The Value of Christmas Trees

"...there is no reason why the joy associated with the Christmas evergreen may not be a means of arousing in the minds of children an appreciation of the beauty and usefulness of trees; and keen appreciation of the beauty and usefulness of trees is a long stop toward the will to plant and care for them (Arthur Sowder, US Forest Service, 1949)."

Wednesday, January 27, 2010

Elongate Hemlock Scale Trials 2009

Photo captions from left to right: Female scale flipped over to show small area, outlined in yellow, through which the scale feeds. Male elonagate hemlock scales produce a white, fluffy covering which can bee seen on the needles and may affect sales. Field shot where scale spread has been monitored over a 12-month period

SUMMARY: In 2009, a series of pesticide trials were conducted to determine timing and materials for scale control. Results indicate that the best scale control is achieved in the summer. Scales can be controlled in the spring, but there will be 5-15% less kill. Treatments made after mid-September also do not result in good control. The best materials for control continue to be Dimethoate plus either Asana or Prev-Am. However, in a fall applied trial, Lorsban gave excellent results. Safari has given variable results, as has the new insecticide, Movento. Horticultural oil continues to give control at about 65-75% kill. At one field site, scale spread to as many as 1/3 more trees from the summer of 2008 to 2009. However, tree growth appeared to be hardly affected. Current control recommendations are found at:

Elongate hemlock scale (EHS) has continued to spread in Christmas tree farms in western North Carolina. I had hoped that a cold winter last year would reduce scale numbers, but that was not the case. I have been conducting EHS control trials since 2003. This past year, I had 4 field trials looking at different materials for scale control as well as assessing scale spread in a 5th field.

Past work has indicated that a mixture of Dimethoate (@ 16 ounces per 100 gallons -- a pretty hot mix) + Asana (@ 10 oz/100 gallons) or the Dimethoate + Prev-Am (@0.4% solution) gives good control in the summer. Last years trials really confirmed that the Dimethoate by itself does not work as well, nor gives as long lasting controls. Past work also indicated that the best control would be achieved in the summer (July through early September). Treatments made in 2008 in the spring did result in good control (92% of scales killed in one test), but slightly better results were achieved in the summer.

Most Christmas tree growers are well acquainted with Dimethoate and Asana. Some may not know as much about Prev-Am.

Prev-Am is an insecticide, miticide and fungicide. It is produced by Oro Agri and is made by a mixture of "Borax, cold-pressed orange oil, and various biodegradable surfactants." According to company reps, Prev-Am will disrupt the exoskelton of the insect. It also will increase translaminar movement of products across the surface of the needles, and reduce surface tension, thereby improving penetration. More information about this product is available at the Oro Agri site at: The Prev-Am is not considered an organic product because of the amount of borax. However, it certainly smells good. It can help mask the smell of Dimethoate. It probably aids Dimethoate by increasing the penetration of chemical into the scale. However, we have seen needle burn a few times when it is used at the full labeled rate of 0.8%. I have not seen burn at lower rates, and so have recommended the 0.4% solution to mix with Dimethoate.

The first picture aboves shows why it is so hard to kill these scales. They are armored scales, but they are covered both on top and underneath. There is only a small area (outlined in yellow) through which the feeding tube fits, and the scale is not protected. The Prev-Am may help in getting materials through to the scale to kill it.

Anyway, that's where things stood at the start of 2009. There were still a lot of questions about scale control. When does the treatment window "close" in the fall? How much will EHS spread in a year? Can the rate of Dimethoate be reduced when using Prev-Am? What other materials can be used for control? And could a grower get as good control with a back pack sprayer as a high pressure sprayer? Jerry Moody wanted this question answered especially as he had several folks with localized scale, and they just wanted spot control.

What were some of these other materials? In 2009 we looked at Movento, Safari, Mavrik, Talstar, Lorsban, and Vintre as an adjuvant to Dimethoate.

Movento (spirotetramat) is an insecticide labeled last year by Bayer. This product is supposed to be an excellent systemic, but it requires the use of a surfactant. Also, they were recommending it be applied twice, with applications made 2 weeks apart. (Some of you may know that Movento labeling issues have arisen. A judge stopped the sale of Movento, because there was not proper public comment posting by EPA. This has been stayed until mid-February, and the company hopes that all labeling issues will be resolved. In the media, there were reports the stop-sale occurred because Movento kills bees. Well, practically everything kills bees. Even spinosad, an organic product, is highly toxic to bees. However, most materials applied in the evening after bees have stopped their activity do not end up harming them).

Safari (dinotefuran) is a neonicotinoid similar to Merit (imidacloprid), the product most often used for hemlock woolly adelgid control. Jerry Moody and I tried it against balsam woolly adelgid, and it worked very well. Research from other states indicated that it was controlling EHS in hemlocks.

