Weed Control in Small Grains

April 2, 1999
The wheat crop across much of Illinois appears to have weathered 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 non–broadleaf 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 that applications must be made before the jointing stage. Table 3 contains information about the herbicides labeled for use in small grains. Before making any herbicide application, consult the respective herbicide label for additional information.

Table 3. Herbicides for use in small grains.


Herbicide

Crop

Maximum growth stage

Rate per acre

Legume
underseeding

2,4-D amine

wheat, oats

before joint

0.5 to 1.5 pints

yes

Buctril

wheat, oats

boot

1 to 1.5 pints

yes

MCPA amine

wheat, oats

before joint

0.5 to 2 pints

yes–0.5 pint

no–over 0.5 pint

Banvel, Clarity

wheat, oats

wheat–before joint

oats–5 leaf

2 to 4 fluid ounces

no

Harmony Extra

wheat, oats

before flag leaf is visible

wheat–0.3 to 0.6 ounce

oats–0.3 to 0.4 ounce

no

Peak

wheat, oats

before second node is detectable

0.38 to 0.5 ounce

no

Stinger

wheat, oats

early boot

0.25 to 0.33 pint

no

2,4-D ester

wheat

before joint

0.5 to 1 pint

no



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, 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) is often used to control wild garlic in wheat. This herbicide is very effective in controlling wild garlic and can provide control of several other weed species, 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.

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 is 10 months.--AH, MM

Author: Aaron Hager Marshall McGlamery