Oystershell scale: a major problem in cotoneaster hedge in Calgary

 In last few years, the cotoneaster hedges are severely infested by Oystershell scale which causes die back of the hedge, fail to leaf out and make dead patchy spots. Oystershell scale affects several plant species including apple, Hawthorne, lilacs. It is a major problem in cotoneaster hedge in Calgary and surrounding areas. Developing oystershell scales feed by sucking the fluids of cells underlying the bark, often killing the cells at the feeding site.

Over winter eggs under the shells of dead mother scales hatch in spring, and crawlers emerge and move about to find new sites and start sucking plant juices and secrete a protective shell. Within few of months, they gradually increase in size and become full-grown in midsummer. Eggs are laid in late summer and early fall and the mother scale dies at the end of the season. Eggs produced in late summer remain under the protective wax cover of the mother throughout winter.

Oysterscale is one of the “Armored Scales” in which adult has the outer shell that is impenetrable to traditional pesticide sprays. Therefore timing of treatment is very crucial for controlling Oystershell scale.

The best defense against Oystershell scale is prevention, keep the hedges healthy by thinning the thick ends of branches and stems to allow more light and air penetration to the inner canopy.

If the Oystershell scale only affects a small area, spot spraying with insecticide kills the bugs and stop further spreading. The best time to spray the insecticides is immediately after babies, called “crawlers,” are hatched and have not developed their protective armored coating. This is generally from first week to third week of June in Calgary, depending on weather. Chemical spray is only effective during this time period. Spraying systemic insecticides offers control for several weeks.

However, if the infestation is really severe, it is better to mow the hedge back to about 6- 8″ above ground in late winter, before bud break.  In June when crawlers start feeding, spray the sprouting stumps. Monitor the pest population is required as new hedge starts growing.  Another spray application after 10-15 days will guarantee better control of the pest. A new hedge will grow back within a few years as long as the roots are healthy. Slow release granular fertilizers can be applied to enhance the growth of the hedge.

Margo moore June 11, 2016

Birch Leafminer: a major issue of Birch tree in Calgary

Birch leafminer is one of the most common leaf problems in Calgary and surrounding areas. The adult fly is a small, black and 4-winged insect. It is active between May and mid-September, and it has two or three generations per year. Leafminer overwinters as pupae in the soil beneath a birch tree. In spring, the emerging adults mate and the females fly to birch leaves to lay their eggs on new leaves. The eggs get hatched in 4 to 14 days. The newly hatched larvae feed within the leaf for 8 to 12 days before emerging from the leaf as mature larvae. Mature larvae then drop to the ground, where they pupate and remain in the soil until maturing onto the adult fly which usually takes 2 to 3 weeks and then they are ready to start the cycle again.

Leafminers cause damage by tunneling or mining between the surface of the leaf with a small brown or reddish-brown, irregular-shaped patch on the upper surface of the leaf. If the mine is occupied, the larvae can be seen when the leaf is held up to a light. Those injected leaves will often appear curled at the edges. The leafminer attacks before the leaves have fully expanded, thereby interfering normal development and deformed leaf. The damage can cause stress and weaken the tree, making it more susceptible to serious problems such as bronze birch borer.

The easiest way to control this pest is to keep your trees healthy by supplying enough water and nutrients. Birch tree needs more water than most other trees. Spraying chemicals for the big trees is not environmental friendly as chemicals will be spread to the surrounding environment. Since the larvae are protected inside the leaf, use of chemicals spray is not effective control measure. A new system of injecting systemic insecticide directly into the trunk of the tree has been developed and has shown promising results in controlling this insect. The best way to get rid of this problem is to call trained certified arborist and discuss the options of controlling this pest. It should be worthwhile to remember that injecting tree with the systemic insecticide at the wrong place and the wrong time will do more harm than injecting insecticide in correct way.