ven2docc10_(grape_diseases_pests) - VEN 2 DISEASES AND...

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VEN 2 DISEASES AND PESTS IN CALIFORNIA VINEYARDS Larry Williams INTRODUCTION Numerous pests and diseases affect grapevines in California. The pests and diseases discussed in VEN 2 will be limited to those that are widespread and/or those that cause vine death. DISEASES A disease is a continuous dysfunction at the cellular level caused by both biotic and abiotic agents. Causal agents that are living organisms causing disease in grapevines include: fungi, bacteria and viruses. The discussion of diseases in VEN 2 will be limited to biotic agents. They are referred to as infectious and parasitic pathogens. Fungi are small, frequently microscopic, multi-cellular or filamentous organisms that lack chlorophyll. Lacking chlorophyll, they must derive their energy either from dead animal or plant materials (they are called saprophytes) or from living animals or plants (they are called parasites or pathogens). Fungi may infect plants through direct penetration of tissue or through an injury or natural opening, such as stomata, hydathodes and lenticels. Bacteria are microscopic, rod-shaped or spherical, prokaryotic organisms. They lack an organized nucleus. Bacteria are usually identified by physiological, biochemical or serological tests. They can enter plants through wounds or natural openings as described above for fungi. Bacteria also may be vectored by insects in grapevines. Plant viruses are submicroscopic particles usually consisting of ribonucleic acid (RNA) wrapped in a protein coat. Virus particles are polyhedral or rod-shaped. Viruses do not reproduce themselves; instead, they induce the host to produce more virus particles. Viruses are transmitted by insect or nematode vectors, by mechanical contact through wounds and by humans through propagation of infected cuttings or buds. Fruit and foliar diseases caused by fungi Powdery mildew is widespread throughout the State of California. More money is spent annually by grape growers to control this disease than any other. The causal organism is an obligate parasite. It can over winter in the vineyard as spores inside black, spherical fruiting bodies or as mycelium or spores inside the compound bud. It will infect all green tissues. Once the sugar gets greater than 12 o Brix in the berries they are not susceptible to infection, however, the rachis still can become infected. It does not do will at temperatures greater than 90 o F and its spores will be killed by UV radiation. 1
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Control measures include, applications of sulfur (either as a powder or wettable sulfur) or with commercial fungicides. Downy mildew is a very harmful disease worldwide, however, it is only found in a few locations (or individual vineyards) here in California. It is an obligate parasite. Mild temperatures and rainy conditions favor the progression of the disease. Commercial fungicides are the only viable means of controlling it (usually some formulation of a copper based product). Botrytis bunch rot exists in all vineyards worldwide and you may also find the fungus
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This note was uploaded on 09/29/2010 for the course VEN 81437 taught by Professor Larrywilliams during the Fall '10 term at UC Davis.

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ven2docc10_(grape_diseases_pests) - VEN 2 DISEASES AND...

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