NDSU Crop and Pest Report
Weeds


ISSUE 8   June 24, 2004

ND GRANTS AERIAL HERBICIDE FOR CORN

ND has issued a Special Local Needs (SLN) registration to Syngenta Crop Protection to allow aerial application of Callisto herbicide on corn because of abnormally high rainfall this spring making use of ground application equipment difficult. Callisto is less prone to injure broadleaf crops and shelterbelts than auxinic herbicides for post-emergence, broadleaf weed control. Callisto effectively controls broadleaf weeds like kochia, lambsquarters, wild mustard, and ragweed species and also is a non-ALS herbicide to reduce risk of developing weed resistance. The EPA-approved labeling for Callisto currently allows only ground application. The SLN registration allows aerial application at the same timing and rate as ground application. Applicators must follow directions, restrictions, worker protection standard requirements and precautions on the EPA-registered label and all use directions on the SLN label. They must also have the SLN label in their possession during application. The SLN registration expires on July 30, 2004. Corn is an increasingly important crop in North Dakota. The state ranks 14th in production of grain corn.

 

CONTROLLING ROUNDUP READY VOLUNTEERS IN ROUNDUP READY CROPS

Several question have been received asking how to control different Roundup Ready crop volunteers in Roundup Ready crops. We have addressed this question in the 2004 ND Weed Control Guide. See page 22 for control of Roundup Ready canola and soybean in Roundup Ready corn and refer to page 27 for control of Roundup Ready canola and corn in Roundup Ready soybean. One situation we have no good answer is how to control soybean in Clearfield or conventional sunflower.

 

WEEDS IN WET FIELDS

Wet fields and late spring conditions may not make planting an option. Weeds will explode with no crop competition and ground cover to suppress germination and growth. Uncontrolled weeds will supply a weed seed bank to last through the next decade. Here are possible suggestions.

Tillage may seem the cheapest and easiest option, but soil compaction will result if the soil is wet and also bare soil is prone to erosion from additional rain storms. Tilling for weed control will not prevent later flushes of weeds so additional tillage will likely be needed which adds to the cost.

A herbicide burndown treatment is an alternative to tillage for fallowing. For non-planted fields, applying 0.75 lb ae/A (1 qt of 3 lb/gal product) would control most weeds. Lower glyphosate rates may not control larger broadleaf weeds. Fields could be sprayed when dry. Even through chemical fallow, additional weeds will emerge because glyphosate has no soil residual. To avoid respraying, the field could be no-till planted to a cover crop to suppress summer annual weeds. Oats would be a good example of an inexpensive cover crop to consider. Rye and winter wheat are other examples but are winter annuals meaning they may survive the winter and be present the next spring.

Fields with perennials like quackgrass, bindweed, and Canada thistle, the best control is to apply 0.75 lb ae/A as soon an the field is dry enough. All perennials are prime for killing with glyphosate when in the late bud to full flower. Adding a pint of 2,4-D to this mix may improve the kill of tall, flowering annual broadleaf weeds like common lambsquarters, ragweed, marshelder, and cocklebur. Glyphosate plus a low rate of dicamba may increase control of wild buckwheat, nightshades and dandelion. Do not use a rate of dicamba that will leave a residue the following year. For degradation of dicamba allow for 45 days (non-frozen ground) per pint of dicamba. 2,4-D or dicamba may help in control of perennials also.

 

DO NOT LET HERBICIDES SIT IN SPRAY TANK

Avoid letting Valor, Authority and Spartan herbicides set in the spray tank for more than 6 hours. The reason is not because of degradation in the tank but tank contamination. If allowed to sit in the tank the active ingredient will bind to hoses, plastic, rubber, and many pluming parts of the sprayer. Regular sprayer cleanout operations may not thoroughly strip the active ingredient out of the sprayer components but may dissolve in later sprayer tank loads. If these other pesticide loads are sprayed on sensitive crops, crop injury may result from the Valor, Authority or Spartan solubilizing back into the spray solution.

 

GLYPHOSATE APPLIED BY AIR

Wet and windy weather have delayed herbicide applications which leaves aerial application as the last resort. Can glyphosate be applied by air? Several glyphosate labels allow aerial application as a general method of application and do not prohibit aerial application to Roundup Ready crops. Although legal, it may be prudent to think through the effect of the application on crops and other plant material around the fields to be sprayed. An aerial application may draw attention to the application and cause neighboring landowners to check fields for damage. If planned, be sure the risks are carefully assessed for each field.

Crops will soon (maybe) exceed the maximum growth stage for postemergence herbicide application. In some fields, the corn and other crops may seem shorter than typical for its growth stage. Make sure to check herbicide labels for the maximum growth stage given as either height or growth stage. Some corn may be V5 and less than 12 inches tall. The corn may reach V6 long before it reaches the 20-inch cut off height restriction listed on several labels. In this case, the growing stage is more important to check when applying some ALS herbicides. Atrazine can be applied to corn 12 inches tall or less.

Richard Zollinger
NDSU Extension Weed Specialist
r.zollinger@ndsu.nodak.edu


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