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Young corn plants in field Photo courtesy of Tom Bechman
INJURY CLUES: ALS-type herbicides can cause stunting in young corn as well as poor root development. Later plantings of corn and soybeans this year also bring more risk for herbicide injury.

Herbicide injury increases in cool, wet conditions

Watch when you apply your herbicide and take extra care if you planted in lighter soils.

With later plantings of corn and soybeans across much of the Mid-Atlantic and Northeast this year, herbicide injury is a concern.

It is rare that the herbicide alone produces crop injury. You must consider the weather (temperature and moisture); planting technique and success; herbicide rates, combinations and timing relative to the crop; and other environmental, soil and management factors that may contribute to the problem. Thoroughly consider the possible reasons for the symptoms before you draw conclusions.

Here is a summary of potential herbicide injury by group and its associated symptoms:

Group 15

This group of herbicides includes Dual II Magnum, Harness, Surpass, Keystone, Outlook, Zidua and their associated atrazine and other premixes, as well as many generic products.

As with most soil-applied herbicides, the injury potential increases on lighter, lower-organic-matter soils under cool, wet conditions with shallow-planted corn.

These herbicides are classified as shoot inhibitors, and injury typically is seen as leafing out underground or tightly wrapped leaves that fail to or have difficulty unfurling. Emerged plants may appear buggy whipped.

The acetamides do not generally impact the root system. The injury potential for the acetamide herbicides to corn is generally not great, and Penn State Extension has rate them as “good crop tolerance.”

The injury potential can increase, though, depending on tank-mix partner with herbicides such as 2,4-D, dicamba and pendimethalin (Prowl), which can sometimes increase the severity of injury.

Group 4

Dicamba is the active ingredient in Banvel, Clarity, Engenia, Xtendimax, and a component of Status and Yukon, as well as many generic products.

Dicamba is classified as a growth regulator herbicide. The potential for injury with soil applications of dicamba increases with lighter, low-organic-matter soils; cool, wet weather; shallow-planted corn; and seed that is not adequately covered during planting and spraying.  

Corn should be planted a minimum of 1.5 inches deep if dicamba is applied preemergence. Dicamba injury from soil applications may range from stunting to pruned and thickened roots, twisting, swelling, and onion leafing of shoots. The injury potential from foliar applications of dicamba generally increases with warmer temperatures and increasing corn maturity.

Foliar applications of dicamba should be applied by V3/V4 to reduce the risk of crop injury. Crop and methylated seed oils as well as rates above 0.25 pounds ai per acre (½ pint Banvel/Clarity) can increase the injury potential with foliar applications.

Group 3

Pendimethalin is the active ingredient in Prowl and several generic brands. Pendimethalin is classified as a root inhibitor herbicide. It should be applied to corn after planting and to corn planted at least 1.5 inches deep.

Its injury potential increases with cool, wet weather; shallow-planted corn; light- or lower-organic-matter soils; and corn seed that is not adequately covered by soil.

It is listed as “good crop tolerance” so long as proper management practices are used. The symptoms of pendimethalin injury include pruned roots, swollen root tips, and stunted plants or seedlings. Emerged plants may appear purple due to the secondary effects of phosphorus deficiency as a result of inhibited root growth.

Soil crusting can enhance injury. Acetamide herbicides are frequently used in combination with pendimethalin and may contribute to the observed injury symptoms.

Group 2

The primary acetolactate synthase-inhibitor corn herbicides used in our region are products that contain thiencarbazone (Corvus), rimsulfuron (Basis Blend and Resolve products), and flumetsulam (Surestart II and Hornet) as well as a few generic products.

As with other soil-applied herbicides, the potential for Group 2 injury increases with cool, wet weather; shallow-planted corn (plant at least 1.5 inches deep); and in soils with lower organic matter. The injury often appears worse in areas such as clay knobs or where corn was planted in compacted areas.

ALS injury potential to corn is listed as “fair.” ALS herbicides can cause stunting of both corn root and shoot growth. The roots can be “bottle brushed” but are more often simply reduced in lateral growth and development. The roots may also appear slightly thickened and swollen. The shoots may appear stunted and purple to yellow with interveinal chlorosis.

The potential for ALS injury increases with rapid uptake of herbicides during warm, wet weather. Much of this injury appears as stunted, somewhat chlorotic corn, and with our injury ratings ranging from 10% to 25%. This type of injury is frequently seen with abundant rainfalls during May, followed by the hot weather of early June, which stimulates herbicide uptake above the tolerance level for corn.

If good growing conditions occur during the weeks following injury, the corn usually recovers with little or no impact on grain yields.

Group 27

Balance Flexx and Corvus (isoxaflutole) and mesotrione (Callisto and a component of Acuron, Lumax, Lexar, and others) are pigment inhibitor herbicides that prevent the development of chlorophyll in susceptible species, turning plants white.

Soil applications of Balance-Corvus hold many of the same restrictions and concerns as pendimethalin and ALS herbicides. Cool, wet weather; shallow-planted corn; open seed furrows; lower organic matter; lighter-textured soils; and higher use rates increase injury possibility.

The potential for mesotrione injury from soil applications is usually less than isoxaflutole. Mesotrione applied post can occasionally injure corn and, like many foliar applications, warm and humid weather generally increases the potential for injury. With mesotrione, corn generally recovers from any post-applied yellowing or bleaching-type symptoms. Mesotrione has a greater risk of injury to corn with certain OP and carbamate insecticides as well as in applications that include methylated seed oils.

Soybean injury potential

Depending on the product used, the potential for injury from soybean herbicides is greatly increased in certain situations.

Products such as metribuzin, Valor, Authority, Prowl and a few others can cause severe injury if the herbicide comes into contact with the germinating seed (open seed furrows) or are used in coarse soils with low organic matter.

Recently, there have been questions about herbicide injury if seed furrows are not completely closed. In some cases, most of the field has open seed furrows and the residual herbicide program has not yet been applied. This is a situation that requires some thought to best determine the next steps and there are no easy answers in this case.

Applying a program containing some of the aforementioned herbicides could cause crop injury since the herbicide has direct access to the seed, but at the same time poor weed control could result if these products aren’t used, especially if the field has marestail or Palmer amaranth.

Assuming the field is planted to Xtend or Enlist E3 soybeans, an early post herbicide that includes glyphosate, dicamba or 2,4-D choline, plus a residual herbicide such as Prefix, Zidua, Warrant, or other can provide control of many weeds.

In LibertyLink, E3 or LLGT27 varieties, Liberty, plus residuals can be used to help control problem weeds such as marestail or Palmer, and other species if a residual herbicide was not applied before planting. Nonetheless, creative herbicide programs will need to be considered to combat weeds yet protect the crop.

Source: Penn State Extension, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.
TAGS: Corn Soybeans
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