Corn Field

Despite the variable weather patterns around the state, burcucumber can still be a problem in corn.

Extension agronomist Dwight Lingenfelter explains it is not until burcucumber gets above the crop canopy that it is often noticed.

In some parts of the state, it has been rather wet compared to other areas. Under these moist conditions, burcucumber can germinate and emerge late into the season.

Penn State research shows that ensiling green burcucumber seed is an effective technique for killing viable seed, but that ensiling does not affect mature seed.

Effect of an eight-week ensiling period on burcucumber seed revealed that if the burcucumber seeds were immature (green or cream-tan colored) only 2% remained viable, as compared to mature seeds (dark brown seed coats), which were 87% viable.

This suggests that early harvesting of a crop as silage may prevent viable seed production in burcucumber-infested fields. Silage harvest also prevents mature seed from re-entering the field through the combine.

If burcucumber cannot be removed with corn silage harvest (as previously suggested), harvest-aid herbicides are generally not effective on burcucumber and will not necessarily control the weed before grain harvest.

In most cases, if the corn is harvested for grain, the mature seeds will simply end up back in the field (or in the grain), making the problem worse for future years.

But, if necessary, Gramoxone/paraquat is probably the most effective preharvest herbicide in this situation. Other late-season corn herbicide options are listed below, but not all of them are effective on burcucumber.

Aim 2EC may be applied three days before harvest at 2 fluid ounces per acre. Use as a harvest aid to desiccate certain broadleaf weeds. Apply in 10 gallons of water per acre. Include necessary adjuvants, and make sure spray coverage is sufficient; otherwise poor control will result.

Another option is Basagran — use 1.5 to 2 pints per acre with appropriate adjuvants. No specific restrictions are provided on the label, but this is usually not effective on burcucumber.

Defol 5L can be applied to desiccate problem weeds in early maturing corn. Apply 4.8 quarts per acre, 14 days before harvest in 10 to 20 gallons of water per acre, and include appropriate adjuvants. Do not graze treated fields or feed fodder or forage until 14 days after application.

An additional option is Impact/Armezon — use 1 fluid ounce per acre with appropriate adjuvants. This can be applied up to 45 days prior to harvest.

Glyphosate can be applied up to 0.75 pounds of acid equivalent per acre (32 fluid ounces of a 3 pounds acid equivalent per gallon formulation) to corn a week or more prior to harvest. Include necessary adjuvants to improve performance. This must be applied to grain when moisture is 35% or less and after maximum kernel fill.

Also, Gramoxone 3SL can be applied at 0.8 to 1.3 pints per acre after black layer and at least seven days before harvest. The higher rate can be used to desiccate mature broadleaves and grasses over 18 inches tall. Be sure to include a nonionic surfactant.

And 2,4–D LV4 can be applied at 1 to 2 pints per acre after the hard dough or dent stage. Use higher rates on larger weeds and those under stress. Do not forage or feed corn fodder for seven days after application.

Keep in mind, in corn this type of application requires high-clearance equipment or aerial application, so hopefully these fields are the exception and not the norm.

Herbicide applications made during this late time frame are used primarily to help desiccate green weed tissue to improve the harvesting process.

Contact herbicides are usually better at this process; however, it can vary by weed species and usually will require at least a week or more to desiccate weeds.

Some of these herbicides are not that effective on large weeds or certain species. Harvest aids are not intended to (and usually do not) help speed up crop maturity. If applied too early they can interfere with the natural crop maturation process.

Illegal herbicide residues can result if specific application timing and other label guidelines are not followed. See specific product label to determine correct rate, timing, weed species controlled, and other restrictions with this type of application.

 

Leon Ressler is a Penn State Extension educator based in Lancaster County, Pennsylvania.

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