Increased Insecticide Use Protects Onions from Viral Infections


Onions infected with iris yellow spot virus

Iris Yellow Spot Virus (IYSV) was first discovered in the 1989 infecting onions in the Treasure Valley of Idaho and Oregon. IYSV typically does not kill plants; however the virus reduces plant vigor and bulb size. Once plants are infected with IYSV, there is no cure. The virus is transmitted to onions by the feeding of an insect: onion thrips. The disease spreads rapidly in fields with large numbers of thrips. Losses up to 100% have been reported. Onion thrips populations are reduced by the application of insecticides in onion fields thus preventing transmission of the disease to onion plants.

Iris yellow spot virus pressure in this region has not been nearly as bad as it was last year, when it wiped out some onion fields. “The virus seems to have been held off well this year,” said Paul Skeen, who farms near Nyssa, Ore. Farmers in the Treasure Valley area of southwestern Idaho and eastern Oregon produce about 25 percent of the nation’s bulb onions and the virus is one of their main production challenges. It weakens the plant and reduces onion production. It can substantially reduce onion bulb size, which is important because larger onions fetch a higher price. The disease is spread to onions by thrips, and Skeen said many growers in the area started spraying for thrips earlier this season and they sprayed more often. Skeen started spraying 10 days earlier and sprayed every seven to 10 days as opposed to every 14-20 as he has done in past seasons. “I’ve got a good crop coming because I stayed on top of it. I think everybody’s been doing that,” he said.

While onion growers in the Treasure Valley area typically start their thrip spraying programs around Memorial Day, many started in early May this year, said Stuart Reitz, an OSU cropping systems extension agent in Malheur County. While onion growers in this area normally make about six applications for thrips in a season, many have made eight or nine already this year and a few are up to 10, he said. “That helped keep the thrips population down,” Reitz said.

Author: Ellis, S.
Affiliation: Reporter.
Title: Onion virus pressure not as severe as last year.
Source: Capital Press. August 8, 2014.

Stopping the Nematode Threat to Potatoes with Fumigation


PCN Damage (right)


PCN cyst hatching

Cyst nematodes are a huge potential threat to potato production in the US. Nematodes are microscopic unsegmented worms. Roots of infected plants contain minute, white bodies of females. When a female dies, its cuticle forms a protective cyst containing 200 to 500 eggs. Cysts containing viable eggs can persist in the soil for up to 20 years. When potatoes are planted, root exudates stimulate juvenile nematodes to emerge from eggs. The juveniles locate and enter potato roots. They cut through cell walls and feed. Infection with nematodes reduces root biomass, which can lead to stunting of plants, yellowing and wilting of foliage and small tubers. Heavy infestations often results in total crop loss. Potato cyst nematodes are widespread in many countries, but only two localized infestations have occurred in the US. The latest infestation, found in Idaho in 2006, has led to a strict treatment program with fumigants.

“Two species of potato cyst nematode are found in the United States: Globodera pallida, the pale cyst nematode (PCN), was first found in Idaho in 2006, whereas the golden nematode, G. rostochiensis (GN), was first found in New York in 1941. Both species are regulated under a Federal Domestic Quarantine Order (USDA-APHIS) and parallel State Rules (Idaho State Dept. of Agriculture, New York State Dept. of Agriculture), and eradication effects are underway.

While some resistance to PCN is present in potato varieties grown in Europe and elsewhere in the U.S., there is no resistance in most of Idaho’s signature russet varieties.

The presence of G. pallida in Idaho has been viewed with alarm by other states and countries that import Idaho potatoes and other farm products. After the initial Idaho PCN detection in 2006, markets for Idaho fresh potato products and nursery stock were lost for Canada, Mexico, and Korea. Japan temporarily closed the market for all U.S. potatoes, and continues to disallow Idaho shipments. Consequently, eradication of PCN is a top priority for the Idaho potato industry, including the Idaho Potato Commission, the Idaho State Department of Agriculture, and USDA-APHIS. Millions of dollars have been spent in Idaho in eradication efforts. A critical component of this work has been treatment of infested fields with the fumigant methyl bromide (MeBr), which has been ongoing since the spring of 2007. Lab tests conducted after each treatment indicate a 95% viability reduction after one year’s fumigation, and over 99% viability reduction after successive treatments.”

Author: Dandurand, L. M.
Affiliation: University of Idaho, Moscow
Title: Novel Eradication Strategies for Pale Cyst Nematode
Source: Potato Progress. September 16, 2013. Volume XIII, Number 10.