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Download the full report – Tomato Potato Psyllid and Blight Management with Mesh Crop Covers: Second Year’s Results and Future Research Directions. July 2013. Report number 5-2013.
- Following a successful ‘scoping’ field trial in 2011/12 that demonstrated the potential for mesh crop covers to control Tomato Potato Psyllid (TPP) and blight on potatoes, an expanded and improved trial was undertaken in 2012/13.
- The trial compared two contrasting mesh crop covers: a Cosio glasshouse quarantine mesh and a Crop Solutions field mesh, with an uncovered (null) control on potatoes (cv. Moonlight) to study the effect of mesh on TPP, yield, both gross and marketable, blight, temperature and humidity.
- The meshes were highly effective at keeping TPP off the potatoes, even with deliberately imperfect sealing of the mesh to the soil. Even where TPP did get under the mesh, they did not proliferate under the sheets.
- The effect of both meshes compared with the control on yield was substantial, with a 23% increase in yield for total yield (tubers > 1 cm diameter) with a maximum yield of 43 tonnes•ha 1 and a 125% (more than doubling) of yield for market grade tubers > 125 g with a maximum yield of 30 tonnes•ha 1, with all differences being statistically significant. There was no difference between the meshes. Considering the effect of TPP on potatoes is generally not large in Canterbury, these differences could be small compared with other potato production regions, e.g. Auckland, Manawatu, Hawkes Bay.
- The effect on tuber size was also very clear with mesh covered tubers having a 55% to 63% increase in mean tuber weight and a 48% to 58% increase in maximum tuber weight compared with tubers from the control plots.
- The effect on sprouting after 51 days of storage in a cool environment was clear-cut with zero sprouts on mesh covered tubers an average of 5.4 sprouts on control tubers.
- The visual effect on crop growth was clear, with all treatments emerging at the same time, but the mesh treatments growing faster, with the Cosio the fastest, but with the haulm under the Crop Solutions mesh senescing about two weeks before the Cosio mesh and the haulm never senescing in the control plots.
- The effect of mesh on blight (a range of foliar fungal diseases including Phytophthora infestans and Alternaria spp.) was also visually obvious, with control plots having considerable blight levels, with much lower levels under the meshes, with the Cosio mesh having slightly less than Crop Solutions.
- There were no large differences in trapped sporangia numbers between the treatments but the Cosio treatment potentially had slightly lower numbers (although borderline for statistical significance), which correlates with the slightly lower foliar blight levels under Cosio mesh. However, as trapped sporangia are both a cause and result of foliar blight, the strongest conclusion that can be safely reached is that airborne sporangia are unlikely to be a dominating cause of the different foliar blight levels.
- The climatic data did not show any large differences between the treatments, including Smith periods, which, coupled with multiple problems with the data loggers, means that the ‘safe’ interpretation is that temperature and relative humidity do not appear to be the primary drivers of the differences in blight levels among the treatments.
- Without any clear cause of the difference in foliar blight, it is possible that there are multiple, cumulative causes, which will require manipulative experiments (as opposed to empirical field trials) to tease out.
- In summary, the results are fully consistent with the previous seasons trial, the two meshes produced identical yields, and similar blight effects, indicating that it was not just due to the properties of the Cosio mesh or a fluke result in the 2011/12 season.
- Taken together, the laboratory work and two seasons field trials are considered a potentially valuable spring board for future research, including:
- Multi-region field trials in New Zealand to empirically validate the results of these trials under a range of climatic and production systems and to compare mesh with current best insecticide treatments.
- Understanding the relative contribution of the multiple effects mesh has on the crop, e.g. reducing TPP and other pests, reducing blight (multiple fungal spp.), and the direct climatic and light interception effects of mesh, so that the design and use of mesh can be optimised.
- Understanding why TPP do not disperse under mesh, which may lead to better understanding of their host detection and dispersal biology which may lead to improved management.
- Resolve if 0.6 mm mesh hole sizes are essential for field use or if mesh with larger hole sizes, e.g. 0.8 mm and larger, are effective, because these are cheaper so they may improve the economics.
- Determine if mesh would be effective for potato tuber moth and aphid control / management in New Zealand, so one product could control all three pests.
- Confirm if mesh is effective at TPP management on field tomatoes, without causing side effects, e.g. fungal diseases.
- Discover the causal mechanism of how the meshes are reducing blight levels and if this can be improved.
- Investigate mesh crop covers for the control of a wide range of potato insect pests globally while suppressing blight / foliar fungal pathogens.
- Systematically look for insect pests and fungal pathogens of food crops globally to identify those where mesh crop covers could be a practical and economic control / management tool, especially there are issues with agrichemical controls. This is considered particularly relevant to developing countries as mesh crop covers are considered to be an ‘appropriate technology’.
Merfield, C. N., Geary, I. J., Hale, R. J. & Hodge, S. (2015). Field evaluation of the effectiveness of mesh crop covers for the protection of potatoes from tomato potato psyllid. New Zealand Journal of Crop and Horticultural Science. http://dx.doi.org/10.1080/01140671.2015.1015576. If you are unable to access a copy of this paper through your institution, please email me and I will email you an ePrint.
PowerPoint presentation from Potatoes NZ grower meetings in Ashburton and Pukekohe Oct 2013 – warning file size is 27 MB.