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Weed Control in Small Grains

April 6, 2001
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 weed control in 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 the wheat's developmental stages. All of these herbicides have maximum crop-growth stages for application, most indicating applications must be made before the jointing stage. Table 7 contains information about the herbicides labeled for use in small grains. Before making any herbicide application, consult the respective herbicide label for additional information.

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 grass-like 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. These bulblets can impart a "garlicy" odor/flavor to wheat during the processing stage and are thus 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, 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 in controlling wild garlic and can provide control of several other weed species (Harmony Extra will control chickweed, but Harmony GT will not), but Harmony Extra will not control wild onion. The label allows Harmony Extra to be applied with liquid fertilizer as the carrier instead of water, but this may increase crop response. Wheat herbicide effectiveness ratings appear in Table 8.

While Peak (prosulfuron) is labeled for use in small grains and is effective on wild garlic, rotational restrictions have greatly limited its usefulness in Illinois. The rotational interval following a Peak application before soybeans are planted ranges from 22 months (north of Interstate 80) to 10 months (south of Interstate 80).--Aaron Hager and Christy Sprague

Author: Aaron Hager Christy Sprague

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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