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Deal with foxtail escapes in corn

Tom J. Bechman Thistle and foxtail in cornfield
MONITOR WEED ESCAPES: Note thistles under the canopy, with young foxtail emerging in the background. Catch escapes earlier, when you can still address them effectively.
Corn Pest Beat: Will foxtail escapes hurt yield enough to warrant spraying?

We switched corn herbicides, and grass control is iffy, with foxtail emerging. How much can we live with? What could we spray?

The panel of Indiana certified crop advisers answering this question includes Betsy Bower, agronomist for Ceres Solutions, Lafayette; Greg Kneubuhler, G&K Concepts Inc., Harlan; Bryan Overstreet, Purdue Extension educator, Jasper County; and Dan Quinn, Purdue Extension corn specialist.

Bower: If corn is at V3 to V4, I recommend controlling grass, even if pressure is low. Remember, grass weeds that emerge as corn emerges will compete all season for water, nutrition and space. Research indicates grass weeds controlled before V4 to V5 result in no yield loss. Grass weeds that emerge later, after V6 to V8, will compete less, but still reduce yield and set seeds.

If corn is resistant to glyphosate (Roundup) or glufosinate (Liberty), use the corresponding herbicide to control grass. For non-GMO hybrids, look to Accent broad-spectrum grass control. Laudis and Resolve can provide fair to good control of most grass species. Identify the grasses so you can use the right product.

Kneubuhler: Sometimes you get what you pay for when making herbicide decisions. Be cautious running programs that are weak on grasses. Grass pressure is extremely damaging to yields. You can do everything right and give up weed control, and totally negate everything you just did right. A little grass early equals a lot of grass late. It’s a judgment call as to how much you can “live with,” but most generally, we don’t like to see any grasses early. Typically, glyphosate is very effective on grasses. If you don’t have Roundup Ready corn, make an alternative choice.

Overstreet: What looks like a small amount of grass now can become a big problem at harvest with reduced yields and harvest challenges. Roundup or Liberty controls the grass fairly easily if your hybrids are tolerant. Otherwise, Accent Q, Steadfast Q or products including Laudis do a nice job on grass control. With all postemergence products, look at height or growth stage limits. If you spray too late, you may do more damage than good on controlling grass.

Marcelo Zeller, Purdue Botanyfoxtail weed running rampant in crop field

FOXTAIL GALORE: Modern herbicides usually take care of foxtail when everything works right. If it doesn’t, foxtail, which includes multiple species, can run rampant.

Quinn: The magnitude of corn yield loss to foxtail can be specific to weed emergence timing relative to crop emergence, soil moisture level, soil fertility level, hybrid competitiveness and presence of other stressors. Weed population thresholds for foxtail species that can result in lost corn yield can range from 3 to 10 plants per square meter. Indiana has three species of foxtail: green, yellow and giant. In addition, a subspecies known as green robust foxtail is similar to green foxtail, but much more competitive. Therefore, identify which specific foxtail is present to determine whether or not corn yield potential will be lost.

Currently, there are many different herbicides, applied either preemergence or postemergence, that provide good control of foxtail in corn. Use the efficacy tables in the 2022 Weed Control Guide for Ohio, Indiana and Illinois to determine which potential herbicides may provide the best postemergence foxtail control specific to your environment, management practices and chemical availability at local suppliers. 

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