Grape Growing Challenges

Scouting is deliberately moving through the vineyard with the purpose of searching for pests, weeds, and pathogens.

Must understand biology of vineyard:

• Pest/beneficial/symptom ID
• Pest development stages
• Weed cycles
• Disease triangle

Must understand abiotics:

• How weather affects
• How soils affect growth
• How vineyard geography effects pest population
• “Hot spots”

Why?

• Stop problems before they are uncontrollable, or populations become large enough to show resistance

• What: Agrobacterium vitis bacteria
• Why: Infects vines (usually in nursery), causing gall growth/vascular disruption
• Where to Scout: Galls often form a base of trunk and leaves above are often red.  Look in low-lying areas
• When to scout: Summer
• Signs/Symptoms: Creamy-white, eventually brown desiccated galls noticeable in summer.  Foliar symptoms often appear in summer
• IPM: Site selection, retraining, buy clean plants, multiple trunks, hot water treatment of cuttings

• What: Erysiphe necator Fungus
• Why: Without fungicides, PM would be the most destructive grape disease worldwide
• Where to Scout: Colonies establish on young, fresh growth.  Infections usual found in shady, cool areas of canopy.  Look on morning sides and areas of congestion
• When to Scout: Visible symptoms may appear 7 to 10 days after “infection event” (.1” wetness, avg temp of 50F)
• Signs/Symptoms: Silvery white fungal infections with a “sheen” on fruit and foliage often close to cordon
• IPM: Shoot thinning and morning-side leaf removal, FRAC group rotation, water management, preventative fungicide applications

Photos: University of Georgia Plant Pathology , University of Georgia, Bugwood.org

• What: Phomopsis viticola fungus
• Why: Rainy weather during early growing season favors development; severe infections cause brittle rachis and cane, crop loss, and leaf damage
• Where to Scout:  Shady, congested areas in the vineyard
• When:  Fruit symptoms appear 3 weeks before harvest, in leaves at senescence
• Signs/Symptoms: Rough, black lesions on shoots, leaves, and rachises are most common. Leaves may also be light green, turning black with yellow margins
• IPM: Canopy and water management, especially during wet years. Remove infected canes during pruning, cane prune.  Spray at 1-3” using M-series fungicides

• What: Ethanol-producing yeast and acetic acid-producing bacteria which is vectored by fruit flies (Drosophila spp)
• Why: Damaged fruit becomes infected by yeast and acetobacter, which produce acetic acid, rots fruit and raises VA of juice
• Where to scout: Congested areas, smell of vinegar
• When:  a few weeks before harvest, 12 to 13 brix
• Signs/Symptoms: Pink-brown discoloration of berry skins and loss of integrity.  Strong smell of vinegar and presence of fruit flies
• IPM: Deficit irrigation to loosen clusters, shoot-thinning and leafing, responsible cropping, control of fruit flies, anti-microbials

• What: Botrytis cinerea fungus
• Why: Fungus colonizes dead/dying fruit/flower tissue, rotting away fruit
• Where: Compact fruit clusters, especially in congested areas of vineyard
• When to scout: Post veraison, when RH is high and temperatures are relatively cool
• Signs/Symptoms: Fuzzy grey fungal growth.  Berries turn pink/brown, eventually drying out
• IPM: Loose-clustered varieties, RDI, botryticides bloom to bunch-closure, open canopies up, remove clusters touching others

• What: Grapevine Leafroll and Redblotch disease-causing viruses
• Why: Viruses cause reduced vigor, poor color, slowed ripening/low sugar
• Where: Symptoms usually start near the center of the cordon
• When to scout: Post-veraison through fall
• Signs/Symptoms: Interveinal/blotchy reddening of leaves in red cultivars, chlorotic in white.  Rolled leaves in leafroll.
• IPM:  Clean plants, vector (3-cornered alfalfa hopper and mealybug) control, rogue and replant if populations are low, good nutrient program to rule out deficiency, testing, low cropping

• What: Range of wood-decaying fungi (Cytospera, Botryspheria, Eutypa, Esca)
• Why: Infections cause wood dieback of spurs, arms, trunks
• Where: Typically in older vines
• When: From budbreak until leaf fall
• Signs/Symptoms: Weak canopy growth, decreased yield, dark coloration of wood, sometimes in wedge shape
• IPM: Pre-pruning, fungicides on pruning wounds, cordon/trunk renewal, pruning during dry periods

