Precision Nutrition Mid and Late Season Vine Nutrition
It is an unfortunate fact that foliar fertilization is most often used after in-season deficiency symptoms become so severe that they can be visually observed. Before visual symptoms appear, the deficiency has existed in the crop for quite some time, and the damage is likely more severe than ever realized. The typical approach is first to observe an unusual leaf color or shade, diagnose the symptom (often with an "educated guess") and then apply what seems to be right based upon "experience".
Here is a common scenario. A field man is walking a vineyard with a client/grower when one of them spots some yellow or, perhaps, reddish leaves on a number of vines. The field man thinks aloud, "These vines obviously need more nitrogen. No, it really looks more like zinc. Wait, I´ve seen potassium look like this before. No, I´m pretty sure it´s zinc. Oh Hell, let´s spray all three. Then we´re sure to have the problem covered." The trusting grower, relying on the expert he employs for sound advice, agrees to a foliar fix-all shotgun application of nitrogen, potassium and zinc.
Does this strike a familiar note? If so, then you need some help. If it is your field man quoted here, you should think about finding another one. His ill-informed approach can cost you considerably in crop yield and/or quality, a cost that was undoubtedly avoidable. Folks, this is AD 2001, the New Millennium. With the technology and information we have at our fingertips, do we any longer need to guess about nutritional requirements? Absolutely not. All we need to do is use the knowledge and tools that are available to us. Soil and tissue fertility are not usually that difficult to manage given the correct tools and good, sound advice.
Let´s analyze this situation. If the observed symptoms are in fact a nutrient deficiency (which is surely questionable), why are those symptoms present at this late time in the season? A simple soil analysis from early Spring or before would certainly have revealed potential for most nutrient deficiencies, allowing ample time to address many shortages with proper soil and foliar applications. Granted, soil analysis may indicate that the particular soils in this vineyard have inherent characteristics that tend to tie up certain elements, making them relatively unavailable to the vine roots. Hence, the case for in-season leaf blade or petiole analysis, and subsequent foliar application of the element(s) in shortage. Had a pre-season soil sample and an early-season tissue sample been used here, potential deficiencies would be realized and correct nutrients could have been foliar applied well before any deficiency symptoms appeared in the vineyard. While our subjects here are apparently satisfied with guessing, they could have used a systematic foolproof approach of combined soil and tissue analysis to entirely avoid an expensive outcome. What can their approach to plant nutrition cost the grower? Considering the importance of must quality in wine grapes, not to mention lost tonnage, the production loss can be extensive.
Let´s now examine the agronomic impact of either deficient or excessive tissue levels of the essential nutrients in this example: nitrogen, zinc and potassium. Nitrogen is often the first choice of the ill-informed plant nutritionist. An N deficiency does result in yellowing of vine foliage. N is easily depleted from soil because it is readily leached with irrigation water and easily taken up by plant roots. It is often (and mistakenly) recognized as the most essential of elements. Plants respond very rapidly to either soil applied or foliar applied nitrogen. However, excess nitrogen during fruit development and ripening can be devastating to disease resistance, brix development (harvest date) and must quality. Furthermore, vines can have excess nitrogen and still display yellow leaves from deficiency of other essential nutrients... such as zinc.
Zinc is of primary importance for all new growth: wood, foliage, roots and flowers/fruit. It is responsible for shoot extension, fruit set, fruit size and rachis elongation (longer bunches = better berry separation = better air flow = less rot disease incidence), only to name a few of its important roles. As with all micronutrients, zinc deficiency during early growth will often set back the crop for the entire season, even when it is later corrected in season with foliar applications. Visual symptoms of zinc deficiency can easily be mistaken for other micronutrient deficiencies such as manganese and iron. However, zinc deficiency is very easily diagnosed with tissue analysis early in the season, and the symptoms can be completely avoided season long with one or a few timely foliar applications of Zinflow.
Of the three essential nutrients in our example, potassium is one that can be problematic during fruit development, even when earlier soil and tissue analyses indicate adequate levels. Summer heat and a developing crop load can induce a potassium shortage any time before harvest, especially when magnesium and/or calcium are abundant in the soil. The same can be said of magnesium when soil potassium is abundant, and the deficiency symptoms can be very similar. In-season potassium deficiency can be easily and effectively corrected with timely foliar Kayphol applications, resulting in a minimum of permanent set-back to the developing crop.
