SCALES AND INTEGRATED PEST MANAGEMENT
by Peter Dmytrasz, City of Toronto

Spring is a time when nature undergoes a rebirth from a seemingly endless period of winter. Increased daylight hours and temperatures, with adequate moisture, provide the impetus for plants, insects and many other organisms to break out of dormancy.

One type of insect that may be problematic in Ontario's urban forests are scales. These insects look like stationary bumps on twigs or occasionally leaves. They suck plant juices and in large enough numbers, may cause leaves to yellow, fall prematurely, or twigs to die. Scale insects often consume more plant juices than they could possibly use. The excess, called honeydew, is excreted as a sweet liquid.

During summer, a fungus colonizes this liquid and develops into a black sooty mould. It may be found over, under and on any plant or fixture within the drip line of the affected tree. Ornamental specimens in a weakened or stressed condition and/or fertilized with a highly water soluble Nitrogen fertilizer, are most often targeted. Trees in this condition have a reduced intrinsic pest resistance and a decrease capacity to recover after severe attacks by these insects.

There are a large number of scale species that feed on an equally large number of tree species. Scales insects are generally oval and small. Adults are often only 1 to 3 mm in length, but some species may be as much as 13 mm long. Emerging young nymphs develop a protective covering, from which their name is derived. This protective covering may be hard, as for armoured scales, or soft, as for Lecanium scales. Each scale species may be characterized as either a hard or soft scale.

Scales, depending on the specific species, may overwinter as eggs, nymphs or adults on their respective hosts. Nymphs are the vulnerable, mobile, crawler stage that may be transported to new hosts by birds or wind. Female nymphs crawl to a suitable feeding location on the host's stem, branches or leaves. They insert their tube, or filament-like mouth parts into the host plant tissues to feed. Their legs are eventually lost during on of the moulting stages. Male adults do not have functional mouthparts and are usually winged. They mate within a few days of emerging and soon die. The stationary, feeding nymphs will develop a characteristic protective covering, unique to each individual species. Adults lay their eggs under this protective shell. In some species, even the un-fertilized females are able to lay eggs asexually.

One such example is Neolecanium cornuparvum , a soft scale better known as Magnolia Scale. This insect, as the name suggests, is a pest of Magnolia, more specifically the Cucumber Tree - M. acuminata , Saucer Magnolia - M. x soulangiana and Star Magnolia - M. stellata . These trees or large shrubs are often prized as specimen ornamentals for their large showy flowers, fruit and leaves, smooth bark and open, often symmetrical form.

They prefer a roomy location with full sun or light shade and a moist deep rich , well drained, acidic to neutral , humusy loam soil. Unfortunately, they are often found in small shady yards in soil that is either sand or clay, usually alkaline and irregularly watered. These stressed and weakened trees are forced to grow at or often beyond the northerly limit of their range or hardiness zone. They are extremely susceptible to, and prime candidates for attack by, the Magnolia Scale.

Integrated Pest Management first incorporates physical, cultural and biological controls and relegates chemical controls to an option of last resort. Physical controls include removing nymphs and adults in July through September. Use a soft bristled brush, your fingernails, a vacuum or water jet spray, with the aid of a stepladder if necessary. New or small infestations may be pruned away.

Cultural controls include: proper fertilizing with slow release Nitrogen and micronutrients; mulching with wood or bark chips; and watering deep through the root zone. Ameliorating with organic matter or compost helps to neutralize alkalinity. Relocating a small specimen to a more hospitable environment is another cultural consideration. Biological controls include attracting and/or releasing beneficial insects. Ladybird beetle, lacewing, rove beetle and ground beetle predators and parasitic wasps will help control pest population levels.

Chemical controls should not be used in consecutive years in order to determine the effectiveness of the previous treatment. Both federal and provincial authorities approve many pesticides. Superior Oil treatments in the dormant season work very well if coverage of the plant is complete.

The selection process that matches plant material requirements to site conditions, prior to planting, is probably the best consideration for a healthy and problem free landscape.

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