Description

• Phytophthora gummosis is caused by two funguslike organisms, Phytophthora parasitica and Phytophthora citrophthora. When conditions are wet, these soil-dwelling organisms produce motile spores called zoospores. The spores swim through the wet soil and seek out the roots of host plants, or are splashed onto trunks during wet and stormy weather. Phytophthora parasitica is most likely to spread at temperatures between 85 and 90 degrees and low elevations. Phytophthora citrophthora prefers temperatures between 75 and 80 degrees.
  
  

Cultural Control

• If you spot infected areas, use a knife to cut away diseased portions of bark, along with a margin of healthy bark. You also can burn the diseased bark with a propane torch. Burn about an inch of healthy bark around the diseased area. Burning may need to be repeated a few times until the infected lesion is dead.
  
  

Fungicide Control

• This condition also can be controlled with fungicides. Copper fungicides, an organic choice, is one option. Products containing fosetyl-al and mefenoxam also readily are available to homeowners. Preplanting fumigation is a possibility if you know your soil contains these fungi. The chemicals chloropicrin and meta sodium are effective fumigants, but must be applied by professionals.
  
  

Avoiding Reinfection

• According to the Texas A&M Agricultural Extension, there is no cure for phytophthora gummosis -- so managing and preventing the disease are your keys to success. Practice good water management. The organisms spread in moist soil so only water your tree as much as is necessary for its size and location. If your tree dies, plant its replacement in a raised bed and be sure the first lateral roots are barely covered with soil. Plant a disease-resistant cultivar if one is available.