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| FIGURE 63. Grape flea beetle adult. |
Many of the same insect and mite species that damaged grapes late in the 1800s continue to cause economic injury today. Damage is direct to the berry clusters or indirect to vines, shoots, roots, or leaves. In this section, the life histories of 10 of the most damaging arthropod (insect and mite) pests of Ohio grapes are described, including a new pest—the multicolored Asian lady beetle. Growers should keep in mind there are more than 50 insect and mite pests of grapes, and some can cause significant injury. Many of the pests are found only in certain regions; others only occasionally reach damaging population levels. Periodic vineyard inspections for grape pests will reduce the risk of arthropod damage.
For accurate identification of grape pests, growers should obtain a copy of Insect and Mite Pests of Grapes in Ohio, Bulletin 730, Ohio State University Extension. This bulletin has 76 photos of the most common pests of Ohio grapes and includes descriptions of pest life cycles and damage. There is a charge for this publication, which is available from Ohio State University Extension, Media Distribution, 2021 Coffey Road, Columbus, OH 43210-1044. Current pesticide recommendations and spray schedules in Ohio are available from Ohio State University Extension.
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| FIGURE 63. Grape flea beetle adult. |
The grape flea beetle is a dark metallic greenish-blue or steel-blue beetle about 3/16-inch long (Figure 63). It is occasionally a serious pest of grapes in the Midwest, feeding on grape buds in the early spring.
Female beetles lay eggs mainly under loose bark of the grapevine. Larvae hatch and crawl to the developing grape leaves, where they feed. Adult beetles and larvae also feed on the foliage, but the injury they cause usually is negligible.
Newly hatched larvae of the grape ea beetle are dark blackish purple and approximately 1/16-inch long. As they grow, their color lightens and they reach a length of almost 1/3 inch (Figure 64). The head is black, and there are six or eight shining black dots on each of the other segments of the body, each dot emitting a single brownish hair. The under surface is paler than the dorsum. Its legs, six in number, are black, and there is a eshy, orange-colored proleg on the terminal segment.
When they are fully developed, the larvae drop to the soil, burrow one inch or less, and pupate. They emerge later as adults. There may be a partial or full second generation each year.
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| FIGURE 64. Flea beetle larva feeding on leaf. Note damage. | FIGURE 65. Flea beetle damage to a swollen bud early in the season. |
Flea beetles cause two types of damage—feeding directly on the buds and feeding on the foliage. The most serious damage occurs in the spring as the adults emerge from over-wintering sites and feed on slightly swollen grape buds (Figure 65). They chew holes in the sides and ends of the newly developing buds, damaging primary and occasionally secondary and tertiary buds.
If all three growing points are destroyed, no grapes will be produced. If secondary or tertiary buds are not destroyed, a partial crop may develop, allowing subsequent clusters to form. These beetles do not cause major damage once the buds have surpassed a half inch in length. Both larvae and adults feed on the upper and lower leaf surfaces, causing some damage, although this injury is usually of little consequence.
The adult beetles eat the contents of the buds, destroying foliage and fruit that normally would develop. Fortunately, the beetle attacks usually are conned to limited areas of the vineyard. If growers are aware of these infestations, they can make an early-season insecticide application the following year to keep populations in check. Another application of spray in June, when larvae are feeding on the grape foliage, may help to control an outbreak the following year.
Wood lots and wasteland areas near cultivated vineyards are a possible source of ea beetles and should be cleaned up if possible. This will help to reduce overwintering sites for the beetles. Cultivating between rows may contribute to control by exposing the delicate pupae to desiccation and death. Cultivating helps but does not completely eliminate emerging beetles from under the trellis and adjoining wood lots.
Grape bud damage caused by the grape ea beetle is often concentrated in vineyard borders near wooded areas. Early vineyard monitoring and past history of beetles in the vineyard will help determine the need for an early-season application of insecticide. Scouting of the vineyard for grape ea beetle should begin in April and continue until bud development is past the critical stage.
These shiny metallic beetles are easily spotted on grape canes and buds on warm, sunny days in the spring. Scouting for adult beetles should be conducted along the vineyard perimeter, on all sides, and near the center of the vineyard. At least 25 vines should be surveyed at each of the five locations.
If bud damage averages 4% or more, one should apply an insecticide to prevent further bud damage. Timing is critical. For specic insecticides used in the control of the grape ea beetle, see annual recommendations.
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| FIGURE 66. The adult grape berry moth is mottled brown with bluish-gray on front wings. |
This is the major insect pest of grape berries in the eastern United States and Canada. When vineyards are left unmanaged, up to 90% of the fruit often is destroyed by the larvae and accompanying diseases facilitated by the damage inicted upon the fruit. Infestations vary greatly from vineyard to vineyard, from year to year, and within a vineyard. However, vineyards bordering wooded areas are most vulnerable to infestation.
