Scales & Needle Drop

Why does Meghan Baker, Watauga County Extension Agent look so happy? We were done collecting shoots! Meghan helped me on Monday collect shoots from a grower's field to help determine if elongate hemlock scale infested trees are more likely to drop their needles after the tree is cut. Several growers and Christmas tree retailers have told me they think scale infested trees are more likely to drop their needles. Other pests such as spider mites and balsam woolly adelgid cause similar problems. Hopefully we'll soon know if it's true of elongate hemlock scale as well.

Meghan and I collected shoots off of 15 infested and 15 uninfested trees. We took three years worth of growth plus a little bit of the fourth year branch in order to stick the shoot in our trays. Since scale goes back multiple years, we wanted to see how it was affected older needles.

Our samples were paired. We took two branches from one area on the tree and another set of two branches from another area, usually on the opposite side of the tree. One of the paired branches will stay in the bucket with water. The other one goes in a tray without water. Having two sets of these pairs will allow us to compare results within a given tree. Needle retention varies greatly between trees even without pest infestation. It can also vary with different positions on a tree. Most of our samples came about 1/2 way up the tree and some branches I cut were practically against the trunk.

This is what all 120 shoots look like today. Each branch is labelled so I can keep track of what tree they came from. Half of the branches are in buckets of water and half in styrofoam trays without water. Yesterday I took data on the scale infested branches, estimating the percentage of needles with scale on the 1st, 2nd, and 3rd year growth. Infestation varied widely. I have some branches with 2nd and 3rd year needles having 100% infestation, and others with less than 25%. I also marked if there were other problems with the foliage such as twig aphid damage or small, yellowed needles that are also more likely to shed. If there was any needle drop already, I also made note of that.

In a week I will take each branch and lightly rub my hand over the foliage and estimate the percentage of needles that fall off, again keeping track if they are from the 1st, 2nd, or 3rd year shoots. I'll take ratings again after 2 weeks, and final data after 4 weeks. Already I'm finding that the 3rd year needles of heavily infested trees were falling off the trees in the field. These trees are such heavy density so it probably wouldn't have mattered, but if they keep coming off in the home, it will cause a mess.

I want to give special thanks to Jeff Owen who has conducted several experiments like this looking at other factors affecting needle drop. He was able to help me with the experimental design. Much of this type of research was originally conducted by Drs. Eric Hinesley and Gary Chastagner. And of course thanks to Meghan for her help, and for the grower, Johnny Greer, who donated his trees. Also a big thanks to the Mountain Horticultural Crops Research Station at Mills River who are donating some space in a spare room to mimic someone's home. (I promise to sweep up all the needles!)

I'll let you know how it all turns out.