Reduced rate performance of Aztec

Aztec, a recent newcomer to the soil insecticide market, combines two chemicals, tebupirimphos, an organophosphate, with cyfluthrin, a pyrethroid. The combination of these two insecticides is designed to control a broader range of pests, such as corn rootworms and black cutworms, than just one of the chemicals alone. Aztec can be applied either in furrow, a band, or in a t-band. The labeled rate is 6.7 ounces of product per 1,000 row feet.

The application of soil insecticides at a reduced rate (i.e. below manufacturer's label rates) for corn rootworm control has been widely tested by university entomologists. The reduced rate concept has generated much interest, and sometimes controversy. But all of the "older" corn rootworm insecticides have been tested at reduced rates and most have been found to be equally as effective at the 3/4 rate as the full rate of the same insecticide, even when exposed to heavy rootworm feeding pressure. A summary of these previous tests can be found in last year's ICM news letter on pages 44-45.

Aztec is a newer chemistry and was not included in the earlier tests conducted in 1988-1992. To answer potential questions about Aztec at reduced rates, Jim Oleson, agricultural specialist in the Department of Entomology, evaluated the performance of Aztec in side-by-side comparisons at both the full rate and 1/2 rate during the past four years. Each insecticide was given a consistency rating based on the percentage of tests in which adequate root protection was achieved. By examining the percentage consistency in the table, it can be shown that Aztec has performed just as well at either the 1/2 rate or the full rate. There was a single test in the t-band evaluations in which the full rate did not provide adequate protection (root rating of 3.5), while the 1/2 rate did; therefore, the 86 percent consistency. Sometimes those things happen!

There are several important factors to remember regarding reduced rates. One, no chemical manufacturer will recommend a reduced rate from that stated on the insecticide label. Two, if a farmer uses a reduced rate, the manufacturer would not have a legal obligation to warranty product performance. Three, all insecticide boxes must be calibrated; when you cut the rate, there is less room for error in applying the amount you need. Four, evaluate reduced rates on a limited number of acres before committing all of the insecticide-treated ground to this method. Five, it is not illegal to use an insecticide at a reduced rate.

Four-year summary of corn rootworm insecticide performance, 1992-1996.

Insecticide* Placement Rate Ounces product per 1,000 row feet Root rating Percentage consistency
Aztec 2.1G furrow 1/2 3.35 2.4 100
Aztec 2.1G furrow full 6.7 2.3 100
Aztec 2.1G t-band 1/2 3.35 2.4 100
Aztec 2.1G t-band full 6.7 2.3 86
Untreated check - - - 4.0 0

Source: Iowa State University

* All data is based on 7 tests except 1/2 rate t-band (5 tests).

This article originally appeared on pages 47-48 of the IC-478 (6) -- April 28, 1997 issue.

Updated 04/27/1997 - 1:00pm