His study consists of seven different treatments to determine the best time to begin spraying:

  • Apply chemicals, similar to the management program used by potato growers, which means a soil treatment at planting and weekly foliar sprays beginning 30 to 45 days after the soil treatment regardless of psyllid numbers. This is the “farmer control” by which all other treatments are compared. Typically, growers use one chemical for two weeks and then switch to one with a different mode of action to try to prevent resistance buildup.
  • Making treatments when three or more psyllids are caught on sticky traps within a week.
  • Sweep-net sampling and treating after at least six psyllids are caught per 10 sweeps in a field.
  • Testing the psyllids to see if they carry the bacterium and spraying if they do.
  • Spraying based on immature psyllids collected per leaf sample. Two per leaf triggers a treatment.
  • Treating weekly as the potato growers do, but using a special mixture of pesticides.
  • An untreated control against which all other treatments are compared.

The field was planted the first week of April and sampling with sticky traps and leaf samples began the second week of May, Bynum said. The first commercial application-type treatment was made the first week of June. To date, psyllid numbers have not been high enough to warrant spraying based on the action threshold treatments.

“We will carry these out until 80 to 100 days after planting, depending on the insect pressure. That will take the crop almost to harvest,” he said.

“Last year we had hot psyllids (those carrying the bacterial pathogen) in both the Olton and Dalhart areas when we surveyed producers’ fields for Dr. John Goolsby,” Bynum said. “In our test at Bushland last year, we started with heavy psyllid pressure early in the season. This year, we are starting with hardly any. So it is unpredictable when pressure will begin and how long it lasts.

“That’s why it is important to see if we can find a sampling method that allows us to better target treatments at appropriate times, instead of the current blanket method of treating throughout the growing season.”

Bynum said last year’s cost comparison between commercial and experimental treatments showed as much as $300 difference per acre in chemical costs.

“If we can come up with a method to make this decision, then producers can save the cost of the chemical and application, and at the same time prevent the exposure to severe incidences of zebra chip,” he said.

This also helps reduce the potential for developing resistance to insecticides, Bynum said.

Michels is looking at both large-farm scale and small-plot chemical control. The current practice of chemical control is based on growers’ efforts to get ahead of the psyllids and stay ahead, fearing that if they wait, they will get behind and not be able to catch up and lose a good portion of the production.

“What is typically being done is treatment with a neonicotinoid insecticide when potato plants emerge,” he said. “That should provide protection for 30 to 40 days. Producers can’t immediately go back with another neonicotinoid for fear of building up resistance, so we are trying to find other chemicals that will provide acceptable control.”

Researchers are looking at four chemical application timings: the commercial grower sequence, only when hot psyllids are found, no treatment and one quitting early.

“That’s what this summer is for, to see if any of the new compounds work.

And we will tie in with Ed Bynum’s work,” Michels said. “The long-term goal is to reduce the amount of chemicals used but be able to give the same amount of protection.

“We want to come up with a sequence of the proper chemicals so we won’t get chemical resistance in the psyllids and also reduce the amount of chemical used.”

In another study on the potato field, small tents have been erected to allow Rush and his team to inoculate plants with 30 psyllids. After allowing them one week to feed, the psyllids are killed off and then the plants are sampled weekly for the zebra chip titer.

“We want to see when the pathogen starts developing in the plant, when the disease starts expressing itself and how that relates to severity of disease in the tubers,” he said.

It is possible that if psyllids come in late, even if they infect the plant, the pathogen may not have time to move to the tubers and cause zebra chip. If that is the case, then there would be no need for end-of-season insecticide applications, Rush said.

“Our long-term goal with all these studies is to develop a pest risk assessment tool that the producers can use and feel confident in.”

SKledbetter@ag.tamu.edu