Alternaria leaf blight
Alternaria dauci
What is Alternaria leaf blight (Alternaria dauci)?
Alternaria leaf blight is a fungal disease caused by Alternaria dauci. It primarily affects carrot plants but can also infect parsley. The disease is distributed in regions where carrots are grown, with notable occurrences in western Idaho and eastern Oregon. Symptoms include dark brown to black irregular lesions on leaf blades and petioles, often surrounded by a yellow margin. Lesions may merge, causing leaf death, and weakened leaves may break off during harvesting.
How does Alternaria leaf blight (Alternaria dauci) occur?
Alternaria dauci reproduces and spreads through spores produced by the fungus. These spores can be carried by air or water splashes to infect healthy plants. Alternaria dauci can survive on carrot debris, volunteer plants, and seeds. When conditions are favorable, such as rainy weather or overhead irrigation, the spores germinate and infect the leaves and stalks of carrots. It can thrives best at 82°F but can infect plants at temperatures as low as 57°F and high as 95°F.
Symptoms
1 - On plants
Alternaria leaf blight can cause significant damage to plants. The disease can reduce the plant's ability to photosynthesize, which can lead to stunted growth and poor flowering. Additionally in severe cases, the disease can kill the plant.
2 - On soil
Alternaria leaf blight does not directly affect the soil. However, the disease can spread from plant to plant through spores that are carried in the soil. This can lead to the spread of the disease to other plants in the garden.
Solutions
1 - Cultural Controls & Prevention:
- Implement rotations of 3-4 years to reduce disease incidence. - Use certified pathogen-free seeds or treat seeds with hot water or fungicides. - Opt for cultivars with tolerance to Alternaria diseases
2 - Organically Acceptable Methods
For organic production, cultural control practices, hot water dips, and the application of Serenade ASO and MAX foliar sprays are acceptable methods for managing Alternaria leaf blight.
3 - Chemical Control
Common fungicides used for managing Alternaria leaf blight in carrots include Chlorothalonil (Bravo, Daconil), Azoxystrobin (Quadris), Mancozeb (Dithane), Propiconazole (Tilt), and Fludioxonil (Switch). However, it is important to consult local agricultural authorities for approved fungicides and their proper usage in your region.
