Phomopsis

Phomopsis

Phomopsis is a cold weather fungal disease and is widely distributed. It is problematic in the regions where the climate following the bud break keeps grapevines wet for extended periods of time. Phomopsis is often confused with Black Rot or Bitter Rot but is distinguished by late appearance, typically just before harvest. The casual agent of phomopsis is Phomopsis viticola. Spores are produced within pycnidia that are formed in previously infested woody tissues in late winter or early spring. The fungus can continue to produce pycnidia and spores for an indeterminate number of years after the first infection, even after infected wood dies. Therefore a serious disease outbreak in one season can provide inoculums for new infections for many years. Spores ooze out in humid/wet weather and are splashed by rain onto new developing tissues, which is most susceptible to infection.

Signs and Symptoms

Yellow lesions on leaf
Sunken lesions on shoot
Black fruiting bodies

On Leaves:
Small light green lesions with irregular margins appear early in the season (image on the right, Photo courtesy- Ohioline, OSU), as disease progress spots turn dark brown to black with yellow halos. The infected tissue may drop out causing a pin –pricked appearance.

On Shoots:
Elongated sunken black lesions appear on shoots (image on the right, Photo courtesy- Ontario crop IPM) and rachises. Older lesions can weaken the stem and can break in high winds. Rachis can become brittle and clusters may break. The infected canes turn bleached or grayish in the dormant season.  

On Berries:
Infected fruit gradually turns brown and shrivel. Pycnidia develop sparsely on the surface of the berry (image on the right, Photo courtesy- extension.org). Eventually, the diseased berries shrivel into raisin like mummies.

Phomopsis Disease Management

Sanitation:
Sanitation is the most important control measure in preventing the spread of the infection. Diseased canes should be removed from the vineyard and destroyed. Maintain a healthy plant by following good growing practice, more information can be found at Midwest grape production guide.

Fungicides:
Broad spectrum fungicides such as mancozeb, captan, folpat, ziram, chlorothalonil, and dithianon are very effective against Phomopsis and should be applied during very early part of growing season. Copper is relatively ineffective against Phomopsis. Commercial growers should consult the most current issue of the Midwest Fruit Pest Management Guide for up to date fungicide recommendations.

Biocontrol:
Currently, there are no bio-control products available that are effective against Phomopsis.

Additional Resources

OSU Phomopsis Cane and Leaf Spot of Grape Factsheet

OSU Fruit Pathology Information Website