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Saturday, May 18, 2024
Growing Together: What’s bugging your garden?
Japanese beetles eat the leaf tissue of more than 300 species. (Joanne Young)
An adult box tree moth. (Joanne Young)

No one ever said that gardening is without its challenges. If it were all easy-peasy, well, where is the fun in that?

It is the challenges that keep us invested in our gardens, keep us learning and keep us persevering while trying to conquer all that nature has to throw at us. 

The key to winning the battle over any insect or disease problems in the garden is to be constantly monitoring your plants – at least on a weekly basis.

If you can catch the issue early on – nipping it in the bud, so to speak – it is much easier to get ahead of the insect or disease damage before the health of the plant is compromised.

By catching it early, it also means that you can possibly treat the problem with the need of using strong chemicals which should never be your first method of control.

Here are a few insects that I have been seeing as I visit different gardens in the area.

The box tree moth (Cydalima perspectalis) is a relatively new inhabitant in Ontario. As the name indicates, it is primarily found on all species and cultivars of boxwood plants, although there have been reports of them on pachysandra as well.

The box tree moth is native to eastern Asia and made its Canadian debut in 2018 with the first report of it in the Etobicoke area and first spotted in the Niagara-on-the-Lake area in 2021.  

The adult moth is medium in size, with a wingspan of about four centimetres. It has white wings with thick, dark brown borders around the entire wing. The body of the moth is also white with a few dark brown specks on it. The larva form is a caterpillar that can reach up to four centimetres in length.

When the larvae first hatch, they are greenish and yellow in colour with a shiny black head. As the larvae mature, they become more green in colour with thick black and thin white stripes along the length of the caterpillar.

It is the larvae that cause damage to the boxwoods as they devour the leaves quickly, just leaving the midrib of the leaf in place. In a matter of a couple of weeks, your boxwood can go from a healthy green to brown or defoliated. 

There can be two to three generations per year. The adult moth only lives for about two weeks, but before they die, they lay eggs on the underside of the boxwood leaves in clusters of 10 to 12 eggs. The eggs hatch in three days and the young larvae feed on the underside of the boxwood leaves and start to form webs between the leaves.

It takes about 14 days for the larvae to mature and pupate. Pupae live about 14 days before becoming adults. The box tree moth overwinters in the larval stage, by spinning a silky cocoon between the leaves.  

Routinely examine your boxwoods for signs of chewed leaves, caterpillars, webbing, and frass (a fancy term for caterpillar poop). The best times to check for larvae and to spray the caterpillars are May 15 to June 15, July 15 to Aug. 15 and Sept. 1 to Sept. 20.

Use a biological control called BTK (Bacillus thuringiensis var. kurstaki) for best control. If you are still seeing caterpillars feeding five to seven days after the first spraying time, repeat the application of BTK. You can also hire a professional to spray for you.

The Japanese beetle (Popillia japonica) is a species of scarab beetle. If you haven’t been seeing them yet in your garden this summer, you will be seeing them in the next couple of weeks.

The beetle has an iridescent copper-coloured body and a green thorax and head. The adults measure about 15 millimetres in length and 10 millimetres in width.

Whenever an insect finds its way to a different part of the world, it usually becomes a big problem quickly because there are no known predators here to keep them under control.

The adult beetles are known as skeletonizers, meaning they eat away all the leaf tissue until just the veins remain. They feed on more than 300 species of plants with some favourites being roses, grapes, lindens, birch, cannas, hibiscus, rhubarb and Virginia creeper.

This will not kill the plants, but it does make them unsightly. However, the grubs (larvae form) can play havoc with your lawns. If you have ever had a lawn to look after before, you will be familiar with white grubs which are the larvae of the Japanese beetles, which feed on the roots of grass, killing patches of your lawn.

The larvae overwinter deeper into the soil and will then pupate four to six weeks after breaking hibernation. The adult beetles typically appear mid to late June and will be visible for 30 to 45 days.

The best control for the grubs is applying nematodes to the lawn. Nematodes are microscopic organisms already present in the soil that feed on and reproduce inside the white grubs.

The next best time to treat your lawn with nematodes would be late August to early September. The best way to treat adult beetles is hanging pheromone traps.  If you have just a small number of beetles present, one of the easiest ways to deal with them is to hand-pick them and drop them into a pail of soapy water.

Remember, not every bug in your garden is a bad bug. Take some time to learn about them before resorting to sprays that will kill beneficial insects as well as harmful insects.

Joanne Young is a Niagara-on-the-Lake garden expert and coach. See her website at joanneyoung.ca

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