Figure 1. Hollow husk symptom in Illinois in 2007 often associated with arrested ear development. Note the longer, tapered "hollow husk" lacking silks adjacent to the normal ear on the left (Photo courtesy of Dr. Emerson Nafziger, University of Illinois).

March 7, 2008

During 2007, the use of foliar fungicides on corn for management of foliar diseases increased in Nebraska and the rest of the Corn Belt. The most commonly used systemic products contain chemicals from one or both of two major fungicide classes, strobilurins and triazoles. Label restrictions for these products vary by class and sometimes by individual products. Some important changes have been made to some of these product labels and company recommendations that may affect the way you use them. These changes should be followed to both adhere to label restrictions and prevent potential phytotoxic effects caused by the products. Below is a summary of some of those items.

Restricted Entry Interval (REI)

The REI for bare-hand detasseling in seed corn fields receiving an application of Headline® (BASF) was reduced from 7 days to 12 hours.

Pre-harvest Interval (PHI)

Application of Quilt® (Syngenta Crop Protection) and Stratego® (Bayer CropScience) were previously restricted for use after the development of brown silks. The new PHI was reduced for these products on corn and applications should not be made within 30 days of harvest. Headline and Quadris still have a seven day PHI for corn.

Phytotoxicity

During 2007, irregular ear development was identified in some fields in Illinois that had received a fungicide application. These symptoms most often developed in fields that received ground applications of a fungicide prior to tasseling and reportedly were not limited to a single product. Initially, affected ears may be recognized because they often have longer, tapered ears with "hollow husks" (Figure 1). The ear inside these hollow husks is small because development was stopped early. Their appearance has been referred to as blunt ear syndrome, beer can ears, and ear stunting and can result from a several causes. Specifically, the phrase "arrested ear development"(Figure 2) has been used most recently to describe these symptoms when fungicides were suspected as a cause and specifically when the symptomatic ears possessed a primordial tip (ear initial).

Figure 2. Photos illustrating arrested ear development in Illinois in 2007 (Photos courtesy of Dr. Emerson Nafziger, University of Illinois).

Development of similar symptoms has also been attributed to numerous other factors, including genetic disorders, late post-emergent application of some herbicides, environmental factors, such as cold temperatures, and problems during pollination. In addition, the application of certain compounds that block ethylene (personal communication, Dr. Fred Below, Professor of Plant Physiology, University of Illinois) and some adjuvants also have been suggested as potential causes of these symptoms.

For more information about corn ear abnormalities, visit these links:

•  

• Troubleshooting Abnormal Corn Ears and Related Disorders, Peter Thomison and Allen Geyer, Ohio State University
• Symptomology of Arrested Ear Development in Corn, Bob Nielsen, Purdue University
• Notes Heading Into Harvest 2007, Emerson Nafziger, University of Illinois at Urbana-Champaign
• Unexpected Problems of Corn Ear Development, Emerson Nafziger, University of Illinois at Urbana-Champaign

Adjuvants and Tank Mixes

Some company recommendations have been changed for the use of some adjuvants and tank mixtures with fungicides and are summarized below.

Because label restrictions for pesticides can change, it is especially important that you read and follow the directions on the most current label. You can find current product labels at the following Web sites or by going directly to the manufacturers' Web sites.

 

Greenbook.net

Crop Data Management Systems, Inc.

Tamra A. Jackson
UNL Extension Plant Pathologist

Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by the University of Nebraska-Lincoln Extension is implied for those mentioned.

Headline® (pyraclostrobin)
	Adjuvant Recommendations for Corn
	Vegetative Growth Stages	Reproductive Growth Stages (VT and later)
Application Method
Ground	None	Flexible Adjuvant
Aerial (2 to < 5 gpa)	Not Recommended	COC
Aerial (5 gpa or more)	None	Flexible Adjuvant
Note: BASF also discourages the use of tank mixtures of Headline� with fertilizers or other pesticides when applications are to be made to corn prior to tassel emergence.
Quadris® (recommended by Syngenta primarily for seed corn production)
	Adjuvant Recommendations for Corn
	Vegetative Growth Stages	Reproductive Growth Stages (VT and later)
Application Method
Ground	COC	COC
Aerial (2 to < 5 gpa)	COC	COC
Aerial (5 gpa or more)	COC	COC
Quilt® (recommended by Syngenta primarily for commercial corn production)
	Adjuvant Recommendations for Corn
	Vegetative Growth Stages	Reproductive Growth Stages (VT and later)
Application Method
Ground	Adjuvants are optional	Adjuvants are optional
Aerial (2-3 gpa)	COC	COC
Aerial (4-5 gpa)	Adjuvants are optional	Adjuvants are optional
Note: Syngenta allows tank mixtures of Quilt® with other pesticides, adjuvants, and controlled release N fertilizers at up to 1 gpa in at least 1:1 mixture with water.
Stratego®
	Adjuvant Recommendations for Corn
	Vegetative Growth Stages	Reproductive Growth Stages (VT and later)
Application Method
Ground	NIS, no COC	NIS
Aerial (2 to < 5 gpa)	Either NIS or COC	COC
Aerial (5 gpa or more)	NIS, no COC	Either NIS or COC