MICRONUTRIENTS. Zinc (Zn) IMPORTANCE SOURCES IN THE SOIL ROLE AND UTILIZATION. DIAGNOSIS OF DEFICIENCY Symptoms

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1 MICRONUTRIENTS Zinc (Zn) IMPORTANCE Zinc (Zn) deficiency has been recognized as a problem in California grape production for more than half a century. Known as the little-leaf disease, it was first identified and corrected as a nutrient deficiency by Chandler and his co-workers in the early 1930s. Zn deficiency, the most widespread micronutrient deficiency of grapes in California, ranks second to nitrogen deficiency in the number of acres involved. An estimated 10 to 20 percent of California vineyards and orchards are affected, and 20,000 or more acres of grapevines show varying degrees of Zn deficiency. It is common in most of the San Joaquin Valley where grapes are grown, rare in the viticultural areas in the north coast counties, and fairly common in vineyards grown in the central coastal region. SOURCES IN THE SOIL Zn is found in minute quantities in all soils; sandy soils have the lowest levels. After being weathered from various minerals, Zn is adsorbed by clay particles and by organic matter and is held in an exchangeable condition. Zn levels tend to be higher in surface soils and often accumulate after being released by decomposing leaves and other plant material. Zn is less available in soils with a ph greater than 6. At lower ph values, the nutrient becomes more soluble and available. Virtually all of the Zn in the soil becomes fixed at ph 9. Calcareous materials, such as limestone, increase the Zn-fixing capacity of coarse-textured soils. Soils high in organic content and clay soils of high magnesium content are often low in available Zn. Soils high in native phosphate also may fix Zn in an unavailable form. Deficiency symptoms are commonly found in San Joaquin Valley vineyards grown on sandy soils and on sites previously used for long periods for corrals or poultry houses. Zn deficiency is also common in vineyards grown on sandy soils with vigorous rootstocks, such as Dogridge, Salt Creek, Harmony, and Couderc 1613, where nematode resistance is needed. Zn deficiency is not usually encountered uniformly across a vineyard, but is found in limited areas such as sand streaks. Areas subject to heavy cuts during land leveling are likely to be deficient in Zn, as are sandy soils that have received repeated, heavy applications of poultry manure for long periods. Application of high-nitrogen fertilizers may accentuate zinc deficiency, because nitrogen stimulates total vine growth and thereby increases the Zn needs beyond the available supply. Likewise, vigorously growing young vines, especially in their second year, commonly show temporary and usually mild Zn deficiency due to rapid growth and a still limited root system. Zn deficiency is very common where grapevine cuttings are planted in methyl-bromide-fumigated soils, such as in nurseries. This results from the temporary reduction of the mycorrhyzal fungi population, which assists roots in the uptake of certain nutrients, including Zn and phosphorus. ROLE AND UTILIZATION Zn is needed for auxin formation, for the elongation of internodes, and in the formation of chloroplasts (chlorophyll-containing bodies) and starch. In grapes, Zn is essential to normal leaf development, shoot elongation, pollen development, and the set of fully developed berries. DIAGNOSIS OF DEFICIENCY Symptoms Foliage. Deficiency symptoms may vary, depending on the degree of the shortage and on the grape variety. Foliar symptoms of mottling usually appear in early summer at about the time that lateral shoot growth is well developed. The new growth on both the primary and secondary shoots has smaller, somewhat distorted leaves, with a chlorotic pattern exposing the veins as a darker green color. Even the small veinlets retain a uniform-width border of green unless the deficiency is quite severe. In contrast to normal leaves, which have a deep sinus or cleft where the petiole is attached to the blade, severely affected leaves have undeveloped

2 basal lobes; the sinus is shallow, showing little or no indentation. (See fig. 6.) The term "little leaf" aptly describes the gross appearance of stunted shoots, which have closely spaced, small, distorted leaves when deficiency is severe. Some varieties, such as Rubired and Royalty, may have leaves with wavy margins in addition to a distinct veinal pattern. Fruit. On grapevines Zn deficiency can seriously affect the set and development of the berries. This leads to reduced yields or to lowered acceptability of table grapes. Vines deficient in Zn tend to produce straggly clusters with fewer berries than do normal vines. The berries usually range in size from normal through small to very small (undeveloped, or shot). In seeded varieties, the small and shot berries have fewer seeds than normal berries, ranging down to none in the very small shot berries. Shot berries often remain hard and green and fail to ripen, but this symptom varies considerably. (See fig. 7 and 8.) Varieties like Muscat of Alexandria are particularly sensitive to Zn deficiency, and development of straggly clusters with berries of various sizes is one of the first effects seen. Leaf symptoms on this variety develop only when the Zn deficiency is more extreme. Thompson Seedless, Carignane, French Colombard, and Tokay, however, always have some degree of foliar symptoms associated with fruit symptoms. The Cardinal, Ribier, and Red Malaga varieties of table grapes respond much like Muscat of Alexandria. Salvador, on the other hand, often shows moderately severe leaf symptoms without an effect on berry set. Laboratory analysis Fortunately, Zn deficiency symptoms on leaves and fruit are distinctive and readily recognizable; thus, tissue analysis is usually not needed for diagnosis. However, laboratory analysis for Zn may be used for questionable symptoms, because other micronutrient deficiency symptoms and those of certain virus diseases, such as fanleaf, can sometimes be confused with Zn deficiency. Soil analysis for Zn content is not a reliable method of determining a vineyard's need for Zn. It is difficult to correlate Zn level in the soil with that in the vine because of differences in the susceptibility of grape varieties to the effects of low Zn, differences among rootstocks in Zn uptake from the soil, and the extensive "feeding" nature of grape root systems that enables a vine to maintain a satisfactory Zn level even though the soil content may be considered