Brown Rot (Monilinia fructicola) is a fungal disease that primarily affects peaches, plums, cherries, and especially nectarines. Controlling it should be of paramount importance to anyone growing stone fruits in humid conditions.
Brown Rot overwinters on mummified fruit, twigs, and in the fissured bark of the tree itself. In the Spring it infects vulnerable parts of the tree, most usually the buds early in the Spring and later in the season, the fruit as it ripens. It can travel back a few inches as well infecting more of the tree.
Remove all diseased fruit and 6″-8″ of the adjoining stem from the tree as early as possible. Keep the underneath of the trees as clear of fallen fruit as is feasible. Compost applied to the base of the trees has been shown to help with disease control as well, presumably due to microbial competition. Burgundy Mixture or Bordeaux Mixture has also been found to be effective if sprayed during dormancy.
In-Season Spray Treatment
Anti-fungal sprays may be used to control brownrot during the season to prevent it from taking hold. The first spray should be applied at ripe-bud stage but before 10% bloom. Apply 2-3 additional sprays in the Spring 7 days apart, or according to spray instructions. A last spray should be applied when fruit begins to change color, roughly 3 weeks before harvest. Note that this is a general guideline, and that some sprays may need a different schedule.
90% wettable sulfur may be mixed with water and sprayed in-season at the rate of 3 Tablespoons per gallon of water, using approximately 1 gallon per 5′ of tree diameter for thorough coverage. A leaf blower used while spraying or dedicated rig will help to get complete coverage. I use a cordless electric leafblower with my electric backpack sprayer with the wand taped to the blower, both locked to on. This makes relatively quick work of spraying a dozen or so trees.
Post Harvest Control.
Dipping harvested fruit for 30-60 seconds at 60°C will effectively control the disease during storage. Temperatures as low as 45°C may also control it (if not quite as well) if the duration is increased to 3 minutes.
A dip of 1-2 minutes in a 0.25% sodium hypochlorite (food grade bleach) and water bath is also effective, although it appears less so than the above mentioned high temperature methods, and may flavor the fruit objectionably. This dilution amount ends up being a little more than 1/4 cup (2.6 ounces) of 12% sodium hypochlorite per gallon of final mix. Rinse afterwards with clean water
A sanitizing solution may also be made with “SaniDate 5.0” Use .25 ounces of SaniDate per 1 gallon of water.
Storage below 4°C will prevent the growth of Brown Rot but will start growing as soon as the temperature increases.