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The NDSU Extension weekly podcast In the Pod: Soybean Updates delivers timely insights and expert advice on soybean production.
You're listening to In The Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension. We are definitely deep into summer temperatures. How does excessive heat affect soybeans? Ana Carcedo, NDSU Extension Agronomist, has some answers. Ana, we are in the cooker this week. Are soybeans okay in high temps?
Ana Carcedo:I had a lot of calls from farmers asking me what are these temperatures doing to my soybeans? And that's a really fair question. Temperatures above 95 degrees will do some harm to your soybeans. 95 is that magical number, it's a threshold that you have to have into consideration. But there is other things that you also have to consider. The crop stage. So if your crop is already flowering that I will expect that it's already. You're going to have some problems with the pollinization. Don't be that afraid. Soybeans naturally lose in the range of 60 to 80% of the flowers that they generate. Losing some flower is not that critical. But if your fields are already in the r three stage, so that means that you have one small pod in any of the four uppermost nodes of your main stem, then in that moment is that you should be a little bit more concerned. The critical period for Soybeans goes from R3 to r 5.5. So from having one small pot to having a full size pot, which the seeds are occupying half of the capacity of the pot size. There is other things as well that you should be considering when we are talking about these high temperatures. Among them we know that the herbicide efficacy when it's hot and dry it might reduce the herbicide performance and also increase the risk of carryover to the next crop. A lot of herbicides, the label does not allow you to apply after r one or r two, so after flowering. If you are considering applying a herbicide, it's really, really important that you read the label and you make sure that you are making a legal application.
Bruce Sundeen:How does heat affect plant development?
Ana Carcedo:If your soybeans did not reach canopy closure yet, this early heat and, like, this moisture stress that we have, they might hinder the capacity of your crop to close the canopy. Also might lead to increase weed pressure and competition. So it's things that you have to consider when you're planning and you're managing your crop. So we were talking a little bit about how from R three to R 5.5 is the most sensible moment for We usually call it a critical moment for soybeans. In this moment, you don't want anything to hinder your soybeans. Anything that happens in this moment will lead to yield penalties. When we're talking about heat stress, we are going to have an increased flower and pot abortion while also having problems reducing the seed size if this prolongs longer than our pipe.
Bruce Sundeen:What about white mold? Should farmers take any action?
Ana Carcedo:It's really important that you continue monitoring for white mold, especially if your soybeans are flowering. When we talk about wine mold, you have to consider that the pathogen enters through that tissue. That means that the dead flowers are like the perfect door for this pathogen to enter.
Bruce Sundeen:Ana, what about insect pressure?
Ana Carcedo:We have two insects that we should be monitoring right now if your soybeans are already flowering. One of them is soybean aphids, that's really common in our area. So far the populations are not really concerned. I've been scouting some fields and I've soybean like three aphids. That's of course way below the threshold. Soybean aphids, usually they don't like that much high temperatures, so in that aspect we're fine. But we have seen increase in grasshopper population, so that's something that you should consider. Always check the borders of your field because they always start from there.
Bruce Sundeen:Thanks, Ana. Our guest has been Ana Carcedo, NDSU Extension agronomist. You're listening to In the Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension supported by the North Dakota Soybean Council.