low. Because the Zn level in the grapevine reflects all of these variables, tissue analysis is preferred over soil analysis. SUPPLYING THE GRAPEVINE'S NEED FOR Zn Once a Zn deficiency has been diagnosed, there are several methods of treating vines with Zn. One method may be better adapted than another to a specific vineyard situation. Daubing For spur-pruned varieties, the most common and successful treatment is to daub or paint all fresh pruning cuts with a solution of zinc sulfate. To improve uptake and prevent "washing" away of the Zn solution, pruning must be timed so that little or no bleeding occurs. Vines usually do not bleed if pruned between December and early February. However, if the soil moisture is low and the vines are "dry," pruning and daubing should be postponed until after a soaking rain or a winter irrigation. Pruning and daubing also should be delayed during periods of cold, desiccating winds or unusual, prolonged cold spells. Under these unfavorable conditions, vines may absorb the Zn solution in amounts that damage the buds and spurs. Best results are obtained when the pruning cuts are made about Y2 inch above the uppermost node and are daubed as soon as possible after pruning, preferably within 3 or 4 hours. Delays of 8 to 12 hours reduce entry of the Zn solution, because gums are produced, plugging the wood. The recommended concentration is 1 pound of zinc sulfate (36 percent metallic Zn content) in 1 gallon of water; a higher concentration may cause injury. The solution should be made by slowly adding the zinc sulfate to the water, stirring rapidly to ensure immediate and complete solubility. Usually 2 to 4 gallons of solution per acre are sufficient. Food coloring is sometimes added as a means of checking the thoroughness of the dauber. A short stick padded on one end with a sponge or absorbent cloth is used to daub the vines. One worker can usually keep pace with three or four pruners by walking back and forth between rows. Instead of daubing, some growers spray the zinc sulfate solution at the same concentration on the spurs, using less than 100 pounds pressure. To be effective, full rows of vines must be pruned out within several hours. Although this technique has not been studied, reports of commercial success indicate that it is worthy of trial, especially on larger vineyard acreages. Foliar sprays Even though daubing is successful on spur-pruned varieties, it is not effective on cane-pruned varieties, because a smaller number of cut surfaces can be

3 treated and the movement of Zn in the vines is limited. Thus, on cane-pruned varieties, such as Thompson Seedless, foliar sprays are normally used. Foliar sprays may also replace daubing in vineyards of spur-pruned varieties when Zn deficiency is mild. In cases of severe deficiency, it may be advisable to apply a foliar spray in addition to the daubing treatment. Zn sprays should be applied 2 or 3 weeks before bloom (late April or early May) if an improvement in berry set is desired. The vines should be sprayed with enough volume to wet the flower clusters and the undersurfaces of the leaves. One spray application is usually sufficient. If foliage symptoms persist or reappear later in the growing season, a second application may be needed. Those who wish to mix their own spray material can add 4 pounds of zinc sulfate (36 percent Zn) plus 3 pounds of spray lime to 100 gallons of water. The spray lime is used as a safener to prevent leaf burn. A suitable wetting agent should be included to ensure complete wetting of the flower clusters and leaves. A number of spray materials containing up to 50 percent Zn are available under various trade names and can also be used effectively by following the label recommendations. They have been neutralized to prevent foliage burn and are often referred to as basic zinc sulfates. Chelated Zn materials can also be used in foliage sprays but, to date, have been less effective on a label-recommended and on a cost-per-acre basis than the basic zinc sulfates. However, Zn chelates may be preferred in concentrate or lowvolume spray application; they are fully soluble in the spray tank. Basic zinc sulfate is not fully soluble and requires good agitation to remain in suspension with a more concentrated tank mix. Also, more attention must be given to occasional flushing of sprayer lines because of possible settling of the material. Recent research results indicate that a fullwetting application with a dilute sprayer (100 to 150 gallons per acre, prebloom) results in more zinc absorption than a concentrate-sprayer application (20 to 30 gallons per acre) when comparable rates of Zn per acre are used. Thus, the choice of application method and type of material may depend on the degree of deficiency a dilute application of basic zinc sulfate being the most effective and therefore preferable for the more serious problems. Some vineyardists use unneutralized zinc sulfate (36 percent Zn) alone, rather than mixing it with lime or using basic zinc sulfate. They use a maximum rate of 1%2 to 2 pounds zinc sulfate per 100 gallons water to avoid foliage burn. Before using this technique, the grower should test it on limited acreage. Usually Zn is the only nutrient needed as a vine foliar spray. Adding other nutrients, such as phosphorus, has not improved the effectiveness of Zn sprays in Madera and Fresno County vineyard trials. Also, it is not advisable to sacrifice an optimum amount of Zn in the spray tank to include other nutrients commonly found in proprietary foliar nutrient mixes. Soil applications Success with soil applications of zinc sulfate has been limited to sandy and sandy loam soils. Such applications probably should be confined to small, chronically deficient areas or to soils where spraying or daubing of vines has not been effective or practical. Because most soils fix large quantities of Zn, deep placement and high rates are required. During the dormant season, a concentrated band of zinc sulfate can be placed in 8- to 10-inchdeep furrows about 18 inches on each side of the vine row. To concentrate the material, the bands should be only 2 to 3 feet long beside each vine, and they should be left exposed so that irrigation will move the material into the soil. The suggested rates are 1 pound per vine for young vines and 2 to 3 pounds for mature vines. Zn EDTA chelates have also been used successfully with furrow applications at rates of 1/2 to 1 ounce elemental Zn per mature vine. However, on a cost-per-acre basis, the chelates are usually no more effective than