Powdery Mildew

Symptoms of powdery mildew can be seen on the terminal leaves of shoots, which are covered in powdery, white fungal growth. Leaves become misshapen and puckered, and fruits develop powdery, white spots that cause scars on mature fruit.

Sphaerotheca pannosa survives as mycelium in bud scales and as cleistothecia. Growth of the pathogen is favored by cool, moist nights and warm days. Generally, fruit is susceptible only up to time of pit hardening, but later infections can occur. Certain cultivars are more susceptible.

Occasionally the apple powdery mildew fungus, Podosphaera leucotricha, will attack nectarine fruit. Inoculum is produced only in apple orchards.

Management of powdery mildew on nectarines focuses on protecting fruit from infections. Watch for the disease during routine monitoring. Avoid growing nectarines near apple varieties that are highly susceptible to powdery mildew, such as Jonathan, Gravenstein, and Rome Beauty. If nearby apples are expected to cause mildew problems on nectarines, control the disease on apples or apply a fungicide to nectarines at jacket split.

Sulfur sprays are acceptable for use in an organically certified crop.

Apply one of the fungicides listed below from bloom until pit hardening or later when necessary. Up to three applications may be necessary in seasons when nights are cool and moist and daytime temperatures are warm. Early treatments are the most important and most effective. It is important to alternate materials of a different chemistry to prevent the development of resistance to a fungicide.