Fall Troubleshooting

Gardening expert Conway Lum on fall lawn care and tent caterpillars in B.C.

Credit: Flickr / jurvetson

Overseeding Season
Fall is a good time to overseed an existing lawn, before the ground becomes too cool for seed germination. This practice, commonly using perennial rye blends, is an effective way to thicken a lawn that has been subjected to wear and tear by kids or pets. It can also crowd out weeds and prevent them from getting established. Be sure the soil is evenly moist and water if the weather is dry.

Tent Caterpillars
These voracious feeders can be seen in the spring feasting on certain deciduous trees and shrubs. Tent caterpillars get their name from the silk webbing or “tent” that the larvae form among branches. The caterpillar emerges from egg masses that resemble a dark, shiny belt encircling a twig. These masses are especially noticeable during winter months. The adults emerge in midsummer as moths (there is only one generation per year). Two types of tent caterpillars predominate in B.C.:

Forest Tent Caterpillar (Malacosoma disstria):
• Caterpillars are bluish-grey with a prominent row of whitish, diamond-shaped spots along the back;
• Mainly found in Interior regions of B.C.;
• Migrate high in the tree to feed on opening buds or flowers;
• The larvae do not form a tent with their webbing but rather a webbed mat where they congregate in a group;
• Host plants include maple, oak, poplar, birch, elm, linden, ash and roses.

Western Tent Caterpillar (Malacosoma californicum pluviale):
• Caterpillars are hairy, yellowish-brown, with a row of blue spots flanked by orange spots along the back;
• Occur in southern half of B.C. and along the north coast;
• Larvae (caterpillars) usually stay in a group and build an increasingly large silken tent between branches;
• Specific host plants include arbutus, holly, apple, plum, cherry, willow poplar, hazel and California lilac.

Recommended Control:
• Prune out infested branches during the tent stage (wait until evening when caterpillars are back at their nest). Destroy the caterpillars by crushing them or drowning them in soapy water.
• Check for egg masses on branches in winter. Prune away branches infested with egg masses and apply dormant oil, as directed on label, to the tree to prevent further outbreaks.
• Encourage parasitic wasp by planting catnip (Nepeta cataria) or Queen Anne’s lace (Anthriscus sylvestris). The wasps will lay eggs on the caterpillar and parasitize it.
• Select a low-toxicity insecticide, such as Btk (Bacillus thuringiensis), and apply as directed on label.

Conway Lum is a Certified Horticultural Technician at Mandeville Garden Centre in Burnaby. Questions can be mailed to Conway at GardenWise, 4th Floor, 4180 Lougheed Highway, Burnaby, B.C. V5C 6A7 or emailed to clum@canadawide.com.