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IPM1007, Practical Weed Science for the Field Scout: Corn and Soybean

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Practical Weed Science for the Field Scout: Corn and Soybean

Amino acid synthesis inhibitors

Severe injury may result in interveinal chlorosis and eventually death in emerging corn seedlings.Severe injury may result in interveinal chlorosis and eventually death in emerging corn seedlings.
 

Drift from imidazolinone herbicides like imazethapyr and imazamox can cause stunting and plants to exhibit more purple color than normal.
Drift from imidazolinone herbicides like imazethapyr and imazamox can cause stunting and plants to exhibit more purple color than normal. Drift from imidazolinone herbicides like imazethapyr and imazamox can cause stunting and plants to exhibit more purple color than normal.
 

Maize dwarf mosaic virus can also cause reddening symptoms that are often confused with imidazolinone herbicide injury. Maize dwarf mosaic virus can also cause reddening symptoms that are often confused with imidazolinone herbicide injury. Maize dwarf mosaic virus can also cause reddening symptoms that are often confused with imidazolinone herbicide injury.
 

Injury from imidazolinone herbicides like imazamox on soybeans appears as stunting and chlorosis of the newest trifoliate.
Injury from imidazolinone herbicides like imazamox on soybeans appears as stunting and chlorosis of the newest trifoliate. Injury from imidazolinone herbicides like imazamox on soybeans appears as stunting and chlorosis of the newest trifoliate.
 

Carryover injury from imidazolinone herbicides like imazaquin is characterized by short, stunted plants, interveinal chlorosis, purpling, and pruning of lateral roots. In the three bottom photos, the healthy plant is on the right, injured plant on the left.
Carryover injury from imidazolinone herbicides like imazaquin is characterized by short, stunted plants, interveinal chlorosis, purpling, and pruning of lateral roots. In the three bottom photos, the healthy plant is on the right, injured plant on the left. Carryover injury from imidazolinone herbicides like imazaquin is characterized by short, stunted plants, interveinal chlorosis, purpling, and pruning of lateral roots. In the three bottom photos, the healthy plant is on the right, injured plant on the left. Carryover injury from imidazolinone herbicides like imazaquin is characterized by short, stunted plants, interveinal chlorosis, purpling, and pruning of lateral roots. In the three bottom photos, the healthy plant is on the right, injured plant on the left.
 

Imidazolinones chemical group

Herbicides

  • Imazaquin (Scepter — soybean)
  • Imazethapyr (Pursuit — soybean, alfalfa and IT/IR/cleanfield corn)
  • Imazethapyr + imazapyr (Lightning — IT/IR/cleanfield corn)
  • Imazamox (Raptor — soybean, alfalfa)

Mode of action and characteristics of activity

  • Inhibition of ALS (acetolactate synthase) or AHAS (acetohydroxyacid synthase) enzyme
  • Controls annual broadleaves and some annual grasses
  • Woody brush species with imazapyr, translocates upward in xylem and to growing points and roots in phloem, both soil and foliar activity, medium to long soil persistence

General symptoms

  • Broadleaf plants die slowly
  • Loss of apical dominance
  • Chlorosis (yellowing) of tissue, and shortening of internodes
  • Grass plants may be stunted with chlorosis or purpling
  • Corn plants may be stunted and show symptoms of root inhibition such as pruning of lateral roots (bottlebrush)
  • Leaves emerging from the corn whorl may not unfurl properly and be yellow to translucent in appearance
  • IT/IR corn tolerates residues better than regular corn
  • Soybean injury can range from stunting to death of the terminal growing point
  • Soybean leaves may be yellow in appearance and leaf veination may appear red or purple in color
  • Soybean plants may also appear to be potassium deficient or affected by soybean cyst nematode
  • Injury is more noted when plants are under stress

Injury from unlabeled sulfonylurea herbicides on soybeans is characterized by severe stunting, death of the newest trifoliates and red or black veins on the underside of the leaf. Injury from unlabeled sulfonylurea herbicides on soybeans is characterized by severe stunting, death of the newest trifoliates and red or black veins on the underside of the leaf. Injury from unlabeled sulfonylurea herbicides on soybeans is characterized by severe stunting, death of the newest trifoliates and red or black veins on the underside of the leaf.
 

Sulfonylurea damage on soybeans is characterized primarily by irregular chlorosis and red or black veins on the underside of the leaf. Imidazolinone herbicides can cause similar symptoms. Sulfonylurea damage on soybeans is characterized primarily by irregular chlorosis and red or black veins on the underside of the leaf. Imidazolinone herbicides can cause similar symptoms. Sulfonylurea damage on soybeans is characterized primarily by irregular chlorosis and red or black veins on the underside of the leaf. Imidazolinone herbicides can cause similar symptoms.
 

