European Elm Scale can be a big hassle

While pruning some dead branches off of our Japanese Zelkova this weekend, we noticed several branches have a bunch of black scaly bumps with some white fringe on them. Do you happen to know what this is and if it’s something we need to treat?

— Tommy

Sounds to me like you have European Elm Scale on your tree.

Zelkova is a cousin to the elm, so it makes sense that it’s on your tree, though I haven’t seen it on Zelkova before this. It also can occur on other unrelated plants.

You’re maybe a little bit late for optimum spray effect, but it’s still helpful to do some spraying now.

The most effective course of action is to use a spray systemic such as Imidacloprid or Acephate. Thoroughly spray the canopy of the tree, concentrating on the undersides of leaves where the newly hatched generation tends to hang out.

You also might consider using a dormant oil spray in late February or early March next year.

A more organic option for right now would be to spray the tree (again concentrating on the undersides of the leaves) with a Season Long Spray Oil. This is a more highly refined spray oil than the dormant oils and is safer to use in the summer.

In spite of that, it is a bit risky since it can still burn the foliage if temperatures are above 90 degrees. I’ve done it with temperatures in the low to mid-90s with no problems, but quirky things can affect it and it still could burn.

Whatever way you go and whatever it is you spray with, I think it’s always advisable to do your spraying early during the cool of the morning.

You could defer any treatment until this winter if you’d like. Elm Scale will sap vigor from the tree and can cause some dieback in severe infestations, but it takes some time for it to build up to that level. The best time to target foliar sprays is about the first of July and again two weeks later.

I’ve been told that I have wireworms infesting my strawberries. What can I use to get rid of them and still enjoy the berries?

— Allen

Wireworms are an extremely difficult insect to control. In fact, there are places that no longer commercially grow crops such as potatoes because of wireworm damage.

Fortunately, they become a problem infrequently.

The old standbys in the insecticide world that were used for wireworm control (such as Chlordane) were banned from the market because of environmental problems and have not been available for years.

We went through a pretty long stretch when we really didn’t have a good solution for homeowners, but we finally have a good option. Bifenthrin is a synthetic pyrethroid that has very low toxicity to warm blooded critters such as you and me, but does a great job on insects.

Spread some granules in the area or drench it with a liquid solution. Do an application now and repeat it again in about a month.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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