Homegrown column Aug. 08, 2009

Indoor glamour comes to the great outdoors

• I’m taking care of my parents’ yard, which has 30-year-old honeylocust trees in it. Recently, the two trees have been continually dropping yellow leaves. Also, the bark seems a little discolored, but maybe it’s because of the age. Should I be worried or is this normal for the weather we have been having this year?  
— Gina

There are a couple of things that could be causing the yellow leaves, but the one that’s most common is a little bug called a honeylocust spider mite. These little guys (and I mean little — they’re smaller than the common two-spot spider mite) start showing up when it starts getting hot and cause yellowing or browning of the foliage and the leaflets to fall off. 
They’re pretty much always on the underside, along the midrib of the leaflet. They’re orange or yellow in color and you really need a magnifying lens to see them. They’re prolific little buggers, too, with a new generation hatching out every four to seven days in the summer, so their numbers can quickly explode.
Honestly, they really don’t hurt the plant to any great extent, but they will stunt growth a bit and make the plant look pretty sad.
There are a number of ways to control them. If the tree is small enough, you can give it a shower with cold water out of the hose every day or two. Use a hard spray and be sure to concentrate on the underside of the leaves. Do this for two weeks and you should see great control.

There are several sprays you can use as well. Insecticidal soap and All Seasons Spray Oil work well. Just make sure to get complete and thorough coverage of the undersides of the leaflets. Also, do the spraying in the morning to minimize the chance of a spray burn occurring. 

Chemical insecticides tend to have a longer residual action and you don’t have to be quite as perfect about good coverage. Just don’t get lazy about doing a good job of spraying; good coverage will give better results. Also, be sure that the product will control (not suppress)
spider mites.

Lots of common insecticides won’t work on spider mites. In fact, using the wrong product can make your mite problems worse in that they’ll kill the mite’s natural predators. Your best chemical miticides would be Bifenthrin and Acephate. Again, spray early in the morning when it’s cool during this hot summer weather. 

• We have an Alberta spruce that we planted about six or seven summers ago. Until last summer, its growth was predictable and uniform. The foliage was dense and even.

Last summer, it began to sprout individual branches from near its crown. These branches differ in color, shape, and texture from the original growth. They are bluer, longer, and more randomly spaced. Even the needle length is different.

My concern is that the Alberta spruce must have been grafted onto the roots of a different tree, and that tree is now manifesting itself and taking over. The space the Alberta is in is small, but the tree’s expected mature size (5 feet wide by 10 feet tall) should create no problems. If the Alberta is somehow becoming a different tree, however, I am afraid I may have to cut it down.

Could you please confirm what is happening and tell me if there is anything I should do?
— Steve

What you’re seeing is not all that common on dwarf Albertas, but not unheard of either. Dwarf Alberta is a variety of white spruce and it was discovered as a “witch’s broom,” which is a naturally occurring mutation of the tree. This is where most all of the dwarf spruce varieties come from. For whatever reason, that branch spontaneously changed its growth habit to the smaller needle and the dense cone shape we know as dwarf Alberta spruce. 

Sometimes, the variety expresses some instability. That is, it will spontaneously revert back to the species type of growth. That’s what you’re seeing in your plant. We really don’t know why they do this. Some think severe weather or some other stress can do it, but the bottom line is that we really don’t know.

Anyway, your plant is not necessarily a loss. Dig down into the plant and find the base of that oversized branch and cut if off completely. You may be left with a small hole in the plant but that will fill in time. If any more of these mutations show up, cut them off as soon as you see them.

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


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