• What: Xylella fastidiosa bacterium
• Why: Blockage of xylem causes vine collapse
• Where: Near riparian areas, throughout vineyard
• When: Symptoms often begin in mid to late summer through senescence
• Signs/Symptoms: Burnt leaf margins similar to drought stress, “matchstick” petioles remain on vine after leaf fall, cane periderm forms in a patchy pattern, delayed bud break, newly set fruit dries up
• IPM: Resistant cultivars, vector (sharpshooter) control, bacteriophage virus treatment?? (https://inphatec.com/xylphi_pd)

• What: Various species of moth caterpillar
• Why: Climb up vines in spring and eat opening buds
• Where: Buds along the cordon/cane
• When to scout: Spring, when buds are between the dormant and expanded leaf stages. Damage usually occurs in aggregated “hotspots”
• Signs/Symptoms: Larvae are rarely seen, more often you find the damaged buds
• IPM: Allow weeds to grow early in spring, use pyrethroid barrier spray, leave extra buds, scout regularly

• What: Various species of sphinx moth caterpillar
• Why:  Feed on grapevine leaves, which can be hard on young vineyards
• Where: Caterpillars in canopy, pupae in soil
• When to scout: Adults lay eggs in spring, which hatch in 3 to 4 weeks. 2 generations
• IPM:  Not generally a threat in established vineyards, so no action necessary, Bt useful, insect growth regulators also used, parasitism common

• What: Daktulospharia vitifoliae insect
• Why: Insect feeds on roots, causing stunting, and eventually death
• Where: Primarily in soil, where weak areas of the vineyard are growing in circular pattern. Sample periphery of circle, not center.  Sampe 1.5ft radius from vine, down to 4ft
• When: Late summer/Early fall when populations are highest
• Signs/Symptoms: Weak, stunted growth and nodules/galls on roots and rarely leaves.  Insects are small and often yellow
• IPM: Rootstocks, selected systemic insecticides, site selection (sandy soils)

• What: Homalodisca vitripennis insect
• Why: Vector of Xylella fasitidiosa
• Where: Tips of new shoots, look for liquid associated with feeding
• When: Use sticky traps (no pheromone) from budbreak to leaf-fall
• Signs/Symptoms: Large (0.5”) cycada-like insect, clear wings with red veination, head brown to black with ivory spots
• IPM:  Site selection, parasitoid release?, insecticide, trap monitoring

• What: Thrips (Thysanoptera) insects
• Why: Can stunt new, growing foliage, especially in a wet winter/spring
• Where: On foliage and fruit.  Hold a piece of paper underneath and tap foliage
• When to scout: Early spring, as shoots are emerging  
• Signs/Symptoms: Cupping of leaves, scaring, and “halo-spotting” of fruit; insects are very small, though can be seen with naked eye
• IPM: Only mow every other row in a session, push water and nutrients to “push through”, insecticide

• What: Erythroneura spp. Insect
• Why: Adults and nymphs suck chlorophyll and nutrients out of leaf cells.  Damage could cause delay in ripening if severe and early, or sunburn fruit if canopy thinned enough
• Where: Shaded canopy leaves
• When to Scout: Starting in spring
• Signs/Symptoms: Stippling effect on leaves, turning entire leaf yellow, molts of insects, insects “hopping” readily as you move through canopy
• IPM: Canopy/water/fertilizer management, (hairy-leafed) variety selection, Surround clay, neonicitinoids, pyrethrins. Accepted threshold=15 insects per leaf after collecting 10 leaves randomly through vineyard

• What: Harrisina metallica insect
• Why: Larvae feed on lower leaf surface, resulting in a “skeletonized” effect of defoliation, which could also lead to sunburn
• Where: Throughout canopy
• When: Late spring forward
• Signs/Symptoms: Skeletonized leaves, barrel shaped eggs laid on lower leaves
• IPM: Bacillus thurengiensis, Spinosad, natural enemies, Granulosis virus

• What: Drosophila spp. insect
• Why: Insects lay eggs in damaged fruit and vector microorganisms that cause sour rot
• Where: Throughout vineyard where berries are damaged, can trap with yeast or apple cider vinegar
• When: Post veraison through harvest
• Signs/Symptoms: Vinegar smell in vineyard, rotting fruit, swarming small fruit flies
• IPM: Variety selection, water management for cluster morphology, Spinosad chemistry