If corn fields are infested with burcucumber, consider chopping it for silage. If not, herbicides used as grain harvest aids are generally not effective on burcucumber.
Despite the variable weather patterns around the state, burcucumber can still be a problem in corn. And it is not until it 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 8-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 seed (dark brown seed coats), that 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 reentering the field through the combine.
If burcucumber cannot be harvested with silage harvest-aid herbicides 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. This late in the corn season, herbicides used as harvest aids are generally not effective on burcucumber. But if necessary, Gramoxone/paraquat is probably the most effective pre-harvest herbicide in this situation. However, other late-season corn herbicide options are listed below.
- Aim 2EC — May be applied 3 days before harvest at 2 fl oz/acre. Use as a harvest aid to desiccate certain broadleaf weeds. Apply in 10 gal/A water. Include necessary adjuvants and make sure spray coverage is sufficient otherwise poor control will result.
- Defol 5L — Can be applied to desiccate problem weeds in early maturing corn. Apply 4.8 qt/acre, 14 days before harvest in 10-20 gallons/acre water and include appropriate adjuvants. Do not graze treated fields or feed fodder/forage until 14 days after application.
- Impact/Armezon — Can be applied up to 45 days prior to harvest.
- Glyphosate — Up to 0.75 lb ae/acre (32 fl oz of a 3 lb ae/gal formulation) to corn a week or more prior to harvest. Include necessary adjuvants to improve performance. Must be applied to grain when moisture is 35% or less and after maximum kernel fill.
- Gramoxone 2SL — Apply 1.2 to 2 pt/acre after black layer and at least 7 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. (Note: use appropriate rates if applying the new Gramoxone SL 3.0 formulation.)
- 2,4–D LV4 — Apply 1 to 2 pt/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 7 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 timeframe 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.