Question
QUESTION: We live in the foothills west of Denver, CO.  Our deck is built around a large, old ponderosa pine.  In the spring we had the tree sprayed for preventing an attack by pine beetles. (astro is the chemical used--never used that previously)  For the first time in 24 years, the tree has been infested with thousands of very tiny grey-white spiders (larger than spider mites), and the deck is constantly speckled with sticky residue.  The tree looks healthy with no yellowing needles or excessive needle drop and lots of new growth.  What are these spiders, are they harmful to the tree, how do we eliminate them, and how do we keep from having them return in the future?  Thanks!

ANSWER: Sounds like spider mites. The Astro would have killed the predators of the spiders and allowed them to grow in population. On large trees is will be difficult to spray the foliage for the spider mites.

Mites are not insects but are more closely related to spiders.  They are very small and not seen easily with the naked eye. They have piercing mouthparts that they use to suck plant sap. Their feeding results in speckling (formation of tiny yellow spots) on needles. Some needles may turn brown and drop off. With heavy infestations, fine webbing may be seen on the plant.  Although most spider mites increase in numbers during hot, dry weather, spruce spider mites are cool-weather mites. Their populations peak during spring and fall, but drop dramatically during the heat of summer when predators feed on them.

To determine whether insecticide use is needed, it helps to know how many mites are present. Hold a white sheet of paper under a branch and strike the branch. The mites that are knocked off will be seen crawling around on the paper. If dozens of mites are seen per whack, serious damage can result. Continue to check population numbers at 7- to 10- day intervals. Pesticides labeled for homeowner use against spruce spider mite include insecticidal soaps and acephate + fenbutin oxide (Ortho Systemic Insect Killer or Ortho Orthenex Garden Insect & Disease Control Concentrate). Completely cover the foliage with the spray. As with any pesticide, read and follow all label directions and precautions before using.  



---------- FOLLOW-UP ----------

QUESTION: Thanks for your speedy response!  A couple of things I'm a little unclear about:  1.  I know what spider mites look like on my indoor ivies, and the critters I see on the tree needles are much bigger in size, but are still very little.  They are easily seen with the naked eye.  There are no webs, either, but there is what I would call some whitish substance on the needles.  Knowing this, would you still think the critters are spider mites?  2.  If I use Ortho Systemic Insect Killer does this still have to be sprayed on the tree, or is it put on the ground around the tree so that the tree will systemically soak it up?

Answer
Lets start anew--spiders have 8 legs and insects have 6 legs as adults. IF you have a magnifying glass check and see how many legs these critters have. There is an insect that makes white fluff on the needles and will produce a sticky secretion. These are aphids --they suck the plant juices from the plant and produce a sticky honeydew that drips down from the tree. These can be controlled with the use of a product called Bayer Advanced Tree and Shrub Insect Control. This is applied to the soil around the tree and the roots will take it to the needles and twigs and when the aphid feeds on the juices it is killed. The label for this product does not list mites as one of the pest it will control so I am not sure it will work on them--but maybe worth the try. the Ortho Systemic Insect control is a spray and will not work through the roots.
Here is a web link to the Bayer product.

http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html