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76 WINES&VINES April 2016 GRAPEGROWING PRACTICAL WINERY & VINEYARD Promote your wines to leading Zinfandel enthusiasts and extend your winery's relationship in the market. Join Us! We are champions of Zinfandel— America's Heritage Wine Become part of our proud legacy zinfandel.org • 530-274-4900 Zinfandel Advocates & Producers is a 501(c)(3) non-profit organization. ZAP is dedicated to advancing public knowledge of and appreciation for American Zinfandel and its unique place in our culture and history. You know how good your Zinfandel is... are dependent on the calcium levels in the plant for activation. 14 Copper is another example where the use of a micronutrient can have long-lasting impact on the vine's ability to resist fungal pathogens. The use of sub-biocidal rates of copper can reduce foliar diseases without direct toxicity to the pathogen. 2,18 Key timing for micronutrient applications would be bud break to bud swell, flower rachis emergence, one to two weeks after rachis emergence, two weeks pre-bloom, bloom, one to two weeks pre-véraison and one to two weeks post-véraison. It is important to monitor vineyard condi- tions and time sprays prior to periods of high disease pressure. ISR and SAR responses re- quire the triggering chemicals be present prior to disease infection to be most effective. Unlike fungicides, these processes will help increase the plan's resistance but can be swamped by extreme disease pressure. They need to be used in an integrated pest management program. Calcium can inhibit pectinase activity of Botrytis cinerea. 19 Botrytis infects grapevines through aborted flowers at bloom. Therefore, the application of calcium at bloom may re- duce the severity of Botrytis bunch rot. 20 Manganese Manganese fertilization has been shown to control powdery mildew of cereals, downy mildew of sorghum, take-all of wheat and powdery mildew in grapevines. 33 Manganese increases the production of soluble phenols, which play a role in the resistance mechanisms of plants against fungal pathogens. 21 Manganese inhibits the production of amino peptidase, which is necessary to supply the pathogen with amino acids, and inhibits pectin methyl esterase, which is needed by the pathogen in order for the organism to pene- trate the plant's cell walls. In response to infec- tion, a plant concentrates manganese around the infection site and changes the oxidation state (charge on the manganese ion) of the manganese from Mn +2 to Mn +4 . 22 The toxicity of manganese to both the pathogen and the plant tissue grows with in- creasing positive charge of the manganese, helping to isolate the infection by lignifying the plant tissue around the infection site and reducing the spread of the pathogen. 22 Man- ganese inhibits protease and pectinase activity in fungal pathogens when used at fertilizer rates and, like calcium, manganese may help reduce infection of the plant. 34 Application of manganese at bloom may also help reduce Botrytis infection. 34 Zinc Zinc is also important in a plant's natural defense mechanisms. It is required for hundreds of enzy- matic pathways. Because of its importance in a plant's natural metabolism, plants deficient in zinc demonstrate increased disease severity after infection by powdery mildew. 23 Zinc is involved in superoxide production in plants, which is re- sponsible for a cascade of plant defense pathways against fungal and bacterial pathogens. 24 Boron An equally important element in disease sup- pression is boron. However, boron can be phytotoxic at relatively low concentrations, so caution should be used when applying it to grapevines. Boron is involved in cell wall structure and lignin synthesis, and boron plays a major role in SAR in the isolation of the pathogen by lig- nifications of the infected tissue. 35 Boron is also involved in the production of phenolic com- pounds that are important in induced systemic resistance. 35 It was also observed that fungi multiplied faster in boron-deficient wheat plants than in boron-sufficient plants. 25 After a single foliar application of boron, manganese and copper, systemic protection was provided against powdery mildew in cucumber plants. 2,3 Seaweed and humic acid extracts Seaweed and humic acid extracts also play a role in a plant's natural defense mechanisms. These non-traditional fertilizing materials can complex micronutrients, increasing their up- take and availability to a plant. These extracts can increase antioxidant levels in plants. 26 A seaweed extract was found to decrease Alternaria and Botrytis infections in carrots. A seaweed extract foliar application reduced a Plasmopara viticola infection in grapes. 36 Sea- weed extract has been shown to increase the activity in defense-related enzymes. 27 Humic acids are important to increase the availability of micronutrients, increasing their uptake into the plant. Seaweed can sometimes contain up to 40% humic acids. Dr. Larry Parker is director of research and development for Westbridge Agricultural Products. Dr. Parker earned his Ph.D. in soil microbiology at Colorado State Univer- sity and was a research assistant professor in soil ecology at New Mexico State University before joining Westbridge in 1983. Boron can be phytotoxic at relatively low concentrations, so caution should be used when applying it to grapevines. The references for this article are available online at winesandvines.com