I have thirty blueberry bushes in my yard. They have blueberry maggots pretty...
I have thirty blueberry bushes in my yard. They have blueberry maggots pretty bad since they decided rotenone was cancer causing. Can I use organicide? Or something else like neem? I also have witches broom and read an article that said cut the whole stalk. Should I wait till spring to put less stress on the plant? Any help will be greatly appreciated. Darlene McConnell
Lamoille County Vermont
Hi Ms. McConnell,
I'm sorry it's taken some time for you to receive a response. Your question was just assigned to me today.
See pp. 26 - 27 of this guide for some organically-compatible options for blueberry maggot: http://nysipm.cornell.edu/organic_guide/blueberry.pdf
It appears that two of the better options are the spinosad-containing bait product (GF-120 NF Naturalyte Fruit Fly Bait) and kaolin clay. While sesame oil (the active ingredient in Organocide) is suggested for some insects of blueberry, it does not seem to be recommended for blueberry maggot.
Some additional information on how to use the bait is provided in the Southeast Regional Organic Blueberry Pest Management Guide (http://www.smallfruits.org/SmallFruitsRegGuide/Guides/2015/BlueberrySprayGuide_organic_final.pdf):
"Begin bait application as soon as blueberry maggot flies are caught in traps, or 2 to 3 weeks before fruit begins to ripen. Repeat every 7 days; apply more often during rainy periods and as fruit ripens. Use a coarse nozzle to apply large spray droplets (4-6 mm) as a directed spray to one side of each row, targeting the interior canopy to protect the bait from sunlight and rain. It is not necessary to apply directly to fruit or leaves."
Here is some additional information on trapping for blueberry maggot to determine when/if to treat: http://www.fruit.cornell.edu/berry/ipm/ipmpdfs/bbmaggotfly.pdf.
For witches broom (http://blueberries.msu.edu/uploads/files/Witches%20broom.pdf), it appears that it's best to kill infected plants with an herbicide unless you can get ride of all fir (Abies spp.) trees within 1000 to 1500 feet (330 - 500 yards). The fungus is systemic in the blueberry plant, meaning that, while you can only see symptoms on one part, it's present pretty much throughout the plant, so pruning out the part with the obvious witches broom will not eliminate the infection. The danger of leaving infected plants in the orchard is that they serve as a source of infectious spores. If either the infected blueberry plants or the fir trees are eliminated, the fungus should not be able to complete its lifecycle and, therefore, should not spread anymore.