If the yellowing is sporadic and nonuniform, then it may be an iron or magnesium deficiency. However, there are many reasons for vine leaves to yellow. If plants begin to fail, have your soil tested for nutrient deficiencies by your area cooperative extension (find it here: http://www.almanac.com/content/cooperative-extension-services). Fertilizer is good if it contains what the plant needs; soil quality is paramount.
If the yellowing is sporadic and nonuniform, then it may be an iron or magnesium deficiency. However, there are many reasons for vine leaves to yellow. If plants begin to fail, have your soil tested for nutrient deficiencies by your area cooperative extension (find it here: http://www.almanac.com/content/cooperative-extension-services). Fertilizer is good if it contains what the plant needs; soil quality is paramount.
We hope this helps.