Below are a few comments from Dr, Dennis Hancock, UGA Forage Agronomist, on the current forage insect situation.
Bermudagrass stem maggot
We have been seeing and getting reports of bermudagrass stem maggot damage all across the southern 2/3 of Georgia. Most folks have cut their second cutting and many have started on their third cut. I’ve had a fairly sizeable number of Agents reporting that they have producers who have gotten 3-8 inches of regrowth on their third cut’s regrowth, only to have it stunted by the BSM. This is often enough regrowth (>6 inches) to shade the base of the bermudagrass such that it won’t try to grow through the damage. As such, this is the worst case scenario, and the only thing for it is to clip the bermudagrass back and use an insecticide to suppress the BSM population long enough for the bermudagrass to grow up.Prompt action by many of our producers has been rewarded. Following the recommendations found here (https://bit.ly/BSM2015), many producers have successfully used a pyrethroid to suppress the BSM fly populations. But, timing is CRITICAL! Producers spraying 7-10 days after the previous crop was mowed have found that this one application will protect the crop at least until it is 3-4 weeks old. Meaning: the second spray is not likely to be needed. By the time it gets 3-4 weeks old, the damage done to the top 2-3 leaves at that point would not be enough to justify the cost of the spray and the damage done by the spray rig driving across the field. If it is 3-4 weeks old and starting to show signs of damage, it would be better to harvest the crop and protect the regrowth. Also, keep in mind that the more susceptible varieties (common, Alicia, Coastal, Russell, Tifton 44, etc.) are generally not going to produce high yields in late August – October, regardless of whether the BSM is present or not. A late season spray will likely cost $12-15/acre in total costs (product + application), so this means the spray needs to salvage 0.1-0.2 tons of dry hay/acre to break-even. Some of these susceptible varieties would struggle to produce 0.5 dry tons/acre normally, even in the absence of the BSM. My point is, spraying a field that is only capable of producing 0.5-0.75 tons of dry hay/acre may not salvage the 0.1-0.2 tons/acre required to be economical.