Keep Those Tree Bands Sticky & Water Your Trees!

July-August 2008

Diseases and Insect Pests in Mid-July to August (pdf)...

BY THE TIME YOU READ THIS, we will have made it through another significant season of Gypsy Moth defoliation. I don’t know about you, but I was finding the caterpillars everywhere this spring. The worst damage always comes during the last couple of weeks of larval feeding. One thing we did see was some good parasitism of the larvae. Quite often we would find the larvae with a little white egg on their back, or clutching a white pupal case against the bottom side of their abdomen. These little hitchhikers are the larval stages of parasites, little parasitic wasps. And are they ever cool to see! If we get enough wet weather during late larval development, often times we will see a crash in the population due to a pathogenic fungus that kills the larvae, leaving the dead bodies hanging loosely from tree trunks; also nice to see. At this time, keep those tree bands sticky and up around the trees. If possible, try to place tree bands above visible pupal cases (otherwise emerged, flightless females will still be able to navigate up high in the tree to lay their egg masses). When removing tree bands, be prepared to scrape off egg masses behind and below the band. The vast majority of trees will recover from defoliation – the best thing you can do is provide those trees with a long, slow irrigation during hot, dry periods.

Stressed-Out Conifers
I’ve had a lot of complaints about needle drop and dieback on conifer species so far this year. This isn’t surprising given how hot and dry the growing season was in 2007, 2005, 2003 and so on. Trees can take 1-3 years to show symptoms of abiotic stress and they can take another few years to recover (or not). The usual suspects include: Austrian pine and Norway and Colorado spruce. Look down at the ground and you will see that these are usually established specimens that are found near driveways, sidewalks and other impermeable or compacted surfaces. Quite often they are packed in tightly with other trees and having to compete for light, water, nutrients and air in the soil. Another thing you will notice about the “usual suspects” is that they are quite often the more exotic species. Blue cultivars of Colorado spruce can be gorgeous trees, but our tough soils and extremely hot summers can take a toll on these beautiful specimens. Colorado spruce seems to be especially sensitive, exhibiting needle discolouration (brown to reddish-purple) and premature needle drop. But wait a minute, doesn’t that sound like a needlecast disease?

Get out your hand lens and take a close look at the needles from the 2006 and 2005 growing seasons on your spruce. Look closely at the individual needles and you will see rows of white dots, those are the stomates. When spruce trees are infected with Rhizosphaera fungus, the white stomates turn black. If none of the 2005 and 2006 needles have black stomates by now, chances are it is not Rhizosphaera needlecast and that either another pest is to blame or the tree is suffering from some sort of abiotic stress. Stressed Austrian pines are often inflicted with Diplodia tip blight – the needles start to emerge in the spring and suddenly die and do not finish emerging and elongating. Unfortunately, both of these diseases can be associated with stressed trees and prolonged leaf wetness periods in the spring (often plant canopies are crowded together).

So, what can we do to help our conifers recover from these tough growing seasons? We can take steps to provide the best soil conditions for the roots to grow and maintain the tree. By opening up compacted soils with fertigation injectors and aeration injection systems, we can encourage pathways for water and air to enter the soil. This can go a long way in helping trees recover. Most importantly, we can avoid compacting, disturbing and paving over the soil around the root system in the first place. We can provide the root system with as big an area as possible to absorb water, nutrients and air. When it’s been dry for a while, we can do some long, slow, deep watering of the tree root system (which extends way beyond the drip line). We can plant trees a little further apart so foliage can dry out after a rain event (this is a tough one for me). We can try to plant more species and perhaps mix native and non-natives where possible.

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:

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.