Biological management of two-spotted spider mites and cyclamen mites in strawberry

Project Code PRR06-160

Project Lead

Bernt Solymár - Earth Tramper Consulting Incorporated

Objective

To evaluate the efficacy of (i) a mite predator to control cyclamen mites and two-spotted spider mites and (ii) a mite predator to control cyclamen mites in strawberry fields

Summary of Results

Background

The strawberry industry in Canada is worth approximately $71 million (Statistics Canada, 2011), producing 19,888 metric tonnes on 3100 hectares (Statistics Canada CANSIM database 2012). The two-spotted spider mite (TSSM), Tetranychus urticae, is considered a major pest of strawberries in Canada. Infestations can reduce photosynthesis, causing a decline in overall health of strawberry plants which reduces both yield and quality. At high populations webbing and feeding activity can result in yield reduction in strawberry fields, particularly in hot, dry seasons. After renovation (the process of rejuvenating June bearing crops after harvest), the presence of high populations can stress plants and affect the plant’s ability to survive the winter. The cyclamen mite, Phytonemus pallidus, is a more sporadic pest of strawberries. The very tiny nymphs and adults feed along the mid-vein ridge of young, unopened strawberry leaves in the crown and can cause severe crinkling, stunting and reduced yield of strawberry plants. Miticides are the current management option for both of these phytophagous (plant feeding) species, but the risk of pest populations developing resistance, as well as environmental concerns and public perceptions of pesticide use have created a need for new, reduced risk approaches to managing mite problems on strawberries. This project was undertaken to assess the efficacy and risk reduction potential and demonstrate to growers the use of Neoseiulus (Amblyseius) fallacis and Feltiella acarisuga, two predators of two-spotted spider mite and cyclamen mite.

Approach

In 2006 and 2007, the two biological control agents, N. fallacis and F. acarisuga were released into 15 commercial strawberry fields in four provinces. Populations of the two-spotted spider mite and cyclamen mite were monitored every two weeks by crop consultants, as were the two species of predators, after release into the plots.

In 2008, due to supply difficulties with N. fallacis, another predator mite, Phytoseilus persimilus, was tested in the field.

On-farm trials to evaluate the use of mite predators were established in 5 geographic regions in Canada: the Fraser Valley in British Columbia, Norfolk County and the Ottawa Valley regions in Ontario, the Montérégie area south of Montréal in Québec and the Annapolis Valley in Nova Scotia, in primarily June-bearing strawberries. In each region, pest management consultants worked with local strawberry growers to monitor pest mites, release biological control agents and collect data on phytophagous mites and predator numbers.

Trials were established in at least second year plantings that were a minimum of 5 acres in size, were healthy and had a history of pest mites. Each planting included release (inoculation) blocks, approximately 2 acres in size for N. fallacis releases and ¼ acre for F. acarisuga releases. An additional 2 or more acres, without predator release, were used as the “check” or non-treated block in each planting. Most of the trials were conducted with June-bearing strawberries, however a few releases in day neutral strawberries were also included. Co-operating growers were asked to make pesticide applications only when pest populations reached provincially-established economic thresholds, based on pest monitoring reports.

The Cornell University Environmental Impact Quotient (EIQ) was used to assess the potential for pesticide risk reduction with the use of biological controls compared with conventional miticides.

Results

Although insufficient data were collected for statistical analysis, observations suggested that N. fallacis had potential to maintain two-spotted spider mite populations below the economic threshold and if established while cyclamen mite populations are low, may also be moderately effective against this pest. The predator was able to establish in strawberry fields following spring, summer and fall release timings. At many sites across the country, predatory mites were collected in both the check and release sites, suggesting that naturalized populations were present in low numbers.

Although P. persimilis cannot survive Canadian winters, it was shown to respond well to high levels of TSSM, suggesting it had potential as an effective short term miticide replacement, when the pest reaches the economic threshold.

F. acarisuga did not appear to be an effective predator of cyclamen mite in these studies, possibly because its development was negatively affected by extended periods of low relative humidity.

Calculations of the EIQ field use ratings for a single treatment of a number of miticides as compared to the use of N.fallacis, showed that the use of this biological control approach resulted in a substantially lower impact on the environment.

These trials were valuable in demonstrating to regional consultants and grower cooperators that the predator mites, N. fallacis and P. persimilis, have the potential to be used successfully in the Canadian strawberry industry as an alternative to miticides, and could reduce the pesticide risk and environmental impact of miticide use in strawberry production.

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