zinc sulfate. Hand soil injection Another means of deep soil placement is to inject a zinc sulfate solution 18 inches deep into the soil with a hand gun attached to a spray rig, using a pressure of about 250 pounds per square inch (psi). Injections should be made no closer than 1 foot from the vine trunk, and only during dormancy. For young vines up to 3 years old, a rate of V2 to 1 pound of zinc sulfate per vine can give complete correction. Severely deficient mature vines may require 2 to 3 pounds per vine. A suggested concentration of the injected solution is 100 pounds zinc sulfate per 100 gallons water. The rate per vine is calibrated by timing the flow rate from the hand gun into a measured bucket. Fresno County studies have shown that hand injection of zinc sulfate solution results in greater response than does furrow application, when equal rates per vine are compared. Soil applications by either means may be effective for 2 or 3 years; retreatment usually is necessary. 1 3

4 Shank injection in continuous bands Shank injection of Zn solutions is not as effective as the aforementioned methods. It does not provide as concentrated a placement near individual vines and therefore requires even higher rates of Zn fertilizer for deficiency correction. However, this method can be practical in nursery rows with their more concentrated plant density. Shank injection is a common practice in nursery soils planted to grapevine cuttings where a methyl bromide fumigation has induced a Zn deficiency. This temporary deficiency can be largely corrected by shank-injecting a Zn chelate solution on each side of the nursery rows to an 8- to 10-inch depth. Five pounds or more of elemental Zn per acre in chelated form are required. Other methods Other corrective measures that have been investigated for grapevines include injection of zinc sulfate solution under pressure directly into vine trunks, application of zinc sulfate dust in dusting sulfur, driving metallic Zn points or galvanized nails into vine trunks, and late fall or dormant season zinc sulfate sprays. None of these methods has been as effective or considered as practical as the daubing or spraying techniques described.

5 Diagnosis and Treatment of Zinc Deficiency in Crops The Need for Zinc Zinc is one of the essential nutrients for crop growth. Unlike the major nutrients ordinarily supplied in mixed fertilizers, zinc is required in only infinitesimal amounts. For example, an acre of healthy oats contains only about one ounce of zinc. Yet without this essential ounce, no crop would grow at all. Because of the small amounts needed by crops, zinc is classed as a "trace" element or micronutrient. Other trace elements are iron, copper, manganese, boron, molybdenum, and chlorine. Even though these elements are needed in only minute traces, many soils do not supply them in sufficient quantity for healthy growth and high yields of crops. On soils where zinc is deficient, treatment with a few pounds of zinc an acre restores fertility. Zinc is effective in such small quantities because it forms part of the enzyme systems which regulate plant life. Thus zinc is needed for the production of auxins, the growth-promoting substances that control growth of shoots. Aside from plants, traces of zinc are also required for animal growth. A 150-pound man needs seven thousandths of an ounce of zinc a day. Since crops must contain zinc to grow, human needs are adequately supplied by the food we eat. However, zinc deficiency does occur in swine as a mange-like skin disease known as parakeratosis, It can be corrected by feeding supplemental zinc. Zinc deficiency also occurs in poultry and other livestock. Zinc deficiency is more common, world-wide, than that of any other trace element. Thousands of tons of zinc compounds are used in fertilizers and sprays each year, and the total area treated amounts to several million acres a year. In the United States zinc deficiency is known in 32 different states. Abroad, zinc deficiencies occur in Canada, Australia, New Zealand, Africa, South America, India, and Europe. Originally, zinc treatment was used primarily on fruit crops. Only in recent years has the need for supplemental zinc been recog- nized in such important field crops as corn. This need appears to be increasing because of the rise in crop yields, the wider use of highanalysis chemical fertilizers, and the cultivation of more new land. In acute form zinc deficiency causes easily recognizable diseases in crops; for example, "white bud" of corn, "little leaf" of apple or pear, pecan "rosette," or "mottle leaf" of citrus. Yields are low, seeds do not form, and the crops may be a total failure. The table of deficiency symptoms and the color plates in this booklet will help identify these cases, and suggest suitable corrective treatment. Soil Factors Causing Zinc Deficiency Zinc deficiency arises from three main causes: (1) low content of total zinc in the soil; (2) unavailability to the crop, of zinc present in the soil; (3) management practices that depress the availability or uptake of zinc. Total zinc is low in highly leached acid, sandy soils such as those found in many coastal areas. Soils derived from granites or gneisses may also be low in total zinc. Since plant growth brings zinc to the surface, many subsoils are low in total zinc. Severe erosion of topsoil may expose zinc-deficient subsoil. More commonly, zinc is present in adequate total amount but is unavailable to the crop because of one or more of the factors listed in the next paragraphs. Most mineral soils contain 80 to 300 parts per million of total zinc. However, exchangeable zinc is usually less than one part per million; the remainder is fixed in unavailable form. Fixed zinc is often difficult to release in available form. Generally it is more economical to add additional zinc than to undertake soil treatments to release fixed zinc. The ease with which zinc is fixed in the soil probably accounts for the poor movement or translocation of zinc through the soil. It is usually concentrated near the surface, where it is deposited by decaying organic matter. Several factors contribute to the unavailability of zinc: 1. Alkalinity. When the soil reaction or ph is above 6.0, the availability of zinc is very low. Zinc is most soluble, and hence available, under acid conditions. At higher ph, solubility and availability decrease. Also, calcareous materials, such as limestone or dolomite, found in arid, alkaline soils, may increase the zinc-fixing capacity of coarse-textured soils.

