Two varieties of long beans are being grown this summer by Field Test members of UC Master Gardeners of Napa County. Gardeners have reported that leaves on their plants have mottled, puckered, yellowed leaves. A mosaic virus is the most likely cause. Aphids are the vectors that spread this viruses from alfalfa, clover or vetch or from bean plant to bean plant. Most of our group reported this problem, making it probable that our seed was the source of the infection. Despite the virus, most plants seem to be vigorous and are producing a good crop.

Viral diseases are difficult to identify because symptoms vary from plant to plant and may also vary depending on the age of the plant and its growing conditions. Common keys to identifying mosaic viruses include:

• The leaves are mottled with yellow, white, and light and dark green spots, which appear to be elevated. This gives the leaves a blister-like appearance.
• Plants are often stunted, or they grow poorly.
• Plants may have other deformities and their leaves may be crinkled or wavy. 
  

  Beautiful bean blossom, yellowed leaves

Once plants are infected, there are no controls. To avoid infection plant resistant varieties when available, and control weeds that may harbor vectors. This virus can survive in seed for more than 30 years, and can survive heat treatments hot enough to kill the seed.

Open this link for more information on bean yellow mosaic potyvirus: 

http://www.ipm.ucdavis.edu/PMG/r52101511.html

Here is a page all about possible problems with beans including three different virus diseases: 

http://www.ipm.ucdavis.edu/PMG/C052/m052bpdamage.html

photos: Jane Callier, Helen Bergin

UC Master Gardeners of Napa County provide free home gardening advice. Visit, call or complete the Plant Problem Diagnosis Sheet  for assistance.

Monday, Wednesday and Friday, 9 a.m. to 12 p.m.
UC Cooperative Extension 
1710 Soscol Avenue, Suite 4, Napa
(707) 253-4143