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Wild
Blueberry Newsletter |
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April 2008 Field training sessions will be offered at three locations to demonstrate and discuss the Integrated Crop Management (ICM) field scouting techniques in Wild Blueberry Fact Sheet No. 204. The first and second sessions will cover mummyberry and blossom blight identification and monitoring, insect sweeping and identification, and weed identification and management. The third session will cover blueberry maggot fly trapping, leaf and soil sampling, and weed identification and management. One recertification credit per session will be offered for certified pesticide applicators.
Background about Mummyberry Disease Mummyberry blight requires three factors to develop: susceptible buds on blueberry plants, spores of the mummyberry fungus, and suitable weather to get infection. Each of these factors can be easily monitored to determine how likely it is that mummyberry fungus has infected blueberry plants in a particular field. Blueberry leaf and flower buds are susceptible to the mummyberry spores once the buds scales have separated (bud scales are the brown protective hard leaves that cover the buds in winter). The buds continue to be susceptible to this fungus as they develop. Only when the mummyberry cups stop producing spores, is there no more chance for infection. About mid-April, mummyberries in the field start to develop small cups that produce the infective spores. These spores are carried by the wind and land on developing blueberry leaf and flower buds. The spores do not survive for long on the buds and require a long enough period of wetness on the buds to get into the plants. Either rain or fog, but not dew, can provide this leaf wetness. The fungus grows slower at cooler temperatures so longer periods of leaf wetness are required for infection at lower temperatures than at higher temperatures. You can determine if an infection period has occurred in your field if you note how long the rain or fog lasted and what the temperature was during the wet period. By looking at the table for temperature and length of leaf wetness in Fact Sheet No. 217, you can determine the chance an infection period has occurred for the wet period in your field. After one to three weeks, depending upon the field and the weather, the mummyberry cups shrivel up produce no more spores and therefore, no more infection will occur. By setting up a small patch of mummyberries in the fall in a field that you will harvest the following year, you can monitor when the mummyberry cups are first produced and how long they last in your own field. Fungicides must be applied within 72 hours of the beginning of an infection period to protect the plants. Infected plants will take 9 to 14 days to show symptoms, so once the symptoms occur it is too late to correct the damage. See Table 1 in Fact Sheet No. 219, 2008 Disease Ccontrol Guide for Wild Blueberries, to compare results of fungicides for control of this disease at http://www.wildblueberries.maine.edu/factsheets/Disease/219.html Seanna Annis will be setting up mummyberry monitoring areas in growers’ fields in Knox, Lincoln, Hancock and Washington Counties in 2008. She will be reporting on the temperature and moisture conditions and if the mummyberry cups are producing spores. She will monitor the sites from the last week of April until the end of May and indicate when mummyberries are producing spores. If you want to find out if the mummyberry fungus is active in your area, you can call the wild blueberry toll-free number at 1-800-897-0757 and push extension 3 for the message or check for the Mummyberry Forecast on the wild blueberry website www.wildblueberries.maine.edu. Refer to Wild Blueberry Fact Sheets No. 211 and 217, found in the Fact Sheet section on the wild blueberry website, for more information on mummyberry disease. Sincerely,
David E.
Yarborough
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