Zinc deficiency in strawberry

Zinc, one of the essential micronutrients and an important constituent of several enzymes and proteins, is only needed by plants in small quantities. However, it is crucial to plant development, as it plays a significant part in a wide range of processes.

The normal range for zinc in plant tissue is 15-60 ppm and in the growing medium between 0.10-2.0 ppm. Zinc deficiency or toxicity does not occur often; however, they both negatively impact crop growth and quality. Any deficiency or toxicity has to be addressed before crop damage is irreversible.

Function of Zinc in Crop Production

Zinc activates enzymes that are responsible for the synthesis of certain proteins. It is used in the formation of chlorophyll and some carbohydrates and is used in the conversion of starches to sugars. Zinc also helps plant tissue withstand cold temperatures. Zinc is essential in the formation of auxins, which help with growth regulation and stem elongation.

What are the Symptoms of Zinc Deficiency?

Like most micronutrients, zinc is immobile, meaning the deficiency symptoms occur in the new leaves. Symptoms vary depending on the crop.

Typically they are expressed as some varying pattern of chlorosis of the new leaves (often interveinal) and necrotic spots may form on the margins or leaf tips. These new leaves are smaller in size and often cupped upward or distorted. The internodes shorten, giving the plant a rosette appearance and bud development is poor resulting in reduced flowering and branching.

Zinc deficiency in Mexican Sunflower
Interveinal chlorosis seen in this Mexican sunflower is a result of zinc deficiency.

What are the Symptoms of Zinc Toxicity?

Although uncommon, zinc toxicity can occur when its levels in the tissue exceed 200 ppm. Symptoms are expressed as smaller leaf size, chlorosis of the newer leaves, necrotic leaf tips, retarded growth of the entire plant, and/or reduced root growth. More often excess zinc found in the growing medium can compete with plant uptake of phosphorus, ironmanganese or copper and can cause deficiencies in plant tissue.

Zinc is more available for plant uptake when the pH of the growing medium is low; so if zinc toxicity is occurring, test the pH and zinc levels within the growing medium. Zinc can also be found in high levels in some water sources and can also be picked up when the water comes in contact with new galvanized metal surfaces. Before testing tissue, rinse the foliage first as certain fungicides have zinc as an active ingredient, which adds to the zinc levels in tissue test results.

Where to Find Zinc?

Zinc is found in most water-soluble fertilizers at rates that should prevent its deficiency, unless fertilizer is not applied. Single-element fertilizers such as zinc sulfate, zinc ammonium nitrate or chelated zinc can be applied. However, if zinc is applied at high enough rates, it competes with other micronutrients, limiting their uptake by plant roots which could lead to a deficiency. Therefore, it is better to use a complete micronutrient fertilizer that contains all micronutrients.