Are fungicide and insecticide applications relevant this late in the game?

We’ve been getting questions recently on whether or not spraying fungicides or insecticides are relevant this late in the game. While many soybean crops are nearing or at R5 and corn has reached the dent stage and is ready to turn, some parts of the country are still trailing behind because of late planting. In this article, I discuss what late-season issues growers are experiencing this year and if growers may see some advantages to spraying in late-planted crops. 

Soybean Aphids
I received several calls last week about whether or not it’s still timely to spray for aphids. In my region, we have a lot of soybeans that are at the R5 stage and pods are about full. If you’re at this stage, it’s past the time for spraying. Aphids typically go for the greener crop, so in fields that are about to turn, it’s not economically worth putting down an insecticide to kill the bugs. There’s not much damage aphids can do at this point to affect yield, so the costs of spraying definitely outweigh the reward.

If you have late-planted soybeans, however, spraying may still yield results. If you’re still at the R4 stage and the insect threshold is a problem, there’s still time for aphids to add stress to the plant and reduce yield. Aphids typically affect the vitality of the plant, sucking the moisture and other liquids of the plan, which can ultimately affect plant vigor and pod fill. If you’re still at this stage, consult a local extension office for further recommendations.

Tar Spot in Corn
We’re hearing a lot of reports of tar spot in Illinois. Tar spot — a fungal disease that affects corn leaves and husks — has been somewhat problematic in the region this year because of excess moisture. This same region saw it affect their crops last year as well. The same message applies here. If your plants are at the R5/dent stage, it’s likely not beneficial to apply a fungicide. In fact, the University of Illinois Extension notes that in fields that are approaching R5 or any point after are at a stage where the pathogen’s effect on yield is “nearly nonexistent.” They suggest that “At R5, there isn’t much left as far as the life of the plant, so any benefit as far as keeping tissues free of diseases and potentially limiting stalk rots will be minimal.” In late-planted crops, it would be beneficial to reach out to your local extension office to consult with them on whether or not a fungicide is still relevant.

White Mold
With all of the late-season moisture we’ve had recently, white mold is popping up in more soybean fields. While fungicides are an option for white mold in corn, not all products are labeled for use in soybeans. That being said, it’s too late in the game to manage white mold in soybeans. The only thing you can do is evaluate your fields and plan ahead. In two years when you rotate back to corn, you may need to consider a traited soybean option with tolerance to white mold.

Soybean Sudden Death Syndrome
I’ve also heard some reports about soybean SDS as of late. An important thing to remember is that SDS is commonly mistaken for brown stem rot, so it’s necessary to split the pith to properly identify the disease. If it’s SDS, there’s not much you can do at this stage. Typically, if it comes in after R5, there’s not a big impact on yield. If SDS is detected in your fields, consider a variety with a good SDS disease package when you rotate back in two years. 

If you’re running in to any of these issues, I recommend you consult with your local extension office for appropriate recommendations on fungicide and insecticide applications and timing. If you’re looking for a high-yielding corn hybrid or soybean variety with an excellent disease and insect package for 2020 and beyond, contact your local Stine sales agronomist.