May 25, 2007

Chemical Weed Control

Although proso millet is an important dryland crop in the Nebraska Panhandle and northeast Colorado, nationally it garners little attention. In fact, only four herbicides are labeled for use in proso millet: 2,4 D amine, Aim™, Clarity™ and Peak™.

	Buffalobur in proso millet can limit marketing options. In some states it is considered a noxious weed and millet with buffalobur seed won't be accepted for processing.

Not all 2,4 D products are labeled for use in proso millet so be sure to check the label first. Most broadleaf weeds in proso millet can be economically controlled with 2,4-D. Apply 2,4-D amine (4L) at a rate of 1 pint per acre to proso millet in the 3- to 5-leaf stage. Crop injury may occur if 2,4-D is applied to plants outside the 3- to 5-leaf growth stage or to plants stressed by heat and drought. Injury will frequently result in poor root development and injured plants will often fall over and lay on the ground. Avoid 2,4-D herbicide application during hot, dry periods.

Clarity is the only dicamba product labeled for use in proso millet. Adding Clarity to 2,4-D amine will increase control of weeds such as kochia, especially triazine-resistant kochia, and wild buckwheat. Clarity also may provide a week or two of residual weed control for some later emerging weeds. Add Clarity at a rate of 4 ounces per acre to 3/4 pint of 2,4-D amine (4L) per acre. Like 2,4-D, Clarity may injure proso millet if it is applied outside the 3- to 5-leaf growth stage or during periods of high temperatures or drought. The risk of crop injury is slightly greater with Clarity than with 2,4-D alone. Clarity should not be used when susceptible crops are within one-half mile of the application site.

Peak provides some residual control of later emerging broadleaf weeds, but cropping flexibility is somewhat limited, for example, sunflower and garbanzo bean cannot be planted for 22 months after a Peak application. Apply Peak at a rate of 0.38 to 0.5 ounces per acre with 3/4 pint of 2,4-D amine (4L) per acre. Add a nonionic surfactant at a rate of 1 quart/100 gallons of spray solution.

Recent research with Aim herbicide suggests that it can significantly improve the control of buffalobur when added as a tank mix partner to 2,4-D or 2,4-D + Clarity. Control of buffalobur was just 20% and 30% with 2,4-D amine or 2,4-D amine + Clarity, respectively. By adding 1/2 ounce of Aim to these two treatments, buffalobur control increased to 93% and 85%, respectively. Peak + 2,4-D amine provided 80% control of buffalobur in this same study.

Buffalobur, with its yellow flowers and spiny stems and leaves, is a common weed throughout western Nebraska. While not a particularly troublesome weed in Nebraska, it is a noxious weed in several western states including Washington, Idaho and Utah. Because of this designation, any product containing buffalobur seed cannot be imported into these states. As a result, bird seed packagers will not buy proso millet seed if it contains buffalobur seed.

Adding Aim to other labeled herbicides also improved control of broadleaf weeds such as kochia and Russian thistle when weeds were drought stressed. Control of these weeds was not improved by adding Aim herbicide in 2004, when weeds were not exhibiting symptoms of drought stress.

Aim herbicide should be applied at a rate of 1/2 ounce per acre. Add a nonionic surfactant at a rate of 1 quart per 100 gallons of spray solution. Plant coverage is essential for good control because Aim is not a translocated herbicide. Aim should be tank-mixed with other herbicides labeled for use in proso millet to broaden the range of weeds controlled.

In addition to proso millet, Aim recently was labeled for use in forage millets, including foxtail and pearl millets. In foxtail millet, Aim provides postemergence broadleaf weed control with little risk for serious crop injury. Crop injury has been a concern with 2,4-D, which is currently the only other herbicide labeled for use in foxtail millet. Not all 2,4-D products are labeled for use in foxtail millet. Be sure to check labels before use

Cultural Weed Control

Because a herbicide is not available that will selectively control grass weeds in proso millet, crop rotation is an important aspect of production. Avoid placing proso millet in rotations with other warm season grass crops such as corn or sorghum, unless grass weeds are successfully controlled in these crops.

Proso millet works best when placed in a rotation with cool season grass and broadleaf crops, for example winter wheat and/or sunflower. Foxtail species have become a problem after several cycles of a winter wheat-proso millet rotation because there was insufficient time between proso crops to allow for the depletion of the foxtail seed bank. There should be at least two years between proso millet crops.

Drew J. Lyon
Extension Dryland Cropping Systems Specialist
Panhandle REC, Scottsbluff