The latest newsletter from Mark Chien at Penn State Cooperative Extension is available to read here. This is always a great source of regional information and practical vineyard management techniques.
The newsletter references two attachments, Tony Wolf’s latest Viticulture Notes, already posted on our website, and grapevine foliar nutrition recommendations from Alice Wise, Cornell extension viticulture specialist on Long Island, which follows:
•Nitrogen – A number of growers manage vineyards with little or no supplemental nitrogen (N). Long term N needs of vines, particularly in sandy soils, can be addressed in whole or in part by improving soil organic matter. Otherwise, N fertilization is best addressed via ground application whether using a dry product or dripping in liquid N. The benefits of foliar N are debated but experience dictates that periodic foliar applications can be of benefit in maintaining a green, photosynthesizing canopy. Some growers feel foliar N helps sluggish early spring growth; others feel the primary benefit is later in the season both in terms of maintaining canopy and helping to avoid sluggish and/or stinky fermentations. There are many different products from which to choose. Price may dictate what a vineyard can afford to use. Note that some phosphorous acid products contain nitrogen. If organic is preferred, there are liquid fish and soy protein products. Experience with the efficacy of these products, esp. the fish, has been mixed.
•Magnesium – Many growers include Epsom salts (magnesium sulfate) in a few of their prebloom sprays. Though replicated research trial results are lacking, there is universal agreement among growers that this foliar nutrient is essential in maintaining a green, healthy canopy.
•Zinc – Considered essential for proper cluster development, berry set and normal shoot growth. Deficiency is seen early summer. New leaves are smaller, distorted and may be chlorotic with darker green veins. Straggly clusters and shot berries may also occur. Soil application of Zn is less effective because Zn can be tightly bound in soil (though past soil test recommendations for our vineyard were soil applications of zinc sulfate). Zinc sulfate, zinc oxide and chelated Zn are used as foliar sprays; follow label for rates and timing. Rely on your soil and petiole analyses to gauge the need for this nutrient. For all the micronutrients, there are proprietary liquid formulations that are OMRI approved. Some have both macro and micronutrients. Many are kelp based.
•Boron – Another micronutrient that is required in very small quantities for proper fruit set. Distorted basal 1-2 leaves at this time of year might indicate B deficiency. A good lab can verify this in a few days. Later deficiency symptoms are stunted zigzag growth and death of shoot tips, poor set with shot berries that are often flattened or oblong. Soil treatment is effective since boron (B) moves with the soil water, however this is best applied in the fall or with the spring herbicide. Common boron products include Solubor and Borosol. For foliar sprays, no more than 0.2 lb./a actual B in 1 or 2 prebloom sprays is the standard recommendation. The low rate reflects the high risk of phytotoxicity with boron. Improper calculation of foliar rates (the minute quantities required leaves less room for error), sprays applied too close together and overzealous soil applications have all resulted in toxicity symptoms. Boron interferes with the dissolving of water-soluble packets used for certain pesticides. When tank mixing, dissolve the packet thoroughly in the spray tank and then add B to the spray mix.
•Manganese – Deficiency is seen mid-late summer starting as interveinal chlorosis on basal leaves. A herringbone pattern is characteristic. At soil pH’s >6.0, e.g. properly limed soils, Mn availability in the soil is relatively low. Where a deficiency is confirmed by petiole analysis, foliar applications of manganese sulfate (2-3 lbs./100 gal.) are recommended as a corrective measure. Other manganese products used at label rates may also be effective. Foliar manganese oxide materials are considered to be less effective.
•Calcium – Calcium deficiency is best addressed through the soil via liming and use of gypsum (calcium sulfate). However, some feel foliar app’s are useful. These are very common in apples but the case for calcium sprays in grapes is a little murkier. If choosing to try this, 1) observe label cautions as phytotoxicity can be an issue; and 2) try to leave an untreated area to gauge efficacy. If getting calcium into leaves is the goal, then earlier sprays might be useful. To improve fruit integrity, make the application when fruit is present as the mobility of Ca in the phloem is very limited. (AW)