The adult is a mottled brown-colored moth with some bluish-gray on the inner halves of the front wings (Figure 66). The larvae of this small moth are active, greenish to purplish caterpillars about 3/8-inch long when fully grown. Grape berry moths overwinter in cocoons within folded leaves in debris on the vineyard oor and within adjacent woodlots.
After emerging in the spring, the adults mate and the females lay eggs on or near owers or berry clusters. Newly hatched larvae feed upon the owers and young fruit clusters. Larvae that hatch in June make up the rst generation of grape berry moth and will mature from mid- to late July or August.
After mating, females lay eggs on developing berries, and this second generation matures in August or September. Larvae of the second generation, after completing their development, form cocoons in which they overwinter. A third generation occurs commonly in the southern range of the pest and occasionally in the northern tier of states.
First-generation larvae web small ower buds or berries together in early June and feed externally on them or on tender stems. Larvae that attack grape bunches during this time are difcult to see.
Second generation larvae tunnel directly into the green berries and feed internally. Conspicuous reddish spots develop on the berries at the point of larval entry. Berries affected in this manner are known as stung berries (Figure 67).
The second generation is more damaging than the rst. A single larva may destroy two to six berries in a cluster, depending on berry size, and several larvae frequently inhabit a single cluster. At veraison the damage is easiest to see on white grapes.
At harvest, severely infected bunches may contain many larvae, and most of the berries may be completely hollowed (Figure 68). In many cases, bunches are covered with bunch rot fungi and infested with Drosophila fruit ies and often have an unhealthy appearance.
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| FIGURE 67. Stung berries have a reddish color where the larvae tunnel directly into the green berries and feed internally. Stung berries are easy to spot. | FIGURE 68. Berries may be completely hollowed. |
An insecticide may be needed to prevent damage in areas heavily infested by grape berry moth. The number of spray applications depends on the infestation level and the type of production—wine, juice, or table grapes. Table grapes that are inspected by consumers in the market place require more attention than grapes grown for juice.
Corrective measures are usually suggested if more than 5% of the clusters are injured. To determine the percentage of clusters damaged, randomly inspect 100 clusters along the perimeter of the vineyard and 100 clusters toward the center of the vineyard. This method will tell you if treatment of the entire vineyard is necessary. Treatment of perimeter rows may be all that is necessary to control this pest. Control of second generation larvae in mid- to late July is particularly important.
Cultural controls can be used to kill the overwintering pupae in leaves. Leaves can be gathered and destroyed in the fall, or leaves can be buried within the soil in the spring, two weeks before bloom, by rototilling or cultivating.
An alternate method of control using pheromone rope ties to disrupt the males of the grape berry moth was approved by the EPA in 1990. Following that sprayable pheromones were tried with some success. However, the sprayable pheromone must be applied several times in order to eliminate the threat. Neither of these approaches is being practiced at present.
Pheromone traps are available to monitor the emergence of male grape berry moths during the season. This information may be useful for optimal spray timing; sprays should target egg hatch and young larval activity, which occurs shortly after the first moths are trapped.
A minimum of three traps for monitoring a single block of approximately 10 to 15 acres is recommended. Traps hung from the top wire of the trellis should be placed around the perimeter of the vineyard before bloom and should be at least 100 feet apart. Sticky trap bottoms should be checked weekly for moths, and pheromone caps should be changed monthly to obtain accurate flight information.
Every vineyard location is unique, and growers should not rely entirely on pheromone trap data especially from other vineyards for timing insecticide sprays. Visual inspection of flower and grape clusters should be conducted throughout the season in order to be aware of any stung berries.
Pheromone traps should be used in vineyards with a history of grape berry moth problems. Trapping of adult male moths indicates the beginning of ight activity. Mating and egg laying will occur over a two- to three-week period following the rst detection of ight activity. A protective cover spray may be required during this period to prevent egg laying and hatch. Early-season control of this pest may prevent it from becoming well established within the vineyard and may eliminate the need for control later in the season.
It should be noted that the second ight activity period occurring in late July and August is the most important. These adult moths in late summer produce the eggs that hatch into larvae capable of causing major damage to the maturing fruit. One should not depend solely upon a pheromone trap for detecting this late-season threat. Scouting should be implemented on a weekly basis after bloom.
If berry cluster damage reaches 6% in grapes used for processing or 3% in those grown for fresh market, a protective cover spray should be applied. Most growers are using a pyrethroid insecticide with very good results in this situation. Remember that pyrethroids have a short residual, usually no longer than seven to 10 days, and reapplication may be necessary, especially if above-average precipitation occurs.
Studies indicate that vineyards in close proximity to external berry-moth sources, such as wood lots, may require an application of insecticide in addition to the pheromone applications. Growers using the grape berry moth pheromone should continue to scout their plantings in the same manner as previously mentioned. If thresholds are reached, the decision to apply an insecticide should be considered.
