The upper surface of maple leaves, especially those of silver and red maples,
is frequently covered with galls - wartlike growths caused by mites. The galls,
in which microscopic mites live and feed, are green when newly formed but
gradually turn red and finally blacken. If numerous, they can result in deformed
leaves and, consequently, mar the overall appearance of the tree.

THE GALLS

Plant galls are usually caused either by mites or insects. How they are caused
is a matter that has attracted the attention of scientists for many years. The
formation of plant galls appears to be linked to the secretion by mites or insects
of plant-growth substances or enzymes that cause abnormal growth. Each species
of gall-causing mite or insect is thought to produce its own type of growth
substance which has a specific effect on plant growth. A plant attacked by mites
of more than one species, therefore, has a variety of galls with sizes and shapes
characteristic for each species of mite.

Research in gall formation has proved to be difficult. Although injections of
crude extracts of insects and insect parts into healthy plant tissue have produced
some galls, no specific chemical growth regulator has yet been isolated.

THE MITES

Several species of eriophyoid mites cause galls on maple leaves. The most
common species in eastern North America is Vasates quadripedes (Shimer),
the bladder gall mite of silver and red maples. Members of another species,
Vasates aceris-crumena (Riley) cause finger galls on silver maple. Females of
these two species induce gall formation on the new foliage in early spring. Each
female becomes enclosed by gall tissue, and the resulting pouch provides a
protected environment which is utilized by the mite as a brood chamber. By
early summer, each gall may contain as many as several hundred needing mites,
all linear descendants of the founding female. As the foliage begins to dry in
mid-summer, specialized females are produced. These females migrate from

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Two different maple bladdergalls found in Canada.

the gall to protected sites around the buds and in the bark, where they remain
until the following spring.

Members of several species of eriophyoid mites in the genera Aceria and
Aculus cause bright purple or reddish felt-like patches, called erinea, on the
underside of maple leaves. These mites have life cycles similar to that of the
gall mites described above, but form colonies within the fibres of the erineum
rather than in enclosed galls.

DAMAGE

Gall mites, even when numerous, will not kill a tree but the galls can spoil
the appearance of an ornamental tree and retard its development. A severe
bladder gall mite infestation on a young maple tree can, therefore, have un-
desirable consequences.

CONTROL

Mites overwinter in protected parts of the tree or crevices in the bark. The
best time to get rid of them is in the spring before they move to the new foliage.
One of the following sprays can be used effectively when the buds are turning
green:

• Commercial lime-sulphur or dormant oil can be applied in early spring,
before the leaves unfold. If good coverage is obtained, one spray should be
sufficient. These can also be used in the late fall after the leaves have dropped.

• Malathion or carbaryl (Sevin R). One application of a 2% solution of either
insecticide when the buds are turning green, followed by a second application
2 weeks later.

• Miticides or acaricides such as Dicofol (Kelthane R). These may not be
readily available in certain parts of the country.

Most of the damage is done when the galls have formed on the leaves and
the mites are inside. Control at this stage is difficult but some measure of success
may be obtained with systemic insecticides. In liquid form, dimethoate can be
used as a foliage spray or it can be "painted" on a smooth area of the bark in a
band 15 to 20 cm (6 to 8 in.) wide around the tree trunk, below the branches.
Thus applied, this systemic insecticide penetrates the bark and is carried
throughout the tree by the sap.

CAUTION

When using any of the above-mentioned insecticides and miticides, it is
necessary to read the recommendations of the manufacturer and to follow
them carefully. Insecticides or miticides must never be placed within the reach
of children or pets, or where their containers may be mistaken for other
materials.

CONVERSION FACTORS FOR METRIC SYSTEM

Approximate

Imperial units conversion factor

Results in:

LINEAR

inch

x 25

millimetre

(mm)

foot

x 30

centimetre

(cm)

yard

x 0.9

metre

(m)

mile

x 1.6

kilometre

(km)

AREA

square inch

x 6.5

square centimetre

(cm2)

square foot

x 0.09

square metre

(m2)

acre

x 0.40

hectare

(ha)

VOLUME

cubic inch

x 16

cubic centimetre

(cm3)

cubic foot

x 28

cubic decimetre

(dm3)

cubic yard

x 0.8

cubic metre

(m3)

fluid ounce

x 28

millilitre

ImLI

pint

x 0.57

litre

(L)

quart

x 1.1

litre

(L)

gallon

x 4.5

litre

(L)

WEIGHT

ounce

x28

gram

(g)

pound

x 0.45

kilogram

(kg)

short ton (20001b)

x 0.9

tonne

(t)

TEMPERATURE

degrees Fahrenheit

(°F-32)x

156

or (°F-32)

x 5/9 degrees Celsius

(°C)

PRESSURE

pounds per square inch x 6.9

kilopascal

(kPa)

POWER

horsepower

x 746

watt

(W)

x 0.75

kilowatt

(kW)

SPEED

feet per second

x 0.30

metres per second

(m/s)

miles per hour

x 1.6

kilometres per hour

(km/h)

AGRICULTURE

gallons per acre

x 11.23

litres per hectare

(L/ha)

quarts per acre

x 2.8

litres per hectare

(L/ha)

pints per acre

x 1.4

litres per hectare

(L/ha)

fluid ounces per acre

x 70

millilitres per hectare

(mL/ha)

tons per acre

x 2.24

tonnes per hectare

(t/ha)

pounds per acre

x 1.12

kilograms per hectare

(kg/ha)

ounces per acre

x 70

grams per hectare

(g/ha)

plants per acre

x 2.47

plants per hectare

(plants/ha)

PUBLICATION 1538, available from

Information Services, Agriculture Canada, Ottawa K1 A 0C7

©Minister of Supply and Services Canada 1981
Cat. No. A43-1 538/1 981 E ISBN: 0-662-11609-7
Revised 1981 10M-7:81