Cause High pH soils have little available iron and can result in iron chlorosis. This is often called "lime chlorosis" as lime additions that increase soil pH impact iron availability. When high soil pH causes iron deficiency, other nutrients may also be deficient. Vitis labrusca and related cultivars tend to be more susceptible than Vitis vinifera.
Symptoms Leaves yellow, starting at the margin and progressing inward until, in severe cases, only the areas around larger veins remain green. Deficiency is usually observed in young leaves, which are smaller. Deficiency is difficult to diagnose based on tissue tests because leaf iron concentrations are often within a normal range. Based on experience in the Pacific Northwest, correcting iron deficiency in vineyards has been difficult and depends largely on the soil of a given site.
- Adjust soil pH to around 7.0. Adding sulfur or organic matter, especially conifer needle mulch, which is highly acidic, may help. Note that grapevine rootstocks can endure a range of soil pH between 5.5 and 7.0.
- Using iron chelate (Fe EDDHA), as a soil treatment or foliar feed, may help chlorotic plants. Read and follow all label instructions.
Reference Smith and Cheng. 2006. HortScience. 41:1498-1501.