Lima Beans: moldy (L); Fungicide Treated (R)

Lima bean has been an important crop grown for canning and freezing in the mid-Atlantic area of the United States since the nineteenth century. Lima bean grown for processing is planted on 6,500 hectares in Delaware, with production valued at $6.5 million. 13,000 hectares of lima bean are grown in the United States, with California being the largest producer of lima bean and Delaware being second. Lima bean is considered to be the cornerstone crop of the vegetable processing industry in Delaware, and Delaware remains one of the few states that produce the crop. Lima bean downy mildew was first reported in Connecticut in 1889, and the disease is in Delaware almost every growing season.

“Currently, P. phaseoli [lima bean downy mildew] is limited to the mid-Atlantic areas of Delaware, Maryland, and New Jersey and has never been reported to occur in California. This is likely to be due, at least in part, to California’s lower humidity compared with the eastern United States.

In 1958, P. phaseoli was responsible for an epidemic, with more than 907,185 kg of bean loss from 4,725 hectares in Delaware. In 2000, race E of P. phaseoli was responsible for an epidemic in Delaware during September and October, which resulted in an estimated production loss of 40%, equal to a farm value loss of $3,000,000.

Fungicide testing for control of downy mildew of lima beans began as early as 1897 when Bordeaux mixture was recommended for control.

Growers currently make preventative applications of copper fungicides either alone or in combination with insecticides for pod-feeding insects. When conditions for downy mildew are favorable and outbreaks occur, applications of Ridomil Gold/Copper (mefenoxam) or Phostrol are made curatively to unsprayed fields or those where copper fungicides have been applied preventatively.

Currently, several fungicides are labeled and effective for control of downy mildew if applied in a timely manner. Ridomil Gold/Copper (mefenoxam/copper), Phostrol (phosphorus acid salts), and copper fungicides are currently labeled on lima bean and are effective.”

Authors: Evans, T. A., et al.
Affiliations: Department of Plant and Soil Sciences, University of Delaware.
Title: Lima bean downy mildew: impact, etiology, and management strategies for Delaware and the mid-atlantic region, U.S.
Source: Plant Disease. 2007. 91[2]:128-135.