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| FIGURE 69. Adult rose chafer. |
Rose chafer adults attack grapes at bloom as the chafers emerge from the soil. Not only do they destroy the fruit at blossom, they also frequently skeletonize the leaves, leaving only the large veins intact. This insect is especially abundant in areas of light, sandy soil where beetles may appear suddenly as grapes begin to bloom.
The ungainly beetles have a straw-colored body, reddish-brown head and thorax with a black undersurface. The adult rose chafer is about 1/2 inch in length with long, spiny, reddish-brown legs that gradually become darker near the tip (Figure 69). As they age, hairs are worn off the head and thorax with normal activity, revealing the black color below. Thus they become mottled in color as they mate and move around in the ower clusters, making it possible to distinguish newly emerged adults from older specimens. Females frequently lose more hairs, particularly on the thorax, in the mating process.
Eggs of the rose chafer are oval, white, shiny in appearance, and about 1/20 inch long and 1/30 inch in width. Larvae are C-shaped white grubs about 1/12 inch long and 1/8 inch wide when fully grown. Mature larvae have three distinct pairs of legs, a brown head capsule, and a dark rectal sac visible through the integument. Larvae are found in sandy soil, feeding on roots of grasses and other weeds, and can be identied by a distinctive rastral pattern. The pupae are light yellowish-brown in color and have prominent legs. They measure about 1/2 inch in length.
Adult rose chafers become active in northeastern North America from late May to early June. The adults appear all of a sudden. It seems as though the entire population reaches maturity practically at the same time, and multitudes of beetles suddenly make their appearance. Beetles feed and mate soon after emerging from the soil. It is common to see mating pairs in the newly formed grape clusters.
Females deposit eggs singly a few centimeters below the soil surface. Mating and egg laying occur continuously for about two weeks, with each female depositing 24 to 36 eggs. The average life-span of the adult is about three weeks.
Approximately two weeks after being deposited, eggs hatch into tiny, white, C-shaped grubs. The larvae feed on the roots of grasses, weeds, grains, and other plants throughout the summer, becoming fully developed by autumn. However, it is not easy to collect the larvae of rose chafer. They have been found occasionally on the roots of orchard grass but never in proportion to the numbers found in adjacent grapes.
Larvae move downward in the soil as soil temperatures decline and form an earthen cell in which they overwinter. In the spring, larvae return to the soil surface, feed for a short time, and pupate in May. After two weeks in the pupal stage, the adults emerge and crawl to the soil surface to begin their cycle again. There is only one generation per year.
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| FIGURE 70. Blossom buds destroyed by the rose chafer. |
Despite its common name, the rose chafer attacks the owers, buds, foliage, and fruit of numerous plants including grape, rose, strawberry, peach, cherry, apple, raspberry, blackberry, clover, hollyhock, corn, bean, beet, pepper, cabbage, peony, and many more plants, trees, and shrubs.
Adults emerge about the time of grape bloom and often cause extensive damage. Blossom buds are often completely destroyed, resulting in little or no grape production (Figure 70). Feeding activity on various plants may continue for four to six weeks. Damage can be especially heavy in sandy areas, the preferred habitat for egg-laying.
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| FIGURE 71. Use the rastral pattern to distinguish grubs of scarab beetles. Rose chafer larvae can be identified by a distinctive rastral pattern, shown here. |
Scouting for this pest within your vineyard should begin in late May and continue through late June. Newly emerged adults may be found feeding primarily on newly formed grape clusters. If numbers reach two beetles per vine, control methods should be considered.
Monitoring may also be conducted by using the attractant developed for rose chafer. Traps should be placed around the perimeter as well as diagonally across the vineyard. The traps used for this purpose are Japanese beetle traps. For monitoring purposes, these traps may be spaced every 100 feet and should be checked daily for newly emerged chafers to let you know when beetle activity has begun. In addition, these traps remove beetles from the population.
If you have areas where the rose chafer is particularly troublesome, it would be a good idea to sample pastures or other grassy areas in the neighborhood to see if the grubs are in the vicinity and might be controlled. In order to distinguish the grubs of scarab beetles, the raster pattern is used (Figure 71).
Adult chafers begin emerging in late May and early June at the time of grape bloom. When only a few beetles are present, one may handpick them from the plant and destroy them. Where populations are large and pose a threat to the grape crop, massive trapping may be a safe alternative to applying insecticide.
An alternative method to chemical control has been developed by the Department of Entomology at Ohio State University for this pest. A lure using a new powerful attractant is placed in a Japanese beetle trap. Results have been very positive. The desired effect of mass trapping, which is to bring the beetle population to below threshold level, is usually achieved after a couple years of trapping.
