Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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MARCH/APRIL 2010
GRAPEGROWING
Fifth-instar larvae spin a grayishwhite silken cocoon in which they pupate. The pupa is approximately ¼ inch long.
Ground surveys for immature insects by vineyard, regulatory, and UC Cooperative Extension personnel were more fruitful. Almost 30 individual properties inNapa County are now presumed positive for at least one life stage of L. botrana. By November 2009, trapping efforts had ended for the season, concurrent with the lack of a population in the adult stage.
Life cycle
In the Mediterranean region, L. botrana typically completes two to three generations per year. Using 50ºF (lower) and 86ºF (upper) thresholds, we tentatively estimate degree-days Fahrenheit to be 833 for the first generation and 904 for the remaining generations.
First generation flights may begin near bud break and continue for four to five weeks; males begin emerging roughly one week before females. Adults live one to three weeks, fly at dusk (above 54ºF), andmate in flight (1 to 6 days after emergence). Females generally mate once in their lifetime.
Egg-laying begins one to two days aftermating, with each female laying 80 to 160 eggs. Eggs of the first generation — laid singly on flat surfaces near or within the flower cluster—hatch in 7 to 11 days. Larvaeweb together individual flowers to form “nests” prior to and during bloom, and feed inside the web.
Under optimal conditions of 80º to 85ºF and 40% to 70% relative humidity, larval development is completed in 20 to 30 days. Pupae form inside webbed cocoons in the flower cluster, in a folded lobe of a leaf blade, under the bark, or in soil cracks. Adults emerge 6 to 14 days after pupation.
Eggs of second and third generation females — laid singly on shaded berries — hatch in 3 to 5 days. A grape cluster is typically infested with multiple larvae that feed individually inside berries. Larvae fed on higher-quality food (ripe fruit or fruit infested with Botrytis
cinerea) grow into larger, longer-lived adults that lay greater numbers of eggs. Therefore, later-season generations have the potential to cause greater crop damage than earlyseason generations.
In autumn, nights longer than 11 hours during egg and/or larval development initiate diapause (a resting state). A diapausing pupa withstands colder temperatures than a non-diapausing pupa and can tolerate even the coldest northern European winters. In early February, during post-diapause development, prior to adult emergence, pupae may die at temperatures below 46ºF.
Damage
L. botrana larvae feed on all parts of the flower cluster in early spring, but more importantly they feed on berries in midsummer and again in late summer, continuing through harvest and into leaf-fall. Feeding triggers infections by the fungus Botrytis cinerea and other rot organisms resulting in bunch rots that are the main cause of fruit loss.
Larvae of the first generation of L. botrana hatch from eggs laid in flower clusters and damages portions of the cluster.
Second generation larvae hatch from one egg per berry prior to veraison, starting about when berries are pea-size and feed inside webbing. Damage is caused by direct feeding on the berries. A dark spot surrounds the point of larval feeding and several berries can be damaged.
Third generation larvae can cause the most damage to clusters, preventing them from being harvested for wine grape production. Larvae penetrate and feed on ripening fruit immediately after hatching.
Infested clusters contain shriveled berries, webbing, and excrement. Feeding holes can be seen in several berries. Shreds of berry epidermal tissue loosely attached to pedicels are present, as are dry, somewhat intact “skins” of fully excavated berries. Bunch rot is present, and depending on climate, the summer bunch rot complex will develop which includes secondary fungal invaders.
Monitoring
Monitoring methods for L. botrana in California vineyards may not be identical to strategies used in Europe or other regionswhere this pest is common; however the objective is the same — to decrease yield losses caused by the feeding damage of this insect. Strategically timed insecticide applications are required to control this pest and, depending on the generation targeted and the material applied, it is essential to identify either the beginning of egg laying or egg hatch.
Monitoringmale flights with a commercially available L. botrana pheromone lure over the entire 2010 grape growing season is advised at this time. Red delta sticky traps, identical to those used for monitoring vine mealybugs, are ideal for this purpose, and should be attached to the trellis immediately above the canopy. Place one trap per 30 vineyard acres, or at least one per ranch in small vineyards.
The lure should be replaced according tomanufacturer’s instructions, and insects removed from the trap bottom after counting. Replace soiled traps as needed to maintain a sticky bottom.
Trapping for L. botrana males should begin at bud break and trap-catch numbers should be recorded weekly. Trapping is used to determine when the adults are active, which helps predict egg-laying activity. There is no close correlation between the number of trapped males and actual population densities. If very few or no males are caught, little to no damage would be predicted; however, if any males are trapped, it increases the likelihood that webbing found in clusters is caused by L. botrana.
First generation — Once peak trap catch has likely been reached, begin to observe 100 flower clusters per block (1 cluster per vine) and look for eggs of the first generation, which are commonly laid on the peduncle (cluster stem). Eggs are lentil-shaped, but slightly smaller. Take note of the egg color and the time it takes to change fromwhite (freshly laid), to yellow, followed by black immediately prior to hatching. A hatched egg can be recognized by the outer shell that remains. If
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