It may be a sign that your vines have been infected with the passion fruit woodiness virus. It can be caused by magnesium deficiency, nitrogen deficiency on sandy soils, or extremely cold weather combined with low humidity. Due to the lack of nutrients, vines turn yellow differently depending on the stage of leaf development. For example, sulfur (S) or copper deficiency is always evident if your new leaves have yellow veins. However, if the yellowing affects the area between the veins, it indicates insufficient iron (Fe) or Molybdenum (Mo) deficiency.
Yellowing of old leaves, especially between the veins, is a sign of magnesium deficiency. A fertilizer rich in magnesium (Mg) is a suitable treatment for this problem. On the hand, yellowing the veins in old leaves is a sure sign of nitrogen deficiency and should be corrected accordingly. There are situations where both the old and new leaves of your favorite fruit vines turn yellow. The best fertilizer for passion fruit vines is Granulated fertilizer, Urea, Potassium sulfate, Diammonium phosphate and Organic fertilizers like manure and vegetable compost.