An application of insecticide may be required in combination with the trapping effort if the population is extremely high. It is our experience that it takes a couple years of intensive trapping to reduce the population within a heavily infested vineyard to the point that chemicals are no longer needed to control this pest.
In addition, it should be kept in mind that the pupal stage is extremely vulnerable to disturbance; therefore, cultivating between rows may be effective in destroying a good number of chafers. However, it has been our experience that growers with numbers of beetles sufcient to inict economic damage will not be able to control this pest by this cultural method alone.
Chemical control methods should be used when beetle pressure exceeds the threshold. To determine the number of beetles per vine, one should randomly survey 25 vines at all four corners of the vineyard and 25 in the center of the vineyard. If this average is above two beetles per vine, then treatment is recommended.
It should be noted that with this survey method, one can determine if the chafer infestation is present throughout the vineyard or localized in a specic area. If the area is localized, spot treatment of the infestation may be all that is required. Treatment with an insecticide should be when the rst newly emerged beetles are detected in adequate numbers to pose concern. A second application may be required if pressure is severe and rainfall is frequent.
Protection of the young grape cluster is critical and should be maintained throughout June. For control of rose chafer, see the Commercial Small Fruit and Grape Spray Guide for your state. These recommendations are updated annually.
Adults are oval, about 5/16 inches long and 1/4 inch wide (Figure 72). There are many different color forms ranging from pale yellow-orange to bright red-orange, with or without black spots on the wing covers. The head, antennae, and mouthparts are generally straw colored but are sometimes tinged with black. The pronotum is white with up to ve black spots or with lateral spots usually joined to form two curved lines, a W- or M-shaped mark, or a solid trapezoid. The wing covers are generally yellow-orange in unspotted beetles.
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| FIGURE 72. Adult Multicolored Asian Lady Beetle. | FIGURE 73. Lady beetle eggs hatch in three to five days. |
Eggs are bright yellow, laid in clusters of about 20 on the leaves and stems of host plants (Figure 73). Larvae are elongate, somewhat attened, and adorned with strong tubercles and spines. The mature fourth-instar larva is strikingly colored—the overall color is mostly black to dark bluish-gray, with a prominent bright yellow-orange patch on the sides of abdominal segments one to ve (Figure 74).
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| FIGURE 74. Lady beetle larval stage. | FIGURE 75. Lady beetle pupation. |
The life cycle from egg to adult requires about a month or so, depending mostly on temperature. Eggs hatch in three to ve days. The larval stage lasts up to 14 days, during which time they consume large numbers of aphids, scale insects, or other soft-bodied insects. Pupation lasts ve to six days (Figure 75), followed by adult emergence.
The adults are rather long lived, with some lady beetles living up to three years. At least two generations, with a partial to complete third generation, occur each growing season.
In the fall when the host plants, such as soybeans, begin to dry and cooler weather approaches, adult lady beetles begin to seek overwintering sites. They are attracted to vertical walls or cliffs where they seek shelter in cracks and crevices. Once one lady beetle lands, many others may follow in their aggregating behavior.
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| FIGURE 76. Multicolored Asian lady beetles on damaged fruit. |
Lady beetles are normally considered as benecial insects. However, at grape harvest, the multicolored Asian lady beetle is now considered a foe. At harvest there may be a huge increase in the presence of lady beetles in many vineyards in the Midwest. Entomologists in the region attribute this population explosion to the sudden arrival of the Chinese soybean aphid. As soybeans mature and dry in late summer, the lady beetles disperse, at which time mature grapes, especially those with damaged clusters, become very attractive to the lady beetles. Beetles remain on the grapes and feed for several weeks, especially where ripe fruit is left in the eld late in the season.
In many instances, 10 or more beetles may be found per cluster on the damaged fruit (Figure 76). The lady beetles seldom cause primary damage biting through the skin of the grapes with their mandibles. However, they do take advantage of breaks in the skins caused by yellow jackets, hornets, birds, raccoons, as well as diseases.
The amount of physical damage they cause is minimal. However, the lady beetles are a menace to grapes due to a substance they produce when touched or squeezed, causing reex bleeding. When harvesting infested grapes, the beetles inadvertently end up in the crusher and thus contaminate the juice with their special aroma.
The hemolymph or blood of the insect is a protective mechanism to keep birds and other predators away. They exude the musty/basement-like odor from the joints of their legs. The detrimental effect is that this hemolymph taints the juice and is able to persist all the way through the process of fermentation into the wine.
Since the multicolored Asian lady beetle is not a native species, few diseases or parasites have been associated with this beetle. However, adult beetles have been found to vector fungal diseases, and therefore their aggregating nature may be favorable to the dissemination of bunch rot and other diseases from one grapevine to another.
Due to the adverse habits of this predatory beetle, some form of cultural or chemical control has become necessary. However, controlling these beetles in grapes at harvest poses a problem. Harvest restriction intervals must be considered.
