Spring's Here and the Insects are Munching

May-June 2008

WELCOME TO ANOTHER WHIRLWIND SPRING in southern Ontario. The leaves are out, the migratory birds are back and the insects are munching. Probably one of the most significant insect pests you saw in May was the viburnum leaf beetle. Yes I know, viburnums aren’t trees, but they are a very popular shrub that has been absolutely decimated by this beetle. Viburnum leaf beetle larvae hatch as the new foliage is emerging in the spring. They feed on the undersides of leaves and skeletonize them (leaving only the veins behind).

This spring, I am investigating the efficacy of a number of low toxic pesticides in their efficacy against the beetle larvae (insecticidal soap, horticultural oil and another essential oil product). Timing is everything though, and it seems as though viburnum leaf beetle larvae are most susceptible to insecticides within the first couple of weeks of egg hatch only. Monitor for tiny larvae (2-5 mm long) on the undersides of leaves. Most contact insecticides should work for the younger larvae, Success (spinosad) is registered on VLB’s cousin, the elm leaf beetle.

Squish, Smash, Karate-Chop
Gypsy moth larvae hatched at the beginning of May. Larvae can be found on several different kinds of plants during their early instar, silk-dispersal stage. When larvae are small, they don’t have those obvious pairs of blue and red dots down their backs, so identification of early instar larvae can be tricky. Early instar larvae are tiny, dark and very hairy, unlike most of the other caterpillars we see this time of year. Once larvae land at their feeding site, they migrate to foliage and start feeding which appears as small holes in the leaves.

When larvae start feeding, a foliar application of Bt (Dipel, Foray) can be used until the head capsule turns yellow and larvae grow to 1 inch long. Success 480 SC (spinosad) insecticide is another good product for Gypsy moth and the nice thing about it is that it’s effective even in the later stages of development. Success is a lower toxicity alternative to acephate and carbaryl.

Apply insecticides to both leaf surfaces where possible. Depending on how much time you (or your client) have on your hands, you can install a burlap skirt at the base of the tree to create a shady, protected area for larvae to hide during the day. These larval afternoon siestas usually peak near the end of May/early June. You will need to inspect burlap skirts and underlying bark crevices daily (1-3 pm is best) and remove/destroy larvae. Depending on your attitude, larvae can be squished/smashed/karate-chopped or for the more faint of heart, you can direct them to a bucket of soapy water. For some homeowners that have been plagued with Gypsy moth in the last few years, this can be a very satisfying afternoon activity.

In mid-June you can install sticky bands around tree trunks to help trap crawling adult females (they cannot fly) and prevent them from laying eggs in the canopy above. Because the females emit pheromones, trapped females on the sticky bands will attract males to the sticky surface, and trap them as well. I’m really hoping that all of this information is putting a smile on your face!

Insect/Mite Database
Dave Cheung is a graduate student working on a Master’s thesis at the U of Guelph. He is putting together a very practical database of high quality electronic images of common insect/mite pests of outdoor ornamentals. Dave is a fabulous photographer and a gifted entomologist. The image database will have free online access when Dave is completed!

We are taking photos of pests and host injury over the next two growing seasons so if you are seeing some pest infestations out there and you want to share samples (or locations), just let me know! We are looking for some of the less common pests and we need your help. Of course, you can always submit some of your own photos and we can include them in the database. Have some fun on the job!

For information on diseases and insect pests in mid-May to early June, check out OMAFRA Publication 383, Nursery & Landscape Plant Production and IPM for more detailed monitoring tables (Chapter #3). To order, call 1-800-668-9938.

Contact Information

This column is written by Jen Llewellyn, Ontario Ministry of Agriculture and Food and Rural Affairs (OMAFRA) Nursery Crops Specialist

Email any questions you have directly to Jen and we'll publish her response.

P: 519-824-4120 ext. 52671 • F: 519-767-0755

OMAF website: http://www.omafra.gov.on.ca/scripts/english/crops/agriphone/index.asp

Nursery Landscape Agriphone: 1-888-290-4441

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.