Grape berry moth (GBM) (Paralobesia viteana) is a common and destructive pest in Midwest vineyards. GBM infests grape clusters, feeds on berries, and can significantly reduce yields. Infestations can also contaminate fruit by introducing plant pathogens that cause plant diseases like bunch rot (Duso et al., 2022; Thiéry et al., 2018). GBM overwinter in cocoons, often within folded leaves and debris on the vineyard floor (Goldammer, 2018). The adult is a mottled-brown moth with some bluish gray on the inner halves of the front wings (Figure 1). Adults are 0.64 cm (approximately 0.25 in.) long. Larvae, which are the destructive stage of this insect, feed directly on grape flowers and fruit. The larvae of this small moth are green-purple caterpillars about 1 cm (approximately 0.37 in.) long when fully grown (Figure 1).
Life Cycle
Two to three generations of grape berry moth are typical per year (Figure 1); however, up to four generations are possible in southern regions. The first generation arises from overwintering adults that emerge in the spring. Mating occurs in the first three days of adult life. After mating, females will lay eggs on or near fruit stems, blossoms, or berry clusters within four to seven days (Thiéry et al., 2018; Isaacs et al., 2012). Eggs hatch in June and larvae feed on grape flowers and developing fruit clusters and then mature from mid- to late July or August (Issacs et al., 2012). These adults emerge from pupae, mate, and then give rise to the second generation of GBM. These second-generation females lay eggs directly on developing berries (Issacs et al., 2012). After hatching, the larvae feed inside a fruit cluster until they mature in August or September. The second-generation larvae form cocoons in which they overwinter.
Damage Symptoms
First-generation grape berry moth larvae create webs around small flower buds or berries in early June and then feed externally on them or on tender stems (Issacs et al., 2012). Larvae that attack grape bunches during this time are difficult to see. Second-generation eggs are commonly laid directly on the green berries to feed internally and can potentially be more damaging than the first generation (Goldammer, 2018). Scout grapes closely as clusters ripen to ensure they are not infested with GBM larvae. A single larva can destroy two to six berries in a cluster, and several larvae frequently inhabit a single cluster. At harvest, severely infested bunches may contain several larvae, and many of the berries may be completely hollowed. In many cases, bunches are covered with bunch rot fungi, infested with fruit flies, and have an unhealthy appearance. Signs of feeding may include conspicuous reddish spots developing on the berries at the point of larval entry. Berries affected in this manner are known as "stung" berries. Typically, infestations are worse along vineyard edges, especially near wooded areas.
Scouting and Management
Grape berry moths can be monitored using pheromone traps (delta trap or wing trap with a lure containing synthetic pheromone). These traps should be placed where activity is likely, such as near an adjacent woodland, before the first bloom in the vineyard (Goldammer, 2018). Approximately three or more traps are needed per vineyard block. Traps should be hung on the top trellis wire. Tracking degree day accumulation can also help estimate the development of this pest. Approximately, 810 growing degree days (base threshold: 47 degrees Fahrenheit) are needed to complete one GBM generation. Traps should be checked weekly. Lures and trap liners should be changed every four to six weeks. To determine the percentage of clusters damaged, randomly inspect 100 clusters within vineyard blocks. Corrective measures are usually suggested if more than 5%–15% of the clusters are injured (Goldammer, 2018). Higher-value grapes may require lower thresholds. If infestation exceeds these thresholds, active management is needed. Alternatively, insecticide applications can also be timed in sequence with the pest’s development. Early-season control of this pest may prevent population establishment and could even eliminate the need for control later in the season. It should be noted that the second flight activity period, occurring in late July and August, is the most important management period needed to control populations. These adult moths produce eggs in late summer that hatch into larvae, which can cause major damage to the maturing fruit (Issacs et al., 2012).
Some management strategies are described below:
- Chemical control of GBM is particularly important before their egg-laying and up until their larvae enter the berries (Goldammer, 2018). Emerging larvae can ingest the chemical before they enter the berry, ensuring a higher GBM mortality rate (Goldammer, 2018). A number of compounds can be applied to control moths, but matching moth development with product is important. Some products will not perform well if they are not applied during the right GBM developmental stage. Due to this pest’s affinity for block edges, treatment of perimeter rows may successfully control this pest. Please consult the Midwest Fruit Pest Management Guide 2023-2024 for product options.
- Pheromone disruption can be used in vineyards with low to moderate GBM pressure. Apply pheromone dispensers evenly across the vineyard to ensure control. Dispensers should be placed prior to adult flight. Vineyards larger than five acres typically benefit the greatest from this tactic. Blocks should be scouted regularly to ensure adequate GBM control.
- Cultural controls like mulching below the vine can reduce the success of overwintering grape berry moth. Leaves from below the vine canopy can also be destroyed to remove any puparium (overwintering GBM).
- Biological control is limited for this pest. Some generalist predators can offer control. Further, research has identified an egg parasitoid (tiny wasp) that can parasitize GBM eggs.
Grape berry moth can be a habitual pest to many vineyards in Ohio and throughout the Midwest. It can be identified in the vineyard by webbing in fruit and/or stung berries. Further, management can be difficult because GBM has multiple generations, but pheromone traps and scouting can improve control measures.
Additional Resources
For more information on evidence-based pest management practices, go to ashleybleach.com.
References
Duso, C., Pozzebon, Al, Lorenzon, M., Fornasiero, D., Tirello, P., Simoni, S., & Bagnoli, B. (2022). The impact of microbial and botanical insecticides on grape berry moths and their effects on secondary pests and beneficials. Agronomy 2022, 12(1), 217.
doi.org/10.3390/agronomy12010217
Goldammer, T. (2018). A guide to viticulture for wine production (3rd ed.). Apex Publishers.
wine-grape-growing.com
Isaacs, R., Teixeira, L. A. F., Jenkins, P. E., Neerdaels, N. B., Loeb, G. M., & Saunders, M. C. (2012). Biology and management of grape berry moth in North American vineyard ecosystems. In Bostanian, N., Vincent, C., & Isaacs, R. (Eds.), Arthropod Management in Vineyards (pp. 361–381). Springer.
doi.org/10.1007/978-94-007-4032-7_15
Thiéry, D., Louâpre, P., Muneret, L., Adrien, R., Sentenac, G., Vogelweith, F., Iltis, C., & Moreau, J., (2018). Biological protection against grape berry moths. A review. Agron. Sustain. Dev. 38(15)..
doi.org/10.1007/s13593-018-0493-7