Pests, Fungi and other Problems
What is Black Knot?
Black Knot is a fungus (apiosporina morbosa) which is characterized by its black, tar-like lumpy growths affecting the Prunus family, such as Chokecherry, Mayday, Apricot and Plum trees. It is an airborne fungus which overwinters in the knots, then releases spores in the early spring of the infection’s second season, typically during rain. The spores are distributed short distances on wind currents and through rain splashing. Black Knot typically affects new green twigs, but can also affect mature branches or trunks, especially if physical damage is present. If left un-checked, these black galls will continue to grow and will eventually girdle the branch or trunk and kill it. The stress caused to the tree can also make it susceptible to other diseases and can affect the overall health of the tree.
- The branch will turn light brown and start swelling (1). Initially these swellings can be difficult to notice.
- The swelling will grow until it is mature. When it is mature, it will turn into hard, black galls (2).
- The fungus will continue to grow internally and externally, which will eventually kill the branch and tree. Black Knot is highly contagious!
- It is an air borne disease!
How to get rid of black knot:
All infected branches must be pruned out at least one foot from the infection site. Disinfect the pruners between each cut with bleach to prevent the spread of infection. When removing cut-off branches do not rub them against healthy branches. Immediately place infected branches into a garbage bag.
DISEASED WOOD MUST BE DESTROYED IMMEDIATELY, by burning it or putting the closed bag of black knot into the garbage. Monitor regularly to make sure it does not come back. If your neighbour’s tree has it, then your tree has a greater chance of becoming infected.
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What is Sawfly?
The yellow headed spruce sawfly is a pest that causes extensive damage to many types of evergreens, mainly spruce trees. Their eggs are pearly-white and ovate. The larva causes the damage to the trees. The yellow headed spruce sawfly prefers young open trees.
Once the eggs hatch, the larvae eat small parts of the new needles. As they develop they will strip the needles from the branch and go after older needles. There will be multiple sawfly larvae on each tree. By July infested trees appear ragged and yellow- brown near the top. Heavily-infested trees may be completely stripped of foliage. If not treated for a few years, the sawfly can kill the tree. Sawfly is infectious!
How to get rid of Sawfly:
If the sawflies are only on a few small trees, they can be controlled by picking off and destroying the larvae when they are first noticed. For shelterbelts or large trees, chemical control is needed. The following insecticides can be used; acephate, carbaryl, diazinon, dimethoate, malathion or permethrin. Insecticide application should be made when damage is first noted.
Trees can recover from sawfly provided they do not become re-infested. It may take several years to fully recover.
What is Pine Weevil?
The white pine weevil is a pest that causes extensive damage to many types of evergreen trees. It is also known as the Engelmann spruce weevil and the Sitka spruce weevil. This harmful pest attacks at least 20 different species of trees. Its preference in this area are Norway spruce, White spruce, Colorado spruce and Eastern White pine.
- Droplets of resin oozing from tiny feeding holes in the leader stem early in the spring. These can be hard to notice. A shepherd’s crook in the leader is a classic sign that an evergreen is infested with the white pine weevil, although other pest attacks may result in similar symptoms. The curling and death of the leader of the tree indicates the presence of larvae in that stem.
- The needles on the affected stem will turn yellowish-green, then reddish-brown, and will eventually fall off. This damage generally appears in mid-June or early July.
Pine Weevil is infectious!
How to get rid of Pine Weevil:
Pruning infested trees can be an effective control if it is done as soon as possible after the first signs of infestation are noticed. You must prune out infected branches, checking to see you have all the grubs(larvae) under the bark. Prune close to the topmost unaffected whorl of branches. Immediately destroy the pruned branches and leader stems to prevent weevil emergence. Burn it or put the closed bag of stems in the garbage. Monitor regularly to make sure it does not come back. If your neighbour’s tree has it then your tree has a greater chance of becoming infected. Best results are from pruning out affected leaders as early as possible; in early summer, as dried off leaders mean the weevil has matured and left this tree to infect many more.
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As much as we love the beautiful sunny winter weather, some plants such as cedars and evergreens can be susceptible to sunscald if not properly protected. If snow is left untouched, the sunlight reflects off of it like a mirror causing sunscald to the plant.In order to protect them, tromp down the snow around the base of these plants. This makes the surface of the snow uneven allowing sun to reflect in different directions.
Rabbits and mice
Prevention of Damage by Animals
Fall is the time to wrap the trunk of your trees with a plastic tree wrap to protect them from damage that can be done from animals eating the bark during the winter months. Be sure to remove the protective wrap in the spring.
Fall Needle Shed
Yellowing of interior needles in the fall is a normal occurrence for evergreen trees. Conifers do not keep their growth of needles on their inside branches and shed them naturally in the fall. The discoloration, which affects the older needles close to the trunk occurs in late August and can continue until freeze up. The amount of shedding can be greater if the tree has been placed under stress caused by droughts, flooding or newly dug trees. These needles are not replaced and this is why evergreens are bare of needles near the trunk and there is usually a carpet of needles under the tree.