Written by Charles Merfield
For more information see the TPP research report page on the FFC website.
Insect mesh crop covers – purchasing information
Tomato Potato Psyllid (TPP, Bactericera cockerelli) is an exotic pest accidently introduced into NZ in 2006. If you were looking for the ‘perfect’ pest, TPP would be a pretty good bet. It only took about three years to travel from Auckland, where it was first spotted, to Invercargill. It feeds on a very wide range of plants in the solanaceae family, both crops and weeds, allowing it to survive and thrive just about anywhere and cause havoc on a wide range of important crops. The worst thing is it packs a punch well above its weight, as it also carries a bacteria and phytoplasma (Candidatus Liberibacter solanacearum and Candidatus Phytoplasma australiense) the former causing zebra chip disease in potatoes and both causing potentially significant crop damage and yield losses. Therefore only a handful of TPP can cause a big yield hit and therefore slash profits.
This makes managing TPP particularly difficult as there needs to be consistently high levels of control – ideally as close to 100% as possible. However, this is pretty challenging: some of the new chemicals approved for use in the last couple of years are doing the job, but they require very good coverage, especially of the underside of leaves where the TPP hang out, which in crops like potatoes is pretty hard. Plus there are considerable concerns about resistance developing with growers recommended to change spray chemistry every month / TPP generation, which means a shed full of different sprays. Also the use of chemicals has put the kibosh on a number of effective biocontrol and IPM programs, setting the aim of reducing pesticides back considerably. The soft / organic chemicals have not really cut the mustard yet, and it is a big ask for them to get a result against such a well hidden pest.
Biological control, and IPM techniques, while showing some positive potential, faces the problem that the ‘using a bug to kill a bug’ technique (classical and conservation biocontrol) rarely reduces pests to very low levels – which is what is required with TPP to keep it below economic thresholds. Inundative biocontrols, i.e. ‘bio-sprays’ such as the famous BT (Bacillus thuringiensis), have the potential for highly effective control due to them continuing to work for a week or few after spraying, and the ability in some for the infective agent to spread under its own volition. However, developing such materials is not easy, and it often takes years, even decades, between finding potential organisms and having a grower ready product on the shelves. That is too long a wait.
The 2012-13 mesh crop cover experiment at the FFC. Photo credit: Charles Merfield
Things could therefore be considered a little bleak. However, research at the Future Farming Centre (FFC) has found a solution that can give 100% control of TPP, and it is used by growers and farmers in Europe across some 50 to 100 thousand hectares of fields, so it is ready to roll out across NZ farms, right now, i.e., no waiting for further development.
The solution is, with hindsight, a bit of a doozer: its like a fly-screen for the whole field crop. Just as fly screens (if you keep them and the doors shut) will keep the house free of flies, mesh crop covers are a physical barrier, that keeps TPP, and just about any pest, from thrips to deer, completely off the crop, and therefore completely eliminate all crop damage. At the same time it lets most of the sunlight, air and all of the rain, irrigation and other sprays, e.g. for blight, through to the crop. The result is pest free crops, the result of which the research at the FFC demonstrated to be a 24% increase in total yield of all tubers and a whopping 125% increase in market grade tubers, i.e., over double the yield. When most yield improvement techniques are happy if they get an extra 5% increase, 125% increase is so good as to almost be unbelievable.
To be fair there are a few caveats. The increase was against an untreated control, but it still had an OK yield of 35 tonne / ha, but in the North Island, that yield would be zero. The acid test will be to compare mesh covers with the current best management option, i.e., chemicals, and do the cost – benefit sums. However, as annual costs are likely to be below the $1,000 / ha that some growers are already spending on chemical sprays, and with it ‘guaranteeing’ 100% control, regardless of the weather etc., mesh may well be cheaper than sprays and produce higher yields.
The next steps is to start producers trialling small areas of mesh on their own farms and expanding the experimental testing.
For more information see the TPP research report page on the FFC website.