Sid Bosworth and Heather Darby, Extension
Associate Professor, Department of Plant and Soil Science, University of
Vermont and Extension Assistant Professor, Northwest Region, University
of Vermont Extension firstname.lastname@example.org
The most critical time to scout field corn is that three to four week period after planting. During this period problems such as poor emergence, insects, and weed pressure can have a big impact on yield and quality. Many of these problems can still be economically rectified if caught and treated quickly. The following is a rundown of potential items to look for in that early part of the corn’s life.
Corn should emerge anywhere from one to three weeks after planting depending on soil temperature. According to Greg Roth, Extension Corn Specialist at Penn State, corn should begin emerging after approximately 100 to 125 growing degree days have accumulated following planting. He recommends looking for the following potential emergence problems:
- No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave evidence of digging or seed and plant parts scattered on the ground.
- Coleoptile (shoot) unfurled underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, or may be due to extended cool wet conditions alone.
- Seed with poorly developed radicle (root) or coleptile.
- Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor.
- Seed swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
- Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.
- Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
Corn Insect Damage
There are several insects that can cause problems during early season. Seed corn maggot is the most common early season corn insect found in Vermont. Other early season insects that cause losses in isolated cases include the black cutworm, armyworms, wireworms, white grubs and potato stem borer.
|Seed corn maggot – Adult flies lay eggs close to decaying plant material or germinating seed to provide a food source for the newly hatched larvae. Large seed, like corn, is very attractive. Fields with regular manure applications also provide exceptional habitat for egg laying. So, there is a very high likelihood that most cornfields in Vermont will have some level of this insect. At high maggot populations, corn losses can typically range from 3,000 to 8,000 plants per acre. There is no treatment once the problem occurs, so the best treatment for this insect is prevention. It is usually quite easy (and relatively inexpensive) to control this insect with a planter box insecticide treatment. Captan-Diazinon Seed Treater or Kernel Guard Supreme will both control seed corn maggot.|
||Wireworms and white grubs – Wireworms are the larvae of click beetles whereas white grubs are larvae of scarab beetles such as June beetles. They feed on the roots of grasses, germinating crops seeds and the base of young plants. Both can cause occasional problems and are most commonly found when corn is following a grass pasture or hay field; however, there is no way to predict a problem in order to justify a preventative treatment of insecticide. In fact, there are no insecticides labeled for white grub. If damage from wireworm is severe enough, the field may have to be replanted. At that time, a preventative insecticide could be justified.|
Scouting early for weeds is critical. Many of the post emergence herbicides that can be used as an emergency treatment need to be applied when the weeds are small in order to be effective. Each herbicide has it’s own set of restrictions based on corn size and maturity and weed size which also varies according to the particular weed specie. Of course, it is important to be able to identify the young weed seedlings so that you can apply the most appropriate products. For example, the newer product Callisto can be applied post emergence to corn up to 30 inches in height. It is effective on many summer annual broadleaf weeds when applied up to 5 inches in height, but it will control crabgrass (large only, not smooth crabgrass) but it has to applied when the grass is less than 2 inches tall. An effective and economical way to control weeds is by cultivation. Cultivation should be implemented before corn canopy closure.
Well kept field records can be very helpful when making management decisions. Click here (pdf format) for a two page scouting report for field corn.
This site is maintained by Sid.Bosworth@uvm.edu, Plant & Soil Science Department, University of Vermont.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont.University of Vermont Extension and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, sex, religion, age, disability, political beliefs, or marital or familial status
Last modified July 02 2009 02:46 PM