Mavrik is another synthetic pyrethroid that Jerry Moody was interested in. Talstar is also a synthetic pyrethroid similar to Asana. I didn't think it would work as well as Asana, but I didn't know for sure.

Lorsban is an organophosphate which I didn't think had that much activity against scales, but which Bryan Davis said folks in Michigan were recommending for scale control. Also, the folks at Oro Agri wanted us to look at another product of theirs called Vintre which doesn't contain Borax and is labeled for organic production instead of the Prev-Am.

I ended up with 4 pesticide trials for EHS control. One was applied in the spring, one in the summer, and 2 in the fall. The spring applied trial (April 28) was mostly to look at Movento. In the summer (July 7 and boy howdy was it hot!), Bryan Davis and I put out 7 different products. At the end of August (the 26th), Jerry Moody and I put out different products with either the back pack sprayer or a high pressure sprayer. Then in early October (the 8th), Bryan Davis and I tried a few products to determine if the treatment window really was closed.

I'm not going to list all the treatments, rates, treatment dates and results as it gets confusing. But I will summarize the results. The best controls (96%+ kill) were with Dimethoate plus either Asana or Vintre in the summer. Dimethoate worked well at both rates -- either 8 or 16 oz/100 gallons when mixed with the Vintre. In the past, lower rates of Dimethoate haven't worked so well with Asana. The Vintre, used at 0.5% solution did cause burn, so I'm going back to the Prev-Am.

Safari and Movento gave variable results. Movento applied in the spring with 2 appliecations made about 14 days apart, gave good control. But when applied just one time in the summer, it didn't. I think we still need to play around with the adjuvants used with Movento until we find the right one. Maybe Prev-Am would work.

Safari when applied in the summer with the Vintre gave good control, but when applied in either August or October -- and without the surfactant -- didn't. Safari's control may take longer than I give it, however. Last year, Jerry Moody had a grower that treated his farm with Safari, and when I went out about 6 weeks later, his EHS control was poor. However, when we went the following spring to pick out a site to spray in, the scales were all gone. So I plan on rechecking these results this coming spring. Also I plan on looking more at both of these materials in 2010.

What didn't work at all? Mavrik didn't, and Talstar + Dimethoate wasn't as good as Asana + Dimethoate. A new encapsulated oil called Saf-T-Side didn't control the scale any better than oil normally does, but it also didn't cause needle burn when applied on a very hot day. Because of these results, I plan on looking closely at Saf-T-Side for twig aphid control ithis spring.

There were a couple of surprises. The real surprise for me was the Lorsban. When applied in early October, it cooked them. I definitely want to work some more with this product in 2010. Another surprise was at the field trial applied in August, control was actually better using the back sprayer than the high pressure sprayer. But then, I was really soaking those handful of trees down. That just proves again the coverage is everything.

The real questions remains, how big of a problem is EHS really? It is definitely spreading, both in Fraser fir and in hemlocks throughout the mountains of North Carolina, and I think in Tennessee and Pennsylvania as well. At one farm (pictured above), Bryan Davis and I flagged trees the summer of 2008 that had scale on them. Then I went back this summer with Meghan Baker, the County Extension Agent in Watauga, and looked at which new trees had scale. In 2008, 26% of the trees had scale and in 2009, 54% did. But several of the trees flagged in 2008 didn't appear to have scale in 2009, and so the real increase was 33%! But even though scale was spreading, the trees actually looked better the summer of 2009 than they did the summer of 2008 -- just because they finally had some rain on them. The trees hadn't been sheared yet, and so I measured the terminals of all the trees. The average terminal growth for trees with scale in 2008 and 2009 was 16.9 inches. For trees with scale only in 2009, terminal length average more -- 19.1 inches. Trees with no scale at all (maybe they are growing so poorly they make bad hosts) had an average length of 15.6 inches. So perhaps scales are reducing growth somewhat, but not that much.

That begs the question -- why control scale then? I think the biggest reason is the unsightly white fuzz that gets on trees in the summer (pictured above) when the males are mostly produced. Christmas trees have to be pretty, and this fuzz is not. Also, trees with scales can't be shipped out of the country.

So what are my current control recommendations? I have them all written out in a new Christmas tree note on the Elongate Hemlock Scale found at:

Of course there are still unanswered question. I guess I be looking at a lot more scales in 2010!

1 comment:

  1. We bought 25 Fraser Fir trees. Not even 1 year after planting deer ate all the needles off all of them. Now I am left with poor looking tree's. The tops seem to be coming in with lots of new growth. About a ft. down the are (naked). Can something be done? Can the bottoms be trimmed up to force the growth up the tree? I have fenced all of them in, so they can't eat anymore. Can anyone help??????????