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Anthracnose

Anthracnose (leaf blight) is a fungus that winters on twig tissue on the tree.  In the spring, spores are transported to new buds and shoots.  The disease is enhanced by cool, wet conditions.  Infected leaves develop tan to reddish brown lesions that extend along the veins of the leaf.  Considerable defoliation, sometimes with complete leaf loss, occurs on many trees by late spring in cool, wet years.

Different species of anthracnose impact a variety of tree species, including oak, ash, maple, elm, hickory, walnut, birch, linden, sycamore and dogwood.  Sycamore, white oak and dogwood are particularly susceptible to anthracnose. 

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Symptoms

The primary signs of anthracnose are tan to red-brown lesions that extend along the veins and edges of the leaf, as well as considerable defoliation, sometimes with complete leaf loss.


Photo A by Joseph O'Brien, USDA Forest Service, Bugwood.org
Photo B taken by Theodor D. Leininger,USDA Forest Service, Bugwood.org

Treatment

Arborjet recommends a trunk injection with a systemic fungicide, either PHOSPHO-jet or Propizol® Fungicide. PHOSPHO-jet inhibits fungal cells while eliciting a plant health response from the tree. PHOSPHO-jet will promote stronger, healthier tree cells, promote root development, and trigger the tree’s natural defense mechanisms to make the tree more resistant to infection and better able to recover. Propizol will have more direct and aggressive activity against the fungus itself and is recommended if infection is chronic or particularly severe.

When to Treat

Generally, the best seasons for injection are fall and spring, as uptake occurs when trees are transpiring. The environmental conditions that favor uptake are adequate soil moisture and relatively high humidity. Soil temperature should be above 40°F for trunk injection. Hot weather or dry soil conditions will result in a reduced rate of uptake, so trees should be watered if applications are made when soil is extremely dry. If treating trees in the summer, inject in the morning for the quickest uptake. Tree health will affect treatment efficacy, so assess tree health prior to treating. For example, a declining tree (>50% canopy dieback) is a poor candidate for treatment.


Propizol applied in the fall will slow the spread of infection the following spring and help the tree to foliate more normally. PHOSPHO-jet may be applied in the fall following leaf coloration or early spring prior to twig infection.

What to Expect After Treatment

Trees may still defoliate despite our best efforts; however, we recommend treatments that enhance tree health. For example, trees treated with PHOSPHO-jet tend to recover more readily from defoliation. Avoid high nitrogen fertilizers, which may exacerbate fungal infection. Rather, apply NutriRoot™, which will supply phosphorous, potassium, iron, manganese, humectants, humic acid and a low dose of nitrogen for healthy leaf and root development. In high pH soils, apply MIN-jet Iron as an injection.

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Uploaded: 10/12/2015

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