Grape Insect Pests to Watch for from: Bud Swell through Immediate Pre-Bloom Stages
By: Andy Muza
Penn State Extension – Erie County
Last week Bryan Hed discussed pre-bloom disease management. This week I will provide a preview of insect pests that may cause problems in the vineyard from bud swell through the immediate pre-bloom period. I will not be providing choices of insecticides registered for use in Pennsylvania for each pest but instead strongly suggest that each grower purchase a copy of the 2015 New York and Pennsylvania Pest Management Guidelines for Grapes. This guideline provides a wealth of information on insect, disease and weed management with specific pesticide recommendations, as well as, a chapter on sprayer technology. Growers interested in organic management of pests can download a copy of Cornell’s 2014 Production Guide for Organic Grapes.
Another valuable, compact resource that can be taken along in the vineyard as you are scouting is A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S. This guide provides concise information along with color photographs on insect/mite pests, natural enemies, diseases and disorders.
Grape flea beetle – beetles are small (3/16”) and metallic blue in color. Beetles overwinter in the adult stage and emerge as grape buds begin to swell. The most significant injury caused by this pest is due to adults feeding on swollen grape buds, often consuming enough tissue to destroy the developing bud. By about 1/2” growth the threat of economic loss from this pest is over. Larvae feed on leaves but the extent of injury is usually negligible.
The largest populations of flea beetles are most often around wooded or overgrown edges of vineyards. Scout vineyard rows bordering these areas frequently during the bud swell stage. Look for injured buds along canes and presence of adults. Beetles will jump like fleas when disturbed. Warm, sunny days are usually the best opportunity to observe adults. Areas with bud injury of 2% or greater would warrant an insecticide treatment.
Climbing Cutworm – several species of cutworm larvae feed on grape buds during the swell stage. The injury to buds can be confused with grape flea beetle damage. The larvae are immature stages of noctuid moths. Larvae have a brown to gray coloration with darker stripes or dots along the body. Larvae hide under stones or weeds beneath vines during the day and climb vines to feed at night. Vineyards with weed cover under the trellis and areas with sandy soils are at greater risk for injury. Scout frequently during the bud swell stage. If bud injury is detected when scouting then examine weeds/soil beneath vines for presence of larvae. Areas with bud injury of 2% or greater warrant an insecticide treatment.
3 – 12 INCH SHOOT GROWTH
Banded Grape Bug and/or Lygocoris inconspicuous – both of these insects have piercing and sucking type mouthparts and are in the same family (Miridae) as tarnished plant bug. Banded grape bug nymphs have antennae with black and white bands, green/brown bodies and are <1/2”. Lygocoris inconspicuous nymphs are slightly smaller with light green antennae (no bands) and light green bodies. Nymphs (immature stage) of both insects feed on developing flower clusters by piercing florets, pedicels and rachises. Although these insects are occasional pests, research by Greg Loeb (Cornell) showed that population levels >1 nymph/10 shoots can cause economic yield losses.
Begin scouting when shoots are 3 – 5” in length and continue until shoots are at least 12”. According to Loeb, flower clusters should be checked on 100 shoots per block with an emphasis near vineyard edges. Due to their body coloration these insects are difficult to see. To determine nymph numbers, hold a white paper plate beneath clusters then tap clusters to dislodge insects. If levels are >10 nymphs/100 shoots an insecticide application is suggested. See scouting video – Banded Grape Bug LERGPvids https://www.youtube.com/watch?v=FrEJ6IJB_is
Grape Phylloxera (leaf form) – phylloxera are native to the eastern U.S. and cause galls on both leaves and roots of grapevines. The life cycle is different for the foliar and root forms of this insect. The root form is the most destructive of the 2 forms but is managed by grafting susceptible varieties (e.g., Vitis vinifera) to phylloxera-resistant/tolerant rootstocks.
Nymphs (crawlers) emerge in the spring and move to shoot tips to start feeding on the upper leaf surface of newly developing leaves. Feeding initiates the formation of galls on the lower leaf surface. Females can lay hundreds of eggs within galls throughout their life. Crawlers hatch from galls on the upper leaf surface, move to and feed on developing leaves, initiating new galls. This cycle continues throughout the season.
Grape varieties vary widely in their susceptibility to leaf galling by phylloxera. Some varieties (e.g., Chambourcin, Seyval, Vidal) can suffer severe leaf galling which reduces leaf function and can affect shoot growth.
Begin scouting early in the season, especially in highly susceptible varieties or newly planted vineyards. Galls may become evident as soon as the 3-5 leaf stage so carefully examine the undersides of terminal leaves for warty looking, green to reddish growths. An insecticide application can be applied when first galls are forming. Additional sprays may be needed 10 -14 days later if galls are present on new leaf growth. Correct timing of sprays is important because nymphs (crawlers) must be active and feeding on leaf surfaces for insecticides to be effective. The most reliable method to determine if crawlers are active is to cut galls open and observe for presence of nymphs. Crawlers are extremely small so a good hand lens is needed.
Additional Insect Pests – During this time period a number of other insects (i.e., grape plume moth, grapevine epimenus, 8 – spotted forester, tumid/tomato gallmaker, grape cane gallmaker, and grape cane girdler) may also be present in the vineyard. Although injury from these insects may look alarming, damage is usually cosmetic and insecticide applications are rarely needed. (See sites for fact sheets below).
Rose Chafer – rose chafer beetles are about 1/2” long, with tan colored bodies and long, spiny legs. These beetles feed on a wide variety of hosts including grape. Large numbers of beetles often emerge from the soil at the same time (about 10 days before grape bloom) and begin feeding on tender flower clusters and leaves. Infested areas can lose extensive numbers of flower clusters if beetles are not detected early and treated.
Vineyards with a history of this pest or blocks with sandy soils should be scouted daily beginning at least 10 days before bloom. A fact sheet on Rose Chafer from Ohio State ( http://www.oardc.ohio-state.edu/grapeipm/rose_chafer.htm ) recommends an insecticide application if a threshold of 2 beetles per vine is reached.
Fact sheets on grape insect pests can be found at the following sites:
Please click on the links below for more fact sheets specifically on insect pests found in the vineyard:
- NYS IPM Fact Sheets for Grapes
- Identifying Grape Insects (Michigan State)
- Midwest Grape Production Guide (Bulletin 919) – (Chapter 4 – information on grape insect pests).
- Mid Atlantic Vineyards Grape IPM (Virginia Tech)
- Ontario GrapeIPM – Grape Insects