill leaves and defoliate the vine.

Grape quality suffers when leaves are unable to perform proper photosynthesis. A well managed canopy and regular sulfur spraying will prevent most powdery mildew occurrences. Spray every ten days when shoots reach 10″ in length, continue up until thirty days before harvest: More on Powdery Mildew, Cornell University

Downy Mildew: Symptoms include light green to yellow spots scattered across the leaf. These spots appear greasy and are commonly referred to as oil spots.

The biggest concern for downy mildew is leaf infection. The fungicides Copper, Captan, and Mancozeb can be sprayed every ten days and is generally mixed with sulfur. Please read the labeling and do your research, local restrictions may apply: More on Downy Mildew, Iowa State University

Black Rot: Symptoms include brown circular lesions on infected leaves. Left untreated it can destroy an entire grape crop. The biggest concern for black rot is the infection of young grape clusters.

Infected berries first appear light brown and then turn to near black as masses of black pycnidia develop on the surface. Again, Copper, Captan, and Mancozeb are the most protective fungicides. For application follow the downy mildew recommendations. Please read the labeling and do your research, local restrictions may apply: More on Black Rot, Cornell University

Bunch Rot: Infected berries appear soft and watery. In high humidity regions berries become covered in a grayish growth of fungus mycelium. Tight-clustered grape varieties are most vulnerable to bunch rot.

Canopy management is your most effective tool in preventing bunch rot. Promote good air circulation, sunlight penetration, and uniform leaf development by practicing proper canopy management. Remove leaves around grape clusters so that sunlight and air flow can help dry wet grape clusters: More on Bunch Rot, Ohio State University

Insects:

It’s much easier to correct and control damage caused by insects then that caused by fungus disease. You can evaluate the problem as it develops and determine if damage is significant enough to warrant spraying. Rarely will insect populations be high enough to require insecticides.

Insects feed on buds, leaves, and fruit. The most damaging are those that feed on fruit because resulting rot can spread throughout the entire cluster.

Use insect specific insecticides to eradicate insects you have identified as damaging to your vines. Certain insects are actually good for your vineyard and you don’t want to destroy them because they feed on mites and other problem insects.

Get local agricultural advice when seeking solutions for insect infestations. There’s tons of good images and information regarding insect eradication online. Search by your state for local information. Some of the most common and damaging insects are discussed and pictured at the following education sites:

Every state monitors insect populations most of which can easily be found online.

Other Pest:

In some areas birds can be a big problem. Their pecking of grape berries can easily initiate rot damage. Scare devices are helpful but can be annoying to neighbors if they are sound related. In some extreme cases netting may be your only solution. Voracious birds can devour a crop in a short period of time.

Deer, bear, kangaroos, raccoons just about every animal loves grapes. Deer the largest animal problem for most grape growers can be fenced out. Fence designs vary depending on what animal you are having problems with. Repellents such as hot sauce and pepper are effective in areas where problems are moderate. Again local knowledge is your best tool.

grapegrowingguide.com

How to Control Pests on Grapevines Without Pesticides

21 September, 2017

Grapevines are susceptible to a number of pests. Mites, scales and mealybugs are only a few of the insects that are likely to plague vineyards at one time or another. However, since the grapes on your grapevine will ultimately be consumed, even organic pesticides should be avoided. The first step to controlling pests on grapevines without pesticides is to properly identify them. Most grapevine pests can be controlled without the application of chemicals. Severe infestations should ultimately be combated by altering growing conditions or by replacing existing vines with pest-resistant varieties.

Release predatory insects onto the grapevines. Mealybugs and scale insects can be effectively controlled by releasing ladybird beetles, lacewings or parasitic wasps that feed on these grapevine pests. Mites can be controlled by releasing predatory mite species that prey on the specific variety of mite that is feeding on your grapevine.

Prune infested grapevine canes. Immobile scale insects affix themselves to grapevine canes, while fig longicorn borers burrow into them. Both of these pests can be treated by pruning the infested canes with a clean, sharp pair of pruning shears. Deposit pruned canes into a plastic bag, seal it and then throw it away.

Remove all dead leaves and any litter lying at the base of your grapevines at least three weeks before your grapevines bloom in spring. Certain grapevine pests like grape flea beetles and grape berry moths survive the winter by burrowing into this debris to keep warm. By removing the debris, you can effectively break their reproductive cycle without using chemical pesticides. Deposit any collected litter into a plastic bag, seal it and then throw it away.

