This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
It is well known that throughout a large part of the United States the elms are skeletonized by a small slug, which renders the trees very unsightly after midsummer. We could find no account of this in the works of the leading entomologists, so set the writer of this at work to observe this season, and this is what he saw: About the middle of May the leaves are seen to be eaten into small holes, and a small beetle, about one-third the size of a potato beetle, is found to do the work. It is green, and has a dark olive-colored line running down each wing. It is an extremely active insect, but " plays 'possum " at the least suspicion that anybody is after it; and when more frightened, drops as if dead to the ground. It appears to be a species of Galeruca. After two or three weeks the eggs hatch, producing the " slugs" which skeletonize the already riddled leaves. Our entomologists would do good service by working the matter up more precisely.
We find this enemy has been fully recognized by the ever watchful Prof. Riley, who detailed its operation in the New York Tribune, for Aug. 7, 1873, as follows:
"The elm is a favorite shade tree here, as well as in New England, and we seem doomed to have them all killed by an insect. One of my neighbors thinks that the eggs are deposited by a bug (see sample inclosed), which flies up into the branches; but others believe that the female ascends by crawling up the body of the tree? Can't you refer this note to some competent person, and publish the simplest known remedy - suitable for poor folk to practice. Tobacco juice will drive them, but it is expensive, and in case of large trees, impracticable." - [Thos. S. Watson. Louisa Co., Va.
Reply by Prof. Charles V. Riley, Entomologist.
"The specimens inclosed in the above letter were badly smashed (all correspondents who send entomological specimens should enclose them in a stout box, or other receptacle, and not loosely in a letter), but were, nevertheless, easily recognizable. There were several specimens of the perfect beetle, and a few of the larvae of one of the most injurious insects of the elm, viz., the striped elm leaf-beetle (Galeruca Colmariensis, Fabr). Almost every one is familiar with the common striped cucumber-beetle (Diabrotica vit-tata) which infests cucurbitaceous vines, and this little elm-leaf beetle bears a close resemblance to it both in size and markings; but instead of having a smooth larva inhabiting the root like its cucumber-feeding congener, the elm species has a brown larva, ornamented with short, stiff hairs springing from polished warts, and feeding externally on the leaf. In this respect it resembles some of the flea beetles, e. g., the common grape-vine flea-beetle (Haltica chalybea, Illi-ger), from whose larva it would hardly be distinguished by the ordinary observer.
The striped elm-leaf beetle is winged in both sexes, and the female consequently flies into the trees with the greatest facility. Those who believe that the female ascends by crawling, confound it with another serious enemy of the elm - the common canker-worm - which produces a moth which in the female sex is apterous, and consequently must climb up the tree to deposit her eggs. The same blunder was once committed by the city fathers of Baltimore. This same little beetle was skeletonizing the leaves of, and doing great damage to, the elms planted for shade and ornament in that city, and the authorities, aware that the elms in Philadelphia had been effectually protected from certain defoliators (in this instance genuine canker-worms) by the use of leaden troughs fastened around the trunks and filled with oil - went to a good deal of trouble and expense to furnish their elms with similar troughs. They found to their sorrow that their efforts were futile, since it was the leaf-beetle, and not the canker-worm they had to deal with.
Had they, instead of blindly jumping to conclusions, sought the advice of some entomologist, both time and money would have been spared.
Galeruca Calmariensis is - like so many of our worst insect enemies - an importation from Europe, and I have known elms in France to wear a sad, blighted and scorched appearance from its ravages. Fortunately, it does not yet occur in fhe State of Missouri, and in suggesting a remedy I cannot speak from personal experience. Nor do