Early, drought-induced deficiency appears at bud break with erratic, slow, distorted shoot growth. The shoots will be dwarfed, with short internodes that may grow in a zigzag manner. The lower leaves on affected shoots are misshapen into a fan shape, with prominent veins and a crinkled appearance. Some shoot tips may die and numerous lateral shoots may grow on the stunted shoots.
Later, true soil deficiency mostly occurs during April to June on the growth that is differentiated in the current season. This is when a low-B soil cannot supply enough B to support rapid spring shoot growth. The most serious and common effects are on berry set and growth. In severely affected vines, a poor fruit set at bloom can result in almost no crop. More moderately affected vines will have many clusters that set numerous shot berries that persist and ripen along with normal berries on the same cluster. The shot berries are distinctive in size and shape: their size is quite uniform and their profile is very round to somewhat flattened on the ends.
Mildly deficient vines may only show fruit symptoms, demonstrating that fruit set is the vine function that is most sensitive to low B. Foliar symptoms will appear with increased severity. Affected leaves show irregular, yellowish mottling between the veins. Some shoot tips stop growing and die. After a few weeks vines resume normal growth, which hides the symptomatic leaves.
Robert H. Beede
L. Peter Christensen
William L. Peacock
Christensen, L.P. 1986. Boron application in vineyards. Calif. Agric. 40(2):17-18.
Christensen, L.P. 2000. Mineral Nutrition and Fertilization (PDF). Pages 102-114 in: Raisin Production Manual. University of California, Agricultural and Natural Resources Publication 3393, Oakland, CA. Buy book
Christensen, L.P., Beede, R., and Peacock, W. 2006. Fall foliar sprays prevent boron-deficiency symptoms in grapes (PDF). Cal Ag 60(2):100-103.
Peacock, W., and Christensen, L.P. 2005. Drip irrigation can effectively apply boron to San Joaquin Valley vineyards (PDF). Cal Ag 59(3):188-191.
2004. Soil Environment and Grapevine Mineral Nutrition Symposium. Proceedings of the American Society of Enology and Viticulture. To Purchase