At full bloom, collect, preferably in the morning, 50 - 75 petioles from leaves that are located opposite the first or second (from bottom) flower cluster of the shoot. Collect no more than 2 petioles per vine. Disconnect the leaf from the petiole at the time of sampling. Rinse petioles carefully with distilled water. Rinse 3 times if plants have recently been sprayed with foliar fertilizer or fungicide. Allow samples to dry before sending to the laboratory. Samples may also be taken late summer if desired (70-100 days after bloom).

Deficiency due to inadequate or ineffective N fertilization. Generally, application of 45 to 50 pounds of N should be applied annually, with 2/3 applied between bud break and bloom, and the remaining 1/3 applied after fruit set. If N is less than 1.2% at bloom or less than 0.8% in late summer, apply an additional 15 to 20 pounds of N per acre. These rates of N fertilizer may be adjusted up or down based on the petiole analysis results, and based on the amount of vine growth. If growth is excessive, reduce N rates.

Deficiency may be due to low soil P, inadequate P fertilization, or poor root development. If petiole P is less than 0.17% (bloom) or 0.14% P (late summer), apply 25-50 pounds of P₂O₅ per acre in a band under the trellis.

Deficiency due to low soil K, inadequate K fertilization, and/or heavy crop load. If petiole K is less than 1.5% (bloom) or less than 1.2% K late summer, apply 50 to 150 pounds of K₂O per acre (depending on the severity of the K deficiency). Apply the K fertilizer in a band under the trellis.

Deficiency is rarely detected because the soil test Ca level must be extremely low for a deficiency to occur. If soil pH is maintainted in the recommended range, soil Ca will be adequate.

Deficiency due to low soil test Mg, which may be more severe if soil pH is low. Deficiency may also be due to high soil K, which may interfere with Mg uptake. If Mg is low in petioles and soil test K is high, discontinue K fertilization. If petiole Mg is less than 0.3% and pH is low, apply dolomitic limestone to correct soil pH, which will also supply Mg. If soil pH is adequate, Mg deficiency may be corrected with 15 - 25 pounds of Mg per acre as magnesium sulfate or other forms of soluble Mg. For more immediate correction, spray foliage with 5 to 10 pounds of magnesium sulfate in 100 gallons of water per acre.

Low levels of B may occur on very sandy soils and soils low in organic matter (less than 1%). If B petiole level (samples collected at full bloom) is less than 30 ppm, apply ¼ to ½ pound of actual B per acre in each of two foliar applications of soluble B fertilizer. Make the first application at 2 weeks prior to bloom and the second at bloom, but no earlier than 10 days after the first application. Apply no more than ½ pound of actual B per acre in each spray using enough water to cover the flower clusters thoroughly. Do not exceed this rate of application and do not reduce the 10 day interval between applications as plant damage may occur. As an alternative to 2 spring foliar applications of soluble B, a single foliar application may be made in the fall, using no more than one pound of actual B in 150 gallons of water per acre. A postharvest foliar application in fall may be more effective and present less potential for plant damage than two half-rate foliar applications in spring. Broadcasting B at five pounds of borax (10% B) per acre to the soil surface in a strip under vines in spring may be used as an option to foliar applications.

Iron deficiency is highly unlikely on the neutral to slightly acid pH levels in soils of Georgia and the Southeast US. Iron deficiency, should it occur, is best diagnosed by visual observation.

Low Mn levels are not likely to occur. If petiole Mn levels are less than 30 ppm, low Mn can be corrected by soil application of 25 pounds of manganese sulfate per acre. As an alternative, a manganese sulfate foliar spray may be applied. Follow label directions.

Copper deficiency is rare but if it occurs, it is most likely on sandy soils with high organic matter. If Cu levels are less than 5 ppm, apply copper sulfate to the soil (contains 25% Cu) at a rate of 4 pounds per acre (one pound Cu per acre) each year until tissue levels improve.

Low Zn levels may occur on very sandy low organic matter soils. If Zn level is less than 25 ppm, apply 10 pounds of zinc sulfate per acre in next year's fertilization program.