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Cedar Leaf Miner
by Marg Fleming
by Marg Fleming



1979 - BSc. Botany University of Toronto, 1981 - MSc. Forestry University of Toronto, 1982-1986 - Horticulture Teaching Master - Niagara College , St. Catherines Ontario., 1986 - 2000 - Owner/Operator of Cedar Valley Botanical Gardens - Brighton Ontario, 2000- Present - Manager of Horticulture Toronto Zoo

Public Speaking Topics - Perennials, house plants, garden design


June 9, 2002

Each year different weather conditions dictate future of problems we can expect in the garden as the year proceeds. Certain temperatures, diurnal conditions, rainfall, and other factors may become favourable for insect pests and therefore unfavourable for garden plants. One of the most visible of these insect pests this year is cedar leaf miner.

Cedar leaf miner affects only white cedar. The larvae of this small moth consume the cells located between the upper and lower leaf epidermis. Their feeding technique is analogous to consuming the filling from a sandwich and leaving the bread. With its internal cells consumed the foliage assumes a faded appearance. The tree loses visual density, and the interior branching structure of the plant is revealed.

Control is difficult because the larvae feed inside the leaf protected by the upper and lower skins, so contact insecticides cannot reach them. The succulent cells between these epidermal (skin) layers are effectively “mined” out, hence the common name “leaf miner”. To effect control only systemic insecticides (compounds absorbed and transported throughout the plant) can reach the insect within. One such product is Cygon 2E. 

Cygon 2E is better known for its effectiveness in controlling birch leaf miner. By simply “painting” a band of Cygon 2E on the trunk of a birch affected with miner, trunk cells can absorb and transport enough of the chemical and distribute it to the loftiest, leafiest branches thereby controlling the resident miners. Treating bushy specimens such as the white cedar involves careful spraying. Not only is Cygon 2E able to absorb through a plant’s epidermis, but ours as well! All precautions described on the product label must be observed to avoid contact with the skin.

In lieu of chemical treatment, we simply must temporarily accept the compromised foliage of birches and cedars. The affliction is seldom fatal. Different weather conditions and seasonal changes will naturally limit the life cycle of the insect responsible for the damage.

Right now, trim cedars back to remove resident miners, and burn the clippings. Be aware though that the natural form of pruning that miners bring about will ironically encourage a fuller specimen in years when conditions for the population of this pest are unfavourable and the tree is given an opportunity to recover.

Late frosts are unwelcome occurrences when tender annuals have all been planted out for summer show. Hopefully future frosts will be mild if they do happen to occur, and if this is the case, moist latent heat released by the warm soil during the night should avoid fatal damage to newly planted annuals.

Cool weather is ideal for the growth of lawns, and late frost can affect turf in a different way. Blades of grass become stiff with frozen dew that eventually melts as the day warms. The blades become supple again in the mild temperatures and growth resumes. But turf which is walked upon before the frost has disappeared will sustain some minor damage. Stiff, frozen blades of grass break like glass as the turf is crushed underfoot. When day breaks and temperatures rise, the contents of damaged cells leak from points of injury and cell death occurs. Patches of turf that have been traversed when frosted sustain footprint-shaped brownish patches for a short period of time. Eventually new blades overwhelm the discolouration with fresh new growth and a uniform green colour will once again dominate the sod.

Many gardeners are dedicating their gardens to complete biological control of pests in the current movement toward a cleaner environment. For many of us adding chemical controls to curb pests on our vegetables and fruits is no longer an acceptable risk. Constant vigilance is essential to notice and eliminate pests as soon as they are detected. Birds can be a great asset in insect control, but a few extras will have to be incorporated into your garden plan to maximize the effectiveness of their contribution.

Most birds prefer to sit while scrutinizing your garden for unwanted (and in a bird’s case – wanted) pests. By hammering a few T-shaped stakes into the ground at strategic locations you can provide perches for these avian predators thereby encouraging them to linger in your garden. A bird bath elsewhere in the yard will entice birds to return to your yard, and a frequently-stocked feeder will help them through lean times.

By tolerating a few blemishes on our fruits and vegetables and encouraging natural means of pest control, we can contribute significantly to a cleaner environment.

 

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