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Cranberry Fruitworm
Order: Lepidoptera || Family: Pyralidae
Acrobasis vaccinii Riley
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Fruitworm Adult (magnified) |
Adults: Adult moths are active during calm evenings from June through early August. During the day they stay hidden among the cranberry vines. The front wings are gray-brown with two very small, dark dots near the front margin. There are also two white markings, one toward the base of the front wings and the other one around the middle of the front margin. The hindwings are also gray-brown. |
Larvae:
The damaging stage of the cranberry fruitworm
is the larval stage. Fruitworm larvae are very small and pale yellow-green
upon hatching. The larvae begin to emerge from the eggs after just three
to five days and immediately crawl to the stem end of the berry. They then
burrow their way into the berry, close the entrance hole with silk, and
begin feeding on the berry's contents with voracious appetite. Click HERE
to watch a larva beginning to create its tunnel. They feed from mid-June
through September, and during that time, each larva will typically move
from one berry to another, hollowing out a total of five to seven berries.
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A young cranberry fruitworm larva - Aug. 2, 2000 |
A close-up of a cranberry fruitworm (head end)--taking a break from its tunneling efforts. |
Berries that have been severely hollowed out will
often have an exit hole (see below) that is considerably larger than the
original entrance hole, as the larva increases greatly in size as it feeds
and must thus chew its way out. The injured berries turn red prematurely,
wrinkle and wither, and are thus commonly referred to as "raisins." When
mature, the fruitworm larva reaches nearly an inch in length and becomes
bright green with a reddish tinge along the dorsal (top) area of its body.
Note: Although Sparganothis fruitworm
is similar in appearance to cranberry fruitworm and also consumes berries,
the cranberry fruitworm leaves frass within the berries and does
not cover over its entrance holes. It also sometimes feeds just on
the outsides of berries, leaving craters in them. Visit the Spag
page for more information on this pest.
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Entrance and exit holes made by a cranberry fruitworm. The entrance hole is just below the exit hole and is white due to the webbing. Spag fruitworm do NOT cover their tunnels with anything. |
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Another entrance hole created by a cranberry fruitworm larva |
A close-up of the hole pictured at left. You can even see some of the strands of the silk webbing. |
CONTROL
Control measures are most reliable when timed
to the plant's stage of growth. When 50% out-of-bloom is reached
(click on the button below for help with this), a pesticide application
3-5 days later is suggested for Stevens, 5-7 days later for Ben Lears,
and 7-9 days later for Early Black and Howes. A second application may
need to be made 10-11 days after the first (if 1 or more eggs are found
per 200-250 berries). A third application may be needed during years
of VERY high fruitworm populations (Again, if 1 or more eggs are found
per 200-250 berries, spray 10-11 days after the 2nd application).
Two sprays appears to be adequate for growers in Maine, and sometimes only
one is needed.
Proper management should limit losses to less than 3 percent of the fruit.
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A Member of the University of Maine System These pages are currently being maintained by the Pest Management Office, University of Maine Cooperative Extension. Page Last Modified: 04/11/08 |
