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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. The soybean aphid is a common villain to soybeans, but right now spider mites are on the move. Jan Knodel, NDSU Extension entomologist, has the latest. Jan, which insect is causing problems?
Jan Knodel:Well, with all the hot, dry weather conditions that we've been having recently, we are starting to see spider mite outbreaks. And August is typically when we start to see movements into the soybean fields.
Bruce Sundeen:How do you scout for spider mites?
Jan Knodel:Well, they're such a tiny insect. They're less than 0.2 inches, and they're found on the underside of the leaf. You really need to get down on your hands and knees to scout for these arthropods. You can also look for the leaf injury symptoms. They kinda appears first as stippling, and then it progresses to yellowing and browning and bronzing of the leaves. This is the feeding injury. It eventually will get so bad it'll lead to leaf drop and beans, and the feeding injury causes significant water loss from the plant and reduce photosynthetic ability. So it can cause significant yield loss. So when you're out there scouting, check the field edges. They typically move into the field edges first. Look at the underside of the leaves and the lower foliage of the leaves for the tiny mice, and also look for the fine spider like webbing. They do a little bit of webbing. You can use a white sheet of paper below the leaves and then tap it to dislodge the mites.
Bruce Sundeen:Is there a threshold for spider mites?
Jan Knodel:Yes. We do have a threshold for spider mites and soybeans. When you're starting to see mice present and damage symptoms present in the lower quarter to third of the canopy, that would be considered a threshold. And the most susceptible crops trait stages are beginning pod r three to the beginning seed r five.
Bruce Sundeen:What can farmers do to control the mites?
Jan Knodel:Well, we do have a few insecticides that you can use. I need to caution everyone that the perisprites in general do not control spider mite populations, and they will disrupt the natural enemies that naturally control spider mites, like predatory mites and thrips. And they actually stimulate mites to move out of the field and increase the reproductive rate. So the only one you can use effective and doesn't do that, I've seen the spider mite players, is Bifentrine. That is the only one that is good on spider mites. Some of the trade names are Bifentrine, Tundra, Brigade, and all the other generics. There are some miticides registered in soybean. We have Zeal SC. That is very good at controlling mice, and it will also kill the immatures and also the eggs, larvae, and nymph. So you might wanna try that. I heard that some folks are using a combination of Bifenthrin and, ZEAL to get the immature stages. The Purifry bifenthrin will not control the immature stage or the eggs.
Bruce Sundeen:Jen, are there any other steps in controlling spider mites?
Jan Knodel:After you spray, it's always a good idea to go back and re scout your field several days later to make sure you got good control of your spider mite population. If you do need to spray multiple times, be sure you rotate to a different mode of action to help prevent the development of insecticide resistance.
Bruce Sundeen:Thanks, Jan. Our guest has been Jan Knodel, NDSU Extension Entomologist. 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.