Ash, maple, rose, sycamore, and many
other
deciduous
trees and shrubs; Vegetables:
esp. members of the Cucurbitae (cucumber, squash). Raspberry.
DESCRIPTION: Symptoms vary with hosts. The most commonly seen
symptom is a brown, irregular, blotchy area that expands between leaf
veins. Black, sunken spots develop on fruits, leaves, and stems of
vegetables. On woody plants there are two types of foliar
symptoms. Most common is necrotic, irregular blotches that
expand. Less common is round necrotic circles scattered
throughout the leaf. Symptoms look much like leaf scorch or frost
injury. On raspberry, circular, sunken spots on canes start out purplish and turn gray in the center.
LIFE
CYCLE: Anthracnose fungi overwinter on blighted twigs or fallen leaf debris.
Initial leaf infection occurs from late spring to mid-summer when
moisture is frequent, humidity is high and temperatures are 70 -
80° F for vegetables and 45-55ºF for woody plants (the
Anthracnose that infects woody plants is inhibited above 55ºF).
Spores are disseminated by wind and splashing rain to buds,
shoots, fruits and expanding leaves. Leaf symptoms become more
noticeable in mid to late summer. The disease is most severe in wet
springs and is checked by dry, hot weather.
CONTROLS:
Cultural: Keep
irrigation off leaves.
Vegetables: Remove and
destroy diseased twigs and leaves. Plant on raised beds and
use plastic mulches to avoid splashing. Raspberries: Remove and destroy old fruiting canes; use resistant cultivars such as Heritage.
Chemical:
Vegetables: If weather is wet and
temperatures
>50°F, protect leaves with sulfur sprays as soon as leaves are
fully expanded, copper and sulfur can injure sensitive plants like
cucurbits, especially cucumber.
Raspberries: Avoid excessive Nitrogen fertilization. Bordeaux or Lime sulfur mix
when first green tissue appears (timing is critical -too early is
ineffective).
Woody Plants: Chemical control is usually not needed. Only
needed if prolonged wet periods between 45-55ºF. Occurs during bud break and early shoot growth. Sulfur is
the least toxic option.
