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May 23, 2007

Christmas Tree Scouting Report #9 - May 23, 2007

Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.

High populations of Eriophyid mites, also referred to as rust mites, are starting to show up in plantings of Norway spruce and Colorado blue spruce this week in Lancaster, Schuylkill and York counties. When populations are heavy, needles will take on a rusting or bronzing color on Norway spruce and a bleached look on Colorado blue spruce. Unfortunately, it is not until this color change that growers are alerted to the infestation. This mite and the spruce spider mite are cool season mites, which means their populations tend to build in the spring and again in the fall when temperatures are below 85 degrees. This year's spring temperatures have been ideal for populations to explode. To scout for eriophyid mites, start by taking an overall look at the trees in a block for any color change. Eriophyid mite damage can be mistaken for nutrient deficiency. To distinguish the difference requires the use of a hand lens. Usually, when the populations of mites are building, it may just be a branch that takes on a bronzing or bleached appearance. Look for wedge shaped orange colored mites less then ½ mm in length on the undersides of needles. When populations get high, needles take on a dirty look when they are viewed through a 10-20x hand-lens, because of the cast skins left by the mites as they develop. To control eriophyid mites, oils can be used before the new growth starts. On Colorado blue spruce, oils will remove the blue bloom from glaucus trees. Eriophyid mites are biologically different from spruce spider mites, so using a product labeled for eriophyid mites such as Avid, Seven, and Judo will give good control. Other general miticides that have given good control in North Carolina are Dimethoate and Sanmite.

Rhabdocline needlecast is still infectious in Dauphin, Lancaster, Schuylkill and York Counties. To test for viability of Rhabdocline needlecast, place a twig that is infected with the brick red bands in warm water, wait 5 minutes, then with a hand-lens, examine the bottom of the needles, where the infectious lesion is, for a swollen, ruptured epidermis with orange spores. When Rhabdocline is no longer infectious, this area will turn black and the needles will drop.

The Douglas fir needle midge is beginning to show damage to the new needles in Berks, Bucks and Schuylkill Counties. New needles that are infested with the midge will be kinked and this area will have a light color change. When the needle is viewed from below with a hand-lens, a small dimple will appear where the needle is bent. This is where the midge entered the needle and will continue its development until November. If new needles are kinked on Douglas fir from Cooley spruce gall adelgid, the presence of the adelgid will be visible when the needle is viewed from below, or cottony wax or cast skins will be found. The adelgid is a surface-feeding insect; whereas the Douglas fir needle midge feeds within the needle. 

Pine bark adelgids can be seen on the new candles on white pine in Lancaster and York counties. This adelgid feeds on the trunk by sucking sap from the phloem tissue and can be found feeding between the new needles on the bark. They can be problematic for small nursery stock, but if trees are healthy, permanent damage should not result. Lady beetles are beginning to feed on adelgids, and only if adelgid populations are high, should insecticides such as insecticidal soap or horticultural oil be used in order to protect the beneficial insects.

The European sawfly was found feeding on the needles of mugo pine in Luzerne and Schuylkill counties. The host of concern for Christmas tree growers is Scotch pine. Other hosts are Austrian and red pine. When this sawfly first hatches, the larvae can only eat the surface of the needle, causing them to turn brown and appear straw-like. As the larvae grow, the whole needle is consumed. Larvae feeding in colonies can strip a whole tree of its old needles, causing damage. The tree does not usually die, but gives it a "bottle brush" effect, because only the current year's needles are present. This insect does not usually infect large numbers of trees in a field. Control can be achieved by shaking the infested branch into a bucket of soapy water or spot spraying with a registered insecticide.

No eggs of the cryptomeria scale were found this week in Berks, Dauphin, Schuylkill or York counties on Fraser or Concolor fir. To scout for eggs, you can flip the scale cover over with your nail or a pin and look for tiny lemon yellow oval shaped eggs with a hand-lens. You can also tap an infested branch over a white surface and then look for eggs. I expect to begin seeing eggs in the next week or two.

Growers using a hand-lens ask me what the black spots on the bottom surface of needles and twigs are. This is a superficial fungus know as "fly speck" that does not harm the plant and can be rubbed of easily.  This fungus disease overwinters on many wild hosts, is disseminated by wind and is most prevalent during humid cool weather.