Project Code: PRR18-030
Project Lead
Jean-Philippe Parent and Justin Renkema - Agriculture and Agri-Food Canada
Objective
To help berry growers diversify their toolbox with alternative solutions for management of white grubs in their crops
White grubs pose a serious threat to the Canadian berry industry. Various levels of feeding damage caused by these pests can lead to reduced yields and quality in strawberry, raspberry and highbush blueberry crops. Root feeding larvae of Japanese beetle (Popillia japonica) and European chafer (Amphimallon majale) are especially problematic on strawberries and blueberries grown in the Eastern Provinces. Additionally, the foliar feeding adult Japanese beetles can skeletonize entire strawberry plants, and this is becoming an emerging concern due to lack of control solutions available. The sustainable management of these pests was identified as a priority gap to be addressed by the stakeholder working group leading the Reduced-Risk management strategy for insect pests of berry crops of the Pest Management Centre.
This 3-year project (2018-2021) addressed pressing needs of berry growers for effective and diverse pest management tools to protect their crops against white grubs. Currently, imidacloprid is the only chemical soil treatment option available for these pests in berry crops. The project aimed to evaluate monitoring techniques for Japanese beetle and European chafer in berries and also determine the efficacy of various soil amendments, such as mulches and composts, and entomopathogenic nematodes (EPN) in supressing white grub populations in soil.
Approaches
To determine effective monitoring techniques, three types of traps were evaluated in 2018 in commercial berry fields near AAFC's Vineland and Harrow Research and Development Centres in Ontario to assess their ability to attract and capture adult Japanese beetles, European chafer and June beetles. Commercially available Japanese beetle traps, light traps, as well as wireworm traps developed by Dr. Christine Noronha (AAFC) were deployed in strawberry, highbush blueberry and raspberry fields. Traps were monitored weekly for several weeks during the season, and collected species were identified and quantified throughout this period.
In 2019, the monitoring technique trials were expanded to include commercial highbush blueberry and strawberry fields in both Ontario and Quebec, as well as a vineyard in Quebec. An additional evaluation was included to assess the impact of insect traps on the white grubs population and level of damage in berry crops in the surrounding areas. This was investigated to determine whether the use of these monitoring traps were attracting increased numbers of pests compared to fields where no traps were installed and whether additional damage was observed in the monitored trial plots. This was achieved by measuring leaf damage to berry plants and determining larvae presence in soil samples surrounding the traps.
To evaluate the use of soil amendments and application of EPNs for controlling white grubs, laboratory investigations and micro-plot trials were conducted at the AAFC's Vineland Research and Development Centre in Ontario. Larvae of both Japanese beetle and European chafer were exposed to soil amended with different combinations of mulches and compost substrates, and two EPN species, Heterorhabditis bacteriophora (Natural Insect Control, Stevensville, Ontario, Canada) and Steinernema scarabaei (Evergreen Bio Innovations Ltd., Ajax, Ontario, Canada). Soil amendment treatments were:
- mixture of woodchips and sawdust (1:1 by volume);
- horse manure plus the woodchips and sawdust mixture (1:1 by volume); and,
- municipal compost plus the woodchips and sawdust mixture (1:1 by volume), all placed as a mulch layer on top of the soil. A soil alone (no-mulch) control was also included. An additional treatment was adding a drench application of one EPN species (either H. bacteriophora or S. scarabaei at a rate of 50 infective juveniles per centimetre squared) to bare soil and each of the amended soil combinations. A water only control was also included. Larval mortality was assessed in soil alone, in soil amended with substrates (without added EPNs), and in soil receiving both the amendment and EPN treatments at 10 days and 20 days post exposure.
Results
Of the three insect traps evaluated in this project, the commercial Japanese beetle trap was very effective at attracting and capturing large quantities of Japanese beetles in berry crops, with peaks higher than 100 adults trapped. This trap specifically targeted Japanese beetles and did not capture other species. The wireworm trap and the light trap were not effective at attracting Japanese beetles, European Chafer or June beetles. Lights traps captured about 5 to 10 adults on average, while no beetles were caught in the wireworm traps.
The negative impact of using the Japanese beetle traps in berry fields was variable throughout the duration of this project. While these traps were very efficient at attracting Japanese beetles, some increased damage to the surrounding vegetation was observed near the traps. However, given the high variability, no significant trends in changing population abundance and foliar damage could be identified compared to areas containing no traps.
Several of the evaluated treatments combining soil amendments and EPN species showed high rates of mortality of both Japanese beetle and European chafer larvae in laboratory trials. Soil amendments containing horse manure or municipal composts (with no added EPNs) caused high mortality rates of 90 to 100% for 2nd instar of Japanese beetle larvae after 20 days of exposure, but only 60% mortality for 3rd instar. Adding treatments with the EPN H. bacteriophora caused high mortality (85 to 100%) of both 2nd and 3rd instars of Japanese beetle larvae regardless of the type of soil amendment. Mortality of beetle larvae exposed to S. scarabaei was lower than other treatments and was highly variable, depending on the soil amendment used. Rates of mortality were variable for both species of beetle larvae in the micro-plot trials. Overall, combining applications of H. bacteriophora with mulches and composts showed promising results as an alternative approach to reduce white grub populations in berry crops. However, additional studies are needed to further explore and determine the best timing and rates of applications for optimal efficacy of these practices and to confirm the feasibility to scale up these practices in commercial farm settings.
Conclusions
To better understand white grubs in berry crops, effective insect traps are required for their surveillance. This study indicated that commercial Japanese beetle traps are a useful tool for monitoring Japanese beetle populations in berry crops, but are not for other beetle species impacting these crops. A combination of H. bacteriophora and soil amendments containing composts demonstrated a potential to achieve integrated management of larval stage of Japanese beetle. Further field tests are required to confirm the applicability of these practices as efficient and economically viable pest control methods for berry growers. Adoption of promising approaches resulting from this project may help growers minimize reliance on, and use of pesticides in berry crops while effectively protecting yields.