Are your grape leaves losing color? It might be chlorosis of grape leaves. What is grape chlorosis and what causes it? The following article contains information on how to recognize the symptoms of grape chlorosis in your grapevines and its treatment.
What is Grape Chlorosis?
While European (vinifera) varieties of grape have resistance to chlorosis, it is a common ailment afflicting American (labrusca) grapes. It is usually the result of an iron deficiency. Grape leaves begin losing their green color and turn yellow while the veins remain green.
What Causes Grape Chlorosis?
Chlorosis of grape leaves is the result of high pH soils which have very little available iron. It is sometimes referred to as ‘lime chlorosis.’ In high pH soils, iron sulfate and usually some iron chelate become unavailable to the vine. Often, this high pH also reduces the availability of micronutrients as well. Symptoms of chlorosis appear in the spring as the vine is starting to leaf out and is most commonly seen on young leaves.
Interestingly, this condition is difficult to diagnose on the basis of tissue tests because the concentration of iron in the leaf is usually in the normal range. If the situation is not remedied, however, the yield will be reduced as well as the sugar content of the grapes and, in severe cases, the vine will die.
Grape Chlorosis Treatment
Since the issue seems to be with a high pH, adjust the pH to about 7.0 by adding sulfur or organic matter (conifer needles are great). This isn’t a cure all but may help with the chlorosis.
Otherwise, during the growing season make two applications of iron sulfate or iron chelate. Applications can be either foliar or a chelate that is especially for alkaline and calcareous soil. Read and follow the manufacturer’s instructions for specific application information.