New ways to grow sweet potato

Sweet potato production in the Highlands had been affected by pest and disease. The National Agricultural Institute with partners sought ways to improve sweet potatoes production, writes Nari crop protection officer WILFRED WAU

FOOD security is a very critical concern for many countries around the world.
For Papua New Guinea, there is a growing need to effectively sustain the production and supply of staple crops such as sweet potato.
In recent years, sweet potato production in the highlands region has been affected by pests and diseases such as weevils, scab and gall mites.
The National Agricultural Institute (Nari) has partnered with Fresh Produce Development Agency to address these challenges.
This has been done through a project funded by the Australian Centre for International Agriculture Research and implemented with the support of the PNG University of Technology, Charles Sturt University and University of Southern Queensland.
The project is aimed at introducing improved ‘best-bet’ crop protection options to support intensive sweet potato production in the country.
The first phase was completed in 2018.
The project is now in the middle of its second phase.
The trials conducted in farmer fields compared farmers’ current (conventional) practices with improved best-bet practices.
Best-bet refers to pest management options that have shown to be effective in other countries and supported through the global pool of knowledge.
The best-bet options include the use of methods like crop isolation, pathogen-tested (PT) planting materials, pheromone traps and crop sanitation processes.
Conventional or traditional farming methods used by sweet potato farmers may minimise or increase threats of pests and diseases.

Such practices include leaving remains of harvested crops in the plots to decay; using planting materials from old gardens to make new garden; making new garden close to old ones, though these have been practiced over time, lack of proper understanding has resulted in these being ineffectively used, across farms and fields.
This has affected the general health and yield of sweet potatoes.
Recent trials have found that the level of pests such as gall mites were higher in the traditional sweet potato plots than in the best-bet trial plots.
In the process of introducing the new ‘best-bet’ options, farmers have also been able to learn and understand the potential of some of their traditional practices for preventing pests and diseases attack on their crops.
This has motivated farmers to appreciate and properly use those methods to reduce risks of crop loss and thereby improve the quality and of yields.
Crop isolation involved planting new (trial) sweet potato plots at least five metres from existing plots.
This is to ensure sufficient distance to reduce incidences of pests and diseases entering new sweet potato plots.
Trails have established that the gap between new and existing plots had actually minimised the transfer of pests such as weevils.
It is advisable to maintain the five metre gap around the whole garden and be fallowed with non-crop weeds or rotated with legume crops.
Sweet potato viruses (pathogens) are a major threat to the local sweet potato industry.
They can affect between 50-90 per cent of yields.
Viruses are mostly spread when farmers use infected seedlings and planting materials.
To avoid this, Nari has taken sweet potato varieties that are currently traded in roadside and urban markets through a process that eliminates all viruses.
This virus free or PT sweet potato planting materials had been multiplied and distributed to farmers.
Pheromone traps are commercial lures that were used to attract and capture sweet potato weevils.
The lures were placed inside traps made of one litre soft drink bottles which were cut in the middle and half-filled with solutions of household detergents.
The lures were held in place by a hook inside the bottles.
Four of these traps were set at corners of the trial plots; a 100 square metres from the conventional ‘control’ plots.
The traps were renewed every six weeks. This resulted in a marked drop in weevil attacks and improvements in the quality of sweet potato tuber yields.
It is possible to achieve these results with limited use of commercial insecticides.
Crop sanitation processes involved in identifying and removing plants that enable diseases and pests to breed and spread into sweet potato fields.
It was also important to collect and burnt remains of harvested crops.
These can be done manually about five metres around plots before and during the growing season to get rid of virus disease vectors such as aphids and whiteflies.
So far, there have been two phases of trials conducted in Eastern Highlands, Jiwaka and Western Highlands.
Each province has four trial sites. Goroka sites are established at Kuka, Nipuka, Gimisave and Meteyufa in Asaro; Jiwaka’s are at Gusamp, Gunn, Kurumul and Kongabil; and the Western Highlands’ at Bombri, Mul, Baiyer and Tonga.
Encouraging results have emerged from trials under the first phase.
The best-bet weevil control package greatly minimised the impacts of diseases and pests.
In fact, the volume of marketable tubers yields from trials had doubled that of conventional plots, for the same period.
In October, a team of project partners from University of Southern Queensland, Charles Stuart University and PNG University of Technology visited the best-bet and conventional plots at the four trial sites at Asaro.
During the visit, they launched the second phase of the trials.
There was great interest and support from farmers in participating communities in the initial phase.
We look forward to continuing to work with them and our partners, under the new phase, to improve the standard of sweet potato farming in the smallholder sector.

• Wilfred Wau is a Junior Crop Protection based at Nari’s Aiyura research station in Eastern Highlands.