Remove large insects by hand. Pests like Japanese and multicolored Asian lady beetles can be picked off by hand. Check for and remove these large pests at least twice a week during the growing season. These pests are least active in the early morning so this is the best time to go after them. Prepare a bucket of soapy water and drop the beetles into the water after you pick them off. When harvesting infested grapes, shake the clusters over the soapy water to dislodge any hiding multicolored Asian lady beetles.

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Spraying Fungicide on Grapevines

Spraying fungicides on grapevines helps prevent problems with fungal diseases.

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Grapevines can suffer from problems with insect pests and disease. Fungal infections are common, and you need to learn their identifying signs and characteristics to select the correct fungicides for prevention and treatment. For optimum control, you may need to apply fungicides throughout the growing season, as well as after harvest. Some fungicides may adversely affect certain grape varieties, so it is essential you follow the manufacturer’s instructions carefully.

Selecting the Right Fungicide

Fungal infections that most frequently attack grapevines include botrytis bunch rot or gray mold, powdery mildew and downy mildew. Other fungal diseases found on grapevines include Phomopsis cane and leafspot, Botryosphaeria canker and black measles. Fungicidal sprays do not prevent and control all fungal diseases equally, so it’s important to identify the most common fungi in your region. For example, sulfur-based fungicides are highly effective for managing powdery mildew, while copper sprays like Bordeaux mixture are only moderately effective at controlling it. On the other hand, copper fungicides provide excellent prevention of downy mildew. Sprays containing cyprodinil have shown the best results for managing botrytis bunch rot and carbonates, like those found in baking soda, also reduce gray mold spore germination.

Application Schedule

In addition to selecting the right fungicides, you need to spray at the right times. For example, the University of California Pest Management Guidelines recommend fungicide application to prevent botrytis bunch rot during dormancy and also at periods of full bloom, preclose, varaison and before and after harvest if rain is forecast. For downy mildew prevention, spraying fungicides at budbreak and full bloom is most critical. In the case of powdery mildew, fungicidal sprays should be applied during dormancy and then again at budbreak and full bloom. Additional applications may be needed depending on other risk considerations.

Adverse Effects

Fungicidal sprays can have negative effects on certain grapevines, depending in the variety. For example, sulfur-based fungicides can injure “Chancellor,” “Concord,” “DeChaunac,” “Foch” and “Rougeon” varieties. Fixed copper fungicides and Bordeaux mixture also can cause phototoxicity, resulting in foliage damage, if not used correctly. Oil-based sprays can damage grapes’ waxy outer coating and although you can still eat the grapes, their appearance is adversely affected.

Problems With Resistance

Fungal infections in grapevines are becoming difficult to manage because of problems with resistance, which make fungicides less effective. Therefore, it is good practice to rotate fungicidal spray products from year to year. State departments of agriculture may restrict use of some fungicides. Your local extension office can provide information about permitted fungicidal sprays, as well as the latest details regarding new fungicides available for use with grapevines.

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Crape Myrtle Diseases & Insect Pests

Factsheet | HGIC 2002 | Updated: Nov 11, 2019 | Print | Download (PDF)

Crape myrtles (Lagerstroemia indica) are essentially trouble-free small trees. The most common problems include powdery mildew, Cercospora leaf spot, aphids, Japanese beetles and sooty mold. More information on successfully growing crape myrtles is available in HGIC 1008, Crape Myrtle, and HGIC 1009, Crape Myrtle Pruning.

Diseases

Powdery Mildew: Powdery mildew is one of the most common problems of crape myrtle, and it is caused by the fungus Erysiphe lagerstroemia. Patches of white to grayish powdery growth occur on the surfaces of leaves, flowers and new shoots. Heavily infected flowers may fail to open. Infected parts of the plant are usually distorted and stunted. The disease is most serious in shady, damp locations, especially where plants are crowded and air circulation is poor. Development of the fungus is favored by high humidity at night and dry, mild daytime conditions, as often occurs during the spring and fall.

Powdery mildew typically coats the flower buds (above) and foliage of crape myrtle. James Blake, ©2007 HGIC, Clemson Extension

Prevention & Treatment: The most effective control measures include locating plants in full sun, removing sprouts from the base of the plant and planting resistant varieties. Susceptible varieties of crape myrtle should be avoided. Removing diseased twigs and branches may be possible, if only a few shoots are infected. Remove sprouts (suckers) at the base of the plant as they occur, since they are very susceptible to powdery mildew. Once these sprouts become infected, the fungus easily spreads to the upper portions of the plant.

Plant Resistant Varieties: The extent of resistance to powdery mildew for a particular variety may vary from location to location and may depend on particular conditions occurring in the environment.

