Fixed Copper Sprays for Apricots

Diseases Calling for Copper

• A member of the Prunus genus, apricots are susceptible to several different diseases. Fixed copper sprays can control shot hole disease, or Coryneum blight, bacterial canker or spot and brown rot. Whenever possible, choosing disease-resistant cultivars is helpful. To minimize or eliminate the need for fixed copper sprays, observe excellent care and sanitation practices like pruning off infected plant parts and using watering practices that do not wet foliage.

Fixed Copper Basics and Effectiveness

• Fixed coppers include copper sulfate, copper oxide, copper hydroxide, copper oxychloride sulfate and copper ions linked to organic molecules. The copper is insoluble and suspended, rather than dissolved, in water, with copper particles that persist as deposits on the plant surface after the spray dies. Each time the plant surface is wetted, copper deposits gradually release copper ions, which destroy enzymes critical for pathogen cell functions.

  The effectiveness of a copper spray depends, in part, on the product used. Finely ground copper has a greater impact than coarsely ground copper. The higher the percentage of copper a product has, the greater disease control it offers. For effective control, a product should contain at least 20 percent copper.

Timing Fixed Copper Sprays

• For disease control on apricots, fixed copper is sprayed to thoroughly cover the tree following leaf drop in fall but before winter rains or snowfall. To address brown rot or if more than 3 inches of rain fell between the application in fall and pink bud stage, a spray before the apricot tree is in pink bud stage is warranted. Always follow manufacturer recommendations for diluting and applying fixed copper for safe and effective use. With a concentrated fixed copper fungicide, the manufacturer may recommend, for example, creating a mixture of 1/2 to 2 percent fixed copper, or about 1 1/4 to 5 tablespoons concentrate per gallon of water.

Potential Injury to Plants

• Phytotoxicity, or injury to the apricot tree, can occur if copper is sprayed repeatedly, usually in an attempt to protect new growth from fungal infection, but there is little rainfall. Also increasing the likelihood of plant tissue injury is a low, or acidic, water pH. At a pH of 7.0, fixed coppers are formulated to be almost completely insoluble. If water is acidic, more copper ions are released in the spray. Using distilled water or knowing with certainty that water from a particular source is neutral eliminates this issue. The potential for a copper spray's injury to an apricot tree is also greater if the spray is applied when it will dry slowly, like when conditions are wet and cool.

  Using as little copper as possible to thoroughly treat apricots and other plants is important because copper can accumulate in soils, impacting plant health and soil-dwelling organisms.