Anthracnose is a collection of fungal diseases that often appears in the Bay Area in April, but knowing more about it before spring begins can help you to prevent it in your garden and landscape.
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.
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:
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.
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.
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.