University of Illinois

No. 14/June 27, 1997

Herbicide Injury

White corn. We previously discussed white corn; but, with Roundup Ready fields now being sprayed, it is wise to alert people that glyphosate drift causes yellowing and whitening of corn leaves especially in the whorl.

Early ALS injury--corn: Several cornfields are exhibiting ALS injury symptoms, that is, bottlebrush roots (radicle, seminal, and nodal); purpling or yellowing of lower leaves, sometimes with bronze tips, plus nutrient deficiencies due to a poor root system. The usual soybean herbicides involved are Squadron (Prowl + Scepter), Steel (Prowl + Pursuit + 0.5X Scepter), Pursuit Plus (Prowl + Pursuit) or Pursuit last year. Sometimes Broadstrike + Dual has been used in corn in 1997. This combination of ALS carryover plus ALS on corn plus cool, wet weather has caused stressed corn, which has created all sorts of symptoms. Individual plants often show extreme differences in height and size.

Contact burn--corn: Bromoxynil (Buctril or Moxy) and flumiclorac (Resource) have been very active, causing contact burn on stressed corn, especially where crop oil was used. This contact activity has sometimes caused slow unfurling of whorls, due to burning of leaf tissue, leading to yellowing or whitening of whorl leaves. Corn has usually outgrown this. Do not forget that applying contact herbicides over the whorl of dew-laden corn leaves can cause a concentrated load of herbicide to be carried to the whorl by coalescence of droplets (rundown).

Contact burn--soybeans: With the hot, muggy (high-humidity) weather, contact activity on soybeans has increased greatly. The burning (yellowing or browning) of leaves is very evident. Soybeans have a marvelous ability to recover from early injury, including defoliation. Terminal (apical) hits on soybeans often lead to new double shoots (Psi effect) at cotyledonary or unifoliate nodes. The Greek letter Psi looks somewhat like a crossed UI symbol. New growth often has a PGR effect similar to that caused by dicamba or clopyralid.

DNA-hypocotyl or -stem--soybeans: The cool, wet weather coupled with slow soybean emergence has increased dinitroaniline Prowl (pendimethalin) or Treflan (trifluralin) injury to soybean hypocotyls and stems. Hypocotyls are swollen and sometimes cracked with disease invasion.

Surface applications have often led to a callous or corky formation at ground level, which may lead to stem breakage. We have had these symptoms in the past. The unusual effect in 1997 has been a terminal effect above the unifoliate, where the first trifoliate is very small or dies, leading to the Psi effect described above with PGR symptoms on new growth. This year is the first we have noticed this in DNA-fields that supposedly only had Prowl or trifluralin.

Marshal McGlamery and Aaron Hager, Department of Crop Sciences, (217)333-4424