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Avoiding Crop Injury When Using ‘Assert’

Monday, February 1, 2010
filed under: Weeds

Numerous producers have applied the postemergent herbicide Assert® to control infestations of wild mustard in their sunflower. And it works. Grower experience and university studies through the years have confirmed the effectiveness of Assert on mustard when applied at the proper stage of sunflower growth and under the right environmental conditions.

For growers using a Clearfield or ExpressSun variety, Beyond and Express will do a good job of controlling wild mustard. With non-herbicide-tolerant varieties, however, the only option other than Assert is Spartan — and Spartan only suppresses mustard (40-50% control, according to NDSU).

While Assert is an important component of the sunflower herbicide arsenal, use of this product also carries risk of serious crop injury — particularly if applied under high temperature and high humidity. Variety, growth stage, weather conditions, humidity, spray volume and additives all can influence the herbicide’s safety for sunflower. Damage can range from plant stunting to head deformation.

North Dakota State University advises applying Assert only when air temperature (Fahrenheit) plus relative humidity totals less than 150. NDSU also cautions against using Assert on sunflower that is under drought or heat stress.

Recent years’ research by Brian Jenks, weed scientist with the NDSU North Central Research Extension Center at Minot, has investigated several facets of sunflower crop injury and yield after treatment with this herbicide. In 2009 specifically, Jenks looked at Assert when applied with NIS, compared to a tank mix with a grass herbicide (Select®) and oil adjuvant (MSO); at the influence of an early application (four- to six-leaf stage) versus a late one (10-leaf stage); and at the effect of spray boom height above the sunflower canopy. Study results can be viewed at

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