  • The Lagerstroemia indica x fauriei hybrids developed at the U. S. National Arboretum in Washington, D. C. are resistant to powdery mildew.
  • Varieties with very good resistance to powdery mildew and fairly good tolerance to Cercospora leaf spot include: ‘Apalachee,’ ‘Basham’s Party Pink,’ ‘Caddo,’ ‘Dodd #2’, ‘Fantasy,’ ‘Glendora White,’ ‘Hopi,’ ‘Lipan,’ ‘Miami,’ ‘Osage,’ ‘Pecos,’ ‘Regal Red,’ ‘Sarah’s Favorite,’ ‘Sioux,’ ‘Tonto,’ ‘Tuscarora,’ ‘Tuskegee,’ ‘Velma’s Royal Delight’ and ‘Wichita.’ ‘Apalachee’ and ‘Fantasy’ are totally resistant to powdery mildew.
  • ‘Catawba,’ ‘Cherokee,’ ‘Seminole’, and ‘Yuma’ have some resistance to powdery mildew.

Varieties to Avoid: ‘Gray’s Red,’ ‘Orbin’s Adkins, ‘ ‘Carolina Beauty,’ ‘Wonderful White,’ ‘Raspberry Sundae’ and ‘Potomac.’

If disease is severe enough to warrant chemical control, select a fungicide containing one of the following: myclobutanil, propiconazole, thiophanate-methyl, or copper-based fungicides (see Table 1 for specific products). Multiple applications may be required. Apply all chemicals according to directions indicated on the label.

Cercospora Leaf Spot: Leaf spots caused by Cercospora lythracearum may appear on crape myrtles and are caused by the fungus Cercospora species. This disease typically occurs during periods of warm, moist weather. Yellow spots (⅛ to ¼ inch diameter) appear on the upper leaf surface with white-grey sporulation of the fungus on the lower leaf surface. The disease can result in almost complete defoliation of the plant in late summer and fall in susceptible cultivars.

Prevention & Treatment: Select resistant varieties for new plantings. The varieties, ‘Fantasy,’ ‘Tonto,’ ‘Tuscarora,’ ‘Tuskegee,’ and ‘Velma’s Royal Delight,’ have exhibited resistance to Cercospora leaf spot in field trials. The amount of resistance may vary from location to location and may depend on particular environmental conditions. Provide good air circulation and avoid overcrowding plants. If disease is severe enough to warrant using chemicals for control, thiophanate-methyl or myclobutanil as used for powdery mildew will control Cercospora leaf spot (see Table 1 for specific products). Apply all chemicals according to directions on the label.

Insects & Other Pests

Very few insects are pests of crape myrtle. In South Carolina, the most important insect pest is the crape myrtle aphid (Sarucallis kahawaluokalani), which is found on the leaves and twigs of crape myrtle. Crape myrtle aphids feed only on crape myrtle trees.

Japanese beetle (Popillia japonica) is also a pest and feeds on both leaves and flowers. In addition to crape myrtle, it will feed on nearly three hundred different plant species.

Crape Myrtle Aphids: Crape myrtle aphids are pale yellowish green in color with black spots on the abdomen. They vary in length from 1 /16 to ⅛ inch long. They overwinter (survive the winter) as eggs, which hatch in the spring. During the growing season, females give birth to live young. Since it takes about 10 days to reach maturity, several generations are produced each growing season. At the end of the growing season, females produce eggs that overwinter.

Aphids feed by inserting their mouthparts into tender new leaves from which they suck plant sap. Plant sap has a high sugar content. When they feed, the aphids excrete large amounts of sugary liquid called honeydew. With a large aphid population, the honeydew can completely coat leaves. The honeydew serves as food for the sooty mold fungi (Capnodium sp.), as well as various insects, including ants, wasps, and flies.

A heavy infestation of aphids on the underside of a leaf.
Image from John Herbert, University of Florida

As the aphid feeds, it injects saliva into the leaf. The saliva causes yellow spots to develop on the leaf. Their feeding on young leaves often causes leaf distortion. Buds, branch tips, and flowers can also be affected by feeding.

Control: The following crape myrtle hybrids (Lagerstroemia indica x fauriei) have moderate resistance to aphids: ‘Muskogee,’ ‘Natchez,’ ‘Tuscarora,’ ‘Acoma,’ ‘Tuskegee,’ ‘Hopi,’ ‘Pecos,’ ‘Zuni,’ ‘Biloxi,’ ‘Miami,’ ‘Wichita,’ ‘Apalache,’ ‘Comanche,’ ‘Lipan,’ ‘Osage,’ ‘Sioux,’ ‘Yuma,’ ‘Caddo,’ ‘Tonto,’ ‘Choctaw,’ and ‘Fantasy.’ Consider using these in new plantings.

