Pest Damages Wheat, Oats, Barley

Each April and May, cereal leaf beetle larvae damage wheat, oats, and barley by feeding on leaves, eating long strips of green tissue between leaf veins. They may skeletonize entire leaves, leaving only the transparent surface tissue on the lower leaf.
    Leaf feeding reduces the plant's ability to make its food and limits grain seed production, particularly if the upper leaves are destroyed. It can reduce yields from 10 to 45 percent, depending on the number of beetles present.
Beetle populations did not explode in the mid-Atlantic states as in the upper Midwest. In the past three to four years, however, populations have greatly increased. Tens of thousands of acres were treated for cereal leaf beetle and/or damaged by it in 1994 and 1995.
    Until an improved management system was developed, growers relied on an old economic threshold for control recommendations. This threshold was one large larva per leaf and as much as 50 percent leaf loss before treatment was recommended.
    With the advent of new higher-yielding varieties and intensive management programs (e.g., better fertilization programs, improved disease control), this old threshold appeared to allow too much yield loss by allowing too much damage to occur.
 

Farmers Were Too Late to Stop Loss

By the time this threshold was reached, farmers could not get to their fields soon enough with sprayers to stop the loss, said Keith Balderson, Essex County agricultural agent with Virginia Cooperative Extension. Spraying too late-after the damage was done-wasted chemicals, causing farmers to lose even more profit, and put undue stress on the environment.
    To solve these problems, a three-year field research project was mounted from 1995 through 1997 by an interstate team of entomologists from Virginia and North Carolina (Ames Herbert with Virginia Tech/ Virginia Cooperative Extension and John Van Duyn and JR Bradley with North Carolina State University).
 

Cooperative Project Sought Answers

The project was cooperatively funded by the Virginia Small Grains Board, the North Carolina Small Grain Growers Association, and the federal IPM program. Over the three-year period, 27 field experiments were conducted at multiple locations in eastern Virginia and North Carolina.
The project gathered data on:

• biology and life cycle of the cereal leaf beetle in the mid-Atlantic region
• impact of beetle feeding on grain yields
• insecticide control strategies

A new economic threshold was released as a result of this work, based on the number of cereal leaf beetle eggs and small larvae present rather than large larvae. This threshold allows the control decision to be made well in advance of excessive leaf damage or potential yield loss. Eggs and small larvae are easy for growers and scouts to locate on leaves in the spring, and the sampling system used to make the treatment decision is relatively easy and time-efficient.
    Proper use of the new threshold allows growers, before any significant leaf damage has been done, to identify and treat fields in danger of potential yield loss from beetle feeding. This new threshold, if it occurs, appears about one month earlier than the old one. Therefore, any required treatments can be tank-mixed with other field application materials, such as nitrogen or fungicides, so the application cost is reduced.
 

Growers Eager to Adopt New Threshold

Acceptance of the new cereal leaf beetle threshold by growers and consultants has been excellent, and adoption is well under way.
    "Using the new threshold resulted in only a few fields actually needing treatments (in 1998)," said Mike Parrish, agricultural agent in Dinwiddie County with Virginia Cooperative Extension. "Most did not, and growers were able to save a lot of money in a year when grain prices and yields were down and savings were critical."
    The cereal leaf beetle project is an excellent example of the value of pooling expertise and resources across state lines and institutions in order to move quickly to solve a critical problem. Growers are already seeing the benefits, and the hope is that this project will serve as the future model in IPM research and Extension programs.
 
 

Cereal leaf beetle eggs (orange) are shown on the upper surface of a wheat leaf.	These wheat leaves have been damaged by the cereal leaf beetle's larval feeding.	After a field scout walked through an infested field, the scout's boots were covered with the larvae of the cereal leaf beetle
A cereal leaf beetle larva covered with its own black fecal material feeds on a wheat leaf.	Eggs and small larvae, like the larvae here feeding on wheat leaves, are easy for growers and scouts to locate in the spring.	This wheat field has been damaged by cereal leaf beetle - leaf feeding can reduce yields from 10 to 45 percent.

 

For more information contact:
D. Ames Herbert
Tidewater Agricultural Research & Extension Center
6321 Holland Road
Suffolk, VA 23437
(757) 657-6450 ext. 122