April's Ag Advice by April Borders I've been out looking at our soybean fields and checking for soybean aphids. I hope that you have been out checking, too. I know that I might sound like a broken record in continuing to remind you to scout your fields, but I really think that it is important.
I have been in fields that have relatively low aphid numbers and then I have been in fields that have very heavy infestations. I was recently in a field and I pulled several plants to do aphid counts on. I finally quit when I had reached 1,000 aphids and there were still leaves yet to be counted. I was finding both winged and non-winged aphids.
I have also been in fields that have been treated and have seen the difference that insecticides can make in aphid counts. Yes, there were still aphids present, you're not out to kill every single aphid around. But the numbers were lower than when I had been in the fields three weeks earlier.
This is the critical time to be looking at control of this insect. We are in the crucial reproductive stages at which these insects will cut into yields if present in large numbers.
I also noticed that the bean leaf beetles are starting to make their presence known in the fields. Keep an eye on these pests as well. If you are spraying for soybean aphids you will get the extra benefit of bean leaf beetle control.
If you have been out in your fields scouting around, you probably noticed some leaf spotting in both the lower canopy and the upper canopy. We are starting to see bacterial blight and septoria brown spot.
Symptoms of bacterial blight include angular, yellow to light brown lesions or spots on the leaves. Lesions enlarge to produce irregular areas of dead tissue surrounded by yellow halos. Dead areas tear away, giving the leaves a ragged appearance. The disease is common during cool, wet weather. This is found in the upper canopy.
Septoria brown spot causes small, angular to somewhat circular, red to brown spots on the unifoliolate and lower trifoliolate leaves. The individual spots may grow together, forming irregular shaped brown blotches in the leaves. Leaves quickly turn yellow and drop from the plant.
There are no controls for these diseases. Generally they do not do enough damage through defoliation to cause any major impact. Most often these diseases go unnoticed but with our wet spring, they have raised their ugly head and we are now seeing the damage from the disease.
Now let me turn your attention to a different topic. August in the past has been our "hot" month, not just because of the heat that we get from Mother Nature but because this is the month when West Nile virus tends to turn up the heat and we start seeing more incidents of the virus.
We now have 10 positive human cases in the state of South Dakota plus two positive blood donor screenings. There have also been 12 positive bird cases, three positive equine cases and four positive pools of mosquitoes statewide.
So we want to again remind you that you need to take precautions when you are outside. When outside, remember to wear proper clothing, like loose-fitting, long-sleeved clothes and to use some type of insect repellent. Insect repellents containing DEET, up to 30 percent, are the most commonly recommended. Take time to protect yourself.