By Mike Allen
Written for the Winnipeg Free Press ‘Tree Care’ Column June 12th, 2005
The warmer days of spring are welcomed by most people as the flowers emerge, the leaves appear, and the grass grows lush with the fresh emerald colours. This is also the time when many of our trees and woody shrubs start to become infested with pests and subject to disease infections. June is the critical month for trees and shrubs. I recommend that those whom are concerned about their woody plants inspect them each day and look for changes that deviate from the normal appearance of the plant. This is one of two articles in which I will devote attention to spring problems. This week I will look at evergreen spruce trees and fruit trees.
Here is a check list of possible problems that are common on southern Manitoba:
Colorado Blue and White Spruces
Spider mites are now feeding on needles and making conspicuous fine webs; five or six generations occur during spring and summer; needles at first become grey-green and slack, and then they start to turn tan to rust in colour,
Cytospora fungus canker or white blister disease can be very prominent on most mature trees; look for bleeding white resin on the bark and branches; the resin will sometimes look bluish white; older infections appear as dark amber brown resin blobs on the branches whereas new infections appear as small oval growths chestnut brown in colour,
Spruce aphids are feeding on white spruce needles causing them to slightly curl and twist often with prominent waxy coatings,
Spruce needle miners are chewing off needles from the twigs and laying them along the axis of twigs or in small piles,
Sirococcus tip blight fungus disease affects the ends of twigs; look for early yellow-green needles near the twig ends; infected twigs lose needles and become slightly or prominently curled,
Look out for spruce bud worm feeding as the new buds start to expand; when the bud cap persists on a bulging bundles of new needles check for the presence of a small cocoon and a green caterpillar with a black head – spruce bud worm; bud worm infestations are increasing in many areas of Winnipeg;
Spruce bud scale and black mould disease were bad last year owing to the heavy rains; the two problems usually occur together when the ‘honey dew’ excrement produced by the dark brown, spherical scales becomes infected with the mould causing needles to die,
Often needles harbouring tip blight disease will also be infected with one or more varieties of needle cast fungus disease and black mould; look for discrete brown or cream coloured bands on the needles, or 2 rows of tiny black dots on grayish-green needles.
It is important to get a proper diagnosis of the problems plaguing spruce trees. Here are some treatments to consider:
Sucking pests such as spider mites, aphids and scales can be power washed off the tree with water,
There is no direct control for Cytospora disease except to keep the tree as healthy as possible; the disease slowly kills individual branches over the course of its life time,
Tip blight, black mould and needle cast diseases in smaller spruce can be treated by the owner with two to three sprayings of copper sulphate fungicides spaced about 10 days apart; larger trees should be sprayed by a professional pesticide applicator who may use a different fungicide; treatments should take place in late May through June; if rain occurs within 24 hours of any spraying, a reapplication will be necessary,
Bud worms, needle miners and other needle chewing insects can be treated with BT (Bacillus thuringiensis) biological pesticide in early June
Probably the most common problem with spruce trees is their close spacing to each other or with other trees, fences and buildings. Unfortunately for most trees it is too late to change their location. You might want to consider relocating recently planted small trees to avoid over-crowding problems.
The year 2004 was a difficult time for fruit trees in southern Manitoba. Here are some of the more common problems:
Older apple, crab apple, pear, plum, cherry and Russian olive trees are becoming increasingly infected with a trunk canker fungus disease that causes the bark and inner sapwood just below the bark to split longitudinally. This systemic disease is part of a very complex grouping of tree and shrub diseases called Botryosphaeria; this disease cannot be treated with fungicides; trees must be kept as healthy as possible; often I find this disease entering an old branch or trunk stub as the expanding bark cannot properly cover or seal the stub; fungus spores enter decaying stub or the base of the stub where bark cannot grow; branches and the tree die prematurely.
Poor pruning practices are ultimately responsible for the spread of this disease; always prune branches back to the point of attachment to a larger branch and trunk; learn how to prune all trees by taking one of my courses this fall; fertilize the tree using the entire area under the crown from 3 feet out from the trunk to the drip line; I recommend carefully removing any grass under the crown of fruit trees and using a pitch fork work in good compost, or leaf mould, or well aged manure into the soil; do this every year.
Black knot disease of Schubert choke cherry and May Day cherry trees are slowly killing mature trees nearly all of them are infected in southern Manitoba; the knots or fungus galls have either not been removed or they have been improperly removed; when they are removed they are simply cut off close to the edge of the gall; the disease spreads rapidly in the tree killing the living wood tissues under the bark.
Prune the galls from the tree in the fall or late winter but before the buds open up; always prune with sharpened tools at least one foot (30 cm) away from the gall preferably at a junction with a larger branch or trunk; if pruning occurs after the buds have opened (now) sterilize your tools after EVERY cut with diluted bleach and water (1 to 9), or methyl hydrate or rubbing alcohol.; when pruning the galls in summer cover the cut with a tree pruning seal asphalt compound (not pruning paint) to prevent diseases from re-entering the wound.
Leaf blight diseases were very common last year in fruit trees as well as in other deciduous trees and shrubs,
Apple, crab apple and plum trees were subject to many leaf spot fungus diseases which caused premature leaf drop; ‘frog eye’ disease leaves a tell-tale purple margin around the spot; in the apple group frog eye is often associated with black spot of fruit,
Fire blight bacterial disease was a serious problem on apple, crab apple and pear trees as well as on mountain ash; leaves turn brown near the source of infection and the twigs darken and curl at the ends.
Applying dormant lime sulfur fungicide spray in April before the buds open helps control many leaf diseases,
Applying a copper sulfate fungicide in early June is also recommended as the new leaves grow,
Remove fire blight infected twigs early in the fall at least one foot (30 cm) from the infection, otherwise treat in the same manner as black knot disease,
Collect disease leaves and fruit as they drop and seal them in trash bags so that they don’t release spores that re-infect susceptible trees.