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Some winter annual weeds, like henbit, may not cause yield reductions even when present at high densities.

On the other hand, common chickweed, cheat and downy brome are some of the winter annual weeds that will cause yield reductions and the presence of these species almost always justifies treatment. 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. Another species that must also be controlled is wild garlic, not necessarily because it will cause wheat yield reductions, but because the aerial bulblets of this weed will contaminate the wheat grain at harvest and can cause significant dockage at the grain bin.

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 from the two-leaf up to the flag leaf stage of wheat.

Another herbicide that is commonly utilized for broadleaf weed control in wheat is 2, 4-D. This is one of our 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 growthregulating 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 that is 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 has historically been one of the few options that we had 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.

Several growers have contacted me recently regarding some of the newer wheat herbicides that have been registered over the past couple of years in Missouri. Some of these include Olympus, Olympus Flex and Osprey. All are products from Bayer CropScience and are ALS-inhibiting herbicides.

Other winter annual weeds, like downy brome or cheat, often cause significant wheat yield losses.

In order to resolve the issue of crop rotational flexibility, Bayer developed a new product called Olympus Flex, which contains the active ingredient in Olympus along with the active ingredient in Osprey. Olympus Flex can be applied from wheat emergence up to jointing and provides relatively good control of many of the Bromus spp., as well as Italian or annual ryegrass and several key winter annual broadleaf weeds like shepherd'spurse, field pennycress, and certain mustards. Soybeans may be planted five months after an Olympus Flex application while the rotational interval for corn following an Olympus Flex application is 12 months.

Osprey is another relatively new herbicide from Bayer CropScience that may be applied to wheat up to the jointing 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" and less than that provided by Olympus Flex. Soybeans may be planted three months after an Osprey application while the rotational interval for corn following an Osprey application is 12 months.

Kevin Bradley
573-882-4039