Potato Early Blight: A Common Disease
Potato early blight is a common disease that affects potatoes in many growing regions. It is caused by the fungus Alternaria solani, which can also infect tomatoes and other members of the potato family. Potatoes become infected with early blight when their leaves get too wet from rain, fog, dew, or irrigation.
Early blight is not usually a fatal disease, but it can cause significant damage to potato plants. It typically affects mature leaves rather than young, tender ones.
Symptoms of Potato Early Blight
The first symptom of potato early blight is the appearance of small, irregular dark brown spots on the lower or oldest leaves of the plant. These spots gradually enlarge and take on an angular shape, often resembling a target. As the disease progresses, the spots may cause the entire leaf to turn yellow and die, but the leaves will remain attached to the plant.
Dark brown to black spots may also develop on the stems of the plant. In severe cases, the tubers (potatoes) can also be affected, developing dark gray to purple, circular to irregular lesions with raised edges. When cut open, the flesh of infected tubers may be brown, dry, and corky or leathery. In advanced stages of the disease, the tuber flesh may appear water soaked and turn yellow to greenish yellow.
Causes of Potato Early Blight
The spores of the fungus that causes potato early blight survive in infested plant debris, soil, and infected tubers. Spores are produced when temperatures are between 41 and 86 degrees Fahrenheit (5-30 degrees Celsius) and there is alternating wetness and dryness. These spores are then spread by wind, splashing rain, and irrigation water.
The fungus enters the potato plant through wounds caused by mechanical injury or insect feeding. Lesions typically begin to appear two or three days after the initial infection.
Potato Early Blight Treatment and Prevention
There are several steps you can take to prevent and treat potato early blight:
- Plant resistant varieties: Choose potato varieties that are resistant to early blight. Late maturing varieties are typically more resistant than early maturing varieties.
- Avoid overhead irrigation: Overhead irrigation can keep the foliage of potato plants wet for extended periods, creating ideal conditions for the fungus to thrive. Instead, use drip irrigation or water at the base of the plants.
- Provide good aeration: Allow for sufficient space between potato plants to allow the foliage to dry quickly after rain or irrigation.
- Practice crop rotation: Do not plant potatoes or other members of the potato family in the same location for two years after a potato crop has been harvested. This will help to reduce the amount of inoculum (fungal spores) in the soil.
- Keep plants healthy: Provide adequate nutrition and water to keep potato plants healthy and stress-free. Healthy plants are more resistant to disease.
- Harvest potatoes carefully: Dig up potatoes only when they are fully mature to avoid damaging them. Any damage to the tubers can provide an entry point for the fungus.
- Remove plant debris: At the end of the growing season, remove all plant debris from the garden to reduce the amount of inoculum that can overwinter and infect plants the following year.
By following these tips, you can help to prevent and control potato early blight and protect your potato crop.