Soil activity of sulfonyl­urea herbicides like chlorimuron or carryover injury from unlabeled herbicides can cause short, stunted plants and chlorosis of the newest growing point. Left, treated soybean plant; right, untreated. Soil activity of sulfonyl­urea herbicides like chlorimuron or carryover injury from unlabeled herbicides can cause short, stunted plants and chlorosis of the newest growing point. Left, treated soybean plant; right, untreated. Soil activity of sulfonylurea herbicides like chlorimuron or carryover injury from unlabeled herbicides can cause short, stunted plants and chlorosis of the newest growing point. Left, treated soybean plant; right, untreated.
 

Pruning of lateral roots, or bottle-brushed roots as a result of cool, wet conditions and sandy soils after a flumetsulam application. Pruning of lateral roots, or "bottle-brushed" roots as a result of cool, wet conditions and sandy soils after a flumetsulam application.
 

In corn, injury from sulfonylurea herbicides will appear as yellow flash. This is most often characterized by chlorosis in the whorl and lower part of the leaf and a crinkled leaf edge near the chlorotic tissue. In corn, injury from sulfonylurea herbicides will appear as yellow flash. This is most often characterized by chlorosis in the whorl and lower part of the leaf and a crinkled leaf edge near the chlorotic tissue. In corn, injury from sulfonylurea herbicides will appear as yellow flash. This is most often characterized by chlorosis in the whorl and lower part of the leaf and a crinkled leaf edge near the chlorotic tissue.
In corn, injury from sulfonylurea herbicides will appear as yellow flash. This is most often characterized by chlorosis in the whorl and lower part of the leaf and a crinkled leaf edge near the chlorotic tissue.In corn, injury from sulfonylurea herbicides will appear as "yellow flash." This is most often characterized by chlorosis in the whorl and lower part of the leaf and a crinkled leaf edge near the chlorotic tissue.
 

Late applications of sulfonylurea herbicides like nicosulfuron and nicosulfuron + rimsulfuron can cause ear pinching and severe yield reductions. Late applications of sulfonylurea herbicides like nicosulfuron and nicosulfuron + rimsulfuron can cause ear "pinching" and severe yield reductions.
 

Injury from sulfonylurea herbicides like foramsulfuron can also appear as stunting and internode stacking in corn. Injury from sulfonylurea herbicides like foramsulfuron can also appear as stunting and internode stacking in corn.
 

Sulfonylureas and triazolopyrimidine sulfonamides chemical group

Herbicides

  • Chlorimuron (Classic — soybean)
  • Thifensulfuron (Harmony GT — soybean),
  • Primisulfuron (Beacon — corn)
  • Nicosulfuron (Accent — corn)
  • Nicosulfuron + rimsulfuron (Steadfast - corn),
  • Rimsulfuron (Resolve - corn)
  • Foramsulfuron (Equip - corn)
  • Prosulfuron (Peak — corn, grain sorghum, small grains)
  • Halosulfuron (Permit — corn, grain sorghum)
  • Flumetsulam (Python, in Hornet — corn and soybean)
  • Cloransulam (FirstRate — soybean)

Mode of action and characteristics of activity

  • Inhibition of ALS or AHAS enzyme
  • Control of annual broadleaf weeds and some grasses, soil and foliar activity, translocation upward in xylem and to growing points and roots in phloem, active at low rates, short to long soil persistence

General symptoms

  • Stunted plant growth, lack of apical dominance, and black or red veins in soybean
  • Same as imidazolinones

Injury to non-Liberty Link corn plants. In photo at right, Liberty Link corn plant stands between two non-Liberty Link corn plants.
Injury to non-Liberty Link corn plants. In photo at right, Liberty Link corn plant stands between two non-Liberty Link corn plants. Injury to non-Liberty Link corn plants. In photo at right, Liberty Link corn plant stands between two non-Liberty Link corn plants.
 

Glufosinate symptoms soon after application will appear as small spots or lesions, indicative of the faster, more contact-nature of glufosinate than glyphosate. Glufosinate symptoms soon after application will appear as small spots or lesions, indicative of the faster, more contact-nature of glufosinate than glyphosate.Glufosinate symptoms soon after application will appear as small spots or lesions, indicative of the faster, more contact-nature of glufosinate than glyphosate. Glufosinate symptoms soon after application will appear as small spots or lesions, indicative of the faster, more contact-nature of glufosinate than glyphosate.
 

