CDFA Surveys Predict Curly Top Vectored by Leafhoppers

By Patrick Cavanaugh, Editor

Curly top virus is a common disease in California. In its worst years, entire fields have been lost to curly top in the foothills of the Central Valley, and it can infect a variety of plants from a total of 44 plant families as well as 300 individual species.

Curly top commonly affects tomatoes, peppers, beets, spinach, potatoes, and beans, as well as a variety of weeds. A common characteristic of curly top is stunting of the plant as well as curling and twisting of the leaves, where it gets its name, curly top. Leafhoppers are the main vector of the virus.

Currently, the CDFA conducts a yearly curly top prediction where they monitor numbers and the leafhopper population as well as the prevalence of the virus to give a scope of what the upcoming year might look like.

“Curly top virus was very low in 2018 as predicted—based on the amount of virus carried by the leafhoppers and the leafhopper population,” said Bob Gilbertson, Plant Pathologist, Department of Plant Pathology at UC Davis.

“We hope that CDFA will continue to carry out the leafhopper screening for the virus and for the population so growers get a prediction of what the curly top incidents will be the coming year,” Gilbertson said. “It’s good that we can tell growers when there’s going to be a bad curly top year so they can implement additional strategies.”

These strategies include changing where they’re going to plant a field or using timed insecticides, particularly systemic insecticides like the new Verimark (From FMC) insecticide to manage curly top.

“We’ve already found that that material can slow down the spread of curly top in a field,” Gilbertson explained. “So in a year where it’s predicted to be bad—high populations of leafhoppers carrying high amounts of the virus—then you as a grower would then want to consider using some of these insecticide approaches.”

Jamming Leafhopper Signals

Jamming Leafhopper Signals to Reduce Insect Populations that Vector Plant Disease

By Patrick Cavanaugh, Farm News Director

An innovative team of researchers at the San Joaquin Valley Agricultural Sciences Center, USDA Agricultural Research Services (ARS) in Parlier Calif., are trying to confuse leafhopper communication in hopes of reducing certain devastating plant diseases. Of particular interest is the glassy-winged sharpshooter, a large leafhopper that can vector or spread the bacteria Xylella fastidiosa from one plant to another which causes devastating plant diseases such as Pierce’s disease in grapes and almond leaf scorch.

Dr. Rodrigo Krugner, a research entomologist on the USDA-ARS Parlier team since 2007, explained, “We started on this glassy-winged sharpshooter communication project about two years ago. These insects use substrate-borne vibrations, or sounds, to talk to, identify and locate each other; actually do courtship; and then mate,” Krugner said.

Click here to hear LEAFHOPPER SOUNDS!

Glassywinged Sharp Shooter

“This area of research started probably 40, or 50 years ago with development of a commercially-available laser doppler vibrometer (LDV), a scientific instrument used to make non-contact vibration measurements of a surface,” Krugner said. “Commonly used in the automotive and aerospace engineering industries, the LDV enabled an entomologist to listen to and amplify leafhoppers communicating,” Krugner said. “We’ve been doing recordings in the laboratory, learning about their communication with the idea of breaking, or disrupting, that communication. Once we disrupt that, we can disrupt mating and thereby reduce their numbers in vineyards and among other crops.”

Krugner noted the research team is evaluating two different approaches: one is to discover signals that disrupt their communication, and the other is lure them away from crops or towards a trap. “We may be looking at female calls, for example. An analogous system would be the pheromones, or long-range attraction volatile chemicals released by female lepidoptera, to attract males.” However, since leafhoppers use only sound, Krugner said, “We’re trying to come up with signals to disrupt their mating communication. We’re also looking at signals to jam their frequency range, 4000-6000 Hz, so they cannot hear each other,” Kruger said. “We’re also looking at signals that can be used to aggregate them, or lure them, into one section of a crop, or maybe repel them from the crop. These are all different approaches that we’re investigating right now.”

Krugner explained, “Researchers are attempting to perfect the disruptive sounds in order to do the things we need—to actually implement a management strategy for disrupting not only glassy-winged sharpshooter, but anything in a vineyard that actually communicates using vibrational communication. We know what they are saying to each other, which is very important. In the laboratory, the signals that we have look promising in disrupting the communication of these insects, so we’re taking them into the field.

Current mating disruption trials are underway in Fresno State vineyards. “We’re going to finish that research, hopefully, next year,” said Krugner, adding, “usually, fieldwork takes two to three years to show something.”

(Featured photo: Rodrigo Krugner, research entomologist, USDA-ARS, Parlier)