Dicamba remains one of the most widely used products for controlling broadleaf weeds in corn. Most growers have experience with Banvel or Clarity and have learned to manage these products to minimize the potential for crop injury. However, several new premixed products are available that growers might not be aware contain dicamba (Table 1). Because of this lack of knowledge some growers might use these products in ways that increase the likelihood of stalk brittleness and greensnap.
The potential for corn brittleness caused by dicamba is influenced by several factors, including corn height at application, rate of dicamba, hybrid sensitivity, corn vigor, environment, and other products included in the spray mix. Because of all the interacting factors it is difficult to predict the likelihood of problems in any given field. However, corn height at application is one of the most consistent factors influencing corn susceptibility to dicamba.
The potential for injury increases as corn size increases because larger corn has more leaf area to intercept the herbicide. Also, the relative growth rate of corn accelerates with increasing size, thereby increasing the potential for a disruption in growth. The use of drop nozzles when corn exceeds 12 to 16 inches in height not only reduces the potential for crop injury but also improves weed control through better coverage of weeds.
Rates of dicamba applied with many of the package mixes are less than those applied with Banvel or Clarity, thereby seemingly reducing the potential for crop injury. However, several of these products require the use of spray additives that may increase adsorption of dicamba, thus counteracting the lower rate. There also may be interactions among the herbicides in package mixes or tank mixes that increase the potential for crop injury. These package mixes may have an equivalent potential to cause an undesirable crop response as the higher rates of dicamba found in Banvel or Clarity.
In summary, dicamba has a history of effective, safe weed control in corn when used appropriately. Delayed applications of dicamba have the greatest risk of causing stalk brittleness, thus timely application to corn less than 10 inches in height is the best strategy to minimize undesirable crop response. When situations require later applications, the use of drop nozzles is essential to maintain an acceptable level of crop tolerance.
Table 1. Products containing dicamba.
|Product||Dicamba Formulation||Dicamba Rate
|Companion Product||Maximum Corn Height|
|Banvel 4S||Dimethylamine salt||0.25-0.5||--||8 in. at 1-pt rate;
36-in. at 0.5-pt rate
|Celebrity||Sodium salt||0.27||Accent||20 in. broadcast;
36 in. with drop nozzles
|Celebrity Plus||Sodium salt||0.12||Accent +
|Clarity 4S||Diglycolamine salt||0.25-0.5||--||8 in. at 16-oz rate;
36 in. at 8-oz. rate
|Distinct||Sodium salt||0.13-0.19||Diflufenzopyr||10 in. at 6-oz rate;
24 in. at 4-oz rate
|Marksman||Potassium salt||0.5||Atrazine||12 in.|
|NorthStar||Sodium salt||0.12||Beacon||20 in. broadcast;
36 in. with drop nozzles
|OpTill||Parent acid||0.17-0.3||Frontier||8 in.|
*ae, acid equivalent.
This article originally appeared on page 92 of the IC-484(12) -- June 5, 2000 issue.