Gardening: Extreme cold weather seals Mountain Pine Beetle’s fate

Weather temperatures, hot or cold play a big part in the garden. Temperature can affect any part of the plant as well as insects and diseases.

Early blooming plants such as Forsythia, Double Flowering Plum and Daphne have already formed next year flower buds by the time they become dormant in the fall. Very cold or prolonged periods of cold will kill the buds resulting in fewer or no flowers in the spring. After a cold winter it isn’t uncommon to see the less hardy shrubs with blooms only at the bottom of a shrub where the branches and flower buds were protected by snow.

Mulch and snow will insulate the roots of plants from the penetrating cold. Allowing the snow to accumulate in flower and shrub beds by not walking or driving over them is the best practise. In sunny areas that melt on warmer sunny days, try to shovel snow back on the bed to protect the plants when temperatures plummet.

Cold isn’t all bad. It will kill insects and diseases. Mountain Pine Beetle have moved east from British Columbia and has been found in the Sundre area as well as the Clearwater County.

The Mountain Pine Beetle drills through the bark making tunnels where they lay eggs which hatch into larva. The larva devour the phloem cells which conduct nutrients to the rest of the tree. This by itself is harmful to the tree but the beetles are also carrying a blue fungi that also plug the trees phloem and xylem networks helping to starve the tree. According to The Alberta Agriculture and Forestry a tree attacked by infected Mountain Pine Beetles can be dead within a month.

While the beetles appear to be here to stay, fluctuating temperatures from above zero to very cold are known to kill the larva. It appears that the cold snap in the fall reduced the number of viable eggs and young overwintering larva.

The first sign of an Mountain Pine Beetle infestation is small holes in the bark but they are hard to spot and often go unnoticed until the sap or resin begins to leak from the holes.

It is also common to see dust from the insects tunneling on the tree bark and around the bottom of the tree. If bark was removed one would see J shaped groves running up the tree with side groves filled with eggs and or larva.

When the tree is cut down a blue/grey staining is seen around the perimeter of the trunk. The staining comes from a blue fungi that attaches itself to the beetles.

Mountain Pine Beetle can spread through firewood. Cutting down an infested tree does not stop the insect’s life-cycle. The tree does not have to be standing for the eggs to hatch, larva to eat and mature into pupa then hatch as adults. When cutting or buying wood, examine the cross section of the trunk for bluish grey hues around part or all of the edges.

Pine Mountain Beetle isn’t the only insect or fungi that will die in extended cold weather, but it is the one that will have the largest economic impact on the area.

For more information on Mountain Pine Beetle go to the Alberta Agriculture and Forestry web site:

Linda Tomlinson is a horticulturalist that lives near Rocky Mountain House. She can be reached at

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