early blight
Beginner
Scientific Name
Alternaria solani
Identification
Circular to angular dark brown lesions with concentric rings that resemble a target board occur on the leaves. The lesions develop first on lower, older leaves. The lesions are usually limited by large veins and surrounded by a narrow light green to yellow halo. In severe infections, the foliage is completely covered by lesions and dries up.
Lesions on tubers are dark brown to black, slightly sunken, round to irregular in shape. They are often surrounded by a raised violet-blue border. The internal decayed tissue is usually dark brown, dry and corky.
On stems, fleck-like brown stem spots may develop if foliar infection is severe
Often Confused With
Late
blight
Botrytis
Grey Mold
Air
pollution
Period of Activity
Early blight is an endemic disease because the inoculum is always present and the disease develops each growing season. Early blight is favored by crop stress. Field scouting should provide the information that growers need for the best management of the disease.
Scouting Notes
- Scouting should start before the rows close.
- Fields should be monitored at least twice a week.
- When walking fields, stop at many sites as possible and check plants at random.
- Always examine the lower part of the plants where initial infection starts
Thresholds
Preventative fungicide applications are an effective management practice to control this endemic disease. The initial fungicide application should be done before the rows close.
Advanced
Scientific Name
Alternaria solani
Identification
Circular to angular dark brown lesions with concentric rings that resemble a target board occur on the leaves. The lesions develop first on lower, older leaves. The lesions are usually limited by large veins and surrounded by a narrow light green to yellow halo. In severe infections, the foliage is completely covered by lesions and dries up.
Lesions on tubers are dark brown to black, slightly sunken, round to irregular in shape. They are often surrounded by a raised violet-blue border. The internal decayed tissue is usually dark brown, dry and corky.
On stems, fleck-like brown stem spots may develop if foliar infection is severe
Often Confused With
Late
blight
Botrytis
Grey Mold
Air
pollution
Biology
The early blight fungus is found in most soils where potatoes are grown, and the disease develops every season. This pathogen overwinters in the field as spores or mycelium on dead leaves and vines, on infected tubers and on weed hosts such as hairy nightshade. In the spring, spores initiate infection. Spores are carried primarily by wind and infect potato leaves under favorable conditions of warm temperatures (20-30°C) and heavy dews or rain. Usually older leaves close to the ground are infected first. The disease progresses rapidly during periods of alternating wet and dry weather. Early blight is usually found first along margins of fields adjacent to fields planted to potatoes the previous year. Several cycles of disease occur within a single growing season. Early blight is often more severe as the potato crop ages or if the crop has been under stress of poor nutrition, injury, insect damage, drought, or other types of stress. Plants infected with Verticillium or expressing common mosaic symptoms are particularly susceptible to early blight.
If early blight is severe, lesions may also be found on stems and tubers. Tuber infection occurs at harvest primarily through cuts, bruises or wounds.
Period of Activity
Early blight is an endemic disease because the inoculum is always present and the disease develops each growing season. Early blight is favored by crop stress. Field scouting should provide the information that growers need for the best management of the disease.
Scouting Notes
- Scouting should start before the rows close.
- Fields should be monitored at least twice a week.
- When walking fields, stop at many sites as possible and check plants at random.
- Always examine the lower part of the plants where initial infection starts
Thresholds
Preventative fungicide applications are an effective management practice to control this endemic disease. The initial fungicide application should be done before the rows close.
Management Notes
Management of early blight requires an integrated program of cultural and chemical practices to minimize sources of inoculum, crop stress, and reduce disease development. This includes the following strategies:
- Crop rotation for at least 2-3 years.
- Avoid crop stress caused by drought, insect damage, overirrigation, inadequate nutrient levels.
- Timely application of crop protection materials.
- Harvest tubers when the skin is set and avoid mechanical injury.
