Diseases
The most serious diseases of the passionfruit are brown spot, root rot and nematodes. Brown spot, caused by the fungus Alternaria passiflorae in warm weather, is easily recognized. On the leaf, the first symptoms are minute reddish-brown spots about 0.3-0.6 cm in diameter which, under the humid conditions required for its development, have a water-soaked margin.
Spores or conidia produced by the fungi are readily spread by the wind and germinate on leaf and fruit surfaces, causing the telltale brown spots.
As infection progresses, the spots enlarge, forming a series of concentric rings with premature leaf drop. Symptoms on the fruit are characterized by circular, sunken necrotic areas, about 2-5 cm diameter, which, as on the leaves, are reddish-brown. Infection occurs on half-grown to nearly mature fruit but apparently does not impair juice quality. However, it is objectionable from the processing standpoint because the brittle, necrotic rind tissues drop into the juice during extraction.
Brown spot can be controlled by Maneb (80% WP) at the rate of 1 kg/ha in 500 l of water applied biweekly or Captan, Zineb or copper fungicide.
Since this is a disease caused by moist conditions, growers probably can minimize fruit damage by picking up the fruit before it can be damaged by fungal spores on the damp soil.
Root rot, the second most serious disease of the passionfruit, is caused by the fungi Pythium splendens and P. aphanidermatum in Hawaii. In South Africa the fungus has been identified as being of the Phytophthora genus.
Symptoms are a general decline in vigor as feeder roots are destroyed by the fungus. Some California vines show these symptoms. Passiflora edulis, the purple passionfruit, is highly susceptible to root-knot nematode attacks. Symptoms are severe stunting of the vine which may eventually die. P. edulis f. flavicarpa seems not to be affected by this disease and is resistant as well to woodiness disease and Fusarium wilt. It is being used in many countries as rootstock for the purple passionfruit.
However, it is evident that maintenance of vigorous, healthy plants by consistently good fertilization and cultural practices will reduce or eliminate disease or minimize their effects.
Viruses
Viral infections will persist in a plant and include Chrysanthemum B carlavirus, Passiflora latent carlavirus, Passiflora ringspot potyvirus, Passionfruit woodiness potyvirus, and Purple granadilla mosaic virus. They are transferred via wounds from sucking insects (greenfly, blackfly) or from utensils that weren't cleaned. The virus and susceptibility depends on the species or hybrid and remains in the plant once it's infected there is no treatment. The damage resembles that of nutrient deficiency: yellowish spots on the leaves, deformed growth and bad flowering or low yield in fruit. A virus can kill your Passiflora, but its immune-system and some regular feeding with fertilizer will keep the plant healthy and happy. The damage is most noticeable in the beginning and end of the season. A trick to produce virus-free plants is by cutting fast growing shoots. In these shoots the virus might not have propagated yet. Any vines whose leaves show mosaic or vein-clearing symptoms should be removed and destroyed. Also, plants should be propagated from seed whenever possible. A vine used as a source of cuttings should be kept insect free in a screen house to protect it from viral infections.
Diseases of passion fruit (Passiflora edulis): Pathogen, Symptoms, Infection, Spread & Management in PDF