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Fruitworm A .pdf version of this bulletin will be available in Spring 2004. For a draft .pdf version or more information e-mail webmaster@blueberryfacts.org. Introduction Hosts Identification  Eggs of CFW are flat, with a round to oval shape, and they appear opaque (Figure 3-5). Upon maturity, the dark head capsule of the developing larva is clearly visible within the egg (Figure 5). Eggs of CBFW are irregularly shaped and initially appear as raised white eggs (Figure 6). As they develop, CBFW eggs go through a progressive change of color from white to yellow to orange (Figure 6-8). Within 24 hours of hatching, the developing larva’s head capsule can be seen as a darkened spot within the egg (Figure 8). Eggs that have already hatched are clear, and look similar to a newly deposited egg.
Life
Cycle  Egg laying starts soon after the first fruit set, peaking in the first two weeks after 100 % petal fall. Although adult flight can continue into July, egg laying drops rapidly after mid June. Both species prefer to lay eggs within the calyx "cup" area of the fruit, though CBFW tend to place their eggs along the inside rim of the calyx.
Larvae begin to pupate in the spring. After a pupal stage that lasts for several weeks, the adults emerge during bloom, and mating and egg laying soon follows for both species. Monitoring
and Control The emergence of adult males and moth flight can be monitored using sticky traps baited with female sex pheromone lures. Monitoring the emergence of adults provides two important pieces of information for pest management. First, the number of male adults caught in traps provides a relative estimate of population level and distribution within the field. Second, because egg laying typically begins shortly after initial adult emergence, adult catch in traps serves as an indicator for when egg monitoring should begin. The second phase of monitoring fruitworms, scouting for eggs, provides the most reliable biofix for egg hatch timing and distribution in the field. Scouting for eggs should begin after there is some early blueberry fruit set and adult flight has commenced. Start by scouting along perimeter rows of blueberries that have a history of fruitworm pressure or are adjacent to woods and/or abandoned blueberry fields. CBFW eggs tend to be laid between 3 ft and 5 ft high on bushes, and "hotspots" are often clustered together within a few bushes. Eggs can be seen in the calyx of fruit, and approximate age of CBFW eggs can be estimated by their color. CFW eggs are more difficult to see than CBFW because of their flattened shape and opaque color. A 15-20X hand lens is helpful to see eggs and confirm identification. The third phase of monitoring fruitworm in blueberry is scouting for larval infestations. This is important for determining the effectiveness of the management strategy that has been utilized. Premature coloring of the fruit can be used to detect fruitworm infestations. Cultural control. Clean cultivation can reduce the populations of CBFW within a field significantly, but insecticide treatments may still be needed to achieve satisfactory control of this pest. Due to the premature coloring larvae cause on fruit, it may be possible to physically remove infested clusters in small plantings. Biological Control. As both CBFW and CFW are native insects, there are a number of parasitic insects that attack them in their egg and/or larval stages. These include parasitic wasps in the families Trichogrammatidae, Ichneumonidae, and Braconidae. Selecting insecticides that have lower toxicity to these parasitoids such as Insect Growth Regulators (IGRs) and B.t.s will enhance the effectiveness of biological control. Chemical Control. When using chemical control, timing and coverage of the fruit is critical. Once the start of egg laying is determined through field monitoring, there is an approximate 3 to 5 day window before egg hatch begins. Some insecticides (e.g. IGRs) are primarily active on eggs of CBFW and CFW and should be applied during this early egg-laying period. Egg hatch often occurs before 100% petal fall, so insecticides toxic to pollinators should not be used. B.t.s and most IGRs don't affect bees so they can be used during late bloom / early fruit set. Larvae are most susceptible to chemical control for a short period between the time that eggs hatch and the larvae enter the fruit. After successful larval entry, the fruit acts as a refuge from contact with chemical residues on the surface. In the case of CFW, complete coverage is critical because larvae may never leave the calyx cup before entering fruit. In the case of CBFW, it is possible to present an additional toxic dose to the larvae as they move from one berry to another, though the larvae are by then larger and more difficult to kill. To learn more about fruitworm biology and management, consult these resources: Pritts, M.P., Hancock, J.F. 1992, Highbush Bluberry Production Guide (NRAES-55). Howitt, A.J. 1993, Common Tree Fruit Pests Michigan State University Extension. |
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Cranberry Fruitworm (Acrobasis vaccinii) and Cherry Fruitworm
(Grapholita packardi) are the most significant Lepidopteran
pests directly attacking the fruit of blueberries in commercial fields
in Michigan. Both pests have similar life histories, which makes it
possible to address them together in one fact-sheet. Both Cranberry
Fruitworm (CBFW) and Cherry Fruitworm (CFW) are native to North America,
as are the blueberries they infest. Without decisive management one
or both of these pests can cause significant economic injury to the
blueberry crop. This fact-sheet will discuss general life stages of
CBFW and CFW, as well as Integrated Pest Management strategies for managing
these pests in blueberries. 
Larvae found within blueberry fruit in June
are likely to be either CBFW or CFW. CBFW larvae are pale yellowish
green, and reach a length of 15 mm when fully developed (Figure 9).
CFW larvae appear pink, are about 8 mm in length, and can be distinguished
from CBFW by the presence of an anal comb (hairs on the tip of the abdomen).
With
favorable weather conditions, eggs hatch in 3 to 5 days. CFW tend to
enter fruit in the calyx where they hatched, while CBFW tend to crawl
around the berry and enter adjacent to the stem, or on the “cheek”
of the berry (Figure 12). One major difference between CFW and CBFW
is the number of fruit that are infested within a single life-cycle.
CBFW can enter up to 6 berries, while CFW generally enter 1 or 2 berries
to complete development. Both species feed on immature green fruit causing
premature ripening (bluing) of fruit (Figure 13). This characteristic
makes infested fruit more readily identifiable. While feeding and moving
between berries, CBFW produce a characteristic mass of webbed frass,
filling the space in and around the fruit cluster (Figure 13). CFW also
silk berries together when moving between fruit, but the frass stays
entirely within the fruit, and the webbing is not as obvious.
Upon
reaching maturity, larvae leave the berries and move to over-wintering
sites. The insects differ in their overwintering strategies. CFW larvae
leave the fruit and enter a dead cane or weed to spend the winter, pupating
in the spring. CBFW crawl to the base of the blueberry bush and form
a hibernaculum in the soil (Figure 10).