EXTENSION 
INSTITUTE OF AGRICULTURE AND NATURAL RESOURCES         
UNIVERSITY OF NEBRASKA-LINCOLN 
NORTHEAST RESEARCH & EXTENSION CENTER       
601 EAST BENJAMIN AVENUE, SUITE 104
NORFOLK, NE 68701-0812
PHONE: (402) 370-4000 
FAX (402) 370-4010

Overall Insect Problems Low

Not much is happening on the insect front right now, except for European corn borer moth flight. We still have the potential for soybean aphids to become a problem but up to now numbers have remained below threshold and hot weather is not ideal for their reproduction.

European Corn Borer Moths are Flying

The second European corn borer flight is occurring in much of Nebraska and just beginning in Northeast Nebraska . If you have not begun yet, start scouting non-Bt cornfields for European corn borer egg masses. Current information on light trap catches near your area can be found through the Entomology Department Website (http://entomology.unl.edu/) or directly at http://entomology.unl.edu/fldcrops/index.htm

Timely and accurate scouting is the key to managing ECB in standard (non-Bt) corn hybrids. Remember that conditions are localized and fields must be scouted on an individual basis to make accurate decisions. We have had it easy the last few years - flights have been relatively low; and have been low again this year. However, this cannot last forever.

Fields with green silks during the peak moth flight period are most susceptible to second-generation egg laying. The white, flat eggs overlap each other like fish scales and are laid in masses of five to 40 eggs. Eggs are most likely found on the underside of leaves, near the mid-rib, on the ear leaf and the three leaves above or below the ear leaf. Approximately 90 percent of the egg masses will be found on these middle seven leaves. A black spot is visible on the eggs for about 24 hours before they hatch. The spot is the head of the developing corn borer; this stage is often referred to as the black head stage.

To determine whether control would be profitable, examine 25 plants at four sites per field (100 plants total). Record the number of egg masses and the number of plants sampled. If you sampled only the middle seven leaves, multiply the number of egg masses by 1.1 to estimate the total present over the whole plant. Use this adjusted mean in the worksheet below. Go through the calculations outlined in the worksheet (also available from NebFact 98-365, Second generation European corn borer scouting and treatment decisions http://www.ianr.unl.edu/pub s /in s ects/nf365.htm ) to determine if an economic infestation is present. You will also need to know the crop stage, expected yield, expected market price for corn, percent control with insecticide, and cost of control (insecticide plus application costs).

An interactive version of this worksheet is available at http://www.ianr.unl.edu/forms/forms.skp/ecb_2nd.html

This worksheet will help you better evaluate the factors influencing the cost/benefit relationship for second generation European corn borer treatments. Average values are suggested in the worksheet but may be modified for local conditions.

1. Borer survival is suggested to be 15%. Larval survival varies with weather conditions and irrigation. In irrigated corn, larval survival may be 20% or more, while in dryland corn with no significant rainfall, it may be 10% or less. Survival of eggs and small larvae decreases greatly in hot, dry weather or with extended periods of heavy rain.

2. Yield loss will be about 4% per borer for infestations occurring before silks turn brown and 3% per borer after silks turn brown but before blister stage. These averages are based on published research but only account for physiological yield losses (reduced grain production) and do not consider yield loss from stalk breakage or ear drop. These factors are difficult to predict and vary with hybrid, cultural practices and weather.

3. Percent control with insecticides is suggested to be 70%; change this value if you think that control will be different in your situation.

Infestations are most damaging when corn borers enter the stalk early in corn's reproductive cycle. There is a short time between first egg hatch and significant stalk tunneling when corn borers are best controlled. Concentrate scouting efforts in this early egg laying period and repeat every three to five days. Often, second generation egg laying may extend to 21 days or more. Although later hatching corn borers do not directly reduce grain yield as much, they may still cause stalk breakage or ear drop. Early harvest of fields damaged by corn borers and selecting varieties with good stalk strength and resistance to stalk rot can reduce this loss.

If treatment is needed, time insecticide applications to coincide with the beginning of egg hatch to achieve acceptable control. Generally, liquid and granular formulations of the same insecticide are equally effective against corn borer larvae. However, in considering other pests that may need to be controlled at this time of year (western bean cutworms, rootworm beetles, grasshoppers, spider mites), liquids may be preferred. Rates and restrictions of registered insecticides for European corn borer control can be found on the label or at the UNL Entomology home page at http://entomology.unl.edu/instabls/ecb2nd.htm (TH&KJ)

 

Management Worksheet for Second Generation European Corn Borers

_______________ Number of egg masses per plant x 3 borers per egg mass* = _______________ borers per plant

_______________ Borers per plant x 4% yield loss per borer** = _______________ percent yield loss

_______________ Percent yield loss x _______________ expected yield (bu per acre) = _______________ bushels per acre loss

_______________ Bushels per acre loss x $_______________ sale price per bu = $_____________ loss per acre

$_______________ loss per acre x 70% control*** = $_______________ preventable loss per acre

$_______________ preventable loss per acre

-$_______________ cost of control (product + application costs)

=$_______________ profit (+) or loss (-) per acre if treatment is applied

If preventable loss exceeds cost of control, insecticide treatment is likely to result in economic benefit.

* Assumes survival rate of three borers per egg mass; may vary with weather and egg mass size. ** Use 3 percent loss per borer per plant if infestation occurs after silks are brown. The potential economic benefits of treatments decline rapidly if infestations occur after the corn reaches the blister stage. *** 70% is an average, you may use another value if desired.