January 2019

Making progress on pale cyst nematode infestation in Idaho By Zeke Jennings

For the past decade, pale cyst nematode (PCN) has been an unwelcome topic for potato growers.

While the destructive parasites aren’t eradicated in eastern Idaho, where most of the potato field contamination has occurred, efforts are making progress. In 2007, nearly 20,000 acres were part of the U.S. Department of Agriculture Animal and Plant Health Inspection Service’s (USDA-APHIS) regulated area. As of Dec. 1, 2018, that number was down to 7,554, with 3,277 acres still classified as infested.

To be infested, inspectors must find at least two cysts from two different soil samples with one of those cysts containing viable PCN eggs or juveniles. Regulated fields are fields that have been exposed to soil or other articles containing PCN and are considered high risk for infestation.

The infestation has been contained to an area with an 8.5-mile radius that spans portions of Bingham and Bonneville counties, mostly located southwest of Idaho Falls.

If unchecked, PCN can cause up to 80 percent yield loss in potato fields, the USDA-APHIS said on its website. Infested potato plants can exhibit yellowing, wilting or death of foliage, none of which has been observed in the affected Idaho fields.

Tina Gresham is the director of the USDA-APHIS’s Pale Cyst Nematode program. She delivered a presentation during the The Big Idaho Potato Harvest Meeting in Fort Hall on Nov. 14. Gresham shared her notes with Spudman from that presentation, which covered the state of the program and the status of PCN eradication.

• In general, the infestations detected in recent years are much smaller than those detected in the early years of the program. In recent years, most new fields are detected at the lowest possible detection level for the survey method in use. This indicates that fields are being detected much earlier in the infestation process and soil movement from those fields (and by cascading effect, the exposure of other fields) is being contained more quickly. Earlier detection means that fewer fields are exposed over time.
• Eradication treatments are ongoing with 1,3-dichloropropene (Telone II) and the trap crop litchi tomato (Solanum sisymbriifolium). Both have been effective at reducing viable PCN populations on infested fields and also have been good alternatives to methyl bromide soil fumigant that the program stopped using after 2014.
• Four fields have been treated with the litchi tomato trap crop since 2015; no viable PCN has been detected on any of them.
• Litchi tomato is listed by ISDA as an invasive species because it is non‐native to Idaho. Its use on PCN-infested fields is permitted with strict requirements to ensure the plant is contained to treatment areas and is not allowed to produce mature fruit (seeds).
• The PCN program monitors all current and past fields treated with litchi tomato (a minimum of five years after treatment) to ensure the plant does not carry over after treatment.
• Despite rumors to the contrary, litchi tomato has not been found anywhere outside of the four treated fields.
• Telone used by the PCN program under a 24c (special local needs label) allowing treatment rate up to 36 gallons per acre, which is higher than the standard application rate (typically ~20 gallons per acre). More than one annual treatment is required but multiple treatments have been effective at reducing PCN viability.
• In 2018, one field (71 acres) was treated with litchi tomato; three fields (430 acres) treated with Telone II. Results from the 2018 treatments are not yet available; results expected over the winter of 2018-19.
• From treatments conducted between 2007 and 2017, nearly 75 percent of all infested acres have reached the point that viable PCN eggs are no longer detected in soil samples.
• Just over 50 percent of all infested acres are also eligible to return to potato production. A soil survey is required following each potato crop to screen for the presence of viable PCN.
• One infested field detected in 2006 has returned to potato production; no viable PCN was detected after the first crop. Results from the second crop (grown in 2018) are pending, with results expected early 2019.

UPDATE: APHIS announces additions, removals to PCN infested area

For information on the USDA-APHIS’s PCN program, visit www.aphis.usda.gov.