Esca, also known as grapevine measles, petri disease, or black goo, can slowly plague a vineyard into decline. Esca pathogens excrete toxins that trigger an array of symptoms. Measles-like symptoms (dark spots with purple halos) appear on fruit, especially on white-fruited cultivars, anytime from fruit set to harvest. Foliar toxin expression of esca appears as a tiger stripe pattern of interveinal necrosis with yellow or red margins. Cross section of the infected trunk, cordon, and cane reveals black spots in the vascular system that may secrete black goo. Severe cases exhibit shoot/tendril dieback and “apoplexy” or complete defoliation and fruit abortion. Spores enter pruning wounds and colonize the vascular system anytime from November to April. New infections can have symptom expressions in the same year, and symptoms become more prevalent in years of wet springs and hot summers.
Causal agent: Several genera of pathogens can cause Esca in grapevines. Phaeomoniella chlamydospora, Phaeoacremonium spp. and Toginia spp. are common species.
Management: The prevention at the time of winter pruning is the best approach for the management. Double pruning, protection of pruning wound using paint with boron (trade name: B-Lock), as well as chemical control, such as use of thiophanate-methyl (trade name: Topsin-M) and/or myclobutanil (trade name: Rally) to protect pruning wounds are known to reduce risk of infection to pruning wounds. Also, it is advised to prune vines on a day followed with several days of sunny condition. (I.e., avoid pruning before the rain) If you decided to use aforementioned fungicides, make sure to obtain the label for the specific uses. Although symptom appears in the vineyard after 5-10 years of planting, young vines are as susceptible as the old vines; therefore, it is advised to implement a management plan from early years of the vineyard.
For infected unproductive vines, remove infected trunk or cordon arm 12 inches below canker, and move the infected woods out from the vineyard for burying or burning. Vine health is extremely important for the recovery after the major pruning of cordon or trunk. Provide sufficient water and nutrients to encourage healthy vegetative growth.