How to Manage Pests
UC Pest Management Guidelines
Affected leaves display small, chlorotic interveinal areas that enlarge and dry out. Foliage symptoms are frequently called "esca." In red varieties dark red margins surround the dead interveinal areas. Severely affected leaves may drop and canes may dieback from the tips. Symptoms may occur at any time during the growing season but are most prevalent during July and August. On berries, small, round, dark spots, each bordered by a brown-purple ring, may occur. These spots may appear at any time between fruit set and ripening. In severely affected vines the berries often crack and dry on the vine or are subject to spoilage.
Measles are caused by several species of Togninia, a fungus that produces perithecia on grapevines in old, rotted vascular tissue. Ascospores are released from fall and winter into spring with rainfall; temperatures do not seem to be limiting for spore release. Ascospores reinfect the vine through pruning wounds. Wounds remain susceptible up to 16 weeks after pruning with susceptibility declining over time. The pathogen enters the current season's vascular tissue and it is believed that symptoms are expressed in the same year that new infections occur. Symptoms are caused by a toxin produced in the vascular tissue and include both leaf striping and fruit spotting. Other symptoms that appear in May are shoot tip dieback and tendril dieback.
Another species of fungus, Phaeomoniella chlamydospora, that causes the disease is closely related to the species of Togninia listed above and is also an endophyte in grapevine. This fungus overwinters as pycnidia in 3-5 year-old pruning wounds and releases pycnidiospores with rainfall from fall through spring. The pathogen also infects the vine through current year pruning wounds and produces symptoms.
With both pathogens, there can occur a 50% reduction in shoot growth.
Measles is more prevalent in areas with consistently high summer temperatures, such as the Central Valley, and in areas with heavy spring rainfall. Generally, plantings that are 10 years of age or older are affected, although measles has been seen on fruit and foliage on younger vines. In table grapes, mark areas of poor budbreak in spring. Examine these areas at harvest for disease symptoms.
Control can be achieved with use of liquid lime sulfur. However, it is important that the product get into the cracks and crevices of the vine because that is where the fungal fruiting bodies reside. Other treatments include use of wax or tree tar to fill the holes on the vine. Though still experimental, there would be no way for the fungus to reinfect the vine if these holes are plugged up.
UC IPM Pest Management Guidelines: Grape