The Society receives many gardening questions. This page was created to share answers to some of the Frequently Asked Questions (FAQs). If you don’t see your question listed here, check out the options on the Gardening FAQs page.

Garden Diseases and Pests

How do I get rid of aphids? 

A strong blast of water from a garden hose is effective. It may be necessary to repeat the application. Using a soft, damp cloth to gently wipe sturdier plant leaves may work, as will handpicking. 

What can I do about carrot rust fly?

If you have a carrot rust problem monitor for adult flies by placing sticky yellow traps near the soil level. This will also trap adults and prevent them from laying eggs.

Manage the problem by:

  • Harvest carrots in blocks instead of individually or selectively as soon as they are ready.
  • Delay planting of carrots until after peak oviposition (egg-laying) period (mid-June)
  • Remove umbelliferous* weeds or space out umbelliferous crops
  • Rotate crops to non-susceptible hosts every year to interrupt the carrot rust fly’s life cycle and suppress population density.
  • Remove all crop residue at the end of the growing season to avoid creating overwintering habitat for carrot rust fly.
  • Use floating row covers (60 cm height) and place over the crop immediately after planting.

* celery, carrot, dill, or parsley family plants

There is also a commercially available beneficial nematode (Steinernema spp.) for carrot rust fly.

Chemical controls are not recommended for this pest as they are generally ineffective at suppressing large populations.

How do I prevent cutworm damage in the vegetable garden?

Keep the area around the vegetables absolutely weed free—this helps control the spread of cutworms because they like laying their eggs on plants that are not their food sources, such as grass. “Collar” your young plants as soon as they emerge out of the soil—you can raid your recycling bin and use empty toilet paper rolls or used single-serve yogurt cups (with the bottoms cut out).  Sink the collars about 2.5 to 5 cm into the soil.

How do I manage delphinium worms?

If you see newly sprouted delphinium leaves sticking together or misshapen, then you probably have delphinium worms. To address the problem, once the new growth has reached 15 to 20 cm tall, cut the growth back to 4 to 6 cm and throw the cuttings in the garbage. Delphinium worms are the larvae of a moth (Polychrysia esmeralda; syn. P. moneta). The worms can also be found on larkspurs and monkshood.

How do I deal with fairy ring in my lawn?

If the rings are small, you can remove the top 5 cm of top soil and turf and reseed.   

How do I deal with powdery mildew? 

Be sure to water only at the base of the plants and do not splash water on the leaves.  Do not over water.  Poor air circulation can encourage the spread of powdery mildew as well—try to separate individual plants so that they are not crowded together and if you have a fan, run it gently near the plants to keep air going over the leaves.  If the plants are really dense, you may need to prune out some of the leaves (but not too many!) to open up the crowns so that more air will pass through.

How do I get rid of red lily beetles?

Although there are some biological controls under trial, the best way to remove the beetles is by handpicking and have them drop into a bucket of soapy water.  Look for adults, larvae, and frass in the soil and on all plant parts.  Diatomaceous earth may be applied to the soil and the leaves (make sure you cover the undersides of foliage, not just the tops). Bear in mind that red lily beetles will overwinter in the soil. They will eat all true lilies (not day lilies), Fritillaria, lily of the valley, and Solomon’s seal.

How do I manage slugs?

Warm wet weather results in a healthy population of slugs. Slugs are soft bodied creatures. Creating a coarse barrier between your plants and slugs can help control these pests, with diatomaceous earth being a good option. Please follow the safe handling instructions on the package of diatomaceous earth.

Hand picking slugs off leaves in the morning or evening can also be used for control. Placing a half grapefruit peel (dome up) in the garden is an attractive shelter for slugs. Check each morning, squish the slugs inside and reposition in the garden. Replace the grapefruit rind when required.

Keeping space between plants and removing decaying foliage will also help by make the environment less inviting to slugs.

How do I prevent vole damage? 

Make sure your lawn is mowed in the fall, just before the snow falls—tall grass provides a place for voles to hide.  You can purchase or make cylindrical guards from hardware cloth for your trees.  Sink the guards at least 5 cm into the soil, and make sure the cloth covers the tree well above what the average snow line would be.  Snap-type mouse traps baited with peanut butter may also work to catch them.

Is there any way to prevent dew worms from making a mess of the lawn?

Spread gypsum or coarse sand over the mounds.  The dew worms will not usually crawl over abrasive surfaces. 

What is snow mould?

Snow mould is a type of fungus that is typically seen in the spring as the snow melts. The term can refer to several species of fungus and often is Microdochium nivale, a pink snow mould, or Typhula spp., a grey snow mould. It can look like a heavy coating of spider webs on garden detritus or the lawn. Often, it is only cosmetic, but a severe mould growth can kill patches of lawn. Treatment is to rake it up, but don’t rake mould containing debris across unaffected areas or the spores can be spread, and let the area dry out. Prevention is the best course of action against snow mould. Preventative measures include stopping high-nitrogen lawn fertilization by August, mowing the lawn short in the fall, and removing leaves from the grass before the first snowfall.

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