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Big Corn and Big Weeds

Bill Johnson and Glenn Nice
Purdue Univesity Cooperative Extension Service
www.btny.purdue.edu/weedscience
Created 6/20/2010
Information listed here is based on research and outreach extension programming at Purdue University and elsewhere. The use of trade names is for clarity to readers of this site, does not imply endorsement of a particular brand nor does exclusion imply non-approval. Always consult the herbicide label for the most current and update precautions and restrictions. Copies, reproductions, or transcriptions of this document or its information must bear the statement ‘Produced and prepared by Purdue University Extension Weed Science’ unless approval is given by the author.

Other Publications Available

Is That A Giant Dandelion?
Pokeweed Control
Musk Thistle and Its Control
Weather Related Weed Management Items
Methods to Control Volunteer Roundup Ready or Glyphosate-Tolerant Corn in a Corn Replant Situation
Glyphosate and Foliar Fertilizer

We have been flooded with calls on how to control big weeds in big corn. The recent wet spell has kept sprayers out of the field and many farmers have reduced their reliance on preemergence residual herbicides in corn production in favor of reliance on glyphosate postemergence. This year is a perfect example of why we should not rely totally on postemergence weed management strategies in corn. We have likely given up thousands of bushels of yield potential across the state because we were not able to protect crop yields from weed competition.  Anyway, most of you know our stance on the value of residual herbicides and you probably expected this sermon.

What can you do? About a month ago we posted an article that showed the crop growth stage restrictions for postemergence herbicides in corn. Here is another chance to look at this table and see what your options are. Also, keep in mind the weed control efficacy table so you know what herbicides control specific weeds. Also, be realistic and if you have weeds over 1 foot tall, do not expect complete control. All you can really hope for is suppression and lessening the impact on final yield.

Figure 1. Maximum Crop Size for Postemergence Corn Herbicides [Taken from the 2010 Weed Control Guide for Ohio and Indiana WS-16].

Herbicide Maximum Crop Size

2,4-D Amine Broadcast up to 8-inch corn; directed spray before tassel stage.
2,4-D Ester Broadcast up to 8-inch corn; directed spray before tassel stage.
Accent Q, NIC-IT Broadcast up to 6 collars or 20-inch corn; directed spray up to 10 collars or 36-inch field corn.
Aim Apply up to 8-collar corn.
Atrazine Apply before corn is 12 inches tall.
Beacon Broadcast 4 to 20-inch corn; directed spray before tassel emergence.
Bromoxynil Apply before tassel emergence.
Bromoxynil + arazine Apply before corn is 12 inches tall.
Cadet Broadcast or directed from 2 collar stage up to 48 inches tall, and before tassel emergence.
Callisto Apply up to 30-inch or 8-leaf corn.
Capreno Apply broadcast from V1 to V6 corn; directed spray up to V7 corn.
Celebrity Plus Broadcast up to 6 collars or 24-inch corn.
dicamba Do not apply with COC when corn height exceeds 5 inches. Broadcast up to 5th-leaf stage or 8-inch corn; directed spray up to 36-inch corn.
dicamba + atrazine Do not apply with COC when corn height exceeds 5 inches. Apply broadcast up to 5-leaf stage or 8-inch corn.
Halex GT Broadcast up to 30-inch or 8-leaf corn.
Hornet Broadcast up to 20-inch corn or 6 collars; directed spray up to 36-inch corn.
Ignite Broadcast up to 5-collar corn.
Impact Apply broadcast or directed up to 45 days before harvest.
Laddok Apply before corn is 12 inches tall.
Laudis Broadcast up to V8 corn.
Laudis + atrazine Broadcast up to 12-inch corn
Lightning Broadcast up to V6 or 20-inch corn; directed spray up to 45 days before harvest.
Northstar SURF, COC or MSO up to 12-inch corn. Only SURF between 12 and 36-inch corn. Broadcast 4 to 20-inch corn; directed spray up to 36-inch corn.
Option Apply broadcast in the V1 to V6 stage; directed spray up to 36-inch corn.
Permit/Sandea Halomax Apply through layby stage of corn.
Resolve Broadcast up to 12-inch or 6 collar corn.
Resolve Q Broadcast up to 20-inch or 6 collar corn.
Shotgun Apply before 12-inch corn.
Spirit Broadcast 4 to 20-inch corn; directed spray up to 24-inch corn or after 6 collar corn.
Starane Broadcast up to the V5 stage; directed spray after the V5 stage.
Status Broadcast from 4 to 36-inch corn (rates up to 5 oz/A)
Steadfast Q Broadcast up to and including 6 collars or 20-inch corn.
Steadfast ATZ Broadcast up to and including 6 collars or 12-inch corn
Stinger Up to 24-inch corn.
WideMatch Broadcast up to the V5 stage; directed spray after the V5 stage.
Yukon Apply broadcast or directed up to 36-inch corn.

Table 2. Weed Response to Postemergence Herbicides in corn. [PDF]