About Ascochyta Leaf Blight
The ascochyta fungi overwinter in infected crop debris, soil, or seed. The fungi begin to produce spores in wet weather and are dispersed to surrounding plants by splashing rain. These spores, called ascospores, can be spread for miles through water and/or wind dispersal. Ascospores are typically released in the spring and continue to be released in the summer if wet weather is prevalent. Early in the season, infection from soil-borne fungi or seed can cause lesions on seedlings. Plants that grow from lesioned seedlings can develop foot rot and lose vigor, or they can grow as a healthy plant. Symptoms of asochyta leaf blight can appear up to two to four days following infection.
Ascochyta Leaf Blight Identification and Habitat
A pea plant infected with ascochyta leaf blight will have small, purplish-brown flecks on its lower canopy where humidity is highest. In conditions with extended humidity, flecks may become larger and combine, causing large portions of leaf tissue to be blighted. Severely affected plants may have stem girdling near the soil line (foot rot). Stem girdling will lead to yield loss and crop lodging. Moist conditions can lead to pod lesions which cause shrunken, discolored seed. In pea crops, most symptoms are caused by mycosphaerella blight (a genus of Ascomycota).
In turf, the fungus is localized, causing infection in grasses to appear in patches. Infected leaves will have a bleached tip dieback covering up to half of the leaf blade. Along with blighting, the fungi produce yellow to dark-brown fruiting bodies on infected leaf tissue. Identifying these fruiting bodies can help to distinguish the disease from other related diseases.
- • Ascochyta leaf blight affects mainly pea crops and turfgrasses
The ascochyta fungus thrives in extended periods of wet, humid weather. The ideal temperature for infection and lesion growth is about 68°F. Dense and wet canopies in the flowering stage of the plant’s development promote lesion expansion on leaf tissue. Lack of rain can cause spore germination and lesion development to be slowed down drastically. That being said, periods of hot weather followed by unusually high moisture levels can aid disease growth. Splashing rain and sprinkler irrigation help spores to spread from plant to plant. In turf, frequent mowing can help disease development by creating wounds in plant tissue.
Ascochyta Leaf Blight Management and Control Methods
For pea crops, crop rotation can be an effective preventative measure. Avoid growing pea crops in the same field more than once every three or four years. Because infection through infected plant residue is common, rotating peas with a suitable non-host is recommended. Another important preventative measure is selecting good quality seed to plant. Look for varieties with at least fair resistance to reduce yield loss. Furthermore, managing stubble in the field is good to help decompose the pea residue. If the conditions are suitable, planting field pea earlier in the spring can reduce yield loss. However, avoid planting too early when conditions may still be overly cold. Giving plants adequate space is vital in improving air circulation so that spore germination is hindered. Lastly, early scouting for symptoms of ascochyta leaf blight is highly advised.
Cultural practices for turfgrass are similar to those of pea crops. Primarily, managing infected plant residue and avoiding the mowing of wet grass will help reduce the incidence of infection and limit spread of the pathogen.
At early flowering, application of foliar fungicides can protect pea plants from infection. Fungicide application can reduce yield loss in crops, making it appealing to many farmers. On the other hand, applying fungicides to turfgrass is less common because the disease is not often fatal and application costs can be expensive.