6 2. Organic matter. Zinc availability is low in soils of high organic content. Thus zinc deficiency is observed in peat soils or in old barnyards and corral sites even old Indian burying grounds. 3. Clays. Clay soils of high magnesium content may also fix zinc in unavailable form by strong adsorption on the clay minerals in place of magnesium. 4. Phosphate. Soils high in native phosphate, such as those found in Kentucky and Tennessee, may cause,fixation of zinc in unavailable form. Besides these natural soil factors; soil management practices often cause zinc deficiency. Among these practices are: 1. Phosphate fertilizers. Heavy application or prolonged use of phosphates frequently reduce zinc uptake by the crop. This effect may arise either from the depressing effect of the calcium in superphosphate on zinc uptake, or from fixation of zinc in unavailable form. Results of studies on the effect of phosphate on zinc are contradictory, possibly because of differences in the zinc content of superphosphate. In the United States, western superphosphates contain five times as much zinc as those produced in the east (6). Similarly, in Australia superphosphate appears to prevent zinc deficiency where the equivalent amount of higher-purity sodium phosphate does not (see Color Plate No. 7). 2. Liming. As already noted, zinc is most available in acid soils and soils low in calcareous materials. Liming increases the ph and may increase the zinc-fixing capacity of the soil, particularly in soils high in natural phosphate. 3. Land leveling. Land leveling for irrigation and other purposes may bury the topsoil and expose the subsoil. As already noted, subsoils are apt to be deficient in total zinc. In land-leveling experiments in North Dakota, two-thirds of the available zinc in the top four feet of soil was found in the uppermost foot (13 ). Also, land-leveling operations may bring the zone of lime accumulation to the surface. The calcareous materials in this zone may fix zinc in unavailable form. 4. Nitrogen fertilizers. High-nitrogen fertilizers, by increasing total crop growth, may increase zinc requirements beyond the available supply. The form of nitrogen used is also important. In one study sodium nitrate decreased zinc uptake while ammonium nitrate and ammonium sulfate increased it (47). 5. Manure. Frequent use of large amounts of poultry manure in orchards may induce zinc deficiency, probably by increasing total organic matter in the soil. 6. Crop rotation. In field crops zinc deficiency is more common after a crop of high zinc uptake such as sugar beets than after such crops as sorghum or potatoes, which have lower uptakes of zinc (9). GRAPE COLOR PLATE NO. 13 Visual Symptoms Yellowing occurs between veins of leaves, "little leaf" shows up in early summer, "hen and chicken" and barrenness of fruit stems result. Corrective Treatment Dormant spray containing 4-8 lb. zinc sulfate per 100 gallons of water. Daubing fresh pruning cuts of spur-pruned varieties with a solution of 1/2 lb. zinc sulfate per gallon of water has been successful. Foliar sprays have not been uniformly successful. Soil treatment with 100 lb. zinc sulfate per acre has been recommended for Concord grapes. 13. GRAPE Normal and zinc-deficient leaders. The deficient one shows small yellowish leaves and barren fruit stems. California Agricultural Extension; Service.

