AgriLife Research expert: Time to scout fields, gardens for psyllids

Writer: Kay Ledbetter, 806-677-5608, skledbetter@ag.tamu.edu
Contact: Dr. Arash Rashed, 806-354-5811, ARashed@ag.tamu.edu
Dr. Charlie Rush, 806-354-5804, crush@ag.tamu.edu

AMARILLO – Potato planting in northwest Texas will begin in about a month, but now is the time to look for the potato psyllid, a growing problem to the industry, according to a Texas A&M AgriLife Research study.

And it is not only the commercial potato grower who should be scouting, the researchers said.

Dr. Arash Rashed, AgriLife Research postdoctoral research scientist, and Dr. Charlie Rush, AgriLife Research plant pathologist in Amarillo, are monitoring the year-round existence of potato psyllids across the state as a project funded by the Texas Department of Agriculture and the Zebra Chip Specialty Crop Research Initiative. The initiative is led by Rush and sponsored by the U.S. Department of Agriculture-National Institute of Food and Agriculture.

The tiny insect is named the potato psyllid because that is the primary crop damaged by the bacterium it carries, which causes zebra chip of the potato, Rush said. While zebra chip is not harmful to humans, infected potatoes show dark stripes when chipped or fried and are rejected by major manufacturers, causing serious economic loss.

Rush said as research has progressed since the start of the initiative in 2009, one thing scientists are looking closer at is crops other than potatoes that can be damaged by the tiny insect or other plants that host them during the off-season.

Rashed’s study is closely monitoring the year-round activities of the psyllid to try to determine if local populations thrive in wild plants in the absence of cultivated potato fields, or migrate every year through the various regions with the help of wind trajectories, warmer temperatures and potato growth, or a combination of both.

“We want to see how the population of psyllids changes throughout the year – especially when the potatoes are not present,” he said.

The general belief is populations build up in northern Mexico or warmer locations and, as the temperatures rise, move northward as far as the Canadian border, Rashed said.

 

However, after a year-long process, which included collecting yellow sticky traps every two weeks in locations from as far south as San Antonio to Dalhart in the north, Rashed said he has trapped psyllids someplace with almost every collection in northern Texas, even during the snowy winter months.

This, combined with recent findings of local over-wintering populations in Idaho, indicates a strong possibility that localized populations may have a cold tolerance and survive harsh winters, he said.

In addition, psyllids can be found on related plants such as tomatoes, eggplants and peppers. And Rashed has caught them on yellow sticky traps in natural vegetation where no potato fields existed. Last year psyllid numbers peaked in natural vegetation adjacent to potato fields prior to potato emergence.

For that reason, Rashed said everyone from the home gardener to the commercial potato grower might need to start scouting for the tiny insect that could be finding alternative host plants to survive on, thus starting localized populations.

Yellow patches of curled leaves developing on what would otherwise be green vegetation might be an indication of their presence, he said. This type of psyllid is almost as big as an aphid and has the shape of a cicada with white stripes or patterns on the abdomen and thorax.

Plants with the psyllids and the pathogen will turn yellow and look stunted. Tomatoes, peppers and potatoes in backyard gardens showing these symptoms can be tested for the presence of the bacterium in the plants or screened for the insects, Rashed said.

“We are continuously monitoring the psyllids to see what happens to them once the potatoes are harvested,” he said. “What we’ve found is they disappeared temporarily after harvest, but only a few weeks later they were found again in locations that were potato-free.”

This year, in addition to the fact the psyllids did not disappear during fall and winter months in some northwestern Texas locations, Rashed said they are seeing a higher percent positive for the zebra chip pathogen.

“Last year, the highest percentage we saw was a little over 2 percent, but this year already we have seen collections with as much as 10 percent positive in areas close to San Antonio,” he said.

“With planting time coming up in the northern parts of Texas, we need to keep a close eye on fluctuations in psyllid numbers and those carrying the pathogen,” he said. “By educating the general public on this issue, they might be able to help us get a better idea of how widespread they are, as well as the damage they cause.”

There are several methods used to monitor the psyllid, with the most common being yellow sticky traps in the fields or natural vegetation next to the field, Rashed said. Some of the newer studies showed other methods such as D-vac, a reverse leaf-blower of sorts, or even sweep nets may provide better estimates of the actual number of psyllids present in the field.

“The yellow sticky traps are good at catching insects on the move,” he said. “But if the insect is already established on the plant, there is minimum movement of the insect and therefore, the numbers on the sticky traps may not represent actual numbers in the field.”

Rashed said homeowners who notice potential damage or collect insects can have plant samples – leaves and stem tissues – and insects tested at the Great Plains Diagnostic Network lab at the Texas A&M AgriLife Research and Extension Center, 6500 W. Amarillo Blvd., for verification. Only after verification would a treatment be recommended.

“The best way to control this disease is to control the vector,” he said. “Pesticides might need to be applied, but we would not recommend that until potato psyllid risk has been verified in a location. This is of particular importance, especially in light of recent reports of pesticide resistance in some psyllid populations.”

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