Fruit and nut tree trunk diseases are some of the most destructive diseases of vineyards and orchards worldwide. Trees are most susceptible after pruning when the open wound is exposed to the environment and becomes infected by disease-causing fungi, which may remain susceptible to infection for several weeks after pruning. These pathogens colonize the plant vascular system, causing wood canker and die-back.
These diseases include Esca, Botryopshaeria dieback, Eutypa dieback and Phompis dieback. Although caused by different types of fungi, these diseases share several common symptoms – dead spurs, stunted shoots and zones of rotten wood inside the trunk, called cankers. In fact, usually, more than one of these pathogens can be found in a vineyard.
In mature vineyards, symptoms of these diseases include overall stunting of shoots, and in subsequent seasons, death or dieback of shoots, spurs, arms and cordons. In young vines, symptoms include poor growth or poor vigor, chlorosis of leaves, and black streaking of tissue observed when vines are cut. Eventually, the vine dies due to canker formation in the vascular tissue.
Once the first symptoms are observed, the affected grapevines usually continue a steady decline until death. In these vineyards, yields are decreased and grape quality is diminished. In addition, the labor involved in pruning out infected wood, retraining dead/dying vines, and replanting adds to overall production costs. When the affected vineyards are no longer economically sustainable to maintain, growers have no alternative but to replant. As a consequence, vineyard longevity can be decreased significantly.
It is difficult to accurately measure the economic impact on grape production of trunk diseases because of the slow movement and the long incubation time of some of these fungi. However, losses in California were estimated as $260 million per annum in 1999 (Siebert 2001).
Esca symptoms include the presence of brown to black spots or streaks in xylem vessels, “tiger-striped” chlorotic and necrotic patterns on leaves, and the formation of necrotic spots or “measles” on berries.
Wood symptoms of Eutypa dieback and Bot canker are difficult to distinguish, as both diseases exhibit wedge-shape cankers in cross section of infected cordons.
Eutypa dieback foliar symptoms typically include the development of stunted shoots and chlorotic and tattered leaves in the spring.