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Softer insecticides playing hardball against pests in desert-grown lettuce

The latest green or soft-based insecticide chemistry soon to hit the market is creating some grand slam results in desert lettuce field studies in Yuma, Ariz. The products will serve as new implements in growers' toolboxes.

“Just because it's soft doesn't mean it's not good or effective. It can be very effective,” said University of Arizona (UA) Research Entomologist John Palumbo who led the research.

“When the Environmental Protection Agency (EPA) places a ‘reduced risk’ connotation on a product, it is essentially green or soft chemistry. It's environmentally benign for the most part. It's easy on worker safety. It's a good label to have on a product.”

Even today's EPA approved products that don't earn the ‘reduced risk’ label are relatively soft, Palumbo said.

Over the last three years Palumbo and his staff have compared the newest ‘reduced risk’ insecticides with current insecticides on the market in desert lettuce field plots at the UA's Yuma Agricultural Center.

New product evaluations were based on side-by-side comparisons in replicated field plots over three or more years. The analyses were derived through summarizations from several trials.

No score was given to products without two or three replicated research trials in at least two growing seasons. One exception was the product Alverde (BASF) on flea beetles. While Palumbo had three trials on different crops over two years, he couldn't summarize them across crops but the results were consistent in each trial. Targeted insects in the studies included lepidopterous (lep) larvae, aphids, whiteflies, flea beetle, thrips, and leafminers.

Palumbo shared his research results with growers, pest control advisors, and other industry leaders at a preseason vegetable workshop in Yuma in August.

Palumbo gave each new product a grade: ‘A+’ for new products that performed consistently better than current or alternative products; ‘A’ for as good or better than alternative products; ‘B’ for good but didn't perform as consistently as the current or alternative products; and ‘C’ for not as good as the alternatives or standards, but does provide suppression.

Palumbo's findings included:

Radiant SC — spinetoram

(Dow AgroSciences)

Chemistry: Second generation spinosyn;

Mode of action (MOA): Nicotinic Acetylcholine receptor agonist;

Activity route: Foliar-locally systemic (translaminar)

Pest spectrum: Lep larvae, thrips, and leafminers;

Toxic profile: Reduced risk.

Key desert fit — “Radiant gets an ‘A’ comparative efficacy grade against lep larvae when compared to the products Success (Dow AgroSciences) and Proclaim (Syngenta). Radiant also earned an ‘A’ compared to Success against leafminers,” Palumbo said. “For thrips, Radiant received an ‘A+’ as opposed to Success largely because of residual benefits.”

Coragen SC — rynaxpyr, (DuPont)

Chemistry: Anthranilic diamide;

MOA: Disruption of Ca balance at the ryanodine receptor;

Activity route: Foliar and soil — contact/translaminar/systemic via root uptake;

Pest spectrum: Lep larvae, leafminer, whitefly;

Toxic profile: Reduced risk.

Key desert fit — “Coragen is a completely different product from a brand new chemistry and with a unique MOA. Instead of acting as a traditional neurotoxin, the product affects the neuromuscular junction — essentially it works where the nerve meets the muscle,” Palumbo said.

In comparative efficacy, Palumbo gave Coragen an ‘A’ against lep larvae for foliar activity when compared to Success and Proclaim. In terms of lep larvae for soil activity where there is no standard, an ‘A+’ was earned. Against leafminers, Coragen earned an ‘A.’ Whitefly control via Coragen was deemed a ‘B’ to a ‘C’ compared to Oberon (Bayer CropScience) and Neonicontinoids such as Admire Pro (Bayer) or Assail (Cerexagri).

Tesoro — pyridalyl (Valent)

Chemistry: pyridalyl;

MOA: Unknown, thought to be unique;

Activity route: Foliar — contact and ingestion (not translaminar);

Pest spectrum: Lep larvae, thrips;

Profile: Organophosphate alternative.

Key desert fit — For lep larvae (beet armyworm), Tesoro received an ‘A’ for efficacy compared to Avaunt (DuPont) and Intrepid (Dow). Yet Tesoro earned a ‘B’ against leps (cabbage looper) against the same two current insecticides. In thrips, Tesoro scored an ‘A’ compared to pyrethroids.

Alverde — metaflumazone (BASF)

Chemistry: Semicarbozone;

MOA: Na channel modulator;

Activity route: Foliar — contact and ingestion (not translaminar);

Pest spectrum: Lep larvae, flea beetle;

Toxic profile: Reduced risk.

