Wet weather’s effect on weeds and herbicides

Wet weather’s effect on weeds and herbicides

This season’s exceptional weather is putting many of the systems we use in crop production to the test. A major one being herbicides and weed control. Here are some quick answers to the most common weed and herbicide questions. Contact your local Jacobsen Seed Representative for more information.  Remember to always read and follow herbicide label directions for the best results

The sprayer wasn’t able to keep up with the planter and now I have weeds and crops emerging without a preemerge herbicide, what now?

Many preemergence herbicides are safe to use once corn has emerged but remember to check the label for possible crop height restrictions. For soybeans, options are must more limited once the crop has emerged. Generally a change in herbicide is required. In both crops it is important to make sure you are getting both a residual product and a product that kills the emerged weeds. The addition of glyphosate (RoundUp) or glusfosinate (Liberty) can usually accomplish this task for a reasonable cost in traited crops.

My crop has emerged and looks like it has been damaged by a herbicide, what’s going on?

The cold and wet conditions make it much harder for the young plants to process and metabolize the preemergence chemistries. In corn, a look of bleaching/whitening of the leaves can be caused by products in the HPPD-inhibiting (Group 27) family. ‘Buggy-whipping’ may be caused by Chloroacetamide herbicides (Group 15). In soybeans, ‘burnt’ or brown lesions on the stems and cotyledons can be caused by PPO-inhibiting (Group 14) herbicides. For both crops, a few plants may be killed but fields generally grow out of it without any effects on yield.

I put my preemergence herbicide on 4-6 weeks ago will this be a problem?

Not necessarily but it is a situation that needs to be managed. Growers who were able to apply herbicides at the end of April or beginning of May will be hitting the natural end of their pre-emergence herbicide control window. They can generally choose three different paths to help control weeds in a young crop. If the crop hasn’t been planted yet, an additional tillage pass just before planting could help disrupt emerging weeds. When the crop has been planted, an additional pass of a residual herbicide (aka make it a 3-pass herbicide system) will hold back weeds. This will let crops get large enough for a normal post-emergence pass or the post-emergence herbicide pass. The pass may need to be made early and rates and products adjusted for the delayed canopy cover. For best control, start scouting early sprayed fields as soon as possible so weeds do not get larger than herbicide labels cover.

I have a field that I will be taking the prevented planting payment on, why do I need to worry about weeds?

Fields that will not be planted this year should still have the weeds controlled in order to keep what we call ‘the weed seed bank’ low. Uncontrolled weeds this season can produce millions of seeds that growers will then fight for many years in the future. The easiest and cheapest way to control weeds in the future is to control them in the present. Tillage, cover crops, or herbicide applications can all help keep fields clean and weed seed production low.