A big mistake that I see growers make in an attempt to be effective in controlling weeds in corn is waiting too long before they take action. Most of the time, it is with good intentions. Too many growers wait in hopes of getting most or all of the weeds to emerge before applying a post-emergence herbicide(s) as they feel it will be effective and efficient.
There are a couple of errors in this thinking. As weeds and the crop grow in size, both will shade and prevent good herbicide contact on smaller weeds simply by interception. The older weeds are more difficult to kill and the crop may reach a growth stage where crop injury may be possible.
Additionally, recent UGA research showed that a delay in application from the V4 stage until the V6 stage of growth resulted in 40% less spray coverage. Thus, delaying POST applications is less efficient and less effective in so many ways.
The ideal weed control program (assuming you will have weeds) is that program which controls all or nearly all your weeds in the most cost-efficient manner. Who doesn’t want it, right? Unfortunately, Nature has a way of throwing lots of challenges in the mix.
Weed biology, soil types, weather, operators, equipment, hybrids, economics and probably some things I can’t think of right now all challenge the effectiveness and efficiency of any weed control program. I strongly encourage paying close attention to the details of everything I listed as one can modify or change the effect of the other.
Try using both residual herbicides and post-emergence control methods. Focus on timing as to achieve the most effective window for post emerge spraying of weeds and the safest corn growth stage. Personally, I like the V3 to V4 stage or ~300 to 400 GDD’s after seedling emergence.
If you don’t know when your corn seedlings first emerged then add 80 to 90 GDDs to the above to get an estimation of total number of GDD’s from planting to hit the window. Choose a proven program from the table below particularly if you are unfamiliar with the weed history of the field. If you have been working the field for years and know the weed species, then certainly shop price & effectiveness of any combination.
The information below was previously published by Dr. Prostko:
- Start clean using a combination of tillage, cover crops, and/or herbicides.
- Use narrow rows (≤ 30”) or twin rows when practical.
- Use at least 2 residual herbicides in the system.
- Make timely post-emergence applications (tallest weeds ≤3” tall, not the average).
- Hand-remove weed escapes before seed is produced.
The table below is our best general recommendation for efficient and effective weed control in field corn.
|Corn Hybrid/System||Pre-emergence||Earl Post-Emergence1
(~17-30 DAP, V3-V5 stage, ~279-411 GDD’s2)
|Conventional||Atrazine3 or Dual II Magnum or Warrant or Outlook||1) Prowl+ Atrazine + Crop Oil or
2) Atrazine + one of the following: (Callisto, Capreno, Armezon /Impact/ImpactZ, Laudis, Revulin Q or Steadfast Q)
|Liberty-Link||Atrazine3 or Dual II Magnum or Warrant or Outlook||Liberty + Atrazine + one of the following: Prowl or Dual Magnum or Warrant or Zidua or Anthem Maxx or Outlook or Acuron (48 oz/A)||Evik|
|Roundup-Ready||Atrazine3 or Dual ll Magnum or Warrant or Outlook||1) Glyphosate + Atrazine + (Prowl or Dual Magnum or Warrant or Zidua or Anthem Maxx or Outlook) or
2) Glyphosate + Atrazine + (Callisto or Capreno or Armezon/Impact/Impact Z, Laudis, Revulin Q or Steadfast Q) or
3) Glyphosate + Atrazine + (2,4-D or dicamba) or
4) Halex GT + Atrazine or
5) Glyphosate + Acuron (48 oz/A)
1When using Counter (INFR) for insect and nematode control, the following herbicides should NOT be applied POST: Acuron, Callisto, Capreno, Halex GT, Revulin Q and Steadfast Q.
2GDD’s = growing degree days (500/860 F)
3A maximum of 2.0 to 2.5 lbs a/A of atrazine can be applied in a single year depending upon application methods.
Examples of herbicide control in corn, UGA weed trials.