The adult beetles feed on the foliage, fruits, and flowers of more than 250 kinds of plants, but grape is one of their preferred hosts. The larvae are C-shaped grubs found in the soil and are serious pests of grass roots. The distinguishing character of the grubs of scarab beetles is the rastral pattern (Figure 77). The adult beetle has a shiny, metallic-green head and thorax, and coppery-brown wing covers. Tufts of white hairs are located along the sides of the body (Figure 78). Adult beetles are about 1/2-inch long.
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| FIGURE 77. The rastral pattern is the distinguishing characteristic of the Japanese beetle. Note the V-shaped formation of hairs on the raster of the grub. | FIGURE 78. Note tufts of white hair alongside the body of the Japanese beetle. |
Larvae feed principally on grass roots and other organic matter. During late spring, larvae move closer to the soil surface and complete their development.
Adult beetles emerge from the ground in late June through July and begin feeding upon foliage. Mating occurs at this time, and eggs are laid in the ground. Eggs hatch in about 10 days, and young grubs begin feeding on plant roots. They overwinter as larvae below the soil surface. Grubs continue to feed and grow until cold weather drives them down, at which time they tunnel down from 3 to 12 inches to make overwintering cells. In the spring when the soil begins to warm, grubs move toward the surface where additional feeding may occur before pupation in late spring. There is only one generation per year.
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| FIGURE 79. Adult Japanese beetles feeding on grape leaves. |
The adults feed on the leaves of both wild and cultivated grapevines (Figure 79). Beetles prefer foliage exposed to direct sunlight and often are seen clustered together, feeding on tender vegetative parts. Vines with thin, smooth leaves, such as French hybrids, are preferred over those with thick, pubescent leaves, such as Concord. Concord vineyards rarely need special control sprays for Japanese beetles. On the other hand, French hybrids and other thin-leaved cultivars require frequent inspection to prevent damage. Damaged leaves have a laced appearance, and severely affected leaves will drop prematurely.
There is no economic threshold on the number of beetles or amount of damage that requires treatment. If a susceptible cultivar is being grown and growers previously have experienced high populations of Japanese beetles, an insecticide should be applied when beetles emerge and thereafter as needed.
A Japanese beetle lure and trap is available for monitoring this pest; however, these beetles are easily detected while walking through the vineyard. If skeletonizing of leaves becomes evident, thin-leaved cultivars may need to be protected with an application of insecticide. The usual threshold for making a spray application is about 15% of the leaves consumed.
Insecticide is usually applied when feeding is apparent on most vines and skeletonized leaves are found. Spot treatment is adequate in some cases. An insecticide with long residual activity is needed when beetle populations are high. Repeated applications may be needed to control new beetles ying in from surrounding areas.
A microbial insecticide is available to control Japanese beetle grubs in turf, although it is slower acting and more expensive than conventional insecticides. This bacterial insecticide causes milky spore disease within the grub stage of development. This microbial insecticide cannot be relied upon to protect grapes from Japanese beetles due to the mobility of the beetles.
To control Japanese beetle and other fruit insects, get a copy of the latest recommendations from your local Extension agent.
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| FIGURE 80. Roots heavily infested with phylloxera. |
Phylloxera is one of the most destructive grape pests worldwide. This small aphid-like insect has a complex life cycle that involves survival on the roots throughout the year and on the leaves during the growing season. The insect forms galls on the leaves and roots of grapevines. The vine will die if its roots become heavily infested with phylloxera (Figure 80). If leaves become heavily infested, premature defoliation and retarded shoot growth may result.
The life cycle is different for the foliar and root forms of this insect. The foliar form survives the winter as an egg under the bark of the grapevine. Asexual, wingless forms hatch in the spring and crawl to tiny new leaves, where they develop galls.
Young crawlers settle on the upper surface of immature leaves, causing galls to form on the under surface of the leaves (Figure 81). The only opening in a gall is to the upper leaf surface. Once mature, the female begins to lay eggs within the gall. Nymphs hatching from these eggs crawl to new leaves at shoot tips, settle on the leaves, and form new galls.
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| FIGURE 81. Phylloxera galls are found on the undersurface of leaves. | FIGURE 82. Phylloxera overwinters as immature forms on roots. |
In the case of the root form of grape phylloxera, the insects overwinter as immature forms on the roots (Figure 82). These forms mature in the spring and produce eggs that hatch into nymphs. The nymphs then start new galls on the roots.
Winged forms develop in the spring, summer, or fall and emerge from the soil to lay eggs on stems. These eggs hatch and produce the true sexual forms that produce the overwintering eggs laid under the bark. Several generations of each form of phylloxera may occur each season. Although the two forms behave differently, both belong to the same species.
