Young vine decline is a disease complex with various names, including black measles, esca, young esca, Petri disease, apoplexy and black goo disease.
It has been an increasing problem in California vineyards, causing significant economic losses due to vineyard replanting and yield reductions. It has also increased in importance in Europe, most likely due to a reduction in the use of sodium arsenite fungicides, which have been banned in most countries.
In California, esca or black measles has been a problem in older vineyards for decades. More recently, it has also become a problem in young vines, following a massive replanting effort which replaced phylloxera-susceptible rootstocks with other more resistant hybrid rootstocks. Unfortunately, the new rootstocks appear to be more susceptible to vine decline.
A 2007-2009 survey conducted by Agriculture and Agri-Food Canada investigated decline problems in Okanagan vineyards (O'Gorman, Haag & Sholberg). The survey confirmed the presence of several fungal pathogens causing vine decline symptoms, including two pathogens associated with esca.
Esca and young vine decline are caused by several fungi which act alone, in combination, or in succession to cause disease.
Fungal pathogens involved in young vine decline in both B.C. and California include Phaeomoniella chlamydospora and Phaeoacremonium aleophilum. Other species of Phaeoacremonium have also been associated with esca vine decline in California but have not yet been detected in B.C.
Several wood-rotting basidiomycete fungi, including a Phellinus species (now known as Fomitiporia punctatus) and Stereum hirsutum were historically associated with esca. While these fungi could be isolated from diseased vines, it was not possible to reproduce the same symptoms by inoculating healthy vines.
It is now thought that infection with Phaeoacremonium and Phaeomoniella species predisposes the vines to wood rots by breaking down toxic phenolics and other host-produced substances which are inhibitory to wood rot fungi.
There are several other diseases that cause decline of grapevines, including Cylindrocarpon black foot, botryosphaeria canker, eutypa, phomopsis canker (not yet found in B.C.) and several root rot diseases.
Phaeomoniella and Phaeoacremonium infect the vascular tissue of young vines, resulting in darkening and plugging of the xylem vessels. Discolouration in the xylem vessels may appear as black streaks when vines are cut longitudinally or as black dots when cut in cross section. Wood rot is usually absent on young vines.
Symptoms range from mild to severe and include chlorotic foliage, defoliation, stunting of growth and reduced yield and quality. Sudden wilting and death (apoplexy) of vines or cordons may occur in midseason, particularly during hot weather. Vine symptoms also include delayed and weak growth in spring, and reduced lignification of canes in the fall.
Foliar symptoms include light green or chlorotic spots between the leaf veins or along the leaf margins. The spots gradually expand and turn yellow brown or red brown, leaving only a narrow strip of green tissue along the main veins. In California, a mosaic has also been observed on terminal leaves followed by shoot tip dieback. It is thought that foliar symptoms are caused at least partially by toxins produced by the fungi and/or reaction products of the infected wood which are translocated to the leaves.
Symptoms on berries may be present without symptoms on the leaves and vice versa. Berries on affected plants tend to be small and may not reach full maturity. Sugar content and flavour can be adversely affected.
Berries sometimes develop spotting or black measles symptoms, with white cultivars being more susceptible. Berry spotting consists of brownish to purplish, small pinprick sized spots on the berry skin. Heavy spotting may lead to skin cracking, berry shrivel, and secondary berry rots.
Esca is known as a disease of adult plants (8-10 years and older). It is caused by the same fungi that cause young vine decline. However, on older vines there are often wood rot pathogens involved as well.
Symptoms are similar to those described on young vines. It causes a decline with characteristic leaf and fruit symptoms, and sudden wilting and death in severe cases.
Additional symptoms in older wood include an internal white heart rot that causes the wood to become soft and spongy. A dark line or a series of black dots generally surrounds the white heart rot. In a longitudinal section, this vascular discolouration appears as black streaks.
Research in California is increasing understanding of the biology of the fungi causing young vine decline. The method of disease spread is not yet certain. However, spore trapping results from infected vineyards have found airborne spores, with large numbers of spores trapped during rainfall. Infection most likely occurs through wounds.
Wet weather and warm temperatures appear to favour the disease. Years with above normal rainfall and high summer temperatures have resulted in more severe symptoms in California.
The wood rot fungi that are associated with esca are wound invaders, which infect through large wounds or pruning cuts on the trunk or cordons of mature vines. These fungi have a wide host range and are commonly found as wood rots in other broadleaf tree species.
Basidiospores produced by fruiting bodies (bracket fungi) on dead wood or other hosts can be spread long distances by wind and can infect grapevines. Observed spread along rows in vineyards may also indicate that spores can be spread by tools during pruning and grafting.
The presence of vine decline affecting a high proportion of plants in recently established vineyards in California also suggests that nursery stock may be carrying the disease. The pathogens have also been isolated from a high proportion of vine cuttings produced in Italy or France.
The type of vine training system can be a factor, as extensive pruning cuts create more potential infection sites. One study found 0.1% esca in lateral cordon vineyards compared to 15-20% in vines trained by double Guyot.
Other ways to prevent spread:
There are no fungicide treatments for esca in Canada.
