April 15 GDD update

The range of GDD for the group of growers in this project is from 4-67 – so you can see the variation by location!  And I expect things will start moving fast soon!


A reminder that insects don’t read books (or my emails) so scouting is always the best way to determine if an insect is present and at what developmental stage.  The GDD ranges give a suggested window for scouting.

Balsam twig aphid management 30-100

Cooley spruce gall adelgid management 22-81

White pine weevil management 7-58 GDD – a few areas have hit this deadline already and more will by April 20.  You might still catch Eastern pine weevils in the traps after 58 GDD and they are hard to distinguish from white pine weevil.


So many pesticide applications state ‘treat before/or after budbreak’.  I understand budbreak on a single bud – when the bud scales open and you can see the new needles inside.  But what about budbreak on a field basis – especially if you have different species or cultivars in the same species?  Just looking at some research papers, I found budbreak defined as:

  • The day when buds in the upper 1/3 of the crown showed green needles under the cap of the bud scales
  • Once one shoot broke its bud scale


Those are pretty different measurements.  So when would you treat for needlecasts, for example, as you are trying to protect new foliage – after budbreak?  Brian’s research on Swiss needlecast on Doug fir is showing that you can get good control starting spraying later when there’s about an inch of new growth and you don’t have to guesstimate bud break.  For control of needlecasts good coverage is essential.  Have you ever tested your spray coverage?


Some insects are good at avoiding contact insecticide applications.  Anything that forms a gall or feeds inside plant stems and those that have scale or waxy filament coverings are essentially wearing pesticide raincoats.  That’s why you need to apply the insecticide at their weakest development stage – before they get under cover.



Have a great week!