Ensilaging Controls Burcucumber Seed

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; see image below) 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.

 
Immature burcucumber seed that would be destroyed by ensiling. (Penn State Weed Science, D. Lingenfelter)

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 pre-harvest herbicide in this situation. However, other late-season corn herbicide options are listed below, but not all of them are effective on burcucumber.

• 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.
• Basagran — Use 1.5 to 2 pints/acre with appropriate adjuvants. No specific restrictions are provided on the label. Usually not effective on burcucumber.
• 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 — Use 1 fl oz/acre with appropriate adjuvants. 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 3SL — Apply 0.8 to 1.3 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.
• 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.