The grape berry moth (GBM) larva is a key pest that can cause serious damage to grapes. The larvae damage
commercial vineyards by feeding on the grape blossoms and berries. Infested berries may appear shriveled with
fine webbing. Damage increases mold, rots and numbers of fruit flies in both wild and cultivated grapes. There
may be 3 or more generations per year.
Figure 1. The adult moth (Moth photo credit: R. Isaacs, Michigan State University) is small, active, and
about 1/4 inch long. At rest with its wings folded, there is a brown band across the middle of the moth’s wings,
the hind portion is gray-blue with brown markings, while the front portion is gray-blue without markings. The full
grown larva is 2/5 inch long, pale olive-green, and can have a purplish tinge from the food it has eaten.
GBM overwinters as a pupa in leaf litter. Adults emerge and lay eggs of the first generation near bloom time.
This degree day model can be used to time application of insecticides to reduce GBM injury. The degree day requirements
were developed by Cornell, Penn State and Michigan State Universities. GBM needs 810 DD base 47°F to complete a generation.
The date to begin accumulating degree days is when 50% of the wild grapes near the vineyard are at 50% bloom. Egg laying
for the second generation begins at 810 DD and for the third at 1620 DD. Generally, sprays are applied 200 DD after the start
of egg laying (200, 1010, and 1820 DD after wild grape bloom) for most insecticides, but the insecticide growth regulators
(Intrepid) that are applied at egg laying should be timed for the biofix date, 810, and 1620 DD.
Degree day targets for the various codling moth insecticides
Degree day target
Biofix – Wild grape bloom
Begin degree day model
Timing for most insecticide sprays (first spray)
Begin of egg laying for 2nd generation, timing for insecticide growth regulators.
Begin of egg laying for 3rd generation, timing for insecticide growth regulators.
Begin of egg laying for possible 4th generation, timing for insecticide growth regulators.
Pheromone traps can be used to determine the need for sprays and to monitor activity in addition to the predictive model.
GBM form leaf-flap cocoons at the end of the season which later drop to the ground. During winter, the cocoons may
be found in leaf litter and debris under the vines. Clean up or bury leaf litter under vines in the winter to eliminate
over wintering pupae.
Figure 2. GBM forms a leaf-flap cocoon at the end of the season.