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Pre-emergence herbicide use on wheat

8/24/2014

Pre-emergence herbicides with residual activity are used routinely in most crops, including corn, grain sorghum and soybeans. They have not, however, commonly been used in wheat.

Pre-emergence herbicides with residual activity are used routinely in most crops, including corn, grain sorghum and soybeans. They have not, however, commonly been used in wheat.

There are five ALS-inhibiting herbicides labeled for preplant or pre-emergence use in wheat: Amber, Finesse, Maverick, Olympus and Pre-Pare. The newest product in the pre-emergence wheat market is Zidua. Zidua has a different mode of action than the other pre-emergence herbicides in wheat and only should be applied as a delayed pre-emergence or early post-emergence treatment.

In wheat, pre-emergence herbicides often are used in no-till situations where they can be tankmixed with glyphosate during burndown applications just prior to or at planting. The addition of one of the pre-emergence herbicides at the time of the final burndown application can give residual control or suppression of susceptible broadleaf and grass weeds.

Pre-emergence treatments in wheat can be inconsistent in effectiveness. They require rainfall to be activated. If weeds emerge before the herbicide is activated, control might be poor, especially the grasses. But when there is enough rain to activate the herbicide before weeds emerge, control or suppression can be good. However, all else being equal, most of the herbicides labeled for pre-emergence applications will be most consistent when applied as fall post-emerge treatments. The one exception is Zidua, which has minimal activity on emerged weeds.

The labels of these herbicides differ somewhat in what is allowed with a pre-emergence application.

Finesse allows for a higher use rate when applied pre-emergence than when applied as a post-emergence treatment. This can provide for good season-long control of susceptible broadleaf weeds, unless they are ALS resistant. However, it does not allow for a follow-up post-emergence treatment later with Finesse, although a follow-up treatment with Olympus or PowerFlex is allowed.

With Amber, the top-end of the range of rates allowed is a little higher for pre-emergence applications than with post-emergence applications. As with Finesse, if Amber is used at the higher rates pre-emergence, producers cannot come back later in the season with another application of Amber, although a followup treatment with Olympus or PowerFlex is allowed.

With Olympus, the allowable rate as a pre-emergence application is 0.6 ounce/acre, which is lower than the rate allowed if Olympus is used as a post-emergence treatment. However, producers are allowed to follow up later with another 0.6 ounce/acre of Olympus if needed.

Maverick has a single standard rate for all application timings. Pre-Pare is marketed primarily in the northern plains and has not provided very good pre-emergence cheatgrass control in research at K-State.

Zidua has a different mode of action than the other pre-emergence wheat herbicides and might be especially helpful to manage ALS-resistant weeds. Zidua is very effective for control of Italian ryegrass, but also can provide suppression of winter annual brome species and some broadleaf weeds. Zidua should not be applied until 80 percent of the germinating wheat seedlings have a shoot at least half an inch long. It also can be applied early post-emergence to wheat, but primarily has pre-emergence activity and generally will not control emerged weeds.

Application rates of Zidua range from 0.7 to 2 ounces/acre depending on application timing and soil texture. Zidua should not be applied preplant to wheat and wheat should not be seeded more than 1.5 inches deep prior to a delayed pre-emergence application. Zidua can cause some temporary stunting of wheat if soils are excessively wet during the early seedling stages of wheat development.

Information provided by Dallas Peterson, KSU Extension Weed Management Specialist.

Stacy Campbell is agriculture Extension agent in Ellis County.