Japanese Beetle soil study

Japanese Beetles may have taken over your garden this year, fortunately, you’re not alone. Unfortunately, there isn’t much that can be done.

As my 3 year old would say “what the heck?” She’s right – what the heck are they doing all over all the raspberries? Not to mention roses, asters, and other native flowers and trees. And what the heck are we going to do about it? 

Japanese beetles are an invasive species that were first introduced to eastern North America in 1916, but introduced to Eastern Canada in 1939 (CFIA). This year, people are seeing more Japanese beetles than previous years and realizing that we have a problem. They seem to like high temperatures and humidity; unfortunately our warming seasons are going to make for more attractive conditions. But as they are an invasive species, we should be finding an ecological approach to making them less comfortable instead of learning to live with them.

What’s Agriculture Canada doing? 

In an interview with CBC News PEI, Christine Noronha, an etymologist with Agriculture Canada suggested two approaches to saving your plants. One approach is to introduce nematodes to feed on the grubs (the beetle’s larvae stage) to reduce the number of adults in the area. The second approach is to tackle the adults, by hand picking them off or using a bacterial spray on the adults. But are these approaches working?

What is Soils Alive doing?

In a complete soil food web, nematodes are present. As are sufficient bacterial and fungal biomass to support the plant’s needs, and of course protozoa. My theory is that plants are being targeted are due to plant stress caused by an incomplete soil food web, specifically low fungal biomass. That’s what is being assessed in this study. 

Stressed plants

We know that when a plant isn’t receiving sufficient nutrients, it becomes stressed. Stressed plants send out pheromones that insects pick up and interpret as a food source. The more stressed a plant is, the more attractive it becomes to an insect. A plant with insufficient soil biology to support its needs may exhibit signs of stress. 

While introducing nematodes isn’t a bad idea, once the food source is gone the nematodes will go too. If we maintain a complete soil food web, the nematodes will always have food to keep them around. 

Study summary

In this study, the whole soil food web is being assessed, but specifically the fungal biomass. Many of the plants targeted are higher in succession, requiring fungal biomass of at least 270 microg per g (and up to 9000 microg per g for deciduous trees); and a fungi to bacteria ratio of 2.0 to 5.0 for some plants, and as high as 10 for others. Additionally, colonization of mycorrhizal fungi is required for higher succession plants. 

In our urban environments where we like to plant things based on sun, space and convenience, we sometimes forget about the conditions below ground and ensuring the soil is optimal for the plant. 

If you live in the Ottawa area and interested in participating, please contact us to visit and collect a sample. Samples will be collected until the end of September. 

Check back for study results and stay tuned for updates on the study next spring. 

Published by juliamdupuis

Green Angel Sustainability Consultant. Environmental Chemist. RRU MEM Graduate.

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