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 No-See’m Weeds Minimize
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Posted by: WCM Staff 5/1/2008 4:25 PM
Despite the recent snow for some, cold weather, and wet fields, weeds are still germinating and emerging. However, pressure may mount to plant corn or soybeans without controlling these weeds first.

No-See’m Weeds

Chris Boerboom, Extension Weed Scientist

Despite the recent snow for some, cold weather, and wet fields, weeds are still germinating and emerging (Figure 1). However, pressure may mount to plant corn or soybeans without controlling these weeds first. Many of these weeds are quite small and may not even appear to be present when scouted from the road. (Ok, scouting from the road is not scouting.) However, they are there and they probably have a 2 week or greater head start on any crop to be planted. The concern is that these weeds will be larger, more competitive, and harder to control unless controlled at planting.  Seedbed tillage certainly solves the problem and resets the clock for these weeds, but if tillage is skipped (I’ve heard this termed as “impromptu no-till”), be prepared to adjust the weed management program to compensate. Here are some thoughts.
 
Our standard recommendation is still to apply a non-selective burndown herbicide such as glyphosate or Gramoxone before no-till planting. 2,4-D is a common addition to increase control of certain broadleaf weeds, which needs a 7 day delay before planting soybeans, or preemergence herbicides can be added for residual weed control.
 
If a preemergence herbicide program is planned, but tillage is skipped, be sure the herbicides have postemergence activity or add a herbicide that does. For instance, a herbicide like Harness Xtra has Harness and atrazine as components. The atrazine can burn off small broadleaf weeds, but the Harness component will not control emerged grasses and atrazine will only burn them off if they are very small (e.g. one or sometimes two leaves). This herbicide may benefit from the addition of a nonselective herbicide if the corn has not emerged or from a low cost, reduced rate of a selective grass herbicide if the corn has emerged.
 
If tillage and burndown treatments are both skipped and a postemergence program is planned, be prepared to apply your postemergence herbicide earlier than expected. The no-see’m weeds of today will rapidly reach 4- to 6-inches in height when they should be controlled.
 
Figure 1: Recently emerged common lambsquarters, common ragweed, and giant foxtail on April 28, 2008.
 
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