Alternaria Blotch On Orange Trees: Signs Of Alternaria Rot In Oranges

Alternaria blotch on oranges is a fungal disease. It’s also known as black rot when it attacks navel oranges. If you have citrus trees in your home orchard, you should learn the basic facts about orange tree alternaria rot. Read on for information about alternaria rot in oranges, including tips on how to prevent alternaria blotch.

Alternaria Blotch on Orange Trees

Alternaria blotch on orange trees is also known as alternaria rot or black rot. It is caused by the pathogen Alternaria citri and is a nontoxic strain of fungus. Alternaria rot can be found on both lemons and oranges. The rot is softer on lemons but more pronounced on oranges, causing hard black spots on the peel. Alternaria blotch on orange and lemon trees can cause the citrus fruit to drop from the tree and develop rotten areas. Sometimes, the decay develops during storage after harvest, but it can still be identified in the orchard. On lemons, the blotches or rot spots present as softened areas of peel. Alternaria rot in oranges causes firm dark brown or blackish areas on the outside of the fruit. If you cut the fruit in half, you’ll find that the dark areas extend into the orange core.

Treating Alternaria Blotch

If you are wondering how to prevent alternaria blotch, the key lies in growing healthy fruit. Stressed or damaged fruit, and particularly split navel oranges, are especially susceptible to the fungal infection. Preventing water and nitrogen stress can reduce the number of split oranges in your home orchard. Provide your trees with adequate water and nutrients. In that way, taking excellent care of your orange trees is one way of preventing and treating alternaria rot. Regular orchard maintenance is also important. The fungi causing alternaria rot in oranges grows in the tissues of fallen fruit in wet weather. Cleaning up orchard debris on a regular basis can prevent this. Can fungicides be used as a method of treating orange tree alternaria rot? Experts say that there is no effective chemical treatment of the fungal disease. However, you can control the problem to some extent with imazalil and/or 2,4-D.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.