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Back to Questions - Pests

Back to questions: first about problems with an aspen; and second, about a recurring common pest on various thornless honeylocusts!
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

June 19, 2011

Above: A typical Sunburst Honeylocust (Author photo), and below, the typical damage done by the common locust pod gall. (Photo by Michael Masiuk.)

It’s back to questions this week. The first one from Susan Homeniuk was sent to Donna Dawson.

“I was hoping you may have some advice for me and my husband with regards to one of our Columnar Aspen Trees. We have a few of them in our yard and along our front street driveway. One tree along the front drive-way has some dark sap running down the bark and there are ants crawling on it. There are holes in the bark, which I am assuming are from the ants burrowing into the wood. Some of the branches do not have any leaves on them; some smaller branches have dried up and can be easily broken off. Will this tree die from the ants bur-rowing and cause havoc? Is there something that we should do or buy that can help us with this problem? Any advice you have for us would be appreciated. Thank you.”

Susan, you seem to have a problem, but I think the ants are secondary to the actual problem. I don’t think the ants will cause any major problems; they are only there because of the tree’s sap running down the bark attracting them. What has caused the holes is the greater concern. There are numerous “new” boring pests affecting various tree species and since you haven’t told us from whence you are writing it is impossible to even think about diagnosing what may be attacking that tree. I suggest you call in a major tree service company expert, and again since I don’t know in what city you reside, I definitely cannot make a recommendation there either.

In reviewing the “Forum” section on this site, I see a new question added to a string about problems with Sunburst Locust trees. Here is the latest from “mh” of unknown location or even zone: “My locust is sick this year 2011 and I would like to know how your trees have survived the green bug infestation.”

This all started back in June 2004, when Peggy wrote from zone 7 thus: “Our mature Sunburst Locust has a very thin canopy this year and the new growth has either died or been eaten. There are several little green aphid-like bugs crawling around on the patio area underneath the tree. Any idea of what the problem might be and what I should do?”

That was followed just about two weeks later in 2004 when Simon in Kingston wrote the following: “Same thing happening here in Kingston. About 60% of the Honeylocusts in town are severely defoliated. I don't know what the pest is but I'm not surprised it's happening. Forward thinking urban foresters have been preaching diversity for years. Two of the examples they gave were Austrian Pine and Honeylocust. Both had an existing pest/pathogen that was gaining strength because of the ever increasing densities of those two tree species.

“As for what to do.... 1) Do nothing and hope the tree recovers and the pest population crashes before the tree is permanently damaged. 2) Treat the tree with a systemic pesticide (i.e. Cygon) knowing that it may help it this year but you will probably have to reapply every year until the pest population crashes. (Cygon is about to be unavailable in Canada). 3) See what the organic pest control people recommend? If it's a large tree, they will probably recommend Option 1. If it's relatively small, they may be able to spray it with Bt or an insecticidal soap?”

Well six years have passed and not only Cygon, but most other good insecticides have been removed from the retail market.

Just on June 27th last year, I wrote about this same problem. Here is what I said.

“Your problem is a common one that I first saw in Niagara Falls in 1962. It seems to vary in its presence for I do remember after some very bad years in the mid-60s it seemed to wane, and then became very prevalent almost a decade later.

“It is Locust Pod Gall, and is caused by a tiny insect, or midge, known as Dasineura gleditschiae. The tiny (3 mm) adult flies over-winter in the soil and will swarm around the trees in early spring just as new foliage begins to show. They lay eggs, virtually microscopic, which hatch in just a few days into larvae about 3 to 6 mm in length. These begin eating on the new young foliage causing the foliage to turn into the galls you notice. Soon the larvae are enclosed in these galls. In a few weeks they pupate, and soon a new adult emerges, and the whole process may be repeated, or there may just be one generation, depending on the year and the climate. The dried up galls eventually fall off making the tree look somewhat bare of good foliage, and some smaller branches may be killed.

As an aside now in 2011, there are other insects, such as leafhoppers which also affect these trees, which are slightly more easily controlled because they remain on the surface of the foliage and branchlets.

Let’s return to my advice of a year ago.

“Although I realize [the original inquiry came from Ontario, but as mentioned, I do not know from whence ‘mh’ is writing.] you are in ‘no-spray’ Ontario, many jurisdictions such as other provinces and many U.S. states recommend spraying weekly, beginning as soon as the foliage begins to open in spring, with Carbaryl (Sevin) or Diazinon, but of course that option is not open to you! In checking on the Web I find no other valid recommendation, but I can tell you of a plan used by some horticulturists in Canada a way back in the 60s and 70s. That is to take a pair of scissors and cut off all or most of the galled foliage, and place it out in the garbage, or burn it. Certainly, do not compost it.

“This is quite a major undertaking, especially if the tree is large. Once it is done, the tree will look thin because of all the tip foliage that has been removed, but, it will look no worse than the tree would just a little later in the season once the galls have dried and fallen off. The theory behind the clipping of the galls is that by ridding the tree of the larvae permanently, and doing it several years in a row, it is quite possible that the number of insects left to re-infect in following years is reduced, and hence the damage in subsequent years will be lessened.

“Another important part of keeping the trees healthy is to keep them growing in a strong way. That means providing extra fertilizer for the trees, either in the form of granular high nitrogen fertilizer applied to the ground surface around the drip spread of the trees, drilling in fertilizer spikes in the drip spread area, or applying liquid fertilizer (20-20-20) to the foliage at least three times during the spring season.”

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