GDD update 9.12.19

Another cool day before more heat – and some of the growing degree day curves are starting to show a little slowing in increase.  And that means it is a good time to scout for spruce spider mite.  Tap some branches over a white paper plate and if something runs, smoosh it.  If it is small and leaves a dark green smear, it is probably a spruce spider mite (really scientific, right?).  While two spotted spider mites like it hot and dry, spruce spider mite likes it cool.  So even if you aren’t in the right GDD range, take a look.  The damage doesn’t disappear so sometimes interior bronzing is your clue, but it’s better to find them before you see that much damage.


You might see predatory mites, too.  Very small and fast and sometimes orangey.  They are good guys and help keep the bad ones under control. Unfortunately, the miticides you use to control the spruce spider mite also may kill the predatory mites so if you see both, scout over time and see if the numbers of bad guys are going down.  Then you don’t need to spray!


Ah, spiders – the bane of some growers existence.  Not that they are doing anything bad, it’s just the potential for their egg sacs to hatch out in people’s houses sending hundreds of babies up the walls. Not sure why that would bother anyone… Got my first picture of an egg mass this fall.  This one looked round and brown and papery but they do vary.  Usually some webbing holding it to the tree.  The grower is holding it in a jar to see if anything hatches out so we will see if I am right.


So what do you do?  There really isn’t anything to do but look carefully and shake the trees. I had a discussion with Dr. Raynor, the spider expert here, about creating alternative habitat so maybe I need to get back to that.


Hmm – it’s an all arachnid post.


Same old same old… not that we want more insect pests but a few could drop off the list….


Spruce spider mite – 2375- 2806 GDD

Doug fir needle midge – remove heavily infested trees (carefully so you don’t spread the pest) before larvae exit the needles (needles will turn brown). Mark infested trees for placing traps in the spring

Elongate hemlock scale – keep scouting for crawlers.

Cooley spruce gall adelgid – prune out galls on spruce before they turn brown (about 1850) – see other information on Cooley above

Cryptomeria scale crawlers – 1750-2130 GDD

Japanese beetle adults – 1029-2154 GDD

Two spotted spider mites– 1300-2000 GDD

Pine needle scale 2nd generation– 1290-1917 GDD


Have a great week!  Palindromic dates (same backwards and forwards) continue for a few more days!