Apple scab is a fungal disease caused by the fungus Venturia inaequalis, which affects leaves, fruit and twigs. While most common in apple trees, the fungus frequently infects both pear and hawthorn as well. Outbreaks will be most severe following particularly wet and cool spring conditions. For best results, apply PHOSPHO-jet or Propizol prior to infection in the fall to minimize or prevent infection in ornamental trees the following spring. Which is the correct treatment for your trees?
Stop Overwintering
The fungus overwinters on fallen leaves and begins to develop spores in the spring prior to bud break. Overwintering is the process by which some organisms pass through that period of the year when “winter” conditions make normal activity difficult or often impossible. The spores are transported by wind, rain or other physical means to infect tender, developing leaves and fruit, which spores spread to other areas of the tree. Hibernation and migration shield the insect from adverse conditions associated with winter and are the two major ways they survive in the winter.
Symptoms of Infection
Infection is commonly evidenced first by brownish-green spots on the leaves or fruit. As the infection progresses, the spots on the fruit become darker and more prominent and take on a somewhat fuzzy texture. When the infection is severe, leaves will turn yellow and drop. The fruit will become deformed and/or drop off after ripening.
Treatment with PHOSPHO-jet
PHOSPHO-jet inhibits fungal cells while eliciting a plant health response from the tree. PHOSPHO-jet will promote stronger, healthier tree cells, root development, and trigger the tree’s natural defense mechanisms to make the tree more resistant to infection and better able to recover.
When to Treat with Propizol
Propizol will have more direct and aggressive activity against the fungus itself and is recommended if the infection is chronic or severe. While Propizol is a more potent fungicide, it will not have the plant health benefits of PHOSPHO-jet. It should not be used on trees where the fruit will be eaten. If treating an established infection, Propizol is recommended as a first treatment, with subsequent treatments of PHOSPHO-jet as necessary.
Tree Recovery
Tree recovery will be proportional to the severity of the infection at the time of treatment. Proactive treatment, either the preceding fall or very early in the spring, prior to bud break, will suppress or prevent infection.
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