In many areas of the world, susceptible cultivars are grafted onto resistant rootstocks to prevent damage by the root form. However, the foliar form still may occur in such cases. There are some natural predators that feed upon the foliar form of grape phylloxera, but none of these provide adequate control of the pest. There is no known completely successful chemical control for the root form of grape phylloxera. Eastern growers usually do not have a problem with the root form of the phylloxera.
Phylloxera is usually spotty in Ohio vineyards, so identifying these areas within your vineyard is important. Spot treatment may be all that is required to control this pest.
To identify the location and extent of phylloxera within a vineyard, one should begin scouting for infested leaves after shoot length has reached ve inches. Young galls will be forming on the underside of the terminal leaves; they are not easily noticed early in the season without taking the time to inspect the leaves closely.
These galls should not be confused with grape tumid galls, commonly called the grape tomato gall. Tumid galls have a smooth outer surface and take on a reddish tomato-like appearance. The grape phylloxera gall is green in appearance except early in the season, when some cultivars tend to have more of a reddish cast to them. The gall itself has a rough-looking surface rather than the smooth surface of the tumid gall. Tumid gall is present but not a problem in Midwestern vineyards.
Among the cultivated American grapes, many tend to have resistance to the foliar form of the grape phylloxera, whereas French hybrids and vinifera grapes are usually very susceptible, and control of phylloxera on these cultivars is recommended. One cannot usually completely eradicate phylloxera from a vineyard that is already infested, but one can take measures to keep the infestation at a tolerable level.
Control of the foliar form of phylloxera may be achieved by applying insecticide at bloom and again 10 to 14 days later. Late-season treatment of grape phylloxera is not effective and seems to be a waste of time and money. Early-season control of this pest is critical. Currently we are fortunate to have a pyrethroid insecticide labeled for controlling the foliar form of grape phylloxera. Some compounds are known to be phytotoxic to certain cultivars. Consult the latest control recommendations for EPA-approved insecticides.
The potato leafhopper (Figure 83), a sucking insect, feeds sporadically on foliage of grapes, strawberries, and many other plants. The adult leafhopper is pale to bright green, wedge-shaped, and about 1/8 inch long. The adults are very active, jumping, ying, or running when disturbed. The immature forms, or nymphs, are pale green and wingless. They run forward, backward, or sideways rapidly when threatened. The potato leafhopper feeds on more than 200 plant species.
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| FIGURE 83. The potato leafhopper feeds on foliage. | FIGURE 84. Toxins injected during potato leafhopper feeding causes leaves to cup and be misshapen. |
The potato leafhopper does not generally overwinter in areas north of the Gulf States. Each year large numbers of potato leafhoppers are carried to northern areas by warm spring air currents. Injury to grapes occurs when the adults y into vineyards and feed on the leaves. Toxins injected while feeding cause leaves to cup and be misshapen (Figure 84). These leaves are most often observed in the top of the vine and are quite obvious, especially at the end of the growing season.
Three of the most common leafhoppers found on grapes in Ohio are the Eastern Grape Leafhopper, Erythroneura comes [Say]; the Three-Banded Leafhopper, Erythroneura tricincta Fitch; and the Virginia Creeper Leafhopper, Erythroneura ziczac Walsh. These three species vary in their coloration and markings.
The adults of these leafhoppers are about 1/8-inch long. Erythroneura comes is pale yellow or white with yellow, red, and blue markings (Figure 85). Overwintering adults are often nearly all red. E. tricincta is brown and black with touches of orange on the wings (Figure 86). E. ziczac is pale yellowish or white with a zigzag stripe down each wing and cross veins are distinctly red.
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| FIGURE 85. The Eastern Grape Leafhopper is pale yellow or white with yellow, red, and blue markings. | FIGURE 86. The Three-Banded Leafhopper is brown and black with touches of orange on the wings. |
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| FIGURE 87. Immature leafhoppers, or nymphs, are wingless. |
The biology of these three species is similar. They overwinter as adults in sheltered places such as the remains of old plants. During the rst warm spring days the leafhoppers become active, and they feed on the foliage of many different plants until grape leaves appear. Eggs are deposited under the leaf epidermis and hatch in about two weeks. The immature leafhoppers, or nymphs, are wingless (Figure 87); they remain and feed on the leaves where they hatch. Nymphs molt ve times, then transform into adults. There are two or three generations of leafhoppers each season.
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| FIGURE 88. Each puncture from a leafhopper causes a white blotch on the leaf (left). The leaf on the right is normal. |
Adults and nymphs feed on leaves by puncturing the leaf cell and sucking out the contents. Each puncture causes a white blotch to appear on the leaf (Figure 88). In heavy infestations, the leaves turn yellow or brown, and many fall off prematurely. Feeding by these leafhoppers may reduce the photosynthetic capacity of the plant, and the quality and quantity of the fruit may be affected.