7 Correcting Zinc Deficiency Supplemental quantities of zinc may be provided for deficient crops in a number of ways: Topdressing or banding the soil. Care must be taken to work the zinc deep into the root zone. Spraying either the dormant trees or the foliage. Dusting. Daubing pruning wounds with zinc solution. Injecting galvanized nails or other zinc-bearing metals into trunks. The local agricultural experiment station can help select the best method for a particular crop and area. Choice of such a method should be based on the over-all crop management program. For example, if -local fertilizer mixers will supply custom formulations containing zinc, the required zinc may be applied most conveniently in mixed fertilizers. On the other hand, if fruits or other crops are given a regular spray program for pest control, the zinc needed can most easily be supplied in pesticidal sprays. Of course, the pesticide manufacturers' recommendations should be followed closely to avoid combining incompatible materials. Several different chemical forms of zinc may be used as plant food supplements. Zinc sulfate (ZnS0 1.7H,0) is commonly used because of its high solubility in water. Zinc carbonate and zinc oxide are insoluble in neutral water, but are used in sprays as slurries. They may also be dissolved in alkalies or acids. Any of these compounds may be used for soil treatment. Zinc oxide and carbonate contain more zinc per pound than zinc sulfate, and should be used at lower rates. One pound of zinc sulfate is equivalent to seven ounces of zinc carbonate and five ounces of zinc oxide. Recently zinc chelates, such as zinc-edta and other organic zinc complexes, have received an increasing amount of attention, particularly for application to soils where high ph or other soil factors make added zinc unavailable (4, 8, 20, 39, 48). This form of supplementation should become more attractive as a wider variety of chelating materials makes lower costs possible. Manufacturers' directions should be followed for rates of treatment. Other plant foods may contain some zinc. As mentioned previously, some phosphates contain enough zinc to prevent the appearance of zinc deficiency symptoms. However, they will not usually correct zinc deficiency once it has occurred. Lime may also contain some zinc, but rarely enough to correct deficiency ( 15). Specific treatments used successfully on over 40 crops in different parts of the world are given in the table beginning on page 26. These treatments are not applicable to all soil and weather conditions; consult local agricultural specialists for recommended methods for specific areas. The treatments are generally of the following types: Soil application at a broadcast rate of pounds of zinc sulfate per acre. This is usually effective for vegetable crops where soil ph is below 7. For banding, 10 pounds zinc sulfate per acre is usually sufficient. The zinc must be worked thoroughly and deeply into the soil to be effective. If merely topdressed, it will remain on the surface where roots cannot reach it. Spray application at the rate of pounds of zinc sulfate per 100 gallons of solution for trees in dormant state. Spray application of 5-10 pounds of zinc sulfate per 100 gallons of solution for foliage. Damage to foliage was formerly prevented by adding half as much hydrated lime or soda ash to the solution. However, present practice is to use weaker solutions without lime or soda ash. Soil applications may last several years, depending on soil conditions and management. Foliar sprays are effective only for the current crop. They are usually most effective before the spring flush growth. Local agricultural supply houses or fertilizer distributors will normally he familiar with sources for the zinc additives required. For more information or the name of the nearest zinc producer, write to American Zinc Institute, Inc., 292 Madison Ave., New York 17, N. Y.

8 Additives don't improve zinc uptake in grapevines Peter Christensen Zinc deficiency, the most widespread micronutrient problem in California vineyards, has commonly been treated by daubing of fresh pruning cuts or foliar spraying with zinc compounds. Foliar spraying has gradually become the most popular of the two methods, because it requires less labor. The increased importance of zinc sprays has led to continuing research to maximize response while minimizing cost. This research has resulted in the following zinc spray recommendations: Spray method: A dilute, full-wetting spray provides more zinc uptake than a concentrate, low-volume spray. Timing: Two weeks before bloom to full bloom (80 percent cap fall), any time during day or night. Material: Neutral zinc or basic zinc sulfate (50 to 52 percent zinc) at maximum label recommendation or 4 to 6 pounds product per acre. Many zinc products are available and used by growers. Some contain chelating or "complexing" agents (lignosulfonate) or other nutritional elements, which increase their cost. Vineyard zinc spray trials to date have yet to show a cost benefit from some of these products as compared with the high-analysis neutral zinc (50 to 52 percent zinc). The two trials reported here are a continuation of research to determine the most cost-effective zinc foliar spray materials and methods for vineyards. One trial compares five zinc compounds at label rates and at equal rates of elemental zinc per acre; the second trial examines possible benefits of adding urea to zinc foliar sprays. Two zinc-deficient Fresno County Thompson Seedless raisin vineyards were used for study. Applications were at approximately 80 percent bloom on May 7 and 8, 1984, as a full-wetting dilute spray at 200 gallons per acre. In each trial, the eight-vine plots were replicated six times in a complete, randomized block design. Uptake was estimated from analysis of zinc in shoot tips. Shoot tips were analyzed to avoid zinc spray deposit that would be present on leaves and petioles. Spray contamination also was avoided by a long enough wait