Corn
Should I be concerned about corn borers?
Second generation corn borers are expected to appear around the last ten days of June through mid July in Mississippi.
Corn
producers in the hills should be alert for this historically Delta pest
as well. Corn borer populations in northeast MS (Alcorn south to Monroe
county) have increased the past several years. Thus, growers in northeast
Mississippi should also be scouting for this potential pest, despite
them historically being limited to the Delta region.
Corn borers are capable of more significant crop damage than leaf-feeding caterpillars, because they actively tunnel into stalk tissue. First and second generation corn borer feeding reduces yield potential mainly by stunting vegetative development and destroying vascular tissue responsible for distributing water, nutrients and energy within the plant. Corn borer feeding also increases harvest losses resulting from dropped ears, broken stalks and stalk lodging.
Intensive field scouting is required to identify significant infestations and accurately time insecticide treatment for effective control. Although pheromone traps are a good timing tool, do not solely rely on pheromone trap counts or your neighbor to assume your fields are infested - you need to intensively scout your fields.
Insecticide
application timing is critical, since pesticide contact is unlikely once
corn borers tunnel into the stalk or ear. However, corn borers hatch
and feed on leaf tissue for up to 10 or 12 days before tunneling. During
this time, they are susceptible to insecticide applications with optimum
(around 80 percent) control normally accomplished by treatment coinciding
with peak egg hatch. However, egg hatch may occur for several weeks,
so frequent scouting is required to make a well-timed insecticide application(s).
Egg masses can be very difficult to find. Corn borer moths normally lay their eggs within two or three leaves of the developing ear. A person should also search for small larvae and leaf feeding activity. Newly hatched larvae leave elongate translucent windowpane and pinhole-feeding scars close to leaf collars. Second and third generation corn borers normally seek the latest corn available.
The treatment threshold for Southwestern corn borers is 25 percent of plants infested with either an egg mass or a larva. The treatment threshold for European corn borers is 50 percent of plants infested. Therefore, count a European larva as one-half of a Southwestern corn borer when scouting mixed populations.
Newly hatched larvae of both species will be less than one-eight of an inch long and have large black head capsules. Southwestern corn borer larvae are off-white colored and have prominent dark spots on their backs. European corn borer larvae are opaque to light gray or tan colored and have less inconspicuous spots. Second and third generation corn borers normally favor later planted corn, if different growth stages are available. Once larvae grow larger than three-eighths of an inch long they will begin tunneling inside stalks.
If live larvae are found, then randomly select enough plants to determine infestation level. Generally, a total of 20-50 plants gathered from various spots in the field should give an adequate estimation.
Infected fields should be scouted at least weekly, so that timely treatment application is made, if necessary.
Labeled insecticide treatments for corn borer include Warrior, Asana XL, Ambush/Pounce, Fury and Intrepid 2F. Treatment must be made before the larvae begin tunneling in the stalk.
Corn hybrids containing Bt toxin should control both Southwestern and European corn borers. Thus, Bt corn hybrids should not require insecticide treatment for these species. However, research suggests some Bt types are less effective for Southwestern corn borer control. Thus, Bt hybrids should be evaluated for efficacy.
Mississippi has had several good corn crops in recent years. This may have given the false impression that corn required little if any management during the season. However, corn yields may be reduced significantly by a variety of potential problems capable of reducing profitability considerably, including corn borers, if left unchecked. Thorough field scouting is the most effective way to monitor corn and pest development so that you can make appropriate, timely and economical management decisions during the season.
Corn Borer Links:
The European
Corn Borer Home Page - Iowa State University
