April 29, 2019

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!


April 15, 2019

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!

April 15, 2019

April 10 Christmas tree update

Anyone seeing bud break yet?  I need to check my (few) trees.


Cooley spruce gall adelgid management is best between nymphs appearing (around 22 GDD) and bud break

Balsam twig aphid management is best between egg hatch (starts around 30 GDD) and bud break

Time for Doug fir needle midge traps (before daily temps are 60 F on N side of previously infested trees) or yellow sticky cards to catch adult midges


I was going to write an email on horticultural oil applications, but Jen Llewellyn did it for me!




Dormant oil can be used to manage:

Spider mites and eriophyid/rust/sheath mites

Cooley spruce gall adelgid

Elongate hemlock scale

Balsam twig aphid

Cryptomeria scale


Remember that Doug fir and spruce can be sensitive and oils will take off the blue coloring of needles



Have a great week!

April 1, 2019

GDD update April 1

Some areas of the state are already in the GDD ‘zone’ for our earliest pests.  Others are still at 0 GDD.  Where are you?  Check out NEWA to find your nearest weather stations and their GDD – base 50 starting March 1. http://newa.cornell.edu/

Here’s the update (more or less) I sent out today.

Get ready to treat for :

White pine weevils – adults 7-58 GDD (soil on warmer side of tree 2” deep should be 50F) if you see adults or drops of sap on leaders – on pine and spruce but can be on Douglas fir and fir


Spruce spider mites – oil for dormant spray about 7- 50 GDD – on fir, spruce, pine, Douglas fir


Pales weevils – treat stumps less than 2 years old to prevent egg laying on fir, pine and spruce


Phenological indicator – silver maple, Cornus mas (Cornellian cherry)


The forecast for the next few days is for no additional accumulation of GDD but things can start changing fast.


Keep scouting for:

 Balsam twig aphid – eggs hatch about GDD 30 – especially on species with early bud break – best control is after egg hatch and before bud break.


Cooley spruce gall adelgid on both Doug fir and spruce – nymphs start to be found around 22 GDD and you need to treat before they wax over


Spruce spider mite – eggs start hatching at 50 GDD, Do you know the residual period for the pesticides you use?  That is another piece of information that can help you determine when you need to apply it, within the GDD range, if your scouting records show you need to use it.


Now that you have the first information – is this still a good weather station for your farm?   Let me know if you want to change or add stations at any time.


If you have time, let me know what’s blooming near you.  Cornus mas (Cornellian cherry) is out here in Ithaca and we are about at 6 GDD.