There are two types of pathogen-caused leaf spot diseases, especially on vegetables such as lettuce and tomato and on stone fruit trees. There are those caused by fungus and those caused by bacteria. Various kinds of leaf spots have a similar appearance and effect and can be prevented or treated with the same practices. Members of the Prunus family such as orange, plum, almond, peach, and cherry are prone to bacterial leaf spot. Vegetables such as pepper and lettuce are also affected by bacterial leaf spot. It also infects perennial and annual flowering plants such as purple coneflowers, geraniums, and black-eyed Susan. Fungal leaf spots mainly attack brassicas and other vegetables such as lettuce, cabbage, broccoli, kale, cauliflower, and turnip. It also attacks poplar trees and aspen.
Causes and Symptoms of Leaf Spot
Citrus leaf spot is caused by warm temperatures and plenty of moisture. Bacteria may be transmitted to the citrus plants by rain and wind. Warm temperatures and sufficient moisture provide an ideal environment for the growth of the bacteria. The bacteria spread in the soil around the infected citrus plants, in seeds and on garden debris. It also remains in the leaves, stems, and twig cankers of the infected trees. Poor crop vigor also favors disease formation.
There are brown or black water-soaked spots with a yellow halo on the foliage which are uniform in size. Under wet conditions, these spots enlarge and increase in number. When seriously infected, the leaves turn yellow, wither and drop.
Prevention and Control
- Prepare orchards using seeds that are free from the disease.
- Consider planting varieties that are resistant to citrus leaf spot disease. Grafted plants are mainly resistant to this disease.
- Rake up fallen fruits and keep the soil under the tree clean.
- Mulch the trees to prevent the disease from splashing onto the leaves and reduce weeds.
- Prune your trees to improve air circulation. Lack of air circulation favors the growth of bacteria.
- Practice field sanitation by removing the infected parts and debris of the citrus plants and destroy them. This will reduce the spreading of the disease to other trees.
Although there is no cure for bacterial leaf spots, various preventive, and organic measures can be employed to control the disease. These include:
- Spray the affected citrus plants with baking soda. However, if applied excessively, baking sodas may burn some leaves.
- Spraying the affected plants with copper-based fungicides such as copper hydroxide and copper sulfate, mancozeb, and sulfur sprays at the recommended rates. Apart from killing the leaf spot, organic fungicides also prevent the formation of spores. However, farmers should apply fungicides that are beneficial to insects and non-toxic to honey bees, especially during flowering.
- Apply manure and fertilizer constantly to maintain good health and crop vigor.
In severe cases, citrus leaf spots may affect the fruits. Farmers should ensure that they employ a consistent spray program to prevent disease development. Poor choice of the seedlings can ruin your citrus fruit farming venture. Non-resistant varieties are prone to the bacterial leaf spot which can reduce the yields greatly. Oxfarm offers high-quality seedlings that are resistant to a wide range of diseases such as citrus leaf spot. When buying seedlings, you should consider buying them at Oxfarm Organic.