BLOOMINGTON, Ill. — As soybeans turn toward the finish line, the focus shifts toward keeping a watchful eye out for yield-robbing pests and diseases and protecting the plants during pod fill.
Cody Pettit, Pioneer field agronomist in east-central Illinois and CCA Soy Envoy, provided recommendations of what to look for in soybean fields at this stage in the growing season during an ILSoyAdvisor podcast from the Illinois Soybean Association.
Here are several issues Pettit noted to watch for in soybean fields.
On Insects
Green stink bugs and brown stink bugs are common in Illinois. There have also been cases of the brown marmorated stink bug. It’s not uncommon to have one to five generations each year, depending on what kind of season. They usually complete their lifecycle within two to three months, so there is always going to have a stink bug population at pod fill.
Adults overwinter and then they will lay eggs in the soybean field. When the nymphs hatch one to three days after the eggs are laid they will begin feeding on the pods, as well as stems, foliage and the blooms.
It’s important to monitor the pods because stink bugs are a piercing, sucking insect which means they’re going to go after that seed and that’s where the most economical damage is going to come from. Seeds can become shriveled, dried, deformed, undersized, and the plant will eventually abort them.
The pods will look flattened as if there’s nothing inside them because there isn’t. So, it’s pretty easy to tell if there’s a lot of damage out in the field. This can also delay maturity and cause some harvest issues with green stem.
The bean leaf beetle also is a regular visitor to Illinois and develops multiple generations in a year — three in the south, less further north. Bean leaf beetles are in the second generation at this point in the growing season.
The adults overwinter in the debris, they lay eggs and now the second generation feed on pods. They can cause some pretty severe damage early on, but usually it’s nothing that’s too economical because the soybean plant can take on a lot of defoliation during those vegetative stages.
However, when it gets to the point of the reproductive stages we want to keep all that we can get. Outside of them just feeding on the pods, they can also transfer a virus — the bean pod mottle virus — early on and that can reduce yields, as well as seed quality. It can cause discoloration, seed mottling on the seed, and leaf distortion.
On Insect Management
If the insect infestation can be caught early enough, the best case scenario is an insecticide application over the top. Catching it early enough is the key because once it’s too late a lot of damage can be done. An insecticide application also reduces the over-winter population.
On Foliar Diseases
Asian soybean rust and frogeye leaf spot as well as stem rot or any type of disease are going to reduce the surface area the plant has to photosynthesize and make sugars.
It’s going to reduce yield potential by reducing the amount of sunlight that the plant can grab because the lesions are taking over, the leaf tissue dies and they are ineffective.
On Fungicide
Big picture, the easiest thing to look at as far growth stage is R3 to R4 to spray fungicide. R3 is when the pods start producing on the four upper most nodes, so you know the lower nodes are going to have a pod on there. It’s a point where we have the most nodes we’re going to get per plant as well as protecting that plant as early possible with fungicide.
We don’t want to wait too long to apply a fungicide or insecticide because it would be less effective. Growers usually put an insecticide in with their fungicide and you want to get that out there as early possible.
On Weather
Weather goes hand-in-hand with insects and diseases. The big key is sunlight. One of the biggest things over the past couple years is growers planting soybeans earlier and earlier.
There have even been growers who have bought separate planters just to plant soybeans the same time they’re planting corn because we have found that we know the more sunlight the better.
So, the earliest you can get out there and get soybeans capturing sunlight the more photosynthesis, more sugars, the better of you’re going to be. It works two-fold because you’re going to potentially miss a lot of the large populations of the bean leaf beetle early on and we tend not to see as much pressure getting into those later growth stages if you’ve planted early.
Sunlight is key and that’s one thing that we can’t reiterate enough to get out there and get stuff in early to capture that sunlight.