What to Watch Out For in Your Fields During July


Based on all of our reports from the field, corn and soybeans are growing fast across the Corn Belt. Growing degree days, or GDDs, are around 1,025 since May 1 (most corn requires 2,800 GDD to reach maturity), so corn is at V12 to V14 growth stage. Meanwhile, soybeans are at R1 to R2 growth stage. Both crops appear to be in good to excellent condition.

But now that we’re into July, there are a few things to keep an eye on for both crops, given the growth stage they’re in.

Insect Activity to Keep an Eye On

Corn insect activity has been light thus far, and there are reports of beneficial insects present in fair numbers across most fields. Beneficial insects, like Lady Beetles and Lacewing moth (along with their larval stage) can help to protect the crop and consume damaging pest larvae and eggs.

lady beetleLady Beetle 

There have been a few reports of True Armyworm and Garden Webworms stripping foliage from corn and reports of soybeans requiring an insecticide application. These pests are attracted to grassy areas of your fields where the adult moth will lay its eggs. When the eggs hatch, and the grass is no longer a viable food source, the worms migrate to adjacent corn or soybean plants. Now is the time to inspect any grassy crop areas and outside borders of fields for armyworm and webworm feeding. Armyworms have gotten their name honestly—they can migrate in horrific numbers and defoliate several acres a day when left unchecked. The larger they get, the larger the their appetite.

true armyworm soybeansTrue Armyworm

Western Corn Rootworm (WCR) beetles have begun to emerge and will continue for the next 4 to 6 weeks. Scout corn fields during the pollination period to ensure there are no silk clipping insect problems and be sure to target continuous corn fields—that’s where you will most likely see greater WCR beetle counts.

garden webworm soybeansGarden Webworm

In a few places across the Midwest, Western Bean Cutworm (WBC) moth flight is just beginning. You’ll want to scout corn fields for WBC eggs the week before tassel emergence to brown silk stage in corn. Eggs (in clusters of 1 to 50 eggs) are generally deposited on leaf surfaces of the five uppermost leaves of the corn plant. With WBC, a low economic threshold of 4 percent eggs is commonly used for control. Unlike common Earworm, which is cannibalistic and leaves one earworm per ear, WBC can have as many as 30 worms per ear. WBC can destroy the entire ear and provide an entry point for a number of secondary pests and diseases.

western bean cutwormWestern Bean Cutworm. Eggs hatching and larvae emerging from the eggs.

Rainfall and Hot Temps are Creating High Humidity Conditions

Many areas within the Corn Belt have received good amounts of rainfall to date and temperatures have remained high, creating an ecosystem of high humidity.

What favors growth in highly humid environments? Fungus.

As of today, disease pressure has still been fairly low, but this could change following several days of high humidity with temperatures between 65 degrees and 86 degrees. When corn and soybean leaves remain wet for more than two hours after sunrise and air temperatures elevate to 70 degrees or more, Mother Nature has created the perfect fungal growth conditions. These conditions enable spores from crop residues to germinate on plant leaves.

Gray Leaf Spot (GLS) is showing up in places on the lower leaves of corn plants. Nothing we’ve heard reported that requires immediate control, but you’ll want to scout your continuous corn on no till fields first. That is where you will find more inoculum in the surface residue and have a greater chance of GLS infection. If it’s not too late, applying a fungicide at early tassel (VT) may provide a good return on investment for corn this year. In fact, overall plant health could also be enhanced by a fungicide application.

Common Rust can also be found in corn fields this time of year, but it is generally not a problem that warrants control.Southern Rust, however, can have a big impact on your yield—these two disease are commonly confused. So far, we haven’t heard much of Southern Rust being reported this season.

common rust cornCommon Rust

Check out our June pest poll recap and read more about what and where FBN network farmers have reported are their biggest pest pressures from June.



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