Project Code: PRR18-040
Project Lead
Justin Renkema - Agriculture and Agri-Food Canada
Objective
To help growers diversify their toolbox through access to reduced-risk options for cyclamen mite management in strawberry crops
Background
The cyclamen mite (Phytonemus pallidus) can significantly affect strawberry production in Canada. High infestation levels can cause distortion, wrinkling and irregular folding of leaves, stunting of plants, necrosis of flower petals, and bronzing of ripening fruit, thus resulting in significant yield reduction and economic losses for strawberry growers. This pest was identified as a priority issue by a stakeholder working group leading the Pesticide Risk Reduction Team’s Reduced-risk management strategy for insect pests of berry crops. In light of the loss of key pesticide uses for this pest (for example diazinon and endosulfan) due to regulatory re-evaluation, many growers currently rely on repeat applications of the miticide abamectin. Therefore, strawberry growers need additional control options to enable effective management of this pest.
This 2 year project aimed to assess the effectiveness of various control approaches, such as steam heat pre-treatments of strawberry transplants and a series of pest control products, including conventional miticides and biopesticides. An additional study compared the distribution of cyclamen mite in Ontario, where it is an established pest, and in Saskatchewan, where it is an emerging pest as well as investigated the effects of field mowing on mite populations.
Approaches
This project was conducted at Agriculture and Agri-Food Canada’s (AAFC) London Research and Development Center at the Vineland campus in Ontario, as well as in commercial strawberry fields in Ontario and Saskatchewan from 2018-2020. To evaluate the efficacy of steam treatment to reduce populations of cyclamen mite, strawberry transplants (‘Jewel’ and ‘Annapolis’ cultivars) from a Nova Scotia nursery were infested with cyclamen mites, and then treated with steam prior to being set in small plots at AAFC’s Jordan Farm near Vineland.
The efficacy of several crop protection products was also evaluated in bare-root strawberry transplants from a Nova Scotia nursery that were set by-hand in AAFC’s Jordan Farm. Following infestation with cyclamen mites, plots were treated with seven different products including the registered conventional miticide Agri-Mek SC (abamectin), unregistered conventional miticide GWN-1708 (fenazaquin), and unregistered biopesticides: Grandevo (Chromobacterium subtsugae strain PRAA4-1); Ecotrol (Rosemary oil, peppermint oil, geraniol); Bp Protec (Beauveria bassiana strain R444); Vegol (Canola Oil); and the mix of Venerate (Heat-killed Burkholderia spp. strain A396) and Ecotrol). Agral 90 (surfactant) and water were used as negative controls. Single applications of conventional miticides and duplicate applications of biopesticides were used.
Infested plants were then monitored one and two weeks after applications for impact of each treatment on cyclamen mite populations and mortality throughout the season. For transplants that received heat treatments, the plant survival, number of leaves and number of runners was monitored throughout the season. Strawberry yield and damage on strawberries were also evaluated in the following 2020 growing season.
In addition, to gain information about the impact of field renovation (mowing) and winter weather on cyclamen mite in strawberry fields, populations were monitored in commercial field sites in both Ontario and Saskatchewan. Matted-row, short-day (June-bearing) strawberry cultivars are commonly mowed just above the crown 1-2 weeks after harvest ends. The populations before and after mowing were compared, and the fall and spring population dynamics were examined.
Results
Several of the tested approaches showed promise for reducing cyclamen mite populations in strawberry transplants that were set in field plots. Steam treatment of transplants was an effective way of removing cyclamen mites prior to setting in the field without detrimental effects to strawberry yields. Treating strawberry transplants at 44 degrees Celsius (°C) for 1 hour (h) reduced cyclamen mite population by an average of 99%, while maintaining survival rates of plants that were similar to those that received no heat treatment. Transplants treated at a higher temperature for a shorter time (48 °C for 0.5 h), also dramatically reduced cyclamen mite populations, but damaged strawberry plants in the process. In the following season (2020), there was no yield difference between transplants treated at 44 °C for 1 h and untreated transplants for either ‘Jewel’ or ‘Annapolis’. In fact, ‘Jewel’ plants treated at 44 °C for 1 h had nearly 50% more yield than untreated plants. For ‘Jewel’, the average number of cyclamen mite damaged strawberries per plot for the entire harvest was just over six, whereas in plots with plants treated at 44 °C for 1 h, the average number of cyclamen mite damaged strawberries was 1.5, that is, reduced by 75%.
For controlling cyclamen mites in established field strawberry crops, the unregistered product, GWN-1708 was the most effective at reducing the cyclamen mite populations. Under the conditions that were tested, this product was more effective than the registered product Agri-Mek SC. Of the five biopesticide products tested, the combination of Venerate and EcoTrol resulted in the lowest number of cyclamen mites; however applications of these products did not result in significant differences compared to the untreated controls, and were not as effective as GWN-1708. The other tested biopesticides did not reduce cyclamen mite populations. In the following season (2020), total strawberry yield and the number of strawberries with cyclamen mite damage (scarring and bronzing on the fruit surface) was not significantly affected by miticide or biopesticide treatments. However, GWN-1708 treated plots tended to have the most yield and lowest number of cyclamen mite damaged strawberries.
The results of monitoring commercial strawberry fields for cyclamen mite populations in Ontario provided useful information about the distribution of this pest throughout the growing season. The average population of mites per sample was approximately 10 times greater before growers mowed fields than it was after mowing. The cyclamen mite populations were also monitored in the fall 2018 and were compared to populations in the spring of 2019. Almost no mites were found in fields in May 2019, likely due to overwintering mortality of a large majority of the population. No cyclamen mites were found in Saskatchewan at any time throughout this study, which confirmed that it is not yet an established pest in this area. These results show that mowing as part of field renovation helps reduce mite populations, but that the reduction is not great enough to replace the recommendation to apply a miticide following mowing. Overwintering mortality is significant in southern Ontario, but cyclamen mite populations will rebound to high levels during the spring and early summer from surviving individuals. Future efforts should focus on determining miticide and biopesticide application efficacy in spring when populations are low.
Conclusions
This multi-pronged study aimed at evaluating several reduced-risk options including, sanitation measures, foliar crop protection products, and cultural approaches to help reduce the damage caused by cyclamen mites in field strawberry. There are currently limited options available in Canada for the control of cyclamen mites in strawberry. This project showed that steam treating transplants, and field applications of fenazaquin were both effective at reducing cyclamen mite populations in strawberry plants. This project also provided valuable information about cyclamen mite population dynamics and distribution in Canadian strawberry fields at various times throughout the growing season and geographic areas. The above approaches and knowledge, combined with the sanitation measures determined in this project, provide useful solutions for growers to help with integrated management of cyclamen mites in strawberries.