New U of I entomologist seeking pest-control options for specialty-crop farmers

The mint stem borer has emerged as a threatening pest of Canyon County mint production, and with no insecticides registered to protect the crop, the region’s farmers lack tools to combat it.

Fortunately, University of Idaho’s new entomologist and Extension specialist, Marcelo Dimase, has prioritized finding an effective insecticide option for mint. Upon identifying a promising product, Dimase will pursue a special local needs exemption, which would grant the area’s mint farmers special permission to use a product approved only for other crops.

Dimase, an assistant professor of entomology who joined the university in early August 2025, is based at U of I’s Parma Research and Extension Center, where he leads pesticide safety and education programs and is the state liaison for Idaho’s IR-4 Project. Funded with a grant from the U.S. Department of Agriculture’s (USDA) National Institute of Food and Agriculture, the IR-4 Project provides research and testing in support of new pesticide registrations for specialty crops, which may have too few acres in production to entice investment by large chemical companies.

“The problem these specialty crop growers face is they don’t have as many tools as growers of larger crops such as potatoes or corn,” Dimase said. “The industry doesn’t necessarily test pesticides on small crops, because it knows it is not going to sell many products to mint growers.”

Since the state’s IR-4 Project started in 1963, the program has resulted in more than 200 new products becoming available to producers of crops such as peas, beans, oilseeds, onions, tree fruit, mint and grasses.

Dimase works closely with Will Meeks, minor use pesticide specialist at U of I, who is based at the Twin Falls Research and Extension Center. Through IR-4, U of I conducts 10 to 15 trials per year — about two-thirds of which take place in the Magic Valley and a third of which are done in the Parma area — and tests the efficacy and residue of various fungicides, herbicides and insecticides on a host of specialty crops. The tests support special-needs exemptions to protect designated specialty crops.

Dimase hypothesizes that Plinazolin, a broad-spectrum insecticide manufactured by Syngenta for several major crops, will also be effective against mint stem borer. Plinazolin has not been registered for any U.S. crops yet, but Syngenta expects to release it within the next one or two years. To expedite reviewing the chemical, Dimase intends to perform trials in commercial fields in the Parma area in cooperation with growers who have had problems with mint stem borer.

Dimase also plans to evaluate how applying Plinazolin on mint crops may adversely affect beneficial insects, such as bees.

Upon finding a viable option for mint farmers, Dimase hopes to obtain IR-4 funding to conduct residue testing, which would be the next step in the approval process.

Another priority project for Dimase will be to research the species composition of Idaho thrips, which are tiny, winged insects that suck plant sap and can cause significant damage to ornamental and food crops. For example, thrips can reduce onion yields by up to 20%, and different species may exhibit differences in insecticide resistance, as well as the window during which insecticide treatments against them are most effective. Furthermore, onion thrips can spread an economically important disease of onions, iris yellow spot virus.

“If you look at the acreage of onions in our area of Canyon County, it has been reduced significantly due to falling onion prices and for pest-management reasons such as increasing pressure from onion thrips and iris yellow spot virus, as well,” Dimase said.

Dimase was born and raised in Brazil, where he studied agricultural engineering as an undergraduate at University of Sao Paulo. He became interested in a career in agriculture based on his experience helping at his grandparents’ small farm, where they raised avocados, mangos, corn, beans, herbs and other crops, mostly for their own consumption.

Seeking to improve his English, he worked for about a year at a couple of farms in Australia, where he drove tractors and fed pigs and sheep.

Dimase went on to earn a master’s degree from Louisiana State University and a doctorate from the University of Florida, both in entomology, before accepting a position as a postdoctoral researcher at Cornell University.

His master’s thesis entailed studying behaviors of Lepidopteran pests — the family of butterflies and moths — of corn, and his doctoral dissertation targeted whiteflies in vegetable crops such as tomatoes, zucchini and eggplant.

He chose to work for U of I over other options based on the flexibility of the job requirements and his admiration of the Vandal faculty he met while interviewing.

He and his wife, Dani, have a 3-year-old son, Maurice. Dimase enjoys playing soccer, especially with Maurice.