So, what if our star´s guess was not quite on the money? Is it possible that the symptoms he observed were actually a combination of iron and manganese micronutrient deficiency, with potassium-induced magnesium deficiency? Without a doubt! Furthermore, the nitrogen levels in this situation could actually be verging on luxuriant. Rather than correcting a developing disaster, our field man´s hipshot recommendation could do a great deal to exacerbate it! The additional foliar nitrogen could tip the scales to create excess foliar growth, promote bunch diseases and delay harvest by a week or much longer. His zinc application would probably do no harm, but the manganese and iron deficiencies left unattended will continue to worsen until harvest, also affecting fruit quality and harvest date. The foliar potassium application is the coup de gras to this year´s crop. This could worsen an existing magnesium deficiency by competing with magnesium metabolism, resulting in inadequate brix, shriveled bunches and, in severe cases, eventual total loss of bunches, canes and even whole vines through Grape Stalk Necrosis.
For the small investment in time and analysis cost, this common scenario can be completely eliminated. The unfortunate fact is that this play takes place every season, and the grower ends up scratching his head in wonder of what went wrong. And the field man states, "We did everything we could, even foliars. It was just a bad year." Take out the guesswork, and employ a field man who will do the same. Analysis doesn´t cost, it pays!
Analysis options through Phosyn - Megalab
Ask your Phosyn representative about Megalab. It is an incomparably valuable tool, and a subject unto itself for another plant nutrition article. Megalab combines the newest laboratory technology with Phosyn recommendations to suit the wine grape grower who demands maximum production and optimum quality. It removes the guesswork in a simple, convenient format.
Will analysis remove all the guesswork?
While soil and tissue analyses are among our most indispensable tools in vine fertility management, a basic knowledge of the grapevine´s life cycle is necessary to help complete the fertility puzzle. Requirements for certain essential elements will increase more than others as the vines undergo their seasonal maturity. There is a logical reason for this: If we have done the best job possible before and during early vine growth of setting up the vineyard for fruit set and fruit development, using analysis and sound soil and foliar nutrient applications, then we have established a strong canopy and a heavy crop load. How much of that crop is dropped to the ground before harvest can be dependent upon the amounts of the proper nutrients that are applied directly to the leaves and fruit.
Nitrogen usually becomes less critical after the canopy is largely filled out, fruit are maturing and harvest approaches. Potassium, calcium, magnesium and phosphorus become increasingly limiting, even when previous soil and tissue analysis has assured us of adequate levels at the time of sampling. The crop load places an unnatural demand upon the root system to supply these nutrients, especially when we consider that a well-developed canopy necessary for crop establishment actually competes heavily for some of the same nutrients that are so necessary to finish the crop. The root system simply becomes inadequate to finish the job we started for it. This is when foliar feeding offers an effective means to increase both quality and yield, and/or bring on an earlier harvest.
Phosphorus - A major nutrient and, therefore, required in relatively large amounts by all plants, this is probably the most difficult element for roots to adequately supply. It is heavily involved in photosynthesis, sugar synthesis and respiration - energy transfer. Direct foliar applications of the best phosphorus sources will increase leaf photosynthetic activity beyond the abilities of a healthy root system, and, thereby, increase sugar production.
Potassium - Another major nutrient, potassium is involved in efficient carbohydrate (brix) translocation from leaves to developing fruit. It is known as an anti-stress nutrient because it is important in cellular osmotic potential regulation (I know... big words, but a very important concept). Again, foliar applications of the best potassium source will temporarily increase leaf levels beyond those provided by the root system, thus enabling sugar produced in the leaves to better reach the fruit.
Magnesium - The central atom to the chlorophyll molecule, magnesium helps maintain a deep green canopy and, therefore, higher photosynthetic activity without the introduction of more nitrogen as harvest approaches. With calcium and phosphorus, magnesium is very important for strong, disease resistant cell walls in fruit and leaves.
Calcium - Extremely important for cell wall strength and disease resistance, calcium best exemplifies the late-season competition for elements between leaf canopy and developing fruit. Calcium will exit the fruit during periods of high transpiration (every Summer) to be transported to foliar growing points. Foliar calcium applications will help maintain calcium levels in developing and ripening fruit and, henceforth, aid in disease resistance.
Judicious foliar application of these essential elements in the proper formulations during fruit development and ripening can help optimize sugar synthesis in leaves, increase fruit Brix, reduce foliar and bunch disease, enable vines to support a heavier crop load and reduce stress to better prepare vines for next year´s growth.
Author: Jack Krause, USA
Published: March 2001