Weed control options in late corn

The prolonged period of rain and high winds has prevented timely application of postemergence herbicides in many fields. By the time conditions allow field work, corn may be beyond the optimum size for postemergence applications. There are several concerns with delayed applications, including: 1) label restrictions regarding crop or weed size, 2) increased sensitivity of large corn to herbicides, and 3) reduced efficacy due to large weed size and/or canopy interference with spray coverage.

The following tables list the maximum corn size specified on herbicide labels. As corn increases in size, the crop canopy intercepts a significant portion of the herbicide spray. This may reduce performance due to inadequate coverage of weeds or enhance the potential for crop injury. Drop nozzles will reduce these risks by directing the spray to the weeds, therefore improving coverage and reducing corn exposure.

Table 1. Application restrictions for postemergence grass control in conventional corn.

Product Maximum Crop Size

For Broadcast Application1
Maximum Crop Size

For Post-Directed Application1
Maximum Foxtail Size
Accent V6, 20" V10, 36" 4"
Accent Gold V6, 12" V6, 12" 3"
Basis Gold V6, 12" V6, 12" 3"
Option V6, 16" V8, 36" 6"
Steadfast V6, 20" V6, 20" 4"

1Use most restrictive measurement.

Table 2. Application restrictions for postemergence broadleaf control in conventional corn.

Product Maximum Crop Size

for Broadcast Application1
Maximum Crop Size

for Directed Application1
All products with atrazine 12" 12"
Callisto 8-leaf, 30" 8-leaf, 30"
Aim V8 V8, higher rates allowed
Banvel/Clarity 36", 15 day before tasseling 36", 15 day before tasseling
Buctril Prior to tasseling Prior to tasseling
Distinct 24" 36", 15 days before tasseling
Hornet 20", V6 36"
NorthStar V6, 20" V6, 36"
Permit Layby Layby
Priority V8 V8
Yukon 36" 36"

1Use most restrictive measurement.

Table 3. Application restrictions for herbicide resistant corn hybrids.

Product (Hybrids) Maximum Crop Size

for Broadcast Application1
Maximum Crop Size for

Directed Application1
Liberty (Liberty Link) V7, 24" 36"
Lightning (Clearfield) V6, 20" >V6, > 20"
Roundup, glyphosate (Roundup Ready) V8, 30" V8, 30";48" w/RR 2 corn

1Use most restrictive measurement.

This article originally appeared on page 55 of the IC-492 (9) -- May 31, 2004 issue.

Updated 05/30/2004 - 1:00pm