Developing improved crop protection options in support of intensification of sweetpotato production in Papua New Guinea

The project has developed improved crop protection options in support of intensification of sweetpotato production in Papua New Guinea, analysed the performance of the new crop protection methods, and communicated these options to end users. On-farm trials of the efficacy of an integrated pest and disease management strategy (comparing this with conventional agronomic practice) extended over the three provinces in which sweetpotato is most important (Eastern Highlands Province, Western Highlands Province and Jiwaka Province), and took place on multiple farms in each province over three production seasons. This was complemented by assessment of crop yields and economic performance in two seasons. This evaluation provided a rich data set from which the robustness of the performance metrics (pest and disease incidence, yield, and economics) for new options can be inferred. The new integrated pest and disease management strategy comprised: (i) the use of pathogen tested planting material, (ii) sanitation, removal of sweetpotato crop residues and weeds, (iii) isolation, separating new crops from existing crops by at least four meters, and (iv) pheromone traps for sweetpotato weevil. Compared with conventional practice, this led to measurable reductions in biotic threats to the crop, especially the two major weevil species, gall mite and scab. This, in turn, translated to increased yields. Over all trials, total yield of storage roots when crops were protected by the integrated pest and disease management strategy averaged 20.16 t/ha. This was almost double the yield in the control treatment consisting of conventional farm practice. An additional benefit was improved quality of the storage roots from the integrated pest and disease management strategy. Illustrating this, unmarketable yields in that treatment were lower (1.46t/ha) than in the control (2.25t/ha) whilst the all-important marketable yield was greatly increased from 7.99t/ha to 18.70t/ha. Importantly, these benefits were robust over sites and provinces rather than resulting from highly levels of performance in a few locations. For example, marketable yields in the control treatment never exceeded an average of 10.28 for any province yet were never below 17.44 in the integrated pest and disease management strategy treatment. This, in turn, led to a major economic advantage (i.e., comparing the net income from the new strategy, after cost of the additional labour and materials, with the net income from the conventional practice) that averaged across provinces 6,284 Kina/ha in the first year and 10,567 Kina/ha in the second year.

Complementary studies identified optimal forms of mulches, species of barrier plants to reduce pest ingress, and entomopathogenic fungi isolates that could be added to the pest and disease management strategy to enhance crop protection. Trials in Eastern Highlands Province and Jiwaka Province compared the expanded integrated pest and disease management strategy with the original best bet strategy. Changes in net income in Jiwaka Province trials from use of mulches were more attractive than the original strategy (giving an average advantage of 1,883 Kina per hectare extra compared with conventional practice) but highly variable across sites and on average negative in the Eastern Highlands. In contrast, adding barrier plants to the best bet strategy gave robust economic benefits in both provinces with an average of up to 12,23 Kina per ha in Jiwaka Province. Laboratory bioassays with a still wider range of entomopathogenic fungi have identified isolates with activity against both weevil species. Two strains of the Metarhizium that were isolated from PNG soils (Western Highlands Province and Unitech Agri. Farm in Morobe Province) were produced on a larger scale to evaluate in an additional trial on the Unitech farm and Poahom village (Morobe Province). These have scope to enhance pest suppression in future work. An additional series of field trials was conducted to partition the respective effects of pheromone traps for weevils, of crop sanitation, and crop isolation, each when paired with the use of pathogen tested planting material. Weevil control, yields and economic performance all benefitted in treatments where pathogen tested planting material was complemented by one or more other method, compared with conventional practice. Overall, multiple different combinations of methods from the ‘toolbox’ of plant protection options can be used with confidence to complement pathogen tested planting materials. Crop isolation, sanitation, mulching and barrier plants are all methods that are likely to have direct or indirect negative effects on virus vectors so contribute to the durability of this germplasm. A range of communication initiatives have been made to deliver impact. An illustrated manual, method-specific information sheets, and animated presentations for social media have been developed to complement a series of farmer training sessions that were held in multiple districts in the Highlands. Overall, the project has addressed the need identified in the preceding Small Research Activity: that pests and diseases were considered damaging by growers but that use of plant protection interventions was uncommon. Growers now have a much more comprehensive ‘toolbox’ of validated methods, that have proven economic benefit, and considerable training and outreach to growers has occurred. The project leaves a legacy of communication materials that will support further adoption.