By Layne Wade, Technical Sales Support, Arysta LifeScience

Like many plants, grapevines have a history, and that history sometimes can repeat itself in terms of disease pressure. The previous season’s grape crop, weather and water stress also play roles in how successful this season’s grape harvest will be.

 Overwintering of PM

In grapes, Powdery mildew (PM) can overwinter and cause numerous problems as early as the budbreak stage. According to research from Cornell University, PM survives the winter by forming minute fruiting bodies called chasmothecia, which contain sexual spores known as ascospores. Ascospores result from mating among individual PM colonies. These spores initiate disease at the start of the growing season in grapes, and they increase the genetic diversity of the overall fungal population. To note, they are distinct from the asexual spores (conidia), which are produced from new infections throughout the season; however, both forms serve to spread disease whenever conditions are favorable.

In spring, with as little as 2 mm of rain, irrigation or dew occurs to wet the cordons or canes. The overwintering chasmothecia release the ascospores, which are scattered by the wind and rain. Infections occurs when the ascospore release is followed by 10 to 13 hours of leaf wetness and temperatures remain between 50° and 80 °F. Each ascospore that lands on green tissue and causes an infection can go on to produce thousands of conidia in approximately 5 to 10 days (if average temperatures are favorable, generally in the 60s and 70s ºF). Typically, chasmothecia begin forming on the surface of infected leaves and clusters in mid- to late summer. They remain firmly attached until they mature, after which they can be washed away by rainfall.

New crops of conidia may lead to secondary infections. Arysta LifeScience works with the University of California-Davis on grape research and recommends the Grape Powdery Mildew Risk Assessment Index to help monitor PM pressure: http://www.ipm.ucdavis.edu/calludt.cgi/GRAPEPMVIEW1.

Management

Season-long control of Powdery mildew is dependent upon reducing early-season inoculum and subsequent infection; therefore, treatment must begin promptly and be repeated at appropriate intervals. Timing of the first application is dependent on the fungicide used, vine growth stage and the potential for disease infection. Free moisture from fog, dew or rain events triggers ascospore release after budbreak, and infections caused by ascospores will occur on green tissue when temperature exceeds 50°F. Growers should apply a contact material as soon as possible to eradicate those colonies prior to the onset of conidial spore production. 

To summarize: through multiple generations, each ascospore present in the fall can be responsible for thousands of secondary infections in grapevines the next summer unless they are controlled.

VITICURE, for the best control

To help fight overwintered PM in grapes, growers trust VITICURE^® Fungicide – an effective and unique imidazole chemistry with no known cross-resistance to other demethylation inhibitor (DMI) fungicides. It is active as both a protectant and as a curative by preventing infection and inhibiting growth after infection has occurred. The anti-sporulant activity of VITICURE reduces spore production after lesions become more visible.

With VITICURE, grape growers should begin applications before bloom and continue on a 14- to 21-day interval. The product is rapidly absorbed and locally systemic, allowing disease protection that is improved by movement across each leaf’s tissue. Additionally, VITICURE is an excellent tank-mix partner with other registered materials including copper fungicides as well as liquid or wettable sulfur.

To learn more about fungicide applications at budbreak in grapes or VITICURE and the Arysta LifeScience portfolio of crop protection products, contact your crop protection retailer, visit www.ArystaSpecialty.com/Grapes or call 866-761-9397.

_{Always read and follow label directions. VITICURE is a registered trademark of Arysta LifeScience North America, LLC. Arysta LifeScience and the Arysta LifeScience logo are registered trademarks of Arysta LifeScience Corporation.}

_{©2017 Arysta LifeScience North America, LLC. SPC-1632 #2}