I got a text message from a grower last week saying, “You need to write an article about why I should be adding insecticide to my fungicide application.” I called him shortly after that and found out he was talking about his corn; well I think I have talked about corn plenty in the past few weeks. Matter of fact, it was brought to my attention that I haven’t talked about soybeans in quite some time. Well, my friends, that streak ends today. I know this is going to sound a bit like a broken record because I have talked about the consideration of a fungicide application a couple of times in the past month. So I promise this will be the last you hear about fungicides for at least a month or so.
Soybeans are an elusive plant that I think is more complicated than we would like to think it is. Compared to corn, soybeans can be high maintenance and need coddling at times, they would rather be led than pushed. Right now we are in the yield determining phases of a soybean plant when every stress matters to the plant; it has a tendency to overreact. When it does, this lowers its yield capacity more than it probably should. Being in a relationship with soybeans is hard, it takes patience, and excellent timing. On top of it all, the reward is hard to measure. Somewhat because we don’t apply the same rules to soybeans as we do corn, some of it is because big gains by percentage are a smaller number by comparison. Now you’re all asking, “What does this have to do with fungicides”? Well, I’m glad you asked.
When I refer to a fungicide application in soybeans nine times out of ten, I am talking about using them as a Plant Health Treatment. If soybeans are hypersensitive to stress, then the answer is we need to do all we can to reduce those stressors. Hopefully, we have managed the fertility. If we have the ability to irrigate, we can keep the moisture stress at bay, but what we need to manage is the soybeans ability to capture sunlight. The Source part of the Relationship is the problem; we can set plenty of pods, but we need to protect our plants ability to fill them.
The fungicide application in itself helps do this in two ways. The first being that we are going to protect the lower leaves that are deeper in the canopy from all the low levels of foliar diseases that are robbing the plant of photosynthetic capability. Even a little bit will help those plants capture sunlight better and convert it to proteins and fill pods. The second is the true plant health piece. The Strobilurin portion of the fungicide will act to reduce ethylene production in the plant that is a stress hormone and will allow the plant to be more efficient during times of heat or moisture stress. Additionally, that chemistry acts as an auxin in the plant and will help with the formation of pods out of flowers.
Now to answer the original question, the addition of an insecticide? The answer to this contains many of the same reasons. Admittedly, there probably isn’t one species of insects in your field right now that is at an economic threshold, but there are a lot of different insects each doing some level of damage to those leaves. So when you add them all together they are doing more damage than you think, so why not, while you’re at it, knock them out. Once again, the goal is to protect as much of the source as you can to help your plant capture the greatest amount of sunlight. The bonus is that the idea of putting these two products together doesn’t typically mean 1+1=2 it normally means 1+1=4 because that synergistic effect of the two is much greater than either one individually.
One last thing, this application has been admittedly hit and miss on how big the yield increase is, but it has been anywhere between 2-7 bushels in my experience. I believe for some portion, we were going too early, but now for the most part we are late R2 to early R4 in some of these soybeans. These stages are where I have seen the most consistent increase in yield. So if you haven’t made this application, I am not asking you to treat all your acres, but to try some. If you have been making this application and seeing the benefit, then by all means proceed. Sometimes what is just as important as #everyplantmatters, every leaf matters too.