Several predators feed on the crape myrtle aphid. These include ladybird beetles (ladybugs) and their larvae (immature forms), green lacewings and their larvae, hover fly maggots, parasitic wasps, and entomophagous (insect feeding) fungi. As much as possible, these natural predators should be allowed to reduce aphid populations. In addition, many aphids can be removed from plants by spraying with a strong stream of water. Spraying with water may have to be repeated regularly, as needed.

As a result of their phenomenal reproductive rate, aphids are very difficult to control with insecticides. If a single aphid survives, a new colony can be produced in a short period of time. In addition, using insecticides means that beneficial predators will also be killed. If it is determined to be absolutely necessary, various insecticides are labeled for use by homeowners against aphids on crape myrtles. These include insecticidal soap, horticultural oil, pyrethrins, neem oil, permethrin, cyfluthrin, lambda cyhalothrin, acephate, or malathion. Soil drenches of imidacloprid in the spring will control aphids and last longer within the plant to prevent future infestations by aphids and other insect pests (see Table 1 for specific products). As with all pesticides, read and follow all label instructions and precautions.

Japanese Beetles: Adult Japanese beetles are about ½ inch in length and coppery-brown in color with metallic green heads. They emerge from the soil and feed from May to August. They lay their eggs in the soil. Grubs hatch from the eggs and feed on grass roots. As the weather cools, the grubs move more deeply into the soil to overwinter.

Both adult beetles and their larvae (grubs) can seriously damage plants as a result of their feeding. Adult Japanese beetles eat flowers and skeletonize leaves (eat leaf tissue between the veins, resulting in a lacy skeleton remaining). The grubs feed on the roots of plants, especially on the roots of grasses.

Control: Multiple approaches are necessary for controlling Japanese beetles. Adults can be handpicked and drowned in a pail of soapy water. Japanese beetle traps are available commercially or can be homemade. They may be effective at reducing adult populations.

Keep traps at least 50 feet from the crape myrtle tree or you may create more of a problem by attracting them to the area. Milky spore, Paenibacillus popilliae, is a disease-causing bacterium that is effective against grubs of Japanese beetles but not the adults. It is commercially available for homeowner use. Many products containing neem oil, cyfluthrin, permethrin, lambda cyhalothrin, or acephate are labeled for use by homeowners against Japanese beetles on crape myrtle. Soil drenches of imidacloprid in the spring will control Japanese beetles and last longer within the plant to prevent future infestations by additional pests (see Table 1 for specific products). As with all pesticides, read and follow all label instructions and precautions.

Crapemyrtle Bark Scale: This crape myrtle pest is a more recent arrival. For information on this insect pest and control measures, please see HGIC 2015, Crapemyrtle Bark Scale.

Other Problems

Sooty Mold: Leaf and stem surfaces are covered with a black sooty substance, causing them to appear black and dirty. Sooty mold indicates that there is an insect problem on the plant. These common molds are caused by fungi that grow on the sugary substance, called honeydew, produced by various insects that suck sap from the plant. Aphids, scales, mealybugs, and whiteflies most commonly cause this problem.

Prevention & Treatment: Sooty molds are unsightly, but are relatively harmless, since they do not directly attack the plant. Controlling the insect problem can reduce excessive amounts of sooty mold. Reduce aphid numbers by allowing beneficial insects, such as lady beetles, to inhabit the plant. Aphids can be removed from the plant with a strong spray of water.

Although not necessary, sooty mold can be washed from the leaves by spraying foliage with a dish soap solution (4 ounces per gallon of water), waiting three to four minutes, and then rinsing the foliage with a strong stream of water.

Lichens: A lichen is an unusual organism composed of a fungus and an alga living together in the same body. Lichens often appear as green to gray-green leafy or crusty growths on the trunks or branches of plants. Typically, they occur in abundance on plants that are declining in health or vigor. They are harmless to the plant, and are in no way responsible for the poor health of the plant. Less vigorous plants tend to be more open with less foliage, which increases sunlight penetration and subsequent lichen growth.

Prevention & Treatment: Controls are not necessary. Lichens will gradually disappear if the health of the plant is restored.

These harmless lichens are growing on an older crape myrtle.
Karen Russ, ©2007 HGIC, Clemson Extension

hgic.clemson.edu

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