Peach (Prunus persica)-Powdery Mildew

Cause Podosphaera pannosa (formerly Sphaerotheca pannosa) and Podosphaera clandestina, fungi that overwinter on infected twigs, shoots, and buds of stone fruits. Leaves are infected as they emerge from the bud. Colonies that develop on leaves produce airborne conidia that infect other leaves and fruit. Fruit are susceptible to infection until pit hardening. Roses are a host of P. pannosa and may increase disease pressure if planted nearby.

A disease in peach called rusty spot is caused by Podosphaera leucotricha. This is the same fungus that causes apple powdery mildew, which is unable to sustain an infection on peach. Peach fruit are most susceptible to P. leucotricha from shuck split, when the ovary is first exposed, until fruit are 2 cm in diameter. Peach or nectarine fruit closest to apple orchards with powdery mildew had a higher incidence of rusty spot. Removing adjacent apple orchards has reduced rusty spot in peach orchards.

Symptoms Terminal growth, including twigs, leaves, and shoots, shows a white fungal growth in spring and early summer, often resulting in twig distortion. On fruit, powdery mildew develops as a fine white fungal growth on the peach surface. Later in the season, affected peaches take on a whitish russeted appearance and may also be malformed and scabby. Nectarine fruit is very susceptible.

Rusty spot is characterized by small, round, orange-tan lesions, which gradually enlarge as the fruit enlarges. Young lesions are initially white due to bleached trichomes. Upon death, the trichomes turn rust colored, starting from center outward. Eventually, as the fruit matures, all the dead trichomes drop off, leaving the cuticle suberized / russeted. Spores are rarely found, the response being one of hypersensitivity.

Cultural control

• Remove affected plant parts during normal orchard operations such as pruning and thinning.
• Use resistant cultivars.
• Remove nearby rose or apple plantings or keep powdery mildew under control on roses and apples.

Chemical control Use at petal fall or shuck split. Then monitor orchard closely for the development of symptoms. Not needed after pit hardening. In Spain, fungicides initiated at 220 degree-days (base 50°F) after bloom were effective. Tank-mix and/or alternate products with different modes of action to prevent the build-up of resistant fungi. Limit the use of any one group during crop production. Selection of products for rotation and/or mixing must consider group 7 fungicides when used through the irrigation as a nematicide.

