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, March 7, 2012

Safari for Scale Control

This is my 100th post on this blog!!! 
Thanks for all the support with this endeavor!

Elongate hemlock scale (EHS) is on everyone's minds these days. In some Christmas tree counties in western North Carolina, as much as 85% of the fields are infested with scales. EHS is difficult to control, but the good news is, with scale control comes control of many of our other pests of Fraser fir including balsam woolly adelgid (BWA) and balsam twig aphid (BTA).

Safari (active ingredient: dinotefuran) is a new material recently labeled for Christmas trees. You have to have a copy of the supplemental label for use in Christmas trees.
Safari is a systemic and works well against BWA and EHS. The following are some of the lessons learned in 2011 in using Safari for EHS control.

Lesson #1: Trunk applications haven't worked well.

Applying Safari to the trunk
This method of application would be preferable because it is easier and it would result in the least impact on the parasitic wasp, Encarsia citrina, that attacks the scale. The recommendation was to apply Safari to the lower trunk of trees using a backpack sprayer and a rate of about one pound per acre.

Several growers tried this application method. I also put out several trials in Mitchell and Avery Counties. In our trials, we used a backpack sprayer for application, as well as a high pressure sprayer -- in some instances wetting the entire trunk. Unfortunately, despite the application method or timing, trunk treatments haven't worked well for us in NC. In 2012, I want to look at high rates, but for right now, foliar sprays of Safari are best.

Lesson #2: Full rate and good coverage give best results.

To date, the best EHS controls in North Carolina have been with a high pressure sprayer and full foliage coverage using 8 ounces of Safari per 100 gallons. This has ended up with a rate of as much as two pounds per acre. This application method has worked well from mid-May through August. When used in early October, control was poor.

An August application combining Safari with a bifenthrin product such as Sniper would control almost all Fraser fir pests --  EHS, BWA, BTA for the following year, Cinara aphids and spruce spider mites (SSM).

Lesson #3: It takes a while to work.

The "white" from the males
In my February 9, 2012 blog post, "Working with Safari," I described how control of Safari improved over time. In fact, it can take as long as four months.

This has made several people think it would be better to put Safari out earlier so it will have time to work. Of particular concern are the male scales that create the white on the foliage. But though the product takes that long to work fully, it is primarily the female scales which are toughest to kill that require the full four months to die. The male scales and crawlers are typically all dead within a month and even many of the female scales. So don't think you have to spray in April to prevent the male "white" on the trees. Even trees treated in August looked great by harvest a couple of months later.

Lesson #4: Natural enemies are important.

A wasp caught on a yellow sticky card.
It is the size of a gnat.
Probably the most important natural enemy of the EHS is the parasitc wasp, Encarsia citrina. This wasp lays its egg inside the immature female scales and develops there, eventually exiting as a full grown wasp from a round hole it makes in the scale's outer shell.

The following website has information about this scale: Entocare, biological pest control. (Please note that this website is mentioned for educational purposes only. The pictures are really nice. There has been no research in releasing Encarsia into Christmas tree fields).

But other predators are important too including lacewings and the twice-stabbed lady beetle.

How can you protect these natural enemies?:
  • First of all, only use an insecticide when you really need to. Scout to determine the need for control. 
  • Don't worry about BTA and mites in young trees. 
  • Reserve the synthetic pyrethroids such as Wisdom, Sniper, Talstar, Asana and Astro to the fall when they have less impact on predators.
Questions that still remain.

There are several questions about using Safari.
  1. How well would it work with a mistblower application? Many growers are set up to use a mistblower. If you would like to help us evaluate Safari applicaitons for scale control using a mistblower, let me and your county extension agent know. We'd love to work with you and follow up to see what works and what doesn't.
  2. What if you have to control BTA in the spring? Can you use Safari plus another product for BTA control and still get good scale control in April? If you're interested in trying this, again, let us know so we can follow results.
  3. Can you wait until September to treat? A September treatment would fit in better with most people's production schedule than an August treatment. First of all it's usually cooler. Secondly, Cinara aphid control would be better in trees to be harvested. Also, there would be less impacts on predators. This is something I plan on looking at this September.
  4. Would a higher rate of Safari work when applied to the trunk of the tree? Again, this is something I plan on trying -- targeting the highest allowable rate which is 2.7 pounds per acre per year.

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