Anthracnose

Anthracnose is a collection of fungal diseases that often appears in San Jose, California, in April, but knowing more about it before spring begins can help you to prevent it in your garden and landscape.

Anthracnose of cucumber (Scot Nelson) Public Domain

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Host plants
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Anthracnose prefers berries, tomatoes, and other soft fruits, but it is also found on avocados, almonds, lettuce, citrus, cucurbits, spinach, turfgrass, and beans, as well as snapdragons, and deciduous and evergreen trees and shrubs.

Anthracnose of tomato (Scot Nelson) Public Domain

Symptoms of anthracnose

Anthracnose can be caused by one of several fungi. The disease is often called twig, leaf, shoot or stem blight, depending on the plant being attacked and the visible symptoms. Symptoms look a lot like leaf spot, and usually appear after spring rains, especially in areas with poor drainage and poor air flow. Symptoms of anthracnose include:

• black, brown, tan, or tarry spots on leaves, especially oak and elm
• irregular dead leaf areas on ash trees
• lesions along major leaf veins of sycamore trees
• cankers on stems, twigs, and canes may result in girdling
• lesions on strawberry fruit and stems
• overall stunting and yellowing
• lesions on crown tissue (usually leads to death of the plant)
• yellow leaf and fruit spots turn brown and purple stem lesions appear on avocado
• blossom blight, spur dieback, and gumming occur on almond trees
• soggy holes (or “shot hole”) appears on lettuce and spinach
• twig dieback, early leaf drop and fruit staining are seen on citrus

Anthracnose lifecycle

These fungi overwinter in infected twigs and canes and in leaf litter. In spring, spores are produced that get bounced onto plants by rain or sprinkler action. In their water vehicle, they attach themselves to a host and use the moisture to germinate. Then they enter vulnerable new twigs and leaves where they start reproducing like crazy, until it gets too hot and too dry.


Anthracnose controls

One of the easiest ways to avoid anthracnose in the landscape is to plant resistant varieties. For those plants that are already in place, avoid overhead watering and be sure to prune and place plants for good air flow. You can also improve drainage with compost and mulch. Remove and dispose of any infected plant material. Many weeds can host this pathogen, including chickweed, vetch, and fiddleneck, so remove them from areas prone to anthracnose. Pesticides advertised as able to prevent anthracnose have not been reliable in controlling the disease. Spores can survive in the soil without a host for up to 9 months, so crop rotation can also help reduce infestation. In extreme cases, soil fumigation, fungicide dips for transplants, and foliar fungicides can be used.


So, protect your blackberries and raspberries, your lima beans and pinto beans, your Poinsettias and those plump tomatoes with good air flow and by watering only at ground level.