Glufosinate injury on non-Liberty LInk soybeans will progress fairly rapidly from chlorosis to necrotic areas throughout.
Glufosinate injury on non-Liberty LInk soybeans will progress fairly rapidly from chlorosis to necrotic areas throughout.Glufosinate injury on non-Liberty LInk soybeans will progress fairly rapidly from chlorosis to necrotic areas throughout.
Glufosinate injury on non-Liberty LInk soybeans will progress fairly rapidly from chlorosis to necrotic areas throughout. Glufosinate injury on non-Liberty LInk soybeans will progress fairly rapidly from chlorosis to necrotic areas throughout.
 

Glufosinate injury to non-Liberty Link corn hybrids will appear as chlorosis of new growth, whereas older leaves and leaf tips will become necrotic first. Glufosinate injury on corn is somewhat similar in appearance to frost damage.
Glufosinate injury to non-Liberty Link corn hybrids will appear as chlorosis of new growth, whereas older leaves and leaf tips will become necrotic first. Glufosinate injury on corn is somewhat similar in appearance to frost damage.Glufosinate injury to non-Liberty Link corn hybrids will appear as chlorosis of new growth, whereas older leaves and leaf tips will become necrotic first. Glufosinate injury on corn is somewhat similar in appearance to frost damage. Glufosinate injury to non-Liberty Link corn hybrids will appear as chlorosis of new growth, whereas older leaves and leaf tips will become necrotic first. Glufosinate injury on corn is somewhat similar in appearance to frost damage.
 

Amino acid derivatives chemical group

Herbicides

  • Glufosinate (Liberty)

Mode of action and characteristics of activity

  • Inhibition of glutamine synthetase
  • Nonselective weed control unless used in Liberty Link crops
  • Limited translocation in xylem and phloem
  • No soil activity

General symptoms

  • Glufosinate causes new growth to turn chlorotic, then necrotic
  • Activity is faster in hot weather
  • Glufosinate symptoms appear more quickly than those of glyphosate in cool weather and typically include more yellowish-green strips or patches followed by necrosis

Glyphosate injury on non-Roundup Ready corn hybrids can appear as tight, rolled leaves in the whorl, known as onion leafing.
Glyphosate injury on non-Roundup Ready corn hybrids can appear as tight, rolled leaves in the whorl, known as onion leafing. Glyphosate injury on non-Roundup Ready corn hybrids can appear as tight, rolled leaves in the whorl, known as "onion leafing."
 

Glyphosate drift or tank contamination can also cause whitening in the whorl and onion leafing. Glyphosate drift or tank contamination can also cause whitening in the whorl and "onion leafing."
 

Significant injury can occur to conventional corn from as little as 0.01 lb/acre of glyphosate as a tank contaminant, as shown here.
Significant injury can occur to conventional corn from as little as 0.01 lb/acre of glyphosate as a tank contaminant, as shown here.Significant injury can occur to conventional corn from as little as 0.01 lb/acre of glyphosate as a tank contaminant, as shown here.
 

Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred. Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred. Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred.
Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred.
Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred.Glyphosate injury on non-Roundup Ready corn hybrids is perhaps most often characterized by the distinctive chlorotic bands that form on the leaves around the plant. These injured leaves developed after the exposure, which indicates when the glyphosate drift or contamination occurred.
 

Glyphosate can also injure Roundup Ready soybean plants, especially when applied later in the season or when overlaps occur. Newest trifoliates are most often affected and are usually chlorotic.
Glyphosate can also injure Roundup Ready soybean plants, especially when applied later in the season or when overlaps occur. Newest trifoliates are most often affected and are usually chlorotic.Glyphosate can also injure Roundup Ready soybean plants, especially when applied later in the season or when overlaps occur. Newest trifoliates are most often affected and are usually chlorotic.
 

Glyphosate injury on non-Roundup Ready soybean plants will progress as general stunting and chlorosis of the newest trifoliates first, followed by eventual chlorosis and necrosis of the entire plant. Glyphosate injury on non-Roundup Ready soybean plants will progress as general stunting and chlorosis of the newest trifoliates first, followed by eventual chlorosis and necrosis of the entire plant.
 

Amino acid derivatives chemical group

Herbicides

  • Glyphosate (Roundup and others)

Mode of action and characteristics of activity

  • Inhibition of EPSP synthase
  • Nonselective weed control unless used in Roundup Ready crops
  • Translocates upward in xylem and to growing points and roots in phloem
  • No soil activity

General symptoms

  • Glyphosate causes new growth to turn chlorotic, then necrotic
  • Plants usually die in 7 to 14 days
  • Activity is faster in hot weather

 

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