The U.S. pesticide industry has evolved over the decades with products which are safer for the environment and more effective on crop pests and diseases.

The first generation of insecticides included highly toxic compounds to safeguard crops. The second generation — synthetic organic compounds — brought safer and more effective means for control.

Old timers in agriculture likely remember organophosphate and carbamate insecticides in the 1940s and 1950s followed by the pyrethroids in the 1970s. Back in the day, most chemistry controlled a broad spectrum of insects through contact activity or ingestion.

Today, the vast majority of insecticides, if not all, have either translaminar (leaf penetration) and/or true systemic (root uptake) activity.

“These developments have made a huge positive difference in insect control,” says John Palumbo, University of Arizona entomologist based at the Yuma Agricultural Center.

“Today, we’re using more soft chemistry than harder chemistry.”

Palumbo addressed past, present, and future insecticidal issues in desert-grown winter vegetables during the Bayer CropScience Vegetable and Citrus Consultants Meeting held in San Diego, Calif., in late July.

Today, insecticide usage is down significantly in winter vegetables. In 1991, Palumbo says growers and pest control advisers (PCAs) applied an average of 12 insecticide sprays per leafy vegetable crop. The number dropped to about eight sprays in 1996. Last year, the number plunged to an average of 4.5 sprays. This represents an almost 70 percent reduction in insecticide sprays over the last 20 years.

“Newer, green products are more efficacious compared to the older products,” Palumbo said.

The use of broader, toxic chemistry has declined due to the loss of product registrations in several types of lettuce. In addition, chemical companies brought new compounds to market in the early to mid-1990s, including the products Confirm, Success, and Admire. More recently, Movento and the diamides have allowed farmers to gain even better insect control with fewer applications.

The diamide class of chemistry “has risen to the top,” says Palumbo, as highly effective insect control products in veggies.

In desert vegetable fields, the top insects which prefer to dine on fall lettuce include whitefly, aphids, and the Leptidopterous pest complex, including the beet armyworm (Spodoptera exigua), cabbage looper (Trichoplusia ni), and corn earworm (Heliocoverpa zea).

Anyone who lived in the arid, low-desert region of southern California and Arizona 20 years ago will remember huge white swarms of Bemisia whitefly which resembled a Biblical pestilence outbreak.

To combat the whitefly epidemic, Arizona and California produce growers, in cooperation with Miles Inc., requested and received a Section 18 emergency use for its new insecticide Admire 2F (imidacloprid-based) to protect vulnerable winter vegetables in Yuma and Imperial counties. Today, Miles Inc. is called Bayer CropScience.

Successful whitefly control was achieved with a 16-ounce rate per acre application of Admire 2F applied by pre-plant injection. The dose provided immediate plant protection, plus 45-60 day residual control.

“The result was the compound basically flat lined whitefly nymph populations,” Palumbo explained.

Over the last 20 years, Palumbo has conducted numerous insecticide trials in vegetables to compare insecticide product efficacy against whitefly. Over the last decade, he has conducted meetings and placed phone calls with PCAs and growers on the insecticides used for insect control plus crop losses.

Although imidacloprid may not provide the same level of control it did 20 years ago, UA research along with reports from PCAs and growers suggest that excellent whitefly control can be achieved with imidacloprid products when used at high rates per acre — for example 10.5 ounces of Admire Pro.

Palumbo said, “Imidacloprid-based products are the most cost effective soil insecticides on the market for whitefly control on lettuce and broccoli.”

Product placement is crucial at the root and secondary root levels which can provide 40 days of whitefly residual control.

Palumbo calls the newer insecticide Movento 2SC (spirotetramat) an effective compound for whitefly control.

“The fact is you can come in over the crop top with Movento, even by air, and still pick up a lot of immature whitefly populations at the basal part of the plant,” Palumbo said. “Movento has very good residual activity.”