The role of non-cucurbit hosts as sources of inoculum has not been investigated. In 2013 Quintec, Pristine, and Procure provided excellent control (93-99%). Fungicides are required to control cucurbit downy mildew. Also, always check with your certifier before purchasing any product. Examine upper and under surfaces of five older leaves at each of 10 sites or until symptoms are found. Although all cucurbits are susceptible, symptoms are less common on cucumber and melon because many commercial cultivars have resistance. Source(s) of initial inoculum for powdery mildew have not been definitively determined. Substitute new for older product if they are in the same FRAC group. Efficacious fungicides include fluopicolide, famoxadone + cymoxanil, cyazofamid, zoxamide and propamocarb hydrochloride. General Chapters They develop late in the growing season. Severe powdery mildew on a susceptible pumpkin cv. In 2019 Vivando was the most effective single product tested providing control statistically similar to the alternation program (Vivando, Quintec, Proline), albeit numerically lower control (75 and 92% control on lower leaf surfaces). State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. Premature senescence of infected leaves can result in reduced market quality because fruit become sunburnt or ripen prematurely or incompletely. Powdery mildew of cucurbits is caused by the fungi Erysiphe cichoracearum and Podosphaera fuliginea. Powdery mildew development is arrested when daytime temperatures are at least 100°F. The disease cycle is initiated by windblown conidia, which infect cucurbits over a range of humidity (50 to 95%) during moderate to warm (68 to 80ºF) temperatures. Before disease appears apply fungicides at 7-day interval for cucumbers and 10-day intervals for other cucurbits. Apply targeted fungicides weekly with protectant fungicides and alternate amongst available chemistry based on FRAC Group code, starting at the action threshold of 1 affected leaf out of 50 older leaves. To manage powdery mildew effectively in cucurbit crops: Please Note: The specific directions on fungicide labels must be adhered to — they supersede these recommendations, if there is a conflict. Verbena, a common ornamental plant, could be an important source of inoculum, especially for cucurbits grown as a crop or transplants in the same greenhouse as verbena. Several biopesticides approved for organic production are registered for this disease in the United States. Based on these criteria, P. xanthii was found to be the predominant fungus, rather than E. cichoracearum as previously claimed, in several countries. Please contact site owner for help. Downy Mildew There are several formulations of copper and sulfur not included. Always implement a resistance management program; do not wait until there is a problem. Reduced sensitivity to fungicides from several chemical groups have been detected in other areas of the world as well. Races 1 and 2 have most common in the eastern United States recently. The most important component of an effective management program is an effective fungicide program. Select varieties with resistance from both parents (homozygous resistance) when possible. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended. Powdery mildew management program often needs adjustments as the pathogen and management tools change. Products listed with OMRI (Organic Materials Review Institute) are NOP compliant. Therefore, tactics should always be used to minimize the potential of resistant pathogen strains being selected, starting when a new product is first available: apply mobile fungicides together with a contact fungicide (tank mix), apply them only when needed most to protect yield (which begins at the start of disease development; contact fungicides alone can suffice late in the season), use highest labeled rates, and alternate among as many different mobile fungicides as possible selecting based on resistance occurrence and on modes of action as indicated by their FRAC code (see link to current fungicide information at top of page). A shift in the predominance of these two fungi may have occurred or the causal organism may have been misidentified. Dryness is favorable for colonization, sporulation, and dispersal. Weed Links Plant breeders are actively searching for new sources of resistance to powdery mildew. Chemical Control On some plants powdery mildew disease will occur, despite the best attempts at cultural control. mtm3@cornell.edu. School of Integrative Plant Science Powdery white spots appear first on leaves, and eventually grow to cover entire leaves. Resistant varieties are now available in most crop groups with new varieties released most years. Luna Experience (FRAC 3 and 7). For a preventive schedule, applications should begin when first female flowers have opened. Toggle navigation As the pathogen continues to colonize the plant, the leaves senesce early and fruit yield and quality can be affected. Severe powdery mildew on a susceptible pumpkin cv. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Possible local sources of initial inoculum include conidia from greenhouse-grown cucurbits, cleistothecia, and alternate hosts. Correct use of fungicides combined with choice of variety will give excellent control throughout the growing periods. Because these fungicides have targeted activity, additional fungicides must be added to the program when there is a need to manage other diseases such as downy mildew and Phytophthora blight. Yellow spots may form on upper leaf surfaces opposite powdery mildew colonies. A spring planting of summer squash will become infected first; therefore, when available, it can be used as an indicator of when to begin scouting vine crops and later plantings of summer squash. Products evaluated in university trials have exhibited a range in efficacy with some being as effective as conventional contact fungicides. The main criterion used is presence of fibrosin bodies in conidia of P. xanthii. Powdery mildew can reduce fruit yield and size, but the amount of damage is directly related to the amount of time plants have been diseased. Cleistothecia have been reported rarely in the United States; however, even when present they can be overlooked. Quintec and Vivando were the most effective of the targeted fungicides evaluated in 2014 (96 and 98%); Pristine was moderately effective (54%); Procure was slightly but not significantly better (70%). Associate Professor Resistant pathogen strains are sufficiently common to render the following fungicides ineffective: Topsin M (FRAC Code 1; MBC fungicide), QoI fungicides (Code 11), which include Quadris, Cabrio and Flint, and SDHI fungicides (Code 7) containing boscalid (Endura and Pristine) or an active ingredient that has exhibited full cross resistance in laboratory testing of pathogen isolates (Merivon). Infected leaves usually wither and die. The pathogen overwinters on wild cucurbit hosts, weeds, and dead vines. School IPM, Author: Howard F. Schwartz and David H. Gent. This site is a project of the Cornell Vegetable Program Work Team (PWT). The conidia (spores produced asexually) of E. cichoracearum and P. xanthii are difficult to distinguish and cleistothecia, which are sexual fruiting bodies (structures containing spores produced through sexual reproduction), have been observed less commonly. Starting treatment after this point will compromise control and promotes resistance development. Once all cultural control options have been exhausted without satisfactory results, chemical control methods can then be considered. CHEMICAL CONTROL If fungicides are used, inspect the crop regularly to detect when infections first occur. Conidia remain viable for 7-8 days based on results from laboratory studies. Prevention & Treatment: Powdery mildew-resistant varieties (Table 1) are available for most cucurbits, thus with proper planning, chemical control should not be necessary. White powdery spots can form on both upper and lower leaf surfaces, and quickly expand into large blotches.