after treatment for the shoot tips to grow beyond the sprayed tissue. Post-treatment shoot tip samples were taken weekly on May 17, 24, and 31 and analyzed for zinc. TABLE 1. Zinc compound and rate comparisons, post-treatment shoot-tip zinc (Zn) levels Treatments Growers can choose zinc compounds on the basis of cost alone Berry weight, berry set (number of berries per centimeter of lateral length), and percent soluble solids ("Brix) were determined at harvest on 48 randomly selected cluster laterals (second lateral from top of each cluster) per plot. Compound and rate comparisons Five compounds were compared at equal rates of zinc per acre (0.72 pound). Three were completely soluble zinc sulfate (36 percent zinc powder), zinc EDTA chelate (6.5 percent zinc liquid), and zinc lignosulfonate "complex" (7 percent zinc liquid) and two were of low solubility neutral zinc (52 percent zinc) and zinc oxide (75 percent zinc). The pound rate was based on the maximum recommended rate of zinc lignosulfonate. This rate is about twice the maximum label recommendation of zinc EDTA and one-fifth that of neutral zinc and zinc oxide. Additionally, neutral zinc and zinc oxide were compared at their maximum label recommendation of 4 pounds zinc per acre. When zinc was applied at the same rates (0.72 pound per acre), all vines except those treated with zinc EDTA had more zinc in the shoot tips than did the untreated check vines (average of three sample dates, table 1). The zinc level was similar in all of the 0.72-pound-zinc vines, except that those treated with zinc EDTA had less than those treated with neutral zinc. Neutral zinc at the 4-pound rate gave the greatest initial and overall uptake (average of three sampling dates). Zinc oxide at the high rate (4 pounds) was second in uptake and better than all of the lower rate treatments at the first sampling. Fruit measurements showed that zinc EDTA produced the greatest berry set (table 2). The other compounds also improved berry set over the untreated check but with no differences among them. Treatment also increased berry weight, except from vines that received the zinc EDTA and lignosulfonate compounds. Fruit from untreated vines had the highest soluble solids ('Brix), while fruit from vines treated with EDTA, neutral zinc (4-pound rate), and zinc oxide (4- pound rate) had lower soluble solids. This result is not surprising, since correction of zinc deficiency increases berry set, berry size, and total fruit volume, which in turn can lower the concentrations of soluble solids. These results indicate that neutral zinc or zinc oxide at the high rate would be the preferred treatment for maximum foliage uptake, as in serious cases of zinc Zinc dry weight* Zn/acre May 17 May 24- May 31 Average effect of treatment Untreated check lb PPm 51 e 41 d 38a 43e Zn EDTA chelate cde 39 d 32 a 47 de Zn lignosulfonate cd 48 cd 39 a 54 cde Zn sulfate cd 49 cd 39 a 54 cde Neutral Zn c 50 cd 45 a 59 c Zn oxide cd 50 cd 38 a 56 cd Neutral Zn a 77 ab 47 a 113 a Zn oxide b 60 be 44 a 100 b Figures with like letters within a column are not significantly different at 5% level, Duncan's Multiple Range Test. tia 22 CALIFORNIA AGRICULTURE, JANUARY-FEBRUARY 1986

9 deficiency. These two treatments produced the highest levels of zinc uptake through a 17-day period after treatment. They also produced favorable fruit response in increased berry set and berry size, although the increased fruit volume contributed to lower fruit soluble solids. Whether soluble or insoluble or containing chelating or complexing compounds, all zinc sources gave some, but variable, responses. Zinc EDTA was least effective in increasing shoot-tip zinc levels and increasing berry size, but it improved berry set the most. Zinc plus urea In the second trial, two compounds, neutral zinc (52 percent zinc) and zinc sulfate (36 percent zinc), were compared with and without urea added to the spray solution. Neutral zinc and zinc sulfate were used at 4 pounds and 1 pound zinc per acre, respectively, and urea (46 percent nitrogen) at 4 pounds nitrogen per acre (7.7 pounds product). The addition of urea had no effect on zinc levels of shoot tips except on the first sampling date, when the addition of urea to the neutral zinc product actually decreased shoot tip zinc levels (table 3). Berry weights (table 4) were not improved with any zinc treatment and were smaller in the neutral zinc-urea combination than in the untreated check (no zinc). Overall, the 4-pound rate of neutral zinc per acre gave the greatest improvement in berry set. The smaller berry size possibly resulted from the effects of increased berry set and berry numbers per cluster. Conclusions The inclusion of chelate, "complexing" agent, or urea to zinc sprays did not improve zinc uptake in this study. This finding corresponds to earlier work showing that the addition of phosphorus and nitrate compounds to zinc sprays does not improve zinc uptake by vine foliage. Such additives thus are not beneficial and only add to treatment cost. Zinc solubility also did not influence uptake. The low-solubility neutral zinc and zinc oxide gave responses similar to the other fully soluble compounds. Growers therefore can choose zinc compounds on the basis of cost alone. Neutral zinc and zinc oxide at maximum recommended rates would be expected to provide the greatest potential for correction. Lower rates may be sufficient in mild cases of deficiency. None of the compounds at rates used caused visible vine foliage toxicity. Higher rates of the soluble compounds should be used with caution. Peter Christensen is Viticulturist, University of California Cooperative Extension, Kearney Agricultural Center, Parlier. Zinc deficiency in Thompson Seedless grapes reduces fruit set and causes "shot" berries (clusters at right). The addition of chelate, "complexing" agent, or urea to zinc sprays did not improve zinc uptake by grapevines. Treatments TABLE 2. Zinc compound and rate comparisons, fruit measurements Zn/acre