Herbicide considerations when interseeding cover crops

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Phone (406) 278-3970 home, or (406) 470-0894 cell email - twistit73@yahoo.com. Leave message weeks before interseeding the cover crop (Table 2). Otherwise, only a burndown of glyphosate and/or dicamba could be used before planting soybean.

Cover crop of wheat and red clover was interseeded into VC or V2 soybean. Warm conditions allowed the wheat to emerge within three days. In both fields, no POST herbicide was used.

Neither grower chose this option, but for those desiring a residual herbicide, a Group 15 product (ex. Zidua®, Outlook®, Warrant®, Dual®) can be used once the cover crop is at least one inch tall as this herbicide mode of action has little to no postemergence activity.

Soybean Study with Wheat Planting Timing for Weed Control

A study was conducted at UNL’s South Central Ag Lab where wheat was planted on April 4 and then soybean was planted a month later on May 4. Prefix® (Dual II

Magnum® + Fomesafen) was applied at 2.5 pint/acre + Metribuzin 75DF at 6 oz/ acre after planting soybean when wheat was green and actively growing. No injury on wheat was observed (Figure 2).

The same study had wheat seeded at the same time of soybean planting on May 4. Sharpen® was applied PRE at 1 fl oz/ac after wheat and soybean planting on the same day. No injury on wheat or soybean was noticed and a combination of Sharpen® and wheat provided excellent control of waterhemp and Palmer amaranth (Figure 3). The photo was taken two weeks after applying Sharpen®.

Interseeding Late in the Season at Corn and Soybean Senescence

Because residual herbicides would have broken down other than for extremely dry conditions, we don’t have additional herbicide considerations for broadcast interseeding cover crops during corn and soybean senescence. The Guide for Weed, Disease and Insect Management also shares Replant Options and Rotation Restrictions for some cover crop species and is a resource in addition to the herbicide label.

Overwintering Cover Crop Survival and Herbicides

Some cover crop species are planted the previous year with the goal of them overwintering to the next spring. Reasons for this can include providing weed and/or soil erosion control, grazing and nitrogen. Some growers have desired for specific cover crop species to survive herbicide applications, while other growers have asked what specific herbicides will kill specific cover crop species.

For example, some growers who planted cereal rye and hairy vetch together wanted to know how to terminate the rye without terminating the vetch. The goal was to allow the vetch to gain more biomass and produce more nitrogen for the corn crop. The farmers we cooperated with found the cereal rye can be terminated using glyphosate at 22-24 fl oz/ac, which we’ve found doesn’t kill the hairy vetch. The hairy vetch can then be terminated with a POST- herbicide application containing an HPPD inhibitor (Group 27 herbicide such as Callisto®, Laudis®, Impact®/Armezon®).