{"id":12137,"date":"2025-05-01T14:22:40","date_gmt":"2025-05-01T18:22:40","guid":{"rendered":"https:\/\/extension.umaine.edu\/highmoor\/?p=12137"},"modified":"2025-05-01T14:31:21","modified_gmt":"2025-05-01T18:31:21","slug":"garlic-ipm-newsletter-no-3-may-1-2025","status":"publish","type":"post","link":"https:\/\/extension.umaine.edu\/highmoor\/2025\/05\/01\/garlic-ipm-newsletter-no-3-may-1-2025\/","title":{"rendered":"Garlic IPM Newsletter No. 3 — May 1, 2025"},"content":{"rendered":"
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Disease Forecast Alert<\/span><\/strong>: Conditions in Bangor, Lewiston, and Milton, NH may be favorable for onion downy mildew and Botrytis leaf blast development in coming days. See NEWA onion diseases<\/a> for details – more on these in a future newsletter.<\/p>\n

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Onion Maggot<\/h3>\n

Onion maggot (Delia antiqua<\/em>) can be a serious pest of allium crops. Overwintered pupae emerge as adults in spring, constituting the first of three generations per year. These adults, which look like small house flies, lay eggs at the base of allium plants or sometimes on their young leaves. The resulting larvae move into the soil and feed on belowground roots and bulbs. Larvae feed there for 2-3 weeks before they pupate in surrounding soil to cycle into the next generation. For images of onion maggot, go to the University of California IPM Maggots<\/a> webpage.<\/p>\n

Affected plants become stunted, wilted, yellow, and may die. This will cause larvae to move to nearby plants. Young and\/or injured plants are especially favored by the maggots simply because they are easier to penetrate. The overwintering generation is the most damaging, as it can reduce stands by more than 50%. Still, damage from second and third generations can distort growth, enable pathogen entry, and render crops unmarketable.<\/p>\n

The overwintering generation of onion maggot begins to emerge at 390 GDD40\u00b0F<\/sub>, with “peak flight” (50% emergence) occurring at 735 GDD40\u00b0F<\/sub>. NEWA has a tool specifically for onion maggot<\/a> – choose the location that best reflects your weather conditions to see how many GDDs have accumulated near you, as well as the 5-day forecast. Near the top of the page, you can click on “More Info” to learn about the pest and model. GDDs for more Maine sites are on the Maine Climate Office<\/a> page; be sure to look at the map labeled for base 40\u00b0F. Current information from both sources is combined below, showing the forecasted GDDs where possible from NEWA.<\/p>\n

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Growing Degree Day Accumulation for Onion Maggot<\/strong><\/h4>\n<\/caption>\n

Location<\/th>\nApr 29 GDD40<\/th>\nMay 6 GDD40 forecast<\/th>\nLocation, cont’d<\/th>\nApr 29 GDD40<\/th>\nMay 6 GDD40 forecast<\/th>\n<\/tr>\n
Augusta<\/td>\n237<\/td>\n327<\/td>\nJackman<\/td>\n92<\/td>\n<\/td>\n<\/tr>\n
Bangor<\/td>\n171<\/td>\n250<\/td>\nKatahdin<\/td>\n12<\/td>\n<\/td>\n<\/tr>\n
Calais<\/td>\n123<\/td>\n<\/td>\nKittery<\/td>\n256<\/td>\n<\/td>\n<\/tr>\n
Caribou<\/td>\n65<\/td>\n<\/td>\nLewiston<\/td>\n205<\/td>\n293<\/td>\n<\/tr>\n
Cherryfield<\/td>\n135<\/td>\n<\/td>\nLincoln<\/td>\n113<\/td>\n<\/td>\n<\/tr>\n
Clayton Lake<\/td>\n70<\/td>\n<\/td>\nMillinocket<\/td>\n104<\/td>\n<\/td>\n<\/tr>\n
Cutler<\/td>\n67<\/td>\n<\/td>\nMilton (NH)<\/td>\n301<\/td>\n376<\/td>\n<\/tr>\n
Damariscotta<\/td>\n195<\/td>\n<\/td>\nNewry<\/td>\n158<\/td>\n<\/td>\n<\/tr>\n
Dover-Foxcroft<\/td>\n129<\/td>\n<\/td>\nNorthfield<\/td>\n121<\/td>\n<\/td>\n<\/tr>\n
Durham (NH)<\/td>\n325<\/td>\n407*<\/td>\nPortland<\/td>\n184<\/td>\n<\/td>\n<\/tr>\n
Ellsworth<\/td>\n146<\/td>\n<\/td>\nRangeley<\/td>\n96<\/td>\n<\/td>\n<\/tr>\n
Embden<\/td>\n144<\/td>\n<\/td>\nRochester (NH)<\/td>\n331<\/td>\n410*<\/td>\n<\/tr>\n
Farmington<\/td>\n149<\/td>\n<\/td>\nSanford<\/td>\n242<\/td>\n<\/td>\n<\/tr>\n
Fort Kent<\/td>\n60<\/td>\n<\/td>\nShelburne (NH)<\/td>\n232<\/td>\n288<\/td>\n<\/tr>\n
Fryeburg<\/td>\n191<\/td>\n<\/td>\nThorndike<\/td>\n141<\/td>\n<\/td>\n<\/tr>\n
Greenville<\/td>\n56<\/td>\n<\/td>\nTopsfield<\/td>\n91<\/td>\n<\/td>\n<\/tr>\n
Houlton<\/td>\n98<\/td>\n<\/td>\nWest Rockport<\/td>\n166<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

GDDs from NEWA and Maine Climate Office. Values with an * indicate the 390 GDD threshold for onion maggot emergence is met.<\/p>\n

Durham and Rochester, NH, will accumulate sufficient GDDs by early next week for onion maggot emergence to begin, and locations in southern Maine will soon follow. You can see in the NEWA charts that 10-20 GDDs easily accumulate daily with the warm weather we’ve been having.<\/p>\n

NOTE<\/span><\/strong>: Just because GDDs are sufficient for pest development does not<\/strong> mean that the pest is present in your field. Anticipate potential infestations based on problems in previous years both in your own field as well as the greater area.<\/p>\n

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Controls<\/h3>\n

There are no known allium cultivars that are resistant to onion maggot, and no controls will be effective in-season once damage has been detected. Therefore, preventing infestation and population buildup is key!<\/p>\n