Farm Talk

September 25, 2013

A silent yield killer

Joshua Coltrain
CNHI

Parsons, Kansas — Mayetiola destructor. Sounds almost like a monster in one of the old mutant lizard movies right? Actually, this is the scientific name for what we commonly call Hessian fly. This pest is often ranked as the most important insect pest in winter wheat, even though some in our area would argue that some aphids are just as important.

I have often wondered the origin of the name Hessian fly. It was first observed in New York in 1779 near a Hessian soldier encampment and this is where the name came from. It was first detected in Kansas in 1871. From 1900 to 1970, only one in every four years or so was classified as being free from fly injury. From the ‘70s to the ‘90s, infestations were lower, but the incidence has increased recently.

For 140 years, Hessian fly has been a voracious pest of wheat causing untold yield loss. However, before we proceed to it’s life cycle, it must be pointed out that there are no control methods available once the crop has been infested. The only management strategy available to producers is prevention.

A Hessian fly adult is tiny, about 1/8 inch long that would look like a gnat. The adults emerge from August through November on warm days. After mating, females lay eggs in the leaf grooves of wheat seedlings. The eggs themselves resemble the early stages of leaf rust and can be seen by the naked eye.

In three to ten days the eggs hatch tiny larvae that move downward during the night when humidity is relatively high. The larvae, technically maggots, cannot survive being left exposed on the surface of the leaf. The larvae feed on the plant by taking sap from near the base of the plant for a week to a month. They often make a home between the leaf sheath and the main stem.

Full grown maggots are white, legless, headless and about 3/16 of an inch long. They gradually form brown, 1/8 inch capsule-like cases (puparia). This stage is commonly called the flaxseed stage as they greatly resemble the seed from a flax plant. The pest overwinters in this stage and also over summers (for lack of a better term) as well.

Symptoms from fall infestations are not always obvious. The infested shoot may be stunted, or even killed. If infestation occurs during seedling emergence, an entire stand may be killed, but this is rare. One of the signs to scout for infestation is an undeveloped central shoot with broad, thickened, and bluish leaves. Though remember, even if the infestation is confirmed, there are no treatments to remedy the problem.

Even though there is no treatment, identifying the amount of infestation is an important step in proper management. Once the level of infestation is understood, other management practices may be implemented.

Infested stubble should be destroyed. Research studies have shown that thorough incorporation can accomplish this. These studies showed that if the residue was buried to a depth of one inch, only 26 percent of the Hessian flies would emerge. At two inches, the percentage drops to six percent. Burning has also been shown to destroy the flaxseeds above ground, but there can be flaxseed survive because fast moving fires do not destroy low enough in the crown.

Hessian fly is more of an issue in a continuous wheat system, so crop rotation is highly recommended.

There is a fly-free date. In the Wildcat Extension District, the fly-free date is October 12 or 13. In theory, waiting to plant until after this date allows for the fall flies to emerge and die before the wheat can be infested. However, many factors can play a role in whether or not this strategy works, most important of which is the relative mildness of a given late fall/winter.

As with most wheat pests, volunteer wheat is the perfect host for Hessian fly. Due to this, volunteer wheat should be destroyed. Not destroying volunteer can render other management strategies ineffective as well. Unfortunately, this also applies to your neighbors volunteer as well.

If you have questions or would like more information, please call me at the office (620) 724-8233, or e-mail me at jcoltrain@ksu. edu, or visit the Wildcat Extension District Website at www.wildcatdistrict.ksu.edu. £