Crop protection
Pests and diseases may attack plants as early as the nursery stage. Caterpillars and slugs may attack the plants, while fungi may cause damping-off and loss of plants. Both insect and fungal problems in passionfruit could be controlled through proper cultural practices and chemical sprays. Nematodes also attack Passiflora species. The purple passion fruit, in fact, is impossible to grow in many situations unless grafted on the root of the yellow passion fruit or another resistant species. Nematodes and 2 fungi, species of Phytophthora and Fusarium, have been found on the roots of declining or drying vines. The yellow passion vine is more resistant to harmful soil organisms than the purple, but it is not immune. Vines may show cankers or stem lesions near the soil line, and slowly decline after growing for as long as 5-7 years. When this happens, it is advisable to start new vines, preferably in a new site, for replacements.
Insect Pests
Beneficial insects as pollinators have already been discussed. There are also harmful insects associated with passion-fruit. This entails solving the problem of eliminating the injurious insects without destroying the beneficial insects.
One approach to this problem is through the proper timing of spray applications. The flower of the commercially grown yellow passionfruit opens during the afternoon hours and closes at night. Observations have shown that insect pollinators are most active during the period when the flowers are in bloom. Therefore, less damage to the pollinating insects might result if spray applications were confined to the early morning hours when pollinators are inactive.
Also, since exposed pollen grains burst upon contact with water, becoming non-functional, it is imperative that any spraying for insect or disease control be done only when the flowers are closed but preferably when the plants are not flowering at all.
Fruit Flies
The most troublesome pests are fruit flies.
Oriental fruit fly (Dacus dorsalis)
Melon fly (Dacus cucurbitae)
Mediterranean fruit fly (Ceratitis capitata)
Generally, the Mediterranean fruit fly is found at high elevations. The Oriental and the melon flies seem to prefer lowlands.
Fruit flies usually puncture the immature passionfruit while the rind is still tender. A woody area develops around the puncture as the fruit enlarges. If the fruit is undeveloped at the time of puncture, damage may be sufficient to cause it to shrivel and drop off. If the fruit is well-developed, it may grow to maturity.
At the time of ripening, the area around the puncture has the appearance of a small woody crater which, while it does not impair juice quality, does disfigure the fruit. The oviposition scars on ripening fruits generally do not contain living larvae, which seem to develop better in immature than in mature fruit.
The main objective in fruit fly control is to destroy the gravid females which usually breed elsewhere but lay eggs in the orchard. An important step, then, is to eliminate nearby overripe fruits on which the adults feed and breed.
Fruit fly adults may be destroyed with various insecticides. One is Malathion 25% wettable powder, which is sprayed at 1.5 kg/ha in 500 l of water. Absolute caution should be exercised in making applications and every precaution taken to do so as safely as possible.
Fruit fly adults may be destroyed also by use of bait sprays made with 1.5 kg of Malathion and 0.5 kg of yeast hydrolysate in 500 l of water per hectare.
Because the adult fruit flies roost on plants that are not necessarily host or crop plants, applications should be made not only on the passionfruit vines but on all nearby vegetation which might harbor the flies.
Frequency of application depends on the population. When adults are numerous, applications twice weekly may be necessary when young fruit is present.
Mites
Several mites are also serious pests.
Spider mites (Brevipalpus phoenicis); Tetranychus telarius; the broad mite (Hemitarsonemus latus).
Mites are generally most damaging in areas of low rainfall and during prolonged dry seasons.
Presence of the spider mite is indicated by scattered reddish patches on the lower surface of the leaf, along the midrib and veins, as well as on the surface of the fruit.
Spider mites cause shriveling, yellowing, premature leaf fall and sometimes complete defoliation. A heavy infestation might also cause vine dieback and shriveling and dropping of immature fruit.
Indications of the presence of the broad mite requires a lens for detection. The very minute female white mites can be seen often carrying the smaller males on their posterior ends. Under the lens, eggs with white markings may also be seen sticking to the leaf surface.
An attack by the broad mite can most readily be detected by the symptoms of injury during the period of vine growth since this mite attacks the young terminal leaves, causing them to be stunted, deformed, slender and rugose.
Mites can be normally controlled by hosing them with a soap solution for at least three days in succession - make sure you spray every part of the plant, especially the underside of the leaves.
Severe infestations of mites on passionfruit can be effectively controlled by spraying wettable sulfur at 2.5 kg/ha in 500 l of water. Monthly applications serve as a precautionary measure.
