Issue No. 2, Article 4/April 1, 2005
Weed Control in Winter Wheat
The wheat crop across much of Illinois appears to have made it through the winter reasonably well. While some concerns about the crop still exist, weed control strategies may soon be considered by producers. The vast majority of herbicide options for wheat are for control of broadleaf species. Wild garlic, especially in the southern portion of Illinois, is an important nonbroadleaf species that can result in significant economic losses if left uncontrolled.
Proper herbicide application timing is critical to achieve good weed control. Additionally, all herbicides commonly used for weed control in Illinois wheat also have application restrictions based on wheat developmental stage. All of these herbicides have maximum crop growth stages for application, most indicating applications must be made before the jointing stage. Table 1 contains information about the herbicides labeled for use in small grains. Figure 1 shows a representation of wheat developmental stages. Before making any herbicide application, consult the respective herbicide label for additional information.
Representation of wheat developmental stages.
As mentioned, wild garlic is a particularly troublesome weed in wheat production. Wild garlic (Allium vineale) is a perennial species in the Lily (Liliaceae) family. Seedlings are grasslike, with hollow leaves that are circular in cross-section. The plant reproduces from seed (rarely), aerial bulblets, and underground bulblets. The aerial bulblets are produced in a cluster at the top of the stem, are surrounded by a papery membrane, and are very difficult to separate from the wheat seed. Because these bulblets can impart a "garlicky" odor and flavor to wheat during the processing stage, they are very undesirable. Significant dockage can result if wild garlic bulblets are present when the wheat is delivered to the elevator. Wild onion (Allium canadense) is a similar species in appearance, except that the leaves are flat and not hollow, it produces no underground bulblets, and the aerial bulb has a fibrous, net-veined outer coating, unlike the thin, membranous outer coating of wild garlic.
Harmony Extra (thifensulfuron + tribenuron) or Harmony GT (thifensulfuron) is often used to control wild garlic in wheat. These herbicides are very effective for controlling wild garlic and can provide control of several other weed species (Harmony Extra will control chickweed, but Harmony GT will not); however, they will not control wild onion. The labels of these products allow them to be applied with liquid fertilizer as the carrier instead of water but also warn that this may increase crop response. Wheat herbicide effectiveness ratings appear in Table 2.
--Aaron Hager and Dawn Nordby