Grapevine Diseases

• Grapevine cultivation is impeded by several diseases that affect both yield and quality of the grapes. Every year these diseases cause significant losses to vineyards due to reduced fruit quality, replanting and pruning costs.
• Control of the grapevine diseases requires proper identification of the disease agent whether it is a case of an existing disease problem or a preventative measure to assure that the propagation material is free of the diseases.

Disease descriptions:

Grapevine leafroll disease

Leafroll disease is one of the most important viral diseases affecting grapevines. Leafroll  causes significant yield losses (up to 30 to 50% depending on a  variety) and delays fruit ripening. The berries of infected vines are low in sugar and color (red varieties).  Infected vines often grow less vigorously than healthy vines. (This is often observed as delayed push of shoots in spring). Most characteristic symptom of the disease is the down-ward cupping of leaves (leafroll) that is first observed in older leaves.  Green veins is also characteristic symptom of the disease, which In the red cultivars is combined with the red leaf color between the veins. In green varieties some chlorosis may be observed.

Grapevine leafroll disease affects all native and Vitis vinifera cultivars, hybrids, and rootstocks. Symptoms, however, are not pronounced on all infected vines. Table grape varieties, for example, show usually way less symptoms and many of the roots stock varieties totally lack symptoms.

There are up to ten different grapevine leafroll virus (GLRaV) types identified to date. The most common GLRaV types are 1, 2 and 3.

Leafroll viruses are spread in propagation material and through grafting of infected wood. Certain mealybugs and soft scale insects are also known to transmit GLRaV types 1, -3, -5, and -9.

Sensitive laboratory tests for detection of GLRaV types 1, 2, 3, 4, 5, 7, 9 and GLRaV-2RG are available at the AL&L Crop Solutions.

Fanleaf disease

Fanleaf disease is a serious disease affecting grapevine production throughout the world.  Characteristic symptoms of the disease are fan-shape leaves, yellow vein banding (common symptom in California) and yellow leaf mosaic. Infected vines are often stunted and shoots show zig-zag type of growth due to shortened internodes.  Fruit clusters are poorly developed containing smaller berries. Fanleaf causes major yield losses up to 80% in some varieties. Fanleaf virus spreads in planting material. It is also spread by a nematode Xiphinema index.

Vine decline

Esca, black measles and Petri disease (young vine decline) are all forms of the same disease caused by Phaeomoniella chlamydospora and several Phaeoacremonium species. Symptoms of Esca can appear both in foliage (tiger-striped leaves) and/or in fruit (black measles). Petri disease symptoms (dark-colored xylem vessels) are often visible in graft union and rootstock end. In all forms of the disease, the growth of the infected vines declines. In some conditions the disease can cause the total collapse of the vine. Grapes become infected by spores of P. chlamydospora and Phaeoacremonium spp. during propagation processes and through pruning wounds in standing vineyards. Stresses such as water deficit, early fruiting, “J” rooting, and salt stress worsen the symptom development.

No effective control measures are currently available for the disease. Existing rootstock varieties are all shown to be susceptible to the disease. The incidence of Esca and Petri diseases has continuously increased in California vineyards for the past 10 years. Pruning of infected wood, replanting, and reduced fruit quality cause significant losses to vineyards every year.

AL&L Crop Solutions offers sensitive screening methods to discover infections caused by the vine decline fungi.

Canker diseases