UC IPM Pest Management Guidelines: Strawberry When conditions are favorable, conidia produced on infected plants are wind dispersed. Identification of powdery mildew fungi. The fungus cannot survive in the absence of living host tissue, and therefore the source of inoculum must either overwinter on infected live strawberry leaves or be brought in on transplants. Conidia typically measure 31.2 μm ± 2.8 × 20.39 μm ± 4.1 (Santos et al., 2002). Powdery mildew development and spread are favored by moderate to high humidity and temperatures between 60°F and 80°F. Acceptable for use on organically grown produce. Spores are wind disseminated and short-lived. Powdery mildew (Podosphaera aphanis) infects the tissue of strawberry plants and despite the fact that it’s mildew, which we usually associate with wet conditions, this strawberry leaf coating is fostered by dry conditions with moderate humidity and temps between 60-80 F. (15-26 C.). Protectant and/or systemic fungicides can be initiated when concerning levels of symptoms are observed. Podosphaera aphanis is an obligate, biotrophic fungus that causes damage to strawberry leaves, flowers, and fruit. Powdery Mildew may occur on strawberry fruit under favorable circumstances. Unlike most fungal pathogens, P. aphanis grows epiphytically on plants, producing hyphae on the lower leaf surface and on the surfaces of flowers and fruit. Fungicide sprays are rarely needed for powdery mildew control in North Carolina annual production systems. In some cases, the REI exceeds the PHI. Warm temperatures with high humidity in the strawberry canopy favors powdery mildew growth on fruit. This page describes the symptoms of the fungal disease, its spread and recommended control measures. Cultural practices are important in helping to prevent disease buildup. Apply mined sulfur or insecticidal soap on organically certified strawberries. The patches may eventually coalesce to cover the entire underside of the leaf. ; Heffer et al., 2006). The standard nursery practice of removing leaves from transplants during harvest and packing helps minimize introduction of the disease, although inoculum may still be present on crowns. These colonies enlarge to cover the entire lower leaf surface, causing the edges of the leaves to roll up. Use less-susceptible cultivars where practical. Flowers, petioles, and fruit also can become infected. Compendium of Strawberry Diseases, 2nd edition. Heffer, V., Johnson, K. B., Powelson, M. L., Shishkoff, N. 2006. Santos, B., Blanco, C., Porras, M., Barrau, C., Romero, F. 2002. Growers are encouraged to test product or product mixes for phytotoxicity before field applications to determine safety margins. Choose a site with good sun exposure and minimal shade. Accordingly, the disease is mostly limited to the coastal growing regions and northern nurseries and causes very little damage in inland growing regions. Use less-susceptible cultivars, such as Albion, San Andreas, and Fronteras, where practical. N.C. Heavy powdery mildew infection may result in a serious reduction in photosynthesis, affecting overall plant vigor, fruit production, and quality. Signs of powdery mildew may be confused with white waxy residue associated with whitefly eggs. Read our If fruiting structures are absent on affected sample, individual leaves or leaflets may be incubated in a moist chamber for 24 to 48 hours to induce sporulation. The following are ranked with the pesticides having the greatest IPM value listed first—the. Preharvest interval (PHI) is the number of days from treatment to harvest. UC ANR Publication 3468, S.T. Chasmothecia, dark round structures resulting from sexual fusion (Figure SS-3), contain a single ascus, which contains eight (sometimes six) uninucleate ascospores. The pathogen also survives as mycelium and chasmothecia (closed spore-bearing structures) on plants coming from nurseries. Sphaerotheca macularis), occurs in most areas of the world where strawberries are grown. Initiation, development, and survival of cleistothecia of Podosphaera aphanis and their role in the epidemiology of strawberry powdery mildew. There are even some plants, such as the lilac, that can have the powdery mildew on it and it doesn’t hurt the plant that much.So using a homemade cure for powdery mildew on the hardier plants isn’t necessary. Powdery mildew is particularly severe in greenhouse and plastic tunnel production systems. P. aphanis is heterothallic, meaning two compatible mating types are required for sexual reproduction. COMMENTS: Sulfur application during high temperatures may burn foliage. Thus, infected transplants are normally the primary source of inoculum for fruiting fields in Florida. Phyto-pathology 103:717-724. During routine field surveys, watch for the leaf distortion and discoloration that are the first signs of powdery mildew, especially in fall and spring. Once established, development and spread of conidia from infected leaves occurs in windy conditions during moderate to high humidity and temperatures between 60-80°F (15-27°C). Infected flowers produce deformed fruit or no fruit at all. COMMENTS. P. aphanis is an obligate parasite that only infects living tissue of wild or cultivated strawberry. 2013. First Confirmation of Sphaerotheca macularis on Strawberry Plants in Southwestern Spain. Do not apply within 3 weeks of an oil application. Infected leaves may curl and purple and reddish blotches can also appear on the lower leaf surface (Figure SS-2), also, numerous black specks (cleistothecia; also called chasmothecia) may be observed (Figure SS-3). Make additional fungicide applications when plants begin to bloom. Find more information at the following NC State Extension websites: Publication date: July 24, 2014 Remove the tape from the leaf and place it sticky side down on a drop of water on a microscope slide. — Read our Powdery mildew is usually not a problem on strawberries in annual production systems. out by fungicide applications. The disease overwinters as mycelium on leaves in California, so it is most likely introduced into the field through planting material or spores from neighboring fields. Young foliage is most susceptible to damage. How to Identify Powdery Mildew Damage. A simple method for making a slide to confirm a powdery mildew diagnosis can be conducted using a small piece of clear tape. Flowers, petioles, and fruit also can become infected. COMMENTS: Under warm, sunny conditions, fruit bronzing may occur. There are no known differences in susceptibility in annual varieties. 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