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Past Articles Library | Plant Diseases & Control | Anthracnose

ANTHRACNOSE

Anthracnose is a fungal disease; four species of fungi are responsible for most anthracnose diseases and not all species affect all tree species. Anthracnose does not seriously harm plants unless defoliation occurs repeatedly or branch dieback or cankering is extensive.

LIFE CYCLE

Anthracnose fungi overwinter primarily in lesions on infected twigs. Spores are produced in the spring and are spread by splashing rain and windborne rain to new growth. If it is moist during the new growth season, these spores germinate and infect new twigs and foliage. More spores are produced and are readily spread to nearby foliage by raindrops or overhead irrigation.

PLANTS MOST AFFECTED

Many kinds of woody and herbaceous plants: vegetables, particularly bean, cucumber, pepper, squash, and tomato; susceptible trees include dogwood, elm, hawthorn, linden, maple, sycamore, and walnut.

DAMAGE

Infection starts as small or large yellow, brown, or purplish spots, often with slightly raised margins, which darken as they age. Spots may eventually merge to cover the entire leaf, giving a scorched appearance; leaves may drop prematurely, and an entire tree can be defoliated. Tips of young tree twigs may be killed before the leaves begin to open; brown spots and patches may appear on young leaves. On fruit, small, sunken spots appear on the surface, and lead to rot.

MEANS OF CONTROL

Rake up and burn or destroy infected leaves; prune out dead wood and burn or destroy it.

Organic Solution: 70% Neem Oil is an effective fungicide for the prevention and control of various fungal diseases including anthracnose. As a preventative, 70% Neem Oil should be applied on a 7 to 14 day schedule until the potential for disease development is no longer present.

Alternate Solution: Apply copper sprays in severe infections. A dormant spray of Bordeaux mix or lime-sulfur may provide some control. In areas of prolonged spring rains or fog, avoid planting highly susceptible species. In areas with summer heat or drought, provide deep irrigation about once a month if affected trees do not otherwise receive regular irrigation.