April's Ag Advice by April Borders I have just finished with my Agronomy Updates and with doing our Crop Production Clinics and I thought that I should share some of the information that we have received. I know that we really don't want to be thinking about insect control this time of year and we sure don't want to be thinking about the soybean aphid, but this is some new information that we need to consider when we are looking at controlling these pests.
The preliminary findings from research that was done last year at Brookings would suggest that we may have to take action against soybean aphids at far lower counts than previously thought. The preliminary findings suggest that as few as 10 soybean aphids per plant, if detected when pods are forming, may justify spraying. This is a big difference from the recommendation of 200 or more aphids per plant. Now please remember that this is a preliminary finding and is based only on one year's worth of data.
The reason that we are looking at this low number is that aphids have the potential to reproduce into thousands. If you look at the life cycle of the aphid, we will see why. Let's start in the buckthorn. The aphid overwinters on the buckthorn as eggs. In the spring, the overwintered eggs hatch into nymphs, and after two generations of wingless aphids on buckthorns, a generation of winged females migrate from buckthorns to soybeans as soon as the soybeans emerge from the soil.
Once on soybeans, the winged aphids give birth to numerous wingless female aphids that, in turn, give birth to numerous other wingless aphids. A newborn aphid grows by molting several times and can start bearing live young aphids within a week. Okay, did you catch that? The aphids don't lay eggs in the soybeans; they give birth to live young aphids. These in turn give birth to live young and there you are � you suddenly have an aphid population explosion. With type of reproductive capabilities, soybean aphids can potentially produce 15 generations of aphids on soybeans per growing season.
The critical time for farmers to take action is in about late July or early August. With early scouting in mid-July we can hopefully catch the aphids before there is a population explosion. We need to be able to protect the soybeans during the critical time when yields are being made. The soybean plant appears to be most susceptible to aphid injury if the aphid infestation starts early in the vegetative stage (V2) of the plant and continues on through the flowering and beginning seed stages (R1-R5) of the soybeans. According to this preliminary data, infestations of aphids as low as 10 aphids per plant at full bloom, could reduce yields by about 15 percent.
Because this insect is so new to South Dakota and the United States, there hasn't been a lot of research done to determine the thresholds and according to Dr. Mike Catangui, the early estimates about thresholds were way too high. Wisconsin, where the pest was found first, was advising farmers to spray when they counted 250 aphids per plant. Minnesota advised taking action at 200 aphids per plant � this is the threshold that we initially adopted.
Another cause of concern that we are looking at is that Minnesota, where the aphid has been established for one year longer than South Dakota, saw its worst damage to date from the insect in 2003. That suggests that South Dakota should see its worst damage so far in 2004.
I want to remind you that this information is from one year's worth of data and it is a preliminary finding. I am encouraging producers to get out early during the V2 stage and start scouting for the aphid. Remember that these insects are small and are found on the underside of the leaves, on the stems and even on the pods. You won't be able to see them as you are driving by your fields; you are going to have to be out there walking those fields and carefully looking at your plants.
I will keep you updated on information as it comes to us. For more information on the soybean aphid or other cropping questions, feel free to call the Extension Office at 677-7111.
PAT Classes � Vermillion on Feb. 23 from 1 to 4 p.m. and 6 to 9 p.m.
PAT Classes � Parker on Feb. 24 1 to 4 p.m. and 6 to 9 p.m.
Alfalfa Management Clinic � Gayville on March 4 from 1 to 4 p.m.