Scout early: Cut wheat weeds down to size

COLUMBUS – With a good-looking winter wheat crop greening up, farmers might need a solid weed control program in place to ensure top yields.

“As a rule, wheat is very competitive with weeds, and some wheat fields don’t require herbicide treatment,” said Mark Loux, Ohio State University weed specialist. “But failure to scout fields and take the appropriate action can result in yield losses and harvesting problems.”

Weeds requiring immediate control are winter annuals such as chickweed, purple deadnettle, field pennycress, shepherdspurse and marestail (horseweed). Farmers can easily control them when small and in the rosette stage before the stem has bolted.

For most mustard species and marestail, 2,4-D is adequate. Mix 2,4-D with dicamba to broaden the spectrum of control.

For deadnettle and chickweed, Harmony Extra will be more effective than 2,4-D.

Many spring-applied wheat herbicides can suppress Canada thistle enough to prevent harvest problems. The effectiveness depends on the size of the weeds at application. Canada thistle is more likely to regrow if the application is made when thistle is very small.

Products that can work very well on Canada thistle are Stinger, Curtail and Express.

On wild garlic, highly effective products are Harmony Extra, Harmony GT and Peak.

Any herbicide labeled for wheat can be safely applied before jointing. After jointing, herbicide choices become limited as products can injure the crop and reduce yields.

Know wheat stages.

Don’t stage wheat based on the plant height, Loux said. Sometimes adverse weather can stall wheat growth and the crop may be at a later developmental stage when certain herbicides cannot be applied.

“Be sure to accurately stage the wheat based on physiological development rather than relying on height, to avoid injury and yield loss from herbicides,” Loux said.

Top-dressing herbicides in a nitrogen fertilizer solution can be convenient, but also can increase injury, Loux said. Some labels recommend adjusting surfactant rates to minimize injury.

If nitrogen is split-applied, herbicide injury can be reduced if product is mixed in the nitrogen solution with water.

Always follow product labels for application timing and other safety procedures, Loux said.

Product limitations. Following are key herbicide limitations:

* 2,4-D – All products are labeled for application before jointing. A few can be applied as late as early boot, although injury risk increases after jointing.

To minimize risk of injury after jointing, use water as the carrier and do not apply more than a half pint of ester or 1 pint of amine.

2-4,D will not control chickweed or henbit and can be weak on smartweed and deadnettle. Two-methyl-4-chlorophenoxyacetic acid (MCPA) products have characteristics and labeling similar to 2,4-D products.

* Banvel – Apply before jointing. It’s not as effective as 2-4,D on mustard species but is more effective on smartweed and weak on chickweed, deadnettle, henbit and wild garlic. It can be tankmixed with 2,4-D.

* Buctril/Moxy – Apply before the boot stage. Applying in fertilizer solution increases leaf burn. Product is weak on most winter annuals, dandelion and wild garlic but is effective on ragweed.

For best results, apply before weeds reach the four-leaf stage or 2 inches tall.

* Curtail – This premix product of 2,4-D and Stinger can be applied before jointing, providing excellent control of ragweed and Canada thistle but weak on chickweed, henbit and wild garlic.

Do not plant double crop soybeans in fields treated with Curtail.

* Harmony Extra – Apply before flag leaf is visible and when weeds are less than 4 inches tall, or the rosette is less than 4 inches wide. Apply with a nonionic surfactant. Product is effective for wild garlic and most winter annuals but weak on ragweed.

* Harmony GT – Effectiveness is similar to Harmony Extra but less effective on Canada thistle, chickweed and a few other winter annuals.

* Express – Apply before flag leaf is visible when weeds are less than 4 inches tall or the rosette is less than 4 inches wide. Product is not as broad spectrum as Harmony Extra but is more effective on Canada thistle. Apply with a nonionic surfactant.

* Peak – Apply before the second node is detectable in wheat stem elongation and when weeds are 1-3 inches tall. Do not plant double crop soybeans in fields treated with Peak. Apply with crop oil concentrate or nonionic surfactant.

* Stinger – This high-cost option effective for Canada thistle and ragweed is best suited for spot treatment before early boot.