Aphids
Severe damage by aphids usually results from their attacks on young plants. Two aphids, Myzus persicae and Macrosiphum solanifolii are efficient vectors of the passionfruit woodiness virus. These aphids are present in Hawaii but the virus is not.
Woodiness disease has been identified in Australia as cucumber mosaic virus 1. It is thought to be transmitted by aphids and is the most serious threat to the purple passionfruit in Australia and Kenya. Much research has been devoted to combating it.
In this disease, the leaves become leathery and malformed; the fruits gradually decrease in size and the rind becomes thick and hard and little pulp is produced.
They are often raised and protected by ant colonies. Note that ants by themselves do not pose a danger, they can often be found feeding on the nectar in the flower. The barnacle scale (Ceroplastes cistudiformis) has been found in large numbers attacking the passionfruit vine. Heavy infestation results in severe defoliation.
Greenfly and blackfly
They attack the young developing parts of the plant, leading to deformities as they grow. The damage can be recognized by isolated brown patches on the leaves, and parts of the leaves (mostly the edges) constricting. These insects are also one of the main causes of viral infections - by sucking the juice out of your plants they can inject viruses.
Snails
Some species of Passiflora attract snails. These have to be dealt with by making the plants unaccessible: create a bed of sharp sand around the base or curl copper around the foot of the plant (snails hate copper). Slug bait should be spread around seedling or a liquid slug control could be incorporated into the fungicide drenches (benomyl) for the control of damping-off.
Caterpillars
Caterpillars have been destructive of the passionfruit plants, especially attacking new leaf growth. Heliconius caterpillars have an appetite for Passiflora and most cause allergic reactions or skin-irritation when picked off by hand. Avoid using chemical weapons but put on pair of gloves and pick them off - some of these insects are more beautiful than your plants and play an important role in the ecosystem. Hairy caterpillars can cause respiratory problems or irritation to exposed skin - wear protective glasses and mask and keep your body covered when removing them. Tortrix moths have caterpillars which are known as leaf-rollers, they fold the leaf to create a protective cocoon whilst munching away at your plant. An insecticide is sprayed at the recommended rate every two to four weeks for caterpillar control.
stinkbug (Chondrocera laticornis) punctures the yellow passionfruit but only the appearance of the fruit seems to be affected.
Although severe attacks appear to be exceedingly rare, the thrip, Selenothrip rubrocinctus, has been observed to attack passionfruit leaves.
The passion vine leaf hopper (Scolypopa australis) requires protective measures in Queensland, Australia.
Biological Controls
Ladybird beetles or Ladybugs (Rodolia cardinalis and Hiippodamia convergens) and Praying Mantes (Mantis religiosa and Paratenodera sinensis) are among the most beneficial insects known to man. They devour many times their own weight in destructive pests.
Ladybugs consume aphids, fruit scales, tree lice, mealy bugs, leaf hoppers, thrips, fleas and the eggs and larvae of many plant-destructive insects.
Young Praying Mantes devour aphids, flies and other small insects; Older ones consume enormous quantities of beetles, caterpillars, grasshoppers and other damaging insects.
The most startling breakthrough in biological controls is evidence found by a team of Penn State chemical ecologists that plants control mating in insects. This contradicts the current theory that female insects manufacture their own sex lures and that each male will respond to a single attractant unique to its species.
Dr. Laurence B. Hendry and his coworkers at Penn State University discovered that the attractants originate in the plants on which the insects feed. He believes the female simply stores the attractants, called pheromones, not changing them in any way. He has found the attractants in plants in concentrations corresponding to the amounts found in females. He also has evidence that males of a single species can be sensitive to as many as 20 different chemicals, depending on their diet.
Dr. Hendry theorizes that the insect is imprinted or programmed, while still in the larval stage, to respond to whatever pheromone is present in its earliest food. Therefore the male and female insects which feed on the same plants as larvae will be imprinted with the same attractant and mate as adults.
Thus, pest-control programs based on sex lures may be the most effective; a field may be sprayed with an inexpensive compound which insect larvae would eat and imprint. Later the same chemical could be used as a sex lure to confuse the males and prevent mating.
Integrated Control
Integrated control is being studied under which all of these - natural enemies, cultural practices, resistant-crop varieties, microbial agents, genetic manipulation, messenger chemicals, selective chemical controls such as green soap and water, and even pesticides - become mutually augmentative, rather than individually exclusive.
Insect pests of passion fruit (Passiflora edulis): Hosts, damage, natural enemies and control in PDF