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Spruce Mites

Has your lovely Fat Albert turned ugly?  Is your Dwarf Alberta Spruce going brown and losing needles?  Is your Colorado Blue looking speckled?  It could be that you have spruce spider mites.

Spruce spider mites are cool weather mites and love our climate.  They’re native to North America and usually feast on spruce trees but can also be found on other conifers.  It’s the spruce, though, that are their favourite buffet.

The first indication of spruce spider mite damage is a stippling on the needles, they look speckled and discoloured.  This usually occurs on the innermost part of the tree.  You may see some webbing that is characteristic of mites and you also may notice some premature needle drop.

What can you do?  There are a few things.  First, you need to figure out just how bad the infestation is.  You can do this by holding a piece of white paper under a branch and giving the branch a shake to see what falls.  The mites are small, green to brown in colour depending on their age and will likely be running after being dislodged.  This makes them a bit easier to spot but a magnifying glass will tell the tale best.

If you see a dozen or more mites then you might consider taking action however if you also dislodge beneficial insects like ladybug, lacewing or red spider mites then you might want to tread carefully as any chemical control will also harm the insects that are trying to look after the problem for you.  You may have to sacrifice a spider mite or two to see what colour stain it leaves when squashed.  Beneficials leave a red stain; the bad guys leave a green stain.

If the infestation isn’t too bad then good blasts with a hose once a week will help keep down the population.  If you feel you need to take more action then spraying horticultural oil will smother eggs but note that the coveted blue or gray needles of your Fat Albert will turn green with an application of oil.  Unsprayed, new growth will still come out blue.

The other option is using insecticidal soap to kill the adults before they lay eggs.  Remember that this will also affect the beneficial insects that are on the tree and it’s most likely that the mite population will worsen over time if you kill nature’s natural controllers.  Pest control in the garden is often about keeping a balance and letting nature take its course.

To understand when to use a control method you’ll need to know a bit about the spruce spider mite life cycle.  Eggs overwinter on the needles and hatch in mid-March to late April.  The mites feed on your tree, which makes the needles look stippled.  When summer turns the heat up the mites slow down, lay eggs and take it easy until fall.  There can be many generations of mites in a year.

Be proactive by looking after the general health of your trees since stressed trees tend to attract the problem insects along with disease.  Mulch every spring and fall with a couple of inches of Sea Soil Original, keeping the mulch away from the trunk of the plant otherwise it will rot the bark.

Water deeply in the dry months but less often, gently digging down with a spade to see how far the water is actually soaking into the ground (I can’t stress this enough.  Even if you think you’ve watered long enough chances are you’ve only dampened the first inch or two of soil so please check).

If you like to use fertilizer then I recommend using one specific for conifers such as GardenPro Evergreen & Broadleaf or Myke Organic Evergreen and not your all-purpose Miracle Grow, as conifers have different requirements than hanging baskets of petunias.

Often when the damage is first noticed in the summer it is too late for treatment so it’s best to take control in the cool months of spring and fall when the mites are most active.

Shirley Eppler

February 2014