Grapevines can tolerate populations of up to 15 insects per leaf with little or no economic damage. However, heavy leafhopper feeding may result in premature leaf drop, lowered sugar content, increased acid, and poor coloration of the fruit.
The sticky excrement (honeydew) of the leafhoppers affects the appearance and supports the growth of sooty molds. Severely infested vines may be unable to produce sufcient wood the following year. Damage to the vine can be serious if infestations are allowed to persist unchecked for two or more years.
Weeds and trash in and around a vineyard are a source of leafhoppers. If this material is removed before spring, the adults lose their protection and feeding sites, although in areas with extensive agriculture, this practice has less value as the adults will just move to an adjacent crop or weedy area.
Certain cultivars are likely to suffer higher leafhopper populations than others. Wine and table grape varieties fit this criteria. Moreover, late-producing cultivars are more likely to favor leafhoppers than early maturing cultivars.
Vigorous vines are preferred by leafhoppers. The heaviest populations are normally found on end vines and on outside rows. This is partly because these vines are usually the most vigorous and therefore the most attractive. It also is partly because of the border or boundary effect. Vigorous vines fortunately can tolerate the highest populations.
Sampling for leafhoppers should be done at 10 days post-bloom, the third week in July, and again the third to fourth week of August. This is approximately the same time one should be assessing grape berry moth risk, and both surveys may be conducted simultaneously.
Ten Days Post-Bloom—Only adult leafhoppers are present at this time of the year, so it is not necessary to count them. If leafhoppers are present, you should see stippling damage on the lower sucker leaves and interior leaves of the grape canopy. By shaking the vines, adult leafhoppers, if present, will y around the vine. If stippling damage is present throughout the vineyard, an application of insecticide is recommended to prevent later damage from occurring.
Early-season damage may indicate that populations may potentially build up to damaging levels later in the season. In vineyards that are at high risk for grape berry moth, insecticide is usually applied at this time, so scouting for leafhoppers at this time is not necessary.
Third Week in July—From mid- to late July, rst generation nymphs are present and feeding on the undersides of grape leaves. At this time, the need to apply an insecticide for leafhopper control should be determined on a block-by-block basis. Sampling for grape berry moth and leafhoppers can be done with a single pass through the vineyard.
The rst step in evaluating leafhopper damage is to look for stippling on leaves while you are doing counts of grape berry moth damage. Most damage will be found on the rst seven leaves from the base of the shoot. If no stippling or minimal stippling is visible on the leaves, there is no point in counting how many leafhoppers are present.
If moderate to heavy stippling is visible, then it is necessary to do counts of leafhopper nymphs to determine if damage levels warrant treatment. The sampling procedure for leafhoppers requires counting all leafhoppers on the undersides of the third through seventh leaves of one shoot on each of ve vines. Sampling for leafhoppers should take only a few minutes per vineyard.
Late August—In years when leafhoppers do build up to damaging levels in vineyards, it is most common for them to do so in late August. Vineyards with greater than 10 leafhoppers per leaf should be treated at this time. If there is very little visible stippling, sampling will not be necessary. Vineyards that had insecticides applied to them earlier in the season will probably not need treatment at this time. In Ohio we experience more of a problem with leafhoppers on the islands in Lake Erie and in vineyards near Lake Erie.
Leafhoppers have few natural enemies. Cold and wet weather conditions in spring and fall are damaging to leafhopper populations, as are wet winters. Cultivation and cleanup of adjacent weedy land in the fall will eliminate favorable overwintering sites in and near a vineyard.
When high populations of leafhoppers are encountered, an application of an insecticide may be required. In order to obtain good control of leafhoppers, complete coverage of the undersides of the leaves is important. Coverage of the fruit is of secondary importance.
For control of leafhoppers, see the Commercial Small Fruit and Grape Spray Guide for your state. These recommendations are updated annually.
Larvae of the grape root borer attack the larger roots and crown of grapevines (Figure 89). They tunnel into these parts of the plant and feed internally. The feeding and boring of the larvae will weaken and may eventually kill the vine.
The adult is a clearwing moth, with brown forewings and clear hind wings with brown borders. The body mimics that of a wasp, brown with yellow markings. Male moths (Figure 90) measure about 5/8 of an inch in length, while the female (Figure 91) is larger, about 3/4-inch long.
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| FIGURE 89. Grape root borer larvae attack the larger roots and crown. | FIGURE 90. Grape root borer, male moth. | |
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| FIGURE 91. Grape root borer, female moth. | FIGURE 92. Grape root borer. | |
The moths emerge from the soil during July and August. Eggs are deposited individually on grape leaves or weeds, or dropped on the ground close to the trunk. The larvae hatch and burrow into the soil, nd their way to the roots and crown, and feed on them. Larvae continue to feed within the vine’s root system for about 22 months (Figure 92). A fully developed larva is about 1/2-inch long and white with a brown head capsule.
