Melon Growers Gain Ground on Cucumber Beetle
June 7, 2023 
The striped cucumber beetle is a vector of the bacterial wilt pathogen.
Photo by Gerald Holmes
Cucumber beetles — both western striped and western spotted — remain a major problem to muskmelon growers in the Sacramento Valley for at least three reasons.
According to Amber Vinchesi-Vahl, an Area Vegetable Crops Advisor with the University of California Cooperative Extension (UCCE), those reasons include:
1. Conventional melon systems have very low thresholds for damage.
2. Cucumber beetle populations tend to be very high.
3. Organic growers rely on a limited number of tools in defense.
“Conventional control relies almost exclusively on insecticides when beetles are detected,” Vinchesi-Vahl says. “The general idea from pest control advisors in my area is: You see one striped beetle, you spray the field; a handful of spotted beetles, you spray the field. This is because the male cucumber beetles release an aggregation pheromone that then draws more beetles to the scene. It can seem like you have one or two beetles, and then overnight you’ll have many more.
“So, we’re working to improve IPM in melons for cucumber beetle.”
Acetamiprid Treatments
That work includes a possible breakthrough in the wake of a successful 2022 insecticide trial involving acetamiprid (Assail/UPL) and western striped cucumber beetles, the No. 1 threat to California melon growers. Considered one of the top conventional treatments, Assail is “very effective” at killing and controlling cucumber beetles, Vinchesi-Vahl says.
The trial, funded by the California Melon Research Board and conducted at a research farm on the UC Davis campus, evaluated acetamiprid alone and paired with a gustatory stimulant (CideTrakL/Trece). When mixed with an insecticide, CideTrakL encourages beetles to eat and, in turn, ingest more of the insecticide.
The combination treatments involved acetamiprid at a full rate and, of significance to organic growers, acetamiprid at a one-quarter rate.
The trial also included an experimental insecticide, indoxacarb (Avaunt/FMC). Although not registered in California on melons, Avaunt has fared well in the Midwest against corn rootworm, which is closely related to the cucumber beetle.
Vinchesi-Vahl and Ian Grettenberger, a Field and Vegetable Crops Entomology Specialist at UC Davis, found no significant differences in dead striped cucumber beetles among all three of the acetamiprid treatments — alone and at both the full and one-quarter rates with CideTrakL. Compared to the untreated control and Avaunt with control, “they were very successful at killing striped cucumber beetles,” Vinchesi-Vahl says.
Scarring Severity
That success carried over to scarring severity ratings — 0 being an acceptable melon with no scars or small scars, and 5 being a melon with extensive damage.
“Anything rated a 1 through a 5 would be considered a cull and not acceptable because it had too much scarring damage,” Vinchesi-Vahl says.
Using only the one-quarter rate of acetamiprid plus the CideTrakL, no melons presented with category 3, 4, or 5 scarring.
“It’s very effective at reducing scarring damage, which is great because if growers can use less of an insecticide, combined with the CideTrakL, they can get the same efficacy as full rate,” Vinchesi-Vahl says. “That’s really exciting news.”
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UCCE is resuming the trial this season.
The department is also continuing to evaluate the efficacy of the aggregation pheromone of the striped cucumber beetle in an attract-and-kill trap design for the western striped cucumber beetle. The project is also funded by the California Melon Research Board.
“CideTrakL paired with Assail looked very promising, even with the reduced rate of the insecticide, and we’re looking forward to diving into this and focusing more on this relationship in 2023,” Vinchesi-Vahl says. “In the long term we hope that improved IPM practices, including monitoring and targeted management, will help prevent and suppress damage by cucumber beetles.”
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