Chapter 16

Vineyard Nutrient Management

Macronutrients and Micronutrients

Molybdenum

Role and Deficiency Symptoms

Molybdenum is essential to vine growth as a component of the enzymes nitrate reductase and nitrogenase.

Only rarely has molybdenum been found to be deficient in vineyard soils. When molybdenum is deficient, necrosis develops and spreads rapidly from the leaf margins inward. The demarcation zone between healthy and necrotic tissue is pronounced, and the unaffected areas appear normal.

Assessing the Need for a Molydenum Fertilizer

As with most micronutrients, tissue sampling can be used to determine the vines’ molybdenum status. Tissue analysis results (Table 16.3) coupled with visual observations should indicate whether to apply molybdenum.

Time of Application

Molybdenum fertilizer can be applied late winter to early spring for soil surface applications. If molybdenum fertilizer is applied via drip irrigation it should be completed 2 or 3 weeks prior to bloom.

Application Methods

Direct Soil Surface Application: Soil surface applications of molybdenum are not very effective because it is not an effective short-term measure in the current season in overcoming molybdenum deficiency before fruit set.

Fertigation: Molybdenum applied to vineyards with the drip system is effective and feasible.

Foliar Application: Most molybdenum deficiencies can be corrected with foliar sprays.

Soil Factors Affecting Availability

Molybdenum deficiencies are found mainly on acid, sandy soils in humid regions. Soils high in iron/aluminum oxides will absorb molybdenum strongly, reducing molybdenum availability.

Molybdenum Toxicity

Marginal leaf scorch and abscission as found in typical salt damage are typical symptoms.

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