Spring Options for Weed Control in Wheat By Kevin Bradley

Henbit, cheat, downy brome, shepherd’s-purse, field pennycress, mustards, and wild garlic are some of the most common weeds encountered in wheat production in Missouri. From this list, common chickweed, cheat, and downy brome are some of the weeds that are more likely to cause yield reductions at relatively common densities. Research indicates that common chickweed can cause significant yield losses at densities of at least 30 plants per square meter while 80 cheat plants per square meter have resulted in yield losses as high as 50 percent. Henbit is one of our most common weeds of wheat, but it does not seem to compete as effectively with wheat as some of the other winter annual species. For example, research conducted in Missouri has revealed that it takes as many as 82 henbit plants per square meter to cause a 13 percent yield reduction in wheat.

Field pennycress Photo by Kevin Bradley

One of the most common (and effective) herbicides utilized for weed control in wheat is Harmony® Extra. Harmony® Extra controls most of the broadleaf weeds that we encounter in wheat, including henbit, field pennycress, shepherd’s-purse, common chickweed and several mustard species. Additionally, Harmony® Extra will provide suppression of wild garlic to the point that the aerial bulblets of this weed will not be produced. Perhaps the most significant weakness of Harmony® Extra is that it does not have any grass activity and therefore does not control cheat and downy brome, two of our most troublesome winter annual grasses. Harmony® Extra can be applied up to the flag leaf stage of wheat so there is still time to make applications of this herbicide in Missouri.

Another herbicide commonly utilized for broadleaf weed control in wheat is 2, 4-D. This is one of the cheapest options for broadleaf weed control in wheat, but like Harmony® Extra, this herbicide has no activity on grasses. It is very important for applications of 2, 4-D and all other growth-regulating herbicides (Banvel, Clarity®, MCPA) to be made after tillering but before the jointing stage of wheat or severe crop injury can occur.

Jointing is a wheat stage that precedes stem elongation and can be determined by feeling the plant for the presence of a ‘joint’ just above the soil surface. You can do this by pinching the existing wheat stem and sliding your fingers upwards from the base of the plant. If a hard bump is felt about an inch or so above the soil surface, slicing into this area will more than likely reveal the presence of a joint, or node, and 2, 4-D applications at this time should be avoided. Research conducted in Missouri has revealed that yield losses as high as 6 bushels per acre can occur if 2, 4-D applications are made to wheat in the jointing stage of growth. Both amine and ester formulations of 2, 4-D are available, but the ester formulation of 2, 4-D is usually more effective at breaking through the cuticle of tough weeds like wild garlic.

In addition to Harmony® Extra and the growth-regulator herbicides, Sencor® is another option that is perhaps less-often utilized for weed control in wheat, most likely due to the sensitivity of many wheat varieties to this herbicide. Sencor® is one of the few options that we currently have for downy brome and cheat control in Missouri. Sencor® may be applied during tillering but before jointing occurs. In addition to cheat and downy brome, Sencor® also provides good control of many of our common winter annual broadleaf weeds like common chickweed, field pennycress and henbit. Prior to making a Sencor® application, you should always check the label and/or contact your Bayer representative regarding the sensitivity of your wheat variety to this herbicide.

Cheat in wheat Photo by Kevin Bradley

Several growers have contacted me recently regarding two of the new herbicides that we have available for use this year in Missouri: Olympus™ and Osprey™. Both are products from Bayer CropScience® and are ALS-inhibiting herbicides. Olympus™ can be applied up to the jointing stage in wheat, and is particularly effective on all kinds of Bromus species like cheat and downy brome. Olympus™ is also registered for the control of some winter annual broadleaf weeds like shepherd’s-purse, field pennycress and certain mustards. Although Olympus™ will provide good control of downy brome and cheat, the crop rotational restrictions may limit the use of this product for growers who wish to double-crop soybeans following wheat or even for growers who wish to rotate to corn next season. For example, corn may not be planted for 18 months after an Olympus™ application while conventional or Roundup Ready® soybeans may not be planted for 12 months after Olympus™ applications. STS soybeans, however, may be planted four months after an Olympus™ application, which allows wheat growers to make a fall application and plant double-crop STS soybeans after wheat harvest. Bayer is working to resolve the issue of crop rotational flexibility by developing a new product called Olympus™ Flex, which may be available to growers next season.

Osprey™ is another new herbicide from Bayer CropScience® that may be applied to wheat up to the 2-tiller stage of growth. Osprey™ provides excellent control of Italian or annual ryegrass, which appears to be a problem for some producers in the southern portion of Missouri, but is not yet a state-wide problem in wheat as it is in many other portions of the U.S. As Osprey™ is an ALS-inhibiting herbicide, it is particularly effective in controlling Hoelon-resistant Italian ryegrass populations that have developed in these other areas. Osprey™ also provides some suppression of downy brome and cheat, but generally less control of these species than what is considered “commercially acceptable.” Soybeans may be planted three months after an Osprey™ application while the rotational interval for corn following an Osprey application is 12 months.

Field pennycress Photo by Kevin Bradley

Kevin Bradley Agronomy 573-882-4039