In 1988 MAF published a booklet on "Passionfruit Culture" which at the time was a comprehensive account of passionfruit growing. Since then we've been in the user pays era and passionfruit, being only a very small industry, has not had the income to contract research to any extent. Consequently the majority of "Passionfruit Culture" is still relevant today. A small number of copies are still available from the Tauranga office of Agriculture New Zealand at a cost of $15.
However, nothing seems to stand still for very long and various developments have taken place in the passionfruit industry either through changing circumstances or times, or as so often happens through innovative growers.
Supporting Structures
The traditional passionfruit structure was the two wire single dimensional fence 1.8m high with rows 3m apart, and this had served the industry well for generations of growers. About 15 years ago a multiplicity of new structures were seen. This was partly due to the downturn in the kiwifruit industry when a significant number of kiwifruit vines were pulled out and passionfruit was planted and trained onto the old kiwifruit T-bar or pergola structures. This was OK in that passionfruit being a vine could be trained onto these structures satisfactorily and cropped well. Overall yields per hectare were not always the best as the inter-row distances for kiwifruit were not always ideal for passionfruit.
An innovative grower somewhere about that time tried an A frame structure. I'm not sure who tried this first but it gave certain advantages. The first A frame I saw was at a passionfruit field day on a property at Waihi Beach and it looked very impressive. It had obviously been well tended with loose laterals tucked in and a certain amount of summer pruning done to keep it tidy.
There are a number of major advantages with the A frame over the single dimensional fence:
Up to 50% more bearing canopy surface can be achieved per unit area of ground.
The fruit falls in the shade when full canopy is achieved, which reduces the need for several pick-ups per day when the season starts in high summer. Two or three hours on the ground in hot sun will greatly reduce the postharvest life of the fruit. This benefit of the fruit falling in the shade is also obtained in a pergola block and to a somewhat limited extent in T-bars depending on the width of the T-bar.
Due to the shade of the canopy there is usually less frequent need for mowing and weed control.
The application of protective copper sprays, so vital in ensuring a successful crop is produced, are more likely to achieve good coverage of the fruit from underneath the canopy than having to penetrate the thick curtain canopy that develops on the single dimensional fence.
Better wind protection of the fruit is achieved.
On the other side of the coin the A frame is more costly to erect in both materials and labour. The foliage can get very dense and consequently more training and pruning are required.
The first A frames were of a typical acute angled top. Experience showed that the top got quite tangled with growth and that this growth and the excessive shade that it caused led to enclosed conditions that stayed wet and humid a long time after rain, greatly increasing the risk of infection from the multiplicity of diseases that can afflict passionfruit. In more recent times the top of the structure has been flattened off to counter the adverse effect of these problems associated with the acute angled top. The same result can also be achieved with the Yframe that at least one innovative grower has experimented with and found successful.
Varieties
The New Zealand passionfruit industry has developed by producing the purple passionfruit Passiflora edulis. In recent times a yellow form has become available, and some fruit has been produced this year. Unfortunately it has so far not proved successful. Although yields have looked encouraging and the flavour appealing and slightly different from that of purple passionfruit, the fruit has tended to be small. This fruit is still green on reaching maturity and falling naturally from the vines, but turns yellow within the next few days, but has a somewhat blotchy appearance in this period. It is probably true to say that it has not made a positive impact on the market at this stage.
Nutrition
It is pleasing to report that serious commercial passionfruit growers are now using leaf analysis on a regular basis as a tool, along with soil analysis, to determine the nutritional programme required. More are responding to the trace element requirements as indicated by the results of leaf analysis. Researchers in Queensland have shown the importance of boron in passionfruit finding vines exhibiting deficiency symptoms with leaf levels of 30ppm. Although the passionfruit grown in Queensland are different from those in New Zealand a special note should be taken on boron levels.
Pests
Some pests not listed in "passionfruit Culture" have made their presence felt in passionfruit blocks since 1988. These include thrips, Fuller's rose weevil and cicadas. Thrips can be a quarantine issue if they hitch a ride on export fruit and are believed to be responsible for export rejections due to fruit markings. Perhaps it is not a coincidence that thrips have also made more economic impact on avocados and citrus in the last 15 years.
Fuller's rose weevil has been responsible for eating out the growing tips of young plants in new plantings, and cicadas have damaged stems of young plants with their egg laying activities. Any damage to the stem of passionfruit, especially close to the ground, can open the door for infection by the dreaded crown canker which is so devastating to passionfruit and therefore needs to be taken seriously. There is no easy control of cicadas but a careful watch needs to be kept for damge on the stems of young plants, and covered with a fungicidal wound dressing as soon as possible.
Acid Treatment
Because it is necessary to apply up to 20 copper sprays in a year for disease control purposes on passionfruit the fruit at harvest are usually covered in a heavy copper deposit. Traditionally this was removed by dipping in 1% hydrochloric acid for 1-2 minutes and then into clean water to remove the acid from the fruit and the risk of skin damage. It has now been found that citric acid at ½-1% can do the same job as the hydrochloric acid. It is possible to obtain food grade citric acid which should be more acceptable than hydrochloric acid in these days of food safety precautions. After all, ½-1% citric acid is equivalent to lemon juice.
There has been growing interest in passionfruit as a crop in the recent times and it must be remembered it is a true subtropical plant with high risks from climatic and disease factors and has a very high labour requirement.
Article by Pat Sale
Horticultural Consultant
Reprinted from "The Orchardist" June 2003
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