• Abound at 12 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied the day of harvest. Sprayers should not be used on apples. Group 11 fungicide. 4-hr reentry.
• Bicarbonate-based products. Might supplement a normal program when powdery mildew is first observed. Do not mix with acidifying agents. Thorough coverage is essential. Poor to moderate control. O
  • Kaligreen (82% potassium bicarbonate) at 2.5 to 3 lb/A. 4-hr reentry.
  • MilStop (85% potassium bicarbonate) at 2.5 to 5 lb/A. Oregon and Washington only. 1-hr reentry.
  • Monterey Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water. H
• Cevya at 5 fl oz/A. May be used day of harvest. Group 3 fungicide. 12-hr reentry.
• Cinnerate at 16 to 64 fl oz/100 gal water plus an adjuvant. 4-hr reentry. O
• Eagle 20 EW at 2 to 3 fl oz/100 gal water for home orchards or landscape use. Can be applied up to the day of harvest. Group 3 fungicide. 24-hr reentry.
• Fontelis at 14 to 20 fl oz/A. Can be used day of harvest. Group 7 fungicide.12-hr reentry.
• Flint Extra at 2.5 to 3.8 oz/A. Do not apply within 1 day of harvest. 'Concord' grapes may be injured if accidentally sprayed. Group 11 fungicide. 12-hr reentry.
• Indar 2F at 6 fl oz/A plus a wetting agent. Group 3 fungicide. 12-hr reentry.
• Inspire Super at 16 to 20 fl oz/A. Do not apply within 2 days of harvest. Group 3 + 9 fungicide. 12-hr reentry.
• JMS Stylet Oil at 1 to 2 gal/100 gal water. Do not apply micronized sulfur within 10 days of an oil application. Do not use oil within 14 days of a sulfur application. Do not use during freezing temperatures, above 90°F, or when plants are under heat or moisture stress. Do not use when foliage is wet because good coverage is essential. 4-hr reentry. O
• Luna Experience at 6 to 10 fl oz/A. May be used day of harvest. Group 3 + 7 fungicide. 12-hr reentry.
• Luna Sensation at 5 to 7.6 fl oz/A. Do not use within 1 day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
• Merivon at 4 to 6.7 fl oz/A. Do not use with EC or oil-based products. Only nonionic surfactants can be used within 14 days of harvest. May be used day of harvest. Group 7 and 11 fungicide. 12-hr reentry.
• Miravis at 5.1 fl oz/A. Can be used up to the day of harvest. Group 7 fungicide. 12-hr reentry.
• Miravis Duo at 13.6 fl oz/A. Can be used up to the day of harvest. Group 3 + 7 fungicide. 12-hr reentry.
• M-Pede at 1 to 2 gal/100 gal water. Good coverage is essential. Do not use within 3 days of applying sulfur. Do not mix with hard water. 12-hr reentry. O
• Oso SC at 6.5 to 13 fl oz/A. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry O
• Ph-D WDG at 6.2 oz/A. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
• Pristine at 10.5 to 14.5 oz/A. Can be used day of harvest. Do not use with an HMO. Group 7 + 11 fungicide. 12-hr reentry.
• Propiconazole-based fungicides are registered. Do not use with an HMO. Group 3 fungicides.
  • Bumper 41.8 EC at 4 oz/A. 12-hr reentry.
  • PropiMax EC at 4 fl oz/A. Do not use within 10 days of harvest. 12-hr reentry.
  • Tilt at 4 oz/A. May be used up to and including day of harvest. 24-hr reentry.
• Quadris at 12 to 15.5 fl oz/A. May be applied the day of harvest. Sprayers used for Abound should not be used on apples. Group 11 fungicide. 4-hr reentry.
• Quadris Top at 12 to 14 fl oz/A. May be applied on the day of harvest. Group 3 + 11 fungicide. 12-hr reentry.
• Quash at 3.5 to 4 oz/A. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
• QuiltXcel at 14 fl oz/A. May be applied the day of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
• Quintec at 7 fl oz/A. A surfactant is not required when used alone but a nonionic surfactant is preferred if needed for tank-mixes. Do not apply within 7 days of harvest. Excellent efficacy. 12-hr reentry.
• Rally 40 WSP at 2.5 to 6 oz/A. Can be applied up to day of harvest. Group 3 fungicide. 24-hr reentry.
• Regalia at 1 to 4 quarts/A. Use on 7-day intervals. May be used day of harvest. Does not benefit from the addition of an adjuvant. Group P5 fungicide. 4-hr reentry. O
• Rex Lime Sulfur Solution (28%) at 0.5 to 2 gal/100 gal water depending on growth stage. Do not use with oil. 48-hr reentry. O
• Rhyme at 7 fl oz/A. Can be used through a drip or microsprinkler system. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
• Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. Can be applied up to the day of harvest. 4-hr reentry. O
• Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 0.5 fl oz/gal water. May be applied up to the day of harvest. Do not use more than seven (7) times per season. Group 3 fungicide. H
• Sulfur-based products have good efficacy. Do not use within 2 weeks of an oil spray. Group M2 fungicides. 24-hr reentry. O
  • Bonide Sulfur Plant Fungicide (90% wettable) at 1 to 3 Tbsp/gal water. H
  • Microthiol Disperss (80% sulfur) at 10 to 20 lb/A. Do not use a spreader-sticker.
  • Thiolux (80% sulfur) at 10 to 30 lb/A.
• Tebucon 45 DF at 4 to 8 oz/A. Can be applied up to and including day of harvest. Generally good to excellent control. Group 3 fungicides.5-day reentry.
• Tesaris at 3.5 to 5.6 fl oz/A. Do not use with oil-based products. May be used day of harvest. Group 7 fungicide. 12-hr reentry.
• Topguard SC at 14 fl oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
• Topguard EQ at 6 to 8 fl oz/A. Do not use with silicone surfactants or within 7 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
• Vivando at 15.4 fl oz/A. Do not use within 7 days of harvest or mix with horticultural oils. Group 50 fungicide. 12-hr reentry.

Note: Some registered products offer only suppression of this disease and thus are not recommended for use. These products include DoubleNickel 55 and Serenade.

Biological control

• Aviv (Bacillus subtilis strain IAB/BS03) at 10 to 30 fl oz/100 gal water. Unknown efficacy. Preharvest interval not specified. 4-hr reentry. O
• Sonata (Bacillus pumilis strain QST 2808) at 2 to 4 quarts/A. May be applied up to and including the day of harvest. 4-hr reentry. O
• Theia (Bacillus subtilis strain AFS032321) at 1.5 to 5 lb/A. May be applied up to and including the day of harvest. 4-hr reentry. O

References Jankovics, T., Dolovac, N., Bulajić, A., Krstić, B., Pascal, T., Bardin, M., Nicot, P. C., and Kiss, L. 2011. Peach rusty spot is caused by the apple powdery mildew fungus, Podosphaera leucotricha. Plant Disease 95:719-724.

Marimon, N., Eduardo, I., Martínez-Minaya, J., Vicente, A., and Luque, J. 2020. A decision support system based on degree-days to initiate fungicide spray programs for peach powdery mildew in Catalonia, Spain. Plant Disease 104:2418-2425.