Tamarillo Psyllid Threat

The $2m a year tamarillo industry has been decimated by the tomato/potato psyllid (TPP) insect and the liberibacter it carries, which kills mature trees. Almost all growers, who are mainly located in the warmer northern and eastern regions of the North Island, now have the TPP pest on their orchards. The pest is most active during summer months when trees are subsequently infected with the bacterium. Tree losses of 50% or more have been recorded, which must be replanted. Significant reductions in fruit availability for local and export markets have resulted this winter. Vector control of the TPP in all life stages by regular insecticide applications is the only way of safeguarding trees and fruit production at this time.

Tamarillos (tree tomatoes) are a member of the Solanaceae family, along with potato, tomato, eggplant and capsicum peppers. It is a native to central America but seems to have all but died out in the wild. New Zealand grows tamarillos on a commercial scale, along with a few other countries (Ecuador, Colombia and Western Australia). Yellow and purple fruited varieties were introduced to NZ in the late 1800s from Asia, and then an Auckland nurseryman introduced red varieties in the 1920s from seed sourced from Latin America. Continued re-selection by growers has led to today’s commercial varieties – Ted’s Red, Mulligans and Laird’s Large. During WW2 large quantities of tamarillos were grown to replace the vitamin C from imported fruit loss, such as bananas, pineapples and citrus. The planted area increased considerably during the horticultural boom period of the 1970os, when taxation incentives were available. The official name of the fruit was changed from tree tomato to tamarillo. Commercial plantings peaked in the early 1990s at an estimated 250-300ha, producing 2000 tonnes of fresh fruit. The spread of mosaic virus impacted large orchards around Kerikeri, many of which have now disappeared.

The Tamarillo Growers Association (TGA) says production in 2008 was $2 million-plus, being about 750 tonnes, of which 600-650 tonnes went to local markets (fresh and processed) and 150 tonnes were exported, to the United States, Australia and some smaller markets.

Australia was closed to NZ tamarillos during 2009 because of the TPP outbreak here, which had come in from the US during 2006 and was first identified in Pukekohe in 2008. A fruit treatment protocol has now been agreed and the Australian market re-opened for 2010. TPP and liberibacter cannot be spread through fruit movements. All domestic and export fruit is washed before sale.

TPP and liberibacter are the greatest threat to the NZ tamarillo industry in its history. First detected around Pukekohe in tomatoes and potatoes in 2008, the insect spread very rapidly to all growing areas during 2009 and 2010. This was a biosecurity breach, because previously TPP were only known to be causing problems in the US. Other countries remain free of the pest. TPP lives and reproduces on all solenaceae plants, which includes tomatoes, potatoes, capsicums, eggplant and such weeds as nightshade. About 20% of all TPP carry the liberibacter (so-called “hot” TPP) and they infect the plant while sucking on the underside of leaves. TPP have three life stages – eggs, nymphs and winged adults. The adults are fast movers and can travel large distances on wind.

Although liberibacter infection can and usually does kill a tamarillo tree, some trees show symptoms and recover, but their fruit are stunted or distorted. The first wave of insect population and disease attack, before growers identified the pest and learned to control TPP populations, was often devastating – up to 90% of trees dying.

Fortunately, the tamarillo industry has some very big brothers who also have problems with TPP, especially the tomato and potato industries. Because these are threatened, a large TPP fighting and research fund of $1.5m to $2m (including government contributions) has been dedicated to understanding the life cycle of the pest, working out optimum spray controls and identifying possible biological controls.

Maungatapere growers Robin Nitschke and Craig Watson have been attending meetings of the TPP research group (based at Plant & Food Research, Mt Albert), and have been monitoring the TPP in their own orchards. They count insects on 10 trees selected at random, refresh yellow sticky traps and send the old bases to Plant & Food, while checking the trees for the presence of TPP and symptomatic trees.

Among the unknowns are the over-wintering of TPP, how the disease kills the tree, other hosts of TPP and the insecticide effectiveness and registration for use on tamarillos. Robin also thinks that liberibacter-resistant trees could be identified and breed from, but Plant & Food say that is a matter for commercial breeders/orchardists at this stage.

Craig Watson has been growing tamarillos for a long time, and has expanded on to nearby leased land on the slopes of Mt Maungatapere (volcanic cone). He peaked at 15,000 trees, but has losses due to TPP/liberibacter and the 2010 drought. Redwood has a modern grading platform which is used daily during the winter picking season. He packs for export and local market, plus gate sales. Craig is also a nursery for tamarillo trees.

Robin and Heather Nitschke have 3.5ha with 5800 trees in three varieties – 50% Lairds Large, 33% Mulligan and 17% Ted’s Red. The ages range from three to one-year. Some 700-800 trees have been replaced because of losses in the older trees, about half and half frost damage and liberibacter deaths. Another 400 are effectively dead and need replacing next spring. As well as domestic market supply, they process into a range of Hancroft relishes, sauces and jams, which are sold along with fresh fruit at the Whangarei and Kerikeri growers’ markets. These products have up to 80% fruit and draw excellent repeat business. Some processed fruit is supplied by tamarillo growers to larger manufacturers, such as Barkers, but the tamarillo content in their products is lower.

The Tamarillo Growers Association receives up to $70,000 annually from the 3% levy on all fruit sales. About one-third goes on marketing, another third on research and the remainder on administration. Marketing is done through supermarket demonstrations, website promotions/competitions and promotion of the tamarillo cookbook by Jan Bilton. The domestic market is under-supplied, especially this year because of liberibacter tree losses, and the export markets could take larger volumes.