Elm Leaf Beetle on Siberian Elm, not a Chinese Elm

Q. Looks like elm leaf beetle or leaf miner damage in the picture I sent. What to do? Let the tree flush a new set of leaves after the larval feeding frenzy? These are trees cared for by volunteers and found in Spring Mountain Park near Blue Diamond. I would rather have the volunteers not use any systemics. Any thoughts?

This is elm leaf beetle damage to Siberian elm. To my knowledge the elm leaf beetle only attacks Siberian elm. Siberian elm is different from Chinese elm.

A. That’s elm leaf beetle (ELB) damage on Siberian elm leaves. We used to see a lot of it when there were more Siberian elms in our community. If you can catch them in the larval stage, they are easy to control by spraying the leaves with any type of insecticide. Any insecticide works including soap and water and salt sprays. You just need to kill them.

That's elm leaf beetle damage taken from a slide over fifty years ago in Colorado.

            The problem is the act of spraying which means specialized equipment because the trees can grow 40+ feet tall. Soap and water sprays kill on contact. They don't have any residual, so you must spray the leaves until the level of control you want is achieved. Otherwise, you must use a systemic insecticide as a soil drench or have it absorbed through the tree trunk.

Larvae of elm leaf beetle adults (don't confuse them with adult cucumber beetles) taken from a slide over fifty years ago. They are ephemeral, meaning they last only a few weeks and they are gone.

This is a nearly mature form of Chinese elm, maybe evergreen elm. Notice how tall Chinese elm can grow. Don't confuse them with Siberian elm which is a trash tree.

            I just ignore them and tell people not to plant Siberian elm when I see it. Recovery of this tree from single feeding by ELB is not a problem. I have only seen ELB eat the surface of Siberian elm leaves, not any of Chinese elm types including lacebark elm. Plus, ELB has only one generation each year while other insects, like the great leaf skeletonizer, is more destructive and mates multiple times each year.

            I consider Siberian elm a “trash” tree and ranks about 2 out of 10 in desirability. Chinese elm, on the other hand, is a much better tree and I would give it an 8 or 9 out of ten. By the way, Siberian elm is no longer sold as a landscape tree. No great loss.

Siberian elm removed with a telehandler...aka forklift... at Aherns

Leaf Damage Can Come from Salts

Q. Do you have any idea what causes deformed leaves to appear on my shrubs? I thought it was from heat this past summer but I also see it on trees not in this sunny spot.

Readers picture of small, deformed leaves from shrub. Except for the scorched leaf margins, the plant looks healthy.

A. If you look at the edges of the deformed leaves on your shrubs, they have brown margins or edges, very typical to salt burn.

            Fertilizer? If too much fertilizer is used or placed too close to the plant, it can cause this kind of brown leaf margins. They can also cause unusual growth. Most fertilizers are salts and can cause salt burn if too much is applied or applied too close to the trunk or main stems.

Extreme salt damage to vegetable leaf

            Salt damage sometimes occurs after a heavy rain. This is because salts are pushed away from the roots with applied irrigation but rain can push the salts back toward the roots. The return of salts to the roots can cause plant damage. For this reason, it’s a good idea to run drip irrigation right after a heavy rain.

Minor salt damage to pepper leaf margins. Enough to cause eventual leaf cupping.

            Salt damage is much worse for plants when air temperatures are hot rather than cool.

            Not enough water applied? This has nothing to do with how often water is applied, how many days each week, but about how much water is applied during each irrigation. Drought like this can also cause smaller leaves with brown margins.

            Salt burn can look a lot like drought.

            Mulch problem? Mulch placed too close to the trunk can cause disease problems when the trunk is in contact with wet mulch too often? This is true of wood chip mulch and rock mulch.

            Zinc deficiency can cause something similar, but I don’t think this is a zinc shortage.

            What to do? Flush the area under the canopy with a large volume of water to wash salts away from the roots. Secondly, pull wood mulch or rock mulch away from the stems or trunk of the plant. Third, add one or two more drip emitters to the plant so as to increase the volume of water applied without having to change the minutes on your irrigation clock.

Damage to Citrus Leaves Varies with Seasons

Q. Someone I know is having problems with something eating the leaves on his citrus tree.  I cannot think of what animal would do this.  Can you?

Feeding damage by insects can vary with the maturity of the leaf

A.  If this damage occurred to citrus leaves earlier in the season when temperatures were warm, it could because the by insects or even snails. If this is happening now, while temperatures are cold, then think of warm blooded animals such as rabbits, ground squirrels or even rats.

Ground squirrels hibernate when temperatures are cold but you may see them active when temperatures are still warm but it is winter time.

Citrus leaves will probably drop when the temperatures get cold enough and so that problem will be gone. I would not worry about it too much at this time of the year. It would be more of a problem if leaves started disappearing during warm weather when the plant is relying on the sun for its source of energy. If it's caused by warm-blooded animals, they will move on to something else.

Leaf Cupping Normally Aphids...But Not This Time!

Q. My Blenheim apricot tree planted in 2012 is not doing well. A few branches have lost all their leaves. Other leaves are starting to curl and cup. This year it had plenty of apricots but few leaves. I thinned them out since the tree is young.

Bougainvillea with Leaf Damage in Circles

Q. I bought a Bougainvillea ('Barbara Karst') last April and planted it in my front yard. After digging the hole I added a local Rose and Flower food in the bottom of the hole. I then added water and then planted the Bougainvillea.

            This plant receives sunlight more than 6 hours every day and I water it as noted on the label. All went well until something started to carve big divots out of the leaves. I sprayed "Ortho Bug B Gone" as I was told and only sprayed it on the plant at night so it would not burn the leaves.

            Well it did the trick but the edges of the plant started to turn brown and shrivel up. As soon as new fresh, unsprayed tender leaves came out, the bug came back and started to carve out holes in the leaves again. Is there something I am doing wrong?