Weed Management Considerations for Fall Small Grains

Burndown: For no-till establishment of winter cereals, glyphosate or Gramoxone can be used to control emerged vegetation. If you want to add 2,4-D, the guidelines are less clear. None of the 2,4-D labels specify application just prior to wheat seeding or wheat emergence. The most relevant guidelines on most 2,4-D product labels pertain to use on “fallow ground” or between crops. The general guidelines state that only labeled crops may be planted within 29 days after application and that risk of crop injury or loss is greatest during the first 14 days. The more soluble amine formulation certainly increases the risk for injury. In corn and soybeans, the recommendation for 2,4-D ester is to delay a minimum of 7 days after application at rates up to 1 pint per acre. I believe this is a reasonable precaution to take for barley and wheat as well. However, because the use of 2,4-D burndown in wheat is ambiguous at best and if injury occurs, liability rests with the consultant or applicator. One exception and there may be others is Rage D-Tech, a mixture of carfentrazone (Aim) and 2,4-D ester. Rage-D-Tech is labeled at 8 fl oz per acre with a 3-day planting interval or up to 16 fl oz per acre with a 7-day planting interval in front of small grains. This provides one-half to one pint equivalent per acre 2,4-D ester. 

The Banvel and Clarity labels state that application may be made before, during, or after planting of small grains. The Banvel label states that it may be applied at 2 fl oz per acre preplant with no waiting period for wheat (not barley). In contrast, the Clarity label states that it may be applied up to 4 fl oz per acre preplant with no waiting period to wheat (there is no biological reason for the discrepancy between these two labels). For higher rates and East of the Mississippi, the interval is 20 days per pint per acre for Banvel or 1.25 days per ounce or 15 days for 8 fl oz per acre for Clarity. Bottom line: review a current herbicide label for all use restrictions and guidelines before making an application.

ALS-resistant chickweed: Continue to be on the lookout for this new resistant weed biotype. Control options for resistant chickweed for small grains include Starane Ultra and maybe suppression with 2,4-D plus Banvel. Prowl H2O preemergence to the weed can provide residual control. Starane Ultra is a plant growth regular herbicide marketed by Dow AgroSciences labeled for wheat, barley, and oats. Starane Ultra is applied at 0.3 to 0.4 pints per acre from the 2-leaf crop growth stage up to flag leaf emergence. Starane Ultra will also suppress horseweed/marestail, and several mustard species, but is not the product of choice for other common winter annuals such as henbit, red deadnettle, etc., so tank mixtures may be necessary.

You will likely need to tank-mix with Harmony Extra or another broad spectrum herbicide. Also, Starane Ultra currently has a 120 day recrop restriction to soybeans, so that may also be a consideration. Prowl H2O will suppress common chickweed and should be applied as a postemergence treatment from the 1st leaf stage of wheat until before the flag leaf is visible. Emerged weeds are not controlled by this treatment, but it will provide residual control.

Last fall and spring, we conducted a trial in barley at a farm in Lancaster County. We included some treatments applied at the spike stage on October 29, on November 18, and in late winter on March 19, 2012. Some of the treatments are not labeled for barley, but that’s what we had to work with. Sharpen is labeled for use in small grains preemergence. Metribuzin is labeled in wheat, but not in the Northeast. Axiom, marketed by Bayer is labeled for wheat after the crop has fully germinated; it is a mixture of metribuzin plus flufenacet (Define). Pulsar is a premixed product from Syngenta that contains the active ingredient in Starane (fluroxypyr) plus dicamba (Clarity). The 12.5 fl oz per acre rate provides the equivalent of 0.26 pt Starane Ultra. As you can see from Table 1, Metribuzin, Axiom, Starane Ultra, and Pulsar provided 92% or better control of common chickweed. Control with Harmony Extra ranged from 23 to 77% depending on application timing confirming that we are dealing with an ALS-resistant population. Scout your fields this fall and plan accordingly.

Winter annual grasses: Finally several weedy grasses have become more problematic in the Northeast in small grains. Annual or Italian ryegrass (Lolium multiflorum) is more common to the south in Maryland and Virginia, but can also be found in some fields in Pennsylvania. ACCase or Hoelon resistant ryegrass is a problem in some fields. The annual brome species have also become problematic in our fall seeded small grains. Downy brome (Bromus tectorum) is generally considered the most common of these different winter annual grassy weeds, and although herbicide susceptibility can differ, the biology, ecology and control are similar for the different Bromus species. Most of the cultural control tactics aimed at reducing the problem of downy brome are aimed at things like delayed planting of wheat and controlling with tillage or preplant herbicide and managing to prevent seed production the previous year, etc.

As for herbicides, winter annual grasses, such as downy brome, cheat, annual bluegrass, and annual ryegrass, should be controlled as soon as an inch of new growth has occurred. The wheat herbicides available for control of grasses, Axial, Osprey, PowerFlex, Maverick, Finesse, and Hoelon, are most effective when applied in the fall, and effective spring activity is dependent upon the weeds being small. Be sure to include the necessary adjuvants in the spray mixture and follow label guidelines to minimize risk of crop injury and yield loss. Labels for some products specify the number of tillers or leaves that wheat or barley should have before treatment is allowed. Also, be cautious of crop rotation intervals, certain herbicides such as Maverick have long recrop intervals for typical cropping systems in the northeast.