Avg. berry wt. Number berries per cm lateral lb g Check 1.07 d 3.69 c ZnEDTA chelate cd 5.14 a Zn lignosulfonate bcd 4.34 b Zn sulfate abc 4.14 be Neutral Zn ab 4.26 b Zn oxide a 4.15 bc Neutral Zn a 4.61 b Zn oxide a 4.55 b Pounds of zinc or nitrogen per acre. TABLE 3. Zinc plus urea posttreatment shoot-tip Zn levels Treatment Rate* May 17 May 24 lb Check 67 d 55 d Neutral Zn a 90 ab Neutral Zn + urea b 82 be Zn sulfate c 66 cd Zn sulfate + urea c 64 cd Zinc dry weight PPm - TABLE 4. Zinc plus urea fruit measurements May a 56 a 58 a 52 a 51 a Brix 19.9 a 17.2 d 18.3 bc 18.8 b 18.4 b 18.8 b 17.8 bcd 17.4 cd Avg. effect of treatment 58 c 113 a 101 a 78 b 75 b Berry set Avg. berry wt., number berries Treatment Rate' grams per cm lateral Brix Check Neutral Zn Neutral Zn + urea Zn sulfate Zn sulfate + urea 'Pounds of zinc or nitrogen per acre lb a 4.34 b ab 5.72 a b 5.61 a a 4.68 b a 4.65 b 17.1 a 16.6 a 16.3 a 14.1 a 15.7 a 4 CALIFORNIA AGRICULTURE, JANUARY-FEBRUARY 1986

10 Rain pattern affects zinc in vineyards By PAUL VERDEGAAL Farm Advisor San Joaquin County, Calif. The rainfall for this past year is a little less than last year. However, the dry September was followed by good rains in October and November. This is the reverse of the previous year. The dry September prevented much fumigation for replanting or new vineyards. The sudden and heavy rains in early November put an abrupt end to attempts in catching up on fumigation in vineyards before the soil temperatures became too cold and soil moisture excessive, for proper fumigation. Zinc deficiency The rainfall pattern will possibly help avoid some problems that began during pruning, but didn't show up until spring budbreak. Soil conditions were very dry from November through January of last winter. Zinc applications by daubing of pruning wounds resulted in the "burning" and stunting of buds on spurpruned varieties such as Zinfandel and Burger. Zinc deficiency is often seen on sandy soils or where a variety is grafted to a very vigorous rootstock (Dogridge, St. George, etc.) The deficiency can be corrected to a great degree by daubing zinc sulfate 36 percent (one pound or less per one gallon after) to fresh pruning wounds. Conditions affecting However, several conditions can speed up or increase the zinc absorbed by the vine: (1) Very dry soil profiles, as we had last year (2) Desiccating winds in cold weather (3) Forgetting to stir up the zinc sulfate solution periodically, especially in very cold weather. Zinc sulfate tends to settle out and the solution will become more concentrated towards the end of the container. This can be concentrated enough to cause toxic levels to be absorbed under even good conditions. Fortunately, it looks as if this year the soil profile may not be quite as dry, but care should be taken whether working with pesticides or fertilizers. Daubing pruning wounds with zinc solution is very effective for increasing cluster flower set and therefore potential crop. It can be a double edged sword if used without caution. California-Arizona Farm Press Saturday, February 13, 1988

11 Zinc Grape varieties ranked by petiole Zn levels Averages of Bloom and Veraison Samples U.C. Kearney Agricultural Center High, above 30 ppm Emperor Ruby Seedless Chenin blanc Calmeria Zante Currant Sauvignon blanc Thompson Seedless Rubired Flame Seedless Medium, ppm Carignane Muscat of Alexandria Italia Exotic Zinfandel Ruby Cabernet Queen Petite Sirah Grenache Low, below 25 ppm Barbera Red Malaga Perlette French Colombard Ribier Semillon Cardinal Salvador ( 0 1

12 ron,,ac; VkAlr.p- '4 IMPORTANCE After zinc and boron, iron (Fe) deficiency is the third most important micronutrient problem in California. Fe deficiency symptoms may have appeared on more total acreage than have those of B, but Fe deficiency is mostly temporary and is often too isolated in occurrence to be of economic importance. Grape varieties particularly susceptible to Fe deficiency include Royalty, Salvador, and Rubired. Vines with a weakened root system sometimes show a higher incidence of Fe chlorosis, particularly under conditions of overcropping. This problem is most common in Muscat of Alexandria vines weakened by a previous season's heavy crop. SOIL AVAILABILITY AND UPTAKE Fe occurs in soils as oxides, hydroxides, and phosphates, as well as in the lattice structure of clay minerals and in some silicates. Under varying soil conditions, small amounts of Fe are released during the weathering of these minerals and are absorbed by roots in the ionic form or as complex organic salts. Deficiency is primarily related to soil conditions that limit root uptake and vine utilization of Fe rather than to total Fe levels in the soil. The condition occurs most commonly in high phosphate and in calcareous (high lime) soils, particularly those associated with recently or partially reclaimed alkali (high sodium) soils. "Lime-induced chlorosis" is a term used to describe Fe deficiency caused by the immobilization or inactivation of Fe by high carbonate or lime content in the soil. Heavy soils, especially if poorly drained, and cold soils are more subject to deficiency. More extensive deficiency problems are encountered during cool, wet periods in the spring, but hot spells in late spring can also promote rapid shoot growth and result in Fe deficiency. Symptoms associated with weather extremes, excessively wet soil conditions, or both, are usually temporary; vines outgrow them within 2 to 4 weeks. UTILIZATION AND ROLE Fe is transported in plants as the ferrous ion (Fe" ) to regions of use, where it is combined with proteins to form complex organic compounds. Fe does not appreciably move from one tissue to another in plants; thus, deficiency is first found in the newly developing and expanding leaf tissues. Much of the Fe in plant tissues can be "fixed" or combined into unavailable forms so that there is little relation between total Fe content and deficiency symptoms. Fe functions in the activation of several enzyme systems. A