Increased Insecticide Use Protects Onions from Viral Infections

weeds

Onions infected with iris yellow spot virus

Iris Yellow Spot Virus (IYSV) was first discovered in the U.S.in 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.

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Fungicides Enable China to Lead in Global Production of Vegetables

Greenhouses in China

Greenhouses in China

China produces nearly half of the world’s vegetables- five times the U.S. share. China’s increase in vegetable acreage between 2000 and 2004 (5.7 million acres) exceeded the entire vegetable acreage in the United States (3.7 million acres). China’s vegetable production has grown mainly to meet domestic demand from its 1.3 billion citizens. There are over 7.3 million acres of greenhouse crops in China and the growing conditions in the greenhouses are conducive to fungal outbreaks making fungicide use necessary.

“Gray mold caused by B. cinerea has become one of the most economically important diseases, since the rapid development of greenhouse cultivation in the 1990s in eastern China. B. cinerea severely reduces the yield and quality of greenhouse vegetables such as eggplant, tomato, cucumber and pepper. Jiangsu and Zhejiang provinces are the major vegetable production regions of eastern China, where unheated plastic greenhouses have been in use since 1998. Growers depend on regular fungicide treatments approximately every 7 days from November to May, besides some cultural practices such as ventilation to control the epidemic of B. cinerea.”

Authors: Zhang, C. Q., et al.
Affiliation: School of Agriculture and Food Science, Zhejiang Forest College, China.
Title: Evolution of resistance to different classes of fungicides in Botrytis cinerea from greenhouse vegetables in eastern China.
Source: Phytoparasitica. 2009. 37:351-359.