The overall goal of this project was to develop sustainable pest management strategies that can be used against key pests in papaya production in Hawaii. We tested three environmentally friendly products that are labeled for organic production: kaolin clay (Surround WP 50 lb/50 gallons, horticultural oil (PureSpray Green, 1%), and Beauveria bassiana (Botanigard ES, 1/2 quart/100 gallons). A total of six trials were completed at four field sites on the islands of Oahu and Hawaii. Kaolin clay was discontinued after the first year due to outbreak of mites and withe peach scale due to the applications. Botanigard was used during the second – third years of the project, but insect counts and yields for this treatment were not different from the standart practice. Botanigard was also the least cost effective treatment. The horticultural oil was, on average, the most cost effective treatment during the first and second years. The oil did not perform well in older fields that had pre-existing pests problems.
- Examine the effectiveness of organic pesticides kaolin clay and petroleum oil against papaya pests.
- Examine the benefits of sunn hemp living mulch as a trap crop for Thrips parvispinus.
- Demonstrate the benefits of strip-till sunn hemp living mulch for nematode and soil health management in a papaya orchard.
- Disseminate research findings to papaya growers and agricultural professionals.
- Conduct economical analysis of sustainable strategies for emerging pests of papaya in Hawaii.
Papaya is an economically significant crop for the State of Hawaii. Its value ranks ninth among Hawaii’s agricultural commodities and accounts for 50% of Hawaii’s total fruit production (NASS Report, 2010). Papaya is attacked by a number of pests. White peach scale (WPS), papaya mealybug (PMB), aphids, and Thrips parvispinus are major pre-harvest insect pests. They can significantly affect tree health, reduce yields, and increase production costs for farmers. PMB and WPS can also become serious post-harvest pests, and, therefore, result in rejection of export shipments (McHugh & Constantinides 2008). Aphids (various species) are important pests in non-GMO papaya, as they transmit papaya ringspot virus (PRSV). Farmers rely on extensive and routine chemical pesticide applications to manage these pests. Sustainable pest management methods for reducing damage from these pests were tested in this project with the objective to reduce dependence on toxic pesticides and target multiple pests at a cost effective rate.
Objective 1: a total of six field trials were carried out at four commercial papaya farms. Two treatments (horticultural oil and kaolin clay) were tested in 2011-2012 and two treatments (horticultural oil and Beauveria bassiana) in 2013-2014. On average, field size had a 1/2 acre and, as much as possible, treatments were distributed by groups of three rows each, with a three replications. For the standard practice, the farmers followed their regular spray schedule given pest status at that particular field trial. Sustainable treatments were sprayed every three weeks. Pest densities were recorded at a monthly level for the first six to eight months and at a weekly level during harvest period. Harvest data was taken weekly for a total of eight to ten weeks. During the harvest period, the following data was recorded: number of fruits and weight per papaya plant for a total of 30 plants per treatment. Fruits were classified by size and insect damage.
Objective 2 -3: Sunnhemp was overcast prior to the establishment of three field (two on big island and one on Oahu). Poor germination rates were observed during these trials, and, therefore, this objective/treatment was discontinued. Possible reason for poor germination rates observed was lack of rain during the planting in fields that are dependent on rainfall for irrigation purposes. A fourth trial was set up, and sunnhemp grew well in a irrigated farm on Oahu, but the farmer decided to turn the sunnhemp field and leave it fallow for several months before establishment of a new papaya field.
Objective 4: For the cost benefit analysis, harvest data (collected in objective 1) and records of pesticide applications were used to determine the cost to yield ratio for each treatment.
Objective 5: Multiple scientific and extension presentations have been given during the course of the project and we are currently working on peer reviewed and extension publications to further disseminate results of this project.
Results from this project showed that the oil treatment was the most effective at mantaining low densities of targeted arthropod pests when preventive sprays were started in young papaya plantations with no pre-existing pest problems. In these cases the oil treatment had the lowest densities of key pests compared to the standard practice and similar production rate at a lower cost (most cost effective treatment).
Kaolin clay did not provide effective control to any of the pests addressed in this project. This treatment caused outbreaks of mites and white peach scale, possibly due to disruption of existing natural enemies. This treatment was discontinued after the first year given that farmers were concerned about increase in pests densities and reduction of yield in their plots.
Botanigard treatment had similar pest densisties and yield as the standard practice but at a significantly higher cost. Given the high cost for pest control, this treatment is not recommended as a routine preventive spray in papaya production.
The oil treatment had more frequent sprays compared to the standard practice but at lower cost that standard practice.
Results from this project have shown that two of the sustainable treatments tested to suppress key arthropod pests addressed in project did not provide effective preventive control, were not cost effective, and, therefore, not recommended for use. The oil treatment was a cost effective treatment if preventive applications were started in young papaya fields with no pest problems (between four to six months after field establishment). The oil treatment did not perform well in fields that were over ten months old with some pest built up at the start of the treatments. In these situations, it is recommended to use conventional pesticides to reduce pest populations prior the start oil treatments.
Educational & Outreach Activities
Since this final report is submitted at the end of the last round of field trials, we are in the process of develping the publications for this project. At the moment we are preparing one extension publication and one peer review publication based on the findings of the project.
A website that include results of this project is also under construction.
We presented results of this project at multiple stages of the study and at multiple venues that include: Hawaii Tropical Fruit Conference 2012, annual grower’s conference of the Papaya Industry Association 2012 & 2013, Ag Pro 2013, Sustainable and Organic Agriculture Research and Extension Update 2013, and at scientific meetings (Entomological Society of America Annual meeting).
The economic analyses showed that the oil treatment was the most cost effective treatment when trials were done in young papaya plantations (between four to six months after field establishment), but not when trials were done in older fields (over 10 months after field establishment). The other treatments tested, kaolin clay and Beauveria bassiana, showed a high cost to yield ratio, and, therefore, are not recommended for use to control any of the pests in papaya production addressed in this project. Even though the oil was the best treatment when applied in a preventive manner at an early stage, in a regular IPM program other pesticides might need to be used depending on pests present and their densities.
All participating farmers have seen first-hand the benefits of the oil treatment, and they have started adopting the treatment and include it in their standard practice. Other farmers that have seen the field during a field day and seen the results at multiple outreach presentations have expressed an interest in adopting this treatment as a pest management strategy on their farms. We are in the process of developing more outreach material and expect that this will impact the adoption of horticultural oil in papaya production in Hawaii.
Areas needing additional study
Given that we got constrasting results with the oil treatment when we had plots with different age papaya plantation at the start of the study, it will be good to do follow up studies to determine the best time to start the the preventive treatments to have the best results with the oil treatment. It will also be good to test lower concentration rates. Even though there were no damaged fruit due to the oil spray, fruits in the oil treatment were more shinny than in the conventional treatment. If apperance of papaya fruit gets to be a concern, this aspect needs to be addressed by lowering oil concentration to a rate that is still effective at controlling pests.