Key desert fit: Against lep BAW and CL, Palumbo graded Alverde a ‘B’ compared to Avaunt and Intrepid. Against the flea beetle, an ‘A’ was earned against pyrethroids and diazinon. Alverde could be on the market within a year, Palumbo said.

Movento — spirotetramat (Bayer)

Chemistry: Ketoenols — tetramic acid derivatives;

MOA: Lipid biosynthesis inhibitor (same as Oberon);

Activity route: Foliar systemic (basipetal and acroptetal movement);

Pest spectrum: Aphids, whitefly;

Toxic profile: Reduced risk.

Key desert fit: Movento earned an ‘A’ against whitefly compared to Oberon and Courier (Nichino). Against the green peach aphid, an ‘A’ mark was earned compared to Assail (Cerexagri) and Beleaf (FMC). For foxglove aphids and lettuce aphids, it received an ‘A+’ mark versus Assail and Beleaf.

Note: Palumbo didn't score Bayer's new Synapse (flubendiamide) since his studies began in fall 2006 with only two trials.

Changing times

In the 1940s the chemical class organochlorines led the battle against insect control. The modern chemical era debuted in the early 1990s with neonicotinoids and the product Admire. From 1996 to 1999, four new chemical classes, all yielding reduced risk products, entered the market including the products Knack (Valent), Courier, Confirm (Dow), and Success.

The evolution of effective insecticides continued to expand from 2000 to 2004 with Proclaim and Platinum (Syngenta), plus the reduced risk products Assail, Intrepid, Fulfill (Syngenta), and Avaunt. From 2005 to 2006, three additional products hit the market including Venom (Valent), Oberon, and Beleaf.

The latest products tested by Palumbo will add even more options for desert lettuce growers.

Generic insecticides

Palumbo said generics would also impact future insecticide use. Since imidacloprid went generic about two years ago, there are 13 imidacloprid generic products licensed in Arizona today including Admire Pro. Bifenthrin, which recently went generic, has nine generics registered in Arizona.

“I find this is interesting because it brings up the question — How will this influence not only present uses of products like the pyrethroids and soil applied imidacloprids, but also future development as far as new chemistry down the road,” Palumbo asked

Yuma insecticide use

Over the last three lettuce growing seasons (2004-2005, 2005-2006, 2006-2007), Yuma County Cooperative Extension has gleaned insecticide use information from growers, PCAs, and other industry leaders.

During the annual lettuce insect loss workshops held each April, Palumbo collected information on which insects caused the most problems in Yuma lettuce fields plus which insecticides were most often used for treatments.

Those sharing information at the workshop represented the majority of Yuma's head lettuce acreage, including 33,970 acres in 2004-2005, 46,270 acres in 2005-2006, and 32,550 acres during the 2006-2007 season.

Here is the three-year summary of insecticide use:

Fall lettuce

Stand establishment (chemigation): Pyrethroid use was fairly steady with about 50 percent of the acreage treated; Diazinon use dropped by 50 percent in 2007.

Lep larvae: Success was a big player in the upper 90 percent range or almost two to one over the other players; Intrepid and Avaunt held steady, upper 50 percent and 20 plus percent respectively; and Proclaim had significant increases in 2006-2007, from the teens to over 40 percent of the acres. Bt had no reported use in 2007.

“The trend suggested in this data is for every two sprays of Success, there's one spray of something else. That's wise resistance management,” Palumbo said. “You can flip-flop any of these, but the fact that they're all being used across the board tells us that PCAs are responsibly using these products to help sustain their use.”

Whiteflies: Imidacloprid, the 1990s standard, peaked in 2006 with about 80 percent of the acreage and dropped in 2007 likely because of Assail usage (20 percent plus use in 2007). Endosulfan increased from 20 percent in 2005 to over 30 percent in 2007.

Miscellaneous insects: Pyrethroids are the major player in fall lettuce in Yuma with three applications on average.

Spring lettuce

Thrips/aphids: Pyrethroids (three sprays) and Success were the big drivers used by growers in treated acreage percentages, 85 percent to 100 percent. Endolsulfan (several generic brands) was a steady player, 40 percent to mid-50 percent range. Lannate (DuPont) peaked in 2006 (over 60 percent) and then fell to 40 percent of the acreage in 2007.

Aphids only: Assail (1.3 applications in 2006, 1.5 in 2007) and Beleaf (1.2 apps) featuring new active ingredients increased. Fulfill and Provado use steadily declined.

Overall Imidacloprid use fell from 80 percent in 2006 to 40 percent in 2007.

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