GDD Update April 22, 2019

For many, there isn’t a huge increase in GDD over the next five days.  Unless you are on the Island – or a few other places.  But we are steadily increasing overall.   I rather like slow springs….


Today’s topics ‘thresholds and ‘keep scouting!’


Thresholds are values – usually number of insects – that indicate it is time to take action to avoid economic loss.  They are complex to calculate as they can vary with time of year, crop, pest, etc.  Consequently, there are very few available for Christmas tree pests.  Two I have found are:


Spruce spider mite – 10 mites/branch scouted (usually with a tap test over white paper)


Balsam twig aphid – 3 aphids per tree,  when 10” of branch on 15 trees of similar age and size are scouted.


In addition to scouting now for spruce spider mite (50-121) and balsam twig aphid (30-100) – and remember to especially scout where you have had the pest before – you should be scouting for:


Cooley spruce gall adelgid (22-19) at base of buds on blue spruce or where there are bent needles or yellow spots on needles of Douglas fir


Elongate hemlock scale (if you are in the zone) – use sticky traps to catch adults (7-120)


Balsam woolly adegid – no GDD available – but scout for flat tops, gouting (swelling at nodes and ends of twigs) and very tiny adults covered in a white waxy covering on the trunk and branches.


Gypsy moth (especially if you have had it before) – you can pick off the egg masses before they hatch  (start about 90) and treat while they are still small (less than 1”) with Bacillus thuringiensis (Bt).  The small larvae can balloon off the tree onto neighboring trees so consider your wind direction and treat trees in that area.


Pine needle scale – check under the scale covers for maroon eggs. Treat when crawlers hatch later.


Zimmerman pine moth – larvae start to hatch 121-246 GDD


Are you still trapping for white pine weevil?  You maybe catching Eastern pine weevil – they are hard to tell apart.


Have a great week!