shortage of usable Fe also impairs chlorophyll production, resulting in the characteristic chlorosis. DIAGNOSIS OF DEFICIENCY Foliar symptoms first appear as an interveinal yellowing on the more rapidly expanding young leaves. This produces a pale yellow leaf with a green network of veins, including the very small ones. (See fig. 13 and 14.) As the deficiency becomes increasingly severe, more of the leaf area becomes yellow and ultimately ivory or even white. Severely chlorotic areas on leaves often turn brown and necrotic. Growth is reduced on severely affected shoots, and the flowers and the stem structure on the clusters may become pale yellow. Fruit set can be poor on such shoots. As grapevines recover from temporary deficiency, the new growth develops with a more normal green color; color improvement is delayed on mature leaves affected earlier. Soil and tissue analysis have not been found useful in diagnosis, because soil and plant tissue Fe levels do not correspond to the occurrence of deficiency. CORRECTING DEFICIENCY SYMPTOMS Fe deficiency is widely considered the most difficult of all nutritional problems to correct in plants, and grapevines are no exception. Foliar spray treatment Fortunately, much Fe chlorosis is temporary, and, by the time foliar spray treatment is applied, the new growth is normal. This normal recovery is often mistaken for response to the foliar spray. Because Fe is nonmobile in plants, a spray benefits only existing foliage. New growth should be sprayed if the chlorosis is severe and persists. Foliar sprays should be used at maximum recommended concentrations, either as iron chelates, using the manufacturer's recommendations, or as ferrous sulfate at 4 to 6 pounds per 100 gallons. The spray should be repeated as necessary at 10- to 20-day intervals. With moderate to severe deficiency, only partial improvement can be expected, at best. The common effect of the Fe spray is a regreening only in spots or islands on affected leaves, which demonstrates the limited absorption and translocation of foliarapplied Fe. 10Z

13 Soil treatment Soil treatments should be tried only on areas of chronically severe deficiency. Such treatments are too costly and the response too short-lived to be practical otherwise. Fe-EDDHA or Fe-DTPA chelate may be tried at manufacturers' recommendations. Fe-EDDHA chelate is more effective in high lime or alkaline soils. Trenching-in or deeply incorporating high rates of soil sulfur can be tried in vineyards where the chlorosis is associated with high-lime soil. Other treatment methods Foreign literature contains recommendations for applying Fe solutions by direct injection into trunks and by daubing fresh pruning cuts. Neither has been practiced commercially in California. Trunk injection has given inconsistent results and has injured vines. Daubing is commercially recommended in Europe at 1.5 to 2.5 pounds ferrous sulfate plus 0.25 to 0.40 pound citric acid per gallon of water. The lower concentrations are suggested on young vines. The effectiveness and safety of this treatment have not been evaluated under California conditions. Grapevine Nutrition and Fertilization in the San Joaquin Valley l 03

14 Manganese (Mn) IMPORTANCE Manganese (Mn) deficiency is uncommon in California vineyards and is rarely severe. It appears more often in strongly basic sandy soils; it also occurs in acid sandy soils in the north coast vineyard districts and in distillate ponding areas. Salvador is the only important commercial variety that is somewhat sensitive to Mn deficiency. Even then, occurrences are rare. SOURCES IN THE SOIL Soil Mn originates from the decomposition of ferromagnesian rocks. It exists as Mn oxides and as the Mn ion in the soil solution and is adsorbed on soil colloids. Soil ph influences availability, which increases with the lower ph values (on the acid side). UTILIZATION AND ROLE Plants take up Mn primarily in the form of the manganous ion (Mn"). It is a relatively immobile element within the plant. Mn serves as an activator for enzymes in growth processes. It assists in chlorophyll formation; thus, leaf chlorosis is an early deficiency symptom. DIAGNOSIS OF DEFICIENCY Symptoms can appear in 2 to 3 weeks after bloom on severely deficient vines. A mild to moderate Mn deficiency will not appear until midsummer to late summer. The symptoms begin on the basal leaves as a chlorosis between the veins. Increasing chloro- sis develops between the primary and secondary veins; the veinlets tend to retain a green border. (See fig. 15.) Thus, a somewhat distinct herringbone chlorosis pattern can ultimately develop on Mndeficient leaves. These symptoms should be distinguished from those of zinc, iron, and magnesium deficiencies. Zinc deficiency symptoms first appear on newer growth and include some leaf malformation. Iron deficiency also appears on newer growth and causes a much finer network of green veins in the yellowing leaf tissue. As with manganese (Mn) deficiency, magnesium (Mg) deficiency chlorosis first appears on the basal leaves, but it is more extensive between the primary and secondary veins, developing into more complete yellowish bands, lacking the herringbone pattern. Laboratory analysis of petiole samples from affected leaves and from normal leaves should be used for final diagnosis. CORRECTION OF SYMPTOMS Mild Mn deficiency has little practical effect on vine yields. It appears in late season on the older leaves, which contribute little to vine function. Apparently its only effect is a reduction of leaf chlorophyll. Deficiency in California has not been considered important enough to warrant field trials. Other viticultural areas report correction with foliar sprays of manganese sulfate at 2 to 3 pounds per 100 gallons water. Higher rates have caused minor but noticeable leaf burn in Fresno County tests. Foliar sprays of manganese chelate products have provided some correction in grower applications. Grapevine Nutrition and Fertilization in the San Joaquin Valley 29