Cause Botrytis cinerea, a fungus. This is an important postharvest problem in cold storage. Overwintering sclerotia and mycelium produce abundant conidia in winter and spring. Conidia infect petals and anthers under warm, moist conditions during bloom. Infection periods occur when the temperature is between 57°F and 77°F during a wetness event of at least 6 hours. Sepals and receptacles can become infected from 30 days after flowering through harvest. Infections remain latent until fruit mature and are harvested. Picking wounds can also be infection sites. Fruit from vines near pollinator vines show a greater incidence of this disease. Necrotic leaves in the canopy is related to the amount of rot in storage. High humidity and low light levels favors disease development. The fungus grows slowly under cold storage conditions.
Symptoms Generally, gray mold is not seen in the field. It is near the stem end of the fruit after 4 to 8 weeks in cold storage. Affected areas appear darker than the healthy part of the fruit. The discoloration advances evenly toward the base of the fruit. Internally, infected tissue turns dark green and is water soaked. White to gray mycelium and sporulation may be present. Sclerotia are jelly-like and white. As decay advances, other fruit may also become involved. Infection through picking wounds may develop into a side rot.
Cultural control
- Create more open canopies by summer pruning.
- Hold kiwifruit at 59°F for 2 days after harvest but before cold storage.
Chemical control Focus on cultural control tactics first. 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.
- Apply registered materials during bloom when rainy weather has been forecast.
- Flint Extra at 3.8 fl oz/A. Do not use on 'Concord' grapes. Do not use within 14 days of harvest. Group 11 fungicide. 12-hr reentry.
- Kenja 400 SC at 13.5 to 15.5 fl oz/A. Do not use within 7 days of harvest. Group 7 fungicide. 12-hr reentry.
- Luna Tranquility at 14 fl oz/A (labeled for Hardy Kiwifruit). Do not use within 45 days of harvest. Group 7 + 9 fungicide. 12-hr reentry.
- Miravis Prime at 10.3 to 13.4 fl oz/A. Do not use within 14 days of harvest. Group 7 + 12 fungicide. 12-hr reentry.
- Ph-D WDG at 6.2 oz/A plus an adjuvant. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
- Scala SC at 9 to 18 fl oz/A or at 9 fl oz when tank-mixed with another product. Do not apply within 7 days of harvest. Group 9 fungicide. 12-hr reentry.
- Vangard 75 WG at 10 oz/A. May be used on the day of harvest. More effective at cooler temperatures. Group 9 fungicide. 12-hr reentry.
- Postharvest applications.
- Scholar SC may be used once postharvest as a dip at 16 to 32 fl oz/100 gal water or as a concentrate spray on 200,000 lb fruit. Do not expose treated fruit to sunlight. Group 12 fungicide.
Note Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Abound (labeled for Hardy Kiwifruit).
Biological control
- BotryStop (Urocladium oudemansii U3 strain) at 2 to 4 lb/A. Keep refrigerated before use. Compatible with many wetting agents, some fungicides and biologicals but not all. Unknown efficacy in the PNW. 4-hr reentry. O
- Howler Evo (Pseudomonas chlororaphis strain AFS009) at 20 to 120 oz/A plus a surfactant. Can be used day of harvest. Unknown efficacy. 4-hr reentry. O
- Serenade OPTI (Bacillus subtilis strain QST 713) at 14 to 20 oz/A. Active ingredient is a small protein. 4-hr reentry. O
Reference Riquelme-Toledo, D., Valdés-Gómez, H., Fermaud, M., and Zoffoli, J. P. 2020. Postharvest Incidence of Stem End Rot in 'Hayward' Kiwifruit Is Related to Preharvests Botrytis cinerea Colonization of Floral Parts and Latent Infection. Plant Disease 104:823-832.