Growing Potatoes, Tomatoes and Peppers with Psyllids!
by Kay Baxter and Scott Lawson
Many gardeners, and small and large commercial growers have lost entire potato crops and even old seed lines over the past couple of seasons. Scott Lawson (True Earth brand), well known for being New Zealand’s largest grower of organic potatoes, no longer grows potatoes commercially. He had to put all of his potato staff of 6 off, and he is focusing instead on researching ways to grow them with psyllids around.
Joseph Land, our main potato grower in the North, has not seen them yet in his garden, but not only must we be prepared, we must also put systems in place to ensure we can grow high quality potatoes with psyllids around in order to keep our potato collection alive and strong.
How are we going to maintain our precious heritage potato lines in the face of this pest? Scott Lawson has put together some notes for us about the psyllids that are taking out our potatoes and tomatoes, thanks heaps Scott!
What is a psyllid? The insect ‘TPP’ stands for ‘Tomato, Potato Psyllid’, the scientific name is Bactericera cockerelli, the adult is about 2-3mm long and resembles a tiny cicada. Mature adults have white strips on their backs. Both the early life cycle stages, nymphs, and the adults, are sucking feeders. The female adults lay up to 500 eggs over their lifetime; these eggs are laid on the edge of the leaf, attached by a short stalk, difficult to see with an untrained eye, a magnifying glass will help. In warmer areas a life cycle can be completed in 4 weeks, so this pest can very quickly build up to large numbers. The nymphs look like small scale insects, slow moving and living on the underside of the leaves. The psyllid spreads a bacteria called Liberibacter solanacearum. This, together with the sucking damage done to the plants, causes great losses in our tomato, potato and other solanaceous crops. This bacterium is not harmful to humans. The first visual sign of the pest on a potato crop are in October and November, with this being earlier in warmer parts of the upper North Island and perhaps after Christmas in the South Island. The psyllid overwinters on a wide range of plants, such as hawthorn, nightshade etc.
History of psyllid: It originated in Mexico and has spread up the western seaboard of the USA up to Oregon, but contained to the west of the Mississippi River. It arrived in Auckland in 2006, suspected to have been carried on imported capsicums or cut flowers, since then the sap sucking pest has wrecked havoc in the solanacea family of tomato, potato, tamarillos, capsicum and eggplant/aubergine. It has spread north from Auckland, and south arriving in Hawkes Bay 2008, and has been found as far south as Timaru. See trapping data on www.potatoesnz.co.nz.
New Zealand has 5 species of native psyllid, none of which are known to affect crop production, only a trained eye under a microscope can tell the difference between species.
Effect on production in NZ: Prior to the arrival of the psyllid NZ enjoyed only a few difficult pests that affected the solanacea family, primarily this was 2 insect pests Heliothis zea, now known as Helicoverpa zea (common name is ‘tomato fruit worm’ in tomatoes and ‘corn ear worm’ in sweetcorn), and Phthorimaea operculella (common name is ‘tuber moth’ in potatoes).
NZ’s growers had developed good cultural and biological controls of these two pests, i.e. parasitic wasps had been released to target the tomato fruit worm, which was effective enough for many conventional growers not to have to use insecticides, sorry to see this has now changed with the arrival of this new pest, with most growers implementing a rigorous spray programme.
Many growers are exiting the industry because the extra costs spent on products to try to control the psyllid pests are not being recovered in market prices. Some organic growers have exited the industry due to inability to produce a marketable crop.
Symptoms: Both the early life cycle stages, nymphs, and the adults are sucking feeders. When feeding they inject saliva into the plants causing psyllid yellows. The plant growth is stunted and often in potatoes the first signs are curling leaves and purple coloured tips. As the plant continues to grow, many varieties of potatoes exhibit aerial tubers, and bulbing of the stems, also the crop tends to set high in the mould, close to the surface and small in size. The effect on the plant is variable between varieties and the time of the year. However yield loss of between 50 and 80% is common in main season potato crops. The balance of the crop produced is very much 2nd grade, often with internal defects affecting the cooking quality, and premature sprouting is something growers are noticing, not good for packed product on a shop shelf. After boiling the texture is often mushy with an earthy taste, not at all what an unaffected tuber will taste like. Commercial Potato Processors have rejected many hundreds of tons due to internal defects such as ‘zebra chip’ caused by Liberibacter, which when fried show dark zebra chip stripes. You can see this in fresh tubers as well, but not as pronounced as when it is fried.
Control Measures: Organic growers are very limited in options available. Biological control is some way off, with this area needing a lot more research, no known predator exists in NZ to offer suitable control.
Products: Entomopathogenic Fungi have been trialled, i.e. a fungi cultured in a lab and then applied to the crop to target the pest, this occurs naturally under the correct conditions and is often seen on brassicas crops infected with white butterfly. The issue is getting the fungi to develop and then attack the pest, variables of the amount of active fungi and low humidity can affect the efficacy of such a product. It is easier to use under a controlled environment indoors in glasshouses, where humidity can be controlled. Conventional growers are having some success with this range of products indoors.
Spraying oils such as the botanical based Eco-Oil can be tried, Neem Oils and Neem extracts such as Neem-Azal, which is a botanical insecticide have some effect as discouraging feeding. Another option to try is naturally derived diatomaceous earth which is 85% silicon dioxide, sold here in NZ to commercial growers as Insecta-Kill and repacked by Koanga Gardens for home gardeners as Psyllid Solution. None of the mentioned treatments work well under a high pressure (i.e.commercial situations, Kay) system.
Research: Plant and Food Research in conjunction with industry groups such as HortNZ, incl. PotatoesNZ and overseas with research facilities have initiated an industry wide collaborated approach. Potato growers are helping to fund the research through their levies and also through voluntary contributions. Potato processors, seed suppliers and marketers are all involved in trying to find an economic and environmental control solution.
These are my (Kay’s) strategies for dealing with Psyllids:
1. High Brix first, probably around 12. Insects will not see the potatoes as insect food, different vibration that they actually aren’t attracted to.
2. Grow your own seed potatoes and select the best croppers each year from the whole crop as explained in our 2010 July catalogue by Gail when describing Joseph’s potato growing techniques. See also www.koanga.org.nz under Seeds/seedplanting/solanaceae.
3. Plant your potatoes early to avoid the psyllid which only becomes active in warmer weather, i.e. plant your potatoes between mid-August and mid-September.
4. Use a combination of weekly sprays to keep psyllids away or to kill them, from the time the weather warms up, possibly Labour weekend on. I suggest Neem Oil fortnightly, and Psyllid Solution every other fortnight.
5. Good luck, we’re keen to hear your stories…