Field Guide     Crop Diseases     Angular Leaf Spot

Angular Leaf Spot

CROPS IMPACTED: cucurbit crops, strawberry, bean plants

Angular Leaf Spot

Family: Xanthomonadaceae, Pseudomonadaceae

Angular Leaf Spot Angular Leaf Spot

About angular leaf spot

Life Cycle

Angular leaf spot is caused by a pathogen called Pseudomonas syringae pv. Lachrymans, which affects cucurbits. There is also a pathogen called Xanthomonas fragaria which affects strawberry plants. Both of these pathogens are capable of overwintering in plant debris, but they cannot survive efficiently in water or soil alone. Upon germination, bacteria multiply and spread to leaf tissue. After one plant is infected, the disease is spread from plant to plant through splashing rain, infected farm equipment, contact with pickers, and insects. Diseased plant debris and infected irrigation water can be windblown to other plants. Leaves are most affected by the leaf spots, but lesions sometimes appear on fruit as well

Angular leaf spot Identification and Habitat

Identification

Small, round/irregularly shaped lesions will appear on infected leaves. These water-soaked spots will slowly grow larger until their growth is stopped by the veins on the leaf, creating an angular appearance. In high humidity, spots can be covered by a white exudate that dries up to create a layer of crust on leaf tissue. On the lower leaves, lesions tend to be shiny. When spots dry, they appear smaller and destroy the leaf tissue that they occupied, leaving large holes in the leaves. Lesions can be surrounded by yellow borders in some plants (e.g. squash). Fruit can also be lesioned, but their lesions are smaller than those on the foliage of the plant. It is typically noticed that young leaves are more vulnerable to infection than old leaves.

Varieties

  • • Xanthomonadaceae (strawberry plants)
  • • Pseudomonadaceae (cucurbits)

Habitat

This pathogen favors frequent summer rains and temperatures between 75 and 82°F. High relative humidity and moist soil are ideal for development and spread of angular leaf spot. After two weeks of dry weather, the disease will cease to develop.

Angular leaf spot Management and Control Methods

Cultural Control

First, planting disease-free seed is essential to avoid introducing disease to new locations. It is advised to avoid working with plants while they are still wet in order to reduce the chances of spreading disease from one plant to another. Similarly, avoid using overhead irrigation as it causes water to splash from plant to plant, increasing the chances of bacteria dispersal. Moreover, cucumbers have many resistant seed varieties, so use those wherever possible. Frequent crop rotation is important to avoid continuous infection and yield loss in the same field. Removing infected plant material from soil is strongly advised to limit the spread of the disease, and to reduce the chances of bacteria overwintering for next season.

Chemical Control

Bactericides (e.g. fixed copper) combined with organic fungicides, if applied early in the season, can be effective at controlling incidents of infection. Insecticides can be useful in controlling insect populations that may spread bacteria from plant to plant while feeding. Before using these spray treatments, carefully read labels for cautionary advice and application guidelines.

Sources

http://ipm.illinois.edu/diseases/series900/rpd919/

http://www.extension.umn.edu/garden/yard-garden/vegetables/diseases-of-cucurbits/angular-leaf-spot/

http://extension.illinois.edu/hortanswers/detailproblem.cfm?PathogenID=130