Tips For Grapevine Trunk Disease Diagnostics, Prevention, and Control
Various pathogens and environmental factors are considered to be major threats to the vineyard’s health. Pathogens are disease-causing organisms such as fungi, bacteria, viruses, nematodes, and insects. In addition, adverse environmental conditions such as frost, hail, heat, chemical injury, nutrient toxicity or deficiency, improper cultural practices, and sanitation have an effect on vineyard health.
As an example, a vineyard might be infected with pathogens without showing symptoms until adverse environment conditions compromise the plant defense mechanisms and trigger disease progression. Our lab focuses on the detection and control of pathogens that are propagated by grafting (i.e., graft transmitted pathogens). However, many fungal pathogens and Agrobacterium spp. can be dispersed (short and long distance) by wind, rain, and/or irrigation splashes.
The fungal pathogens most frequently found in the vineyard can cause different diseases depending on the age of the vine. Species of Phaeoacremonium and Phaeomoniella cause young vine decline or Petri Disease in young vines. The same fungal species cause Esca in vines 10 years and older in age. In addition, this disease can manifest as a chronic illness (i.e., the vine slowly declines in the period of many years) or as an acute reaction in which the vines die within a few days of symptom onset.
The Cylindrocarpon spp. (recently re-named Ilyonectria spp.) cause black foot — a soil-borne disease, In addition, many soilborne pathogens such as Armillaria spp., Verticillium spp., Phytophthora spp., and Fusarium spp. can infect and cause disease in grapevines. Canker-causing organisms are also diverse and the symptoms they cause may be indistinguishable.
However, Botryosphaeriaceae spp. and Diatrypaceae spp. have been associated with specific diseases, Bot canker and Eutypa dieback, respectively. Other fungal species, such as Seimatosporium, Pestalotia, Pestalotiopsis, Truncatella, and Phomopsis, manifest similar wedge-shaped necrosis symptoms without a specific disease name. To complicate matters, it is common to find mixed infections of several fungal, viral and bacterial species in the same affected vineyard.
In the past several years we have seen an increased frequency in the development of aerial galls associated with Agrobacterium vitis infections. These bacteria can be found in planting grapevine material (propagated with the scion cuttings and/or the rootstock) as well as living epiphytically or in the vineyard rhizoplane. Some scion and rootstock varieties have shown tolerance to the disease.
These varieties can become infected and can be considered carriers of the pathogen with the ability to disseminate the disease to areas where the pathogen was not previously present (i.e., new virgin soils). It is important to know that Agrobacterium vitis infects and causes crown gall in grapevines specifically and is not able to infect other crops.
Disease Prevention and Control
The best way to control disease in the vineyard is to plant material that is tested free of pathogens. However, current certification programs do not exclude fungal or Agrobacterium species from propagation material. Therefore the first line of defense is to test planting material in our laboratory for the presence of these organisms and reject any planting material that is infected.
Many of these pathogens are soil-borne and or airborne and may be present in the vineyard. To reduce the incidence of trunk diseases in vineyards, disease management and control focuses on applying late pruning if the vineyard size is small enough to allow completion of the task at last minute.
The application of fungicide as well as pruning wound protectants have been shown to be an effective measure in reducing the incidence of trunk diseases in California vineyards. When the vineyard is too large to apply late pruning, double pruning — early trimming of the whole vineyard leaving long shoots that are to be pruned early in the spring — is very effective in disease control.
Preliminary work performed in Kendra Baumgartner’s laboratory at the USDA-ARS at University of California (UC)-Davis has shown that preventative measures must be adopted early in the life of the vineyard to be economically feasible. The later these practices are adopted, the more difficult it is to recover the cost of application. Sanitation of the vineyard with the removal of pruning cuttings is very important in controlling the spread and propagation of disease.
Pathogen Testing in the Laboratory
Assessment of the health status of scion and rootstock planting selections is a crucial step in ensuring a healthy vineyard and consequently a successful vintage. Many growers rely on planting “healthy looking” material from their own or neighboring vineyards.
Derived vines should be planted with caution as vines can harbor pathogens without showing notable signs of infection. To ensure disease-free stock, representative samples should be submitted to a laboratory to test for major disease-causing agents. To assure the highest quality, planting material from certified sources must always be tested as our experience has shown that it is possible to detect pathogens in such stock.
The Eurofins STA HealthCheck Panels were developed to specifically survey and identify many grapevine pathogens. The HealthCheck CG can detect Agrobacterium vitis using a combination of selective culture and molecular detection using PCR.
The HealthCheck Fungal Panel uses traditional microbiological diagnostic methods with the aid of a microscope complemented with sequencing a portion of the fungal pathogen’s genome for their rapid and accurate identification. The availability of different diagnostic approaches allows our lab to handle pathogens that are difficult to identify due to their inability to produce typical spores, lack of specific morphological features, and/or genetic variation.
Our lab can identify any fungal and virus variants found infecting grapevines. Our expert team excels at handling special situations and strives to report the most accurate results.
This article is a summary of a webinar entitled “Grapevine Trunk Disease Prevention and Control,” found online here. For more information on upcoming or previous webinars, including one on Grapevine Red Blotch Disease, click here.