Damon Smith, Oklahoma State University
Diseases are a limiting factor in the production of juice, wine, and table grapes worldwide. The foundation of a truly integrated disease management program is:
- Site selection. Choose the best site possible for the cultivar(s) to be planted or make corrections to the site before planting a vine. An excellent site will result in healthy vines better able to tolerate pest pressure.
- Cultivar selection. Choosing cultivars even moderately resistant to a disease can greatly reduce the number of fungicide applications necessary. Make sure the cultivar selected matches the site.
- Acquire healthy nursery stock free of pathogens that cause diseases such as crown gall and Pierce’s disease.
- Proper training systems to ensure air circulation will decrease the drying time of plant parts, thereby limiting the number of infection periods of many pathogens.
- Sanitation is also an important tool in managing disease.
Disease management is not just the application of fungicides, although fungicides can be important tools when used appropriately. However, bear in mind that for diseases like black rot, which attack all green tissues of the vine such as first year shoots, expanding leaves, and developing fruit, fungicides must be applied several times during the critical period when leaf and fruit are susceptible to infection. It is important that the right fungicides be applied at the right time to limit infections. By understanding the life cycles of plant pathogens, how and when they cause disease, and how current environmental conditions impact disease development, fungicide applications can be applied in a timely manner to keep disease pressure from reaching economically important levels.
Combining site selection, cultivar resistance, training systems, fungicides, cultural control practices, and improving your knowledge and understanding of plant pathogens affecting grapes can result in a high quality crop even in years conducive for disease.
Pathogens of Grape
Organisms such as fungi, bacteria, mycoplasmas (organisms similar to bacteria), viruses, nematodes, and parasitic higher plants can be found in grape plantings all over the world.
Fungi are multi-celled, often filamentous, microscopic organisms that lack chlorophyll. Because fungi lack chlorophyll, they must derive energy from animals or plants as either parasites or as saprophytes (capable of feeding on dead animals or plants). Fungi grow by apical expansion of their threadlike body (hypha). A mass of these threads is called mycelium. Fungi have the capability to penetrate plant tissue directly, or they can gain entry through wounds or natural openings such as stomata (openings in leaf tissue) or lenticels (openings in woody tissue).
Bacteria are single-celled microscopic organisms. Their cells can be rod-shaped, spherical, or even take on a filamentous form. Bacteria are spread in films of water and splashing rain or running water. Therefore, bacteria can be spread in soil, plant debris, by insects, on pruning tools, or any other material that can sustain films of water. Some bacterial organisms, such as the bacterium that causes Pierce’s disease, are confined to certain plant tissues. However, these bacteria can be transmitted by insects and by grafting practices.
Viruses are submicroscopic (very small) particles that consist of genetic material (typically ribonucleic acid, or RNA) wrapped in a protein coat. Viruses come in different shapes and are obligate parasites (require a living host to survive and replicate). Viruses do not reproduce by themselves. They must enter the plant cell and use the plant cell to make more virus particles. Given the unique behavior and survival strategy of viruses, the diseases they cause typically do not kill plants, but can cause severe stunting, off colors, or other symptoms indicating an unthrifty vine. Viruses are most often transmitted by insects and nematodes. However, transmission via mechanical wounding and grafting can also occur.
Plant-infecting nematodes are soil inhabiting and/or root infecting organisms that are microscopic. These animals are worm-like with smooth nonsegmented bodies. Plant-parasitic nematodes have a cell piercing feeding apparatus called a stylet, which is used to extract nutrients from the plant cell. Nematodes are transmitted by anything that can move soil, including machinery, wind, and water.
Grape Diseases, PowerPoint presentation, Iowa State University
Early Season Disease Management for Grapes, University of Massachusetts
Scouting for Diseases in Grapes PowerPoint, Michigan State University
Field Guide for Integrated Pest Management in Pacific Northwest Vineyards, Washington State University
Reviewed by Tim Weigle, Cornell University and Stephen Jordan, University of Wisconsin-Madison