Mature larvae move to places just under the surface of the soil and pupate in earthen cells. Adults start emerging in July and continue to emerge through August (Figure 93).
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| FIGURE 93. Grape root borer adults emerge in July and August. |
Larvae attack the roots and crown of grapevines. They tunnel into the roots or crown and feed internally. Feeding and boring weaken the grapevine and may eventually kill it. Larvae also provide entry points for disease organisms. Vines that are severely infested may wilt under stress; sometimes only part of the vine will show stress.
Weed control is important in managing this insect pest. Weed control decreases the number of oviposition sites and provides an area under the trellis suitable for applying an insecticide. Researchers in North Carolina also have achieved good control of root borers with polyethylene mulch; this technique can be easily accomplished at planting. It works well in the short term, but the mulch must be maintained over the years in order to be successful.
An alternative method of control is to use pheromone rope ties to disrupt the ability of the males to locate the female grape root borer. This method has been successful in some cases. This method prevents the male root borers from locating the female borers and mating, thus reducing the number of fertile root borer females in a treated vineyard.
Ties are dispensed manually at a rate of 100 ties per acre. They should be placed on the top trellis wire every six or seven vines. Results from these trials look promising, but bringing the borer population down to acceptable levels requires several years.
Another method of using the grape root borer pheromone for control is being studied at two southern Ohio vineyards. This method uses the sex pheromone and 1C Pherocon traps. Traps baited with the pheromone are placed throughout the vineyard in an attempt to reduce the number of males available for mating. Three years of study has shown that the male population is continuing to decline where the pheromone is utilized.
External wood lots containing wild grapes are a good source of grape root borers. Such areas adjacent to vineyards should be considered as possible reservoirs when trying to manage this pest. Extermination of wild grapes from within these areas should help to reduce root borer pressure.
Chemical control of this pest is difcult due to its cryptic nature. Other management strategies are being evaluated at Ohio State University. One of these utilized parasitic nematodes that attack the larvae of the grape root borer. This method of control is showing promise. However, a little more research is needed to confirm its utility.
Pheromone traps are the only means to easily monitor this pest. Response by male root borers to this sex pheromone is strong. A minimum of three pheromone traps should be placed transecting the vineyard in a diagonal manner. Traps should be in place by late June and checked on a weekly basis thereafter. A single pheromone cap within a trap will last the entire season.
Trapping-out uses the sex pheromone placed within 1C Pherocon sticky traps. This method is still experimental at this time but certainly appears to be working. Traps are placed around the vineyard perimeter in late June at 35- to 50-foot intervals. These traps should be checked on a weekly basis. Where infestations are high, many borers will be trapped, resulting in the need for removal of some of the trapped adults or replacement of the trap bottoms. This method requires a continued effort year after year to reduce pressure in subsequent years.
Chemical control of emerging adults or entering newly hatched larvae will give some assistance if repeated over a wide area.
See the Commercial Small Fruit and Grape Spray Guide for your state for recommendations.
The European red mite causes considerable damage to apples in some orchards; it also becomes a problem in vineyards from time to time.
The adult female of the European red mite is dark red to reddish-brown, has eight legs, and is about 1/50-inch long (Figure 94). Adult male mites are smaller and have a pointed abdomen; they are usually dull green to brown.
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| FIGURE 94. Adult female European red mite. | FIGURE 95. Red mite eggs are laid around cane nodes where they overwinter. |
Eggs, which are globe-shaped and red, are laid on the undersides of leaves in the summer. The eggs are tiny and require a magnifying glass to be seen. During late summer and early fall, eggs are laid around cane nodes, where they overwinter (Figure 95). Several generations occur each season.
The adults and nymphs of this species feed on the undersurfaces of leaves, and in heavy infestations, the leaves turn a bronze color. If bronzing occurs early enough in the season, a negative effect on fruit ripening may occur as feeding may interfere with the normal photosynthetic process of the leaves.
Growers should apply miticide sprays before bronzing occurs. In some vineyards, this pest is kept at low levels by naturally occurring predatory mites and predaceous insects.
Monitoring for European red mite can be accomplished by looking at the underside of the leaves for their presence at the same time you are scouting your vineyard for leafhoppers and grape berry moth. You may also keep a close eye out for bronzing while traveling through the vineyard on your tractor. This can be done at the same time you are applying fungicide sprays to the vineyard.
Some chemicals reduce leafhopper and/or spider mite populations while allowing predaceous mites to maintain control of the latter. Ideally, treatments should be applied so that mites are reduced below economic levels without killing predaceous mites or reducing their food source to the extent that they starve.
For a list of miticides available for controlling mites in the Midwest, see the Commercial Small Fruit and Grape Spray Guide for your state.