Mike Hunter, Jefferson County CCE
Available on the Web: http://www.ccenny.com/index.php/field-crops/crop-pest-management/corn/
Based on the large volume of phone calls and requests for field visits to look at weed control issues in corn fields, I felt it was most appropriate to send this crop update to local corn growers.- Mike Hunter, Cornell Cooperative Extension of Jefferson County
Many corn fields were sprayed with preemergence herbicide followed by 7 to 10 days without rain to activate them. Widespread field observations and reports indicate that the dry weather conditions in May have resulted in inadequate weed control in numerous corn fields throughout the region. After any herbicide application is made you should check those fields to make certain that you have controlled the weeds. If you have not checked your corn field since it has been sprayed, now is the time to do so.
In order for most preemergence herbicides to do their job they must be present in the soil solution where the weed seeds germinate. Most weed seeds will germinate in the top one inch of the soil. It requires about ½ inch of rainfall to sufficiently move the herbicide to the soil depth require for effective weed control. This is the main reason for so many failed preemergence herbicide treatments this season.
If you have emerged weeds in a corn field that received a preemergence herbicide application you can do one of two things.
- You can wait and see if the recent rainfall will provide any “reachback” activity. Reachback is a term used to describe the potential for a preemergence herbicide to kill small emerged weeds. It involves the herbicide being moved into soil solution and taken up by the roots of the weeds. This type of herbicide activity is highly inconsistent but does exist. If it does not look like you will be getting any reachback activity then you need to take action and apply a postemergence herbicide before it is too late. Once the broadleaf weeds and annual grasses get much bigger than a couple of inches tall, the chance for any reachback is gone. Not all preemergence herbicides will be able to provide control in this manner. If you have applied products such as atrazine, Lumax, Lexar, Bicep Lite II Magnum, Cinch ATZ Lite, G-Max Lite, Bullet, Verdict, Capreno, Dual, Outlook (or other acteadmides) there is a chance for this to occur. Do not expect any reachback from Prowl, Pendimax (or other dinitroaninlines).
- You can decide to take action now and make a postemergence herbicide application. Assuming that all of these situations are conventional corn, there are many good choices available to control most any emerged weed in a corn field. Proper weed identification is necessary when choosing the herbicide. If you are dealing with emerged grasses it is very important to know what grass species are present.
If you would like additional information or have any questions feel free to contact me anytime to discuss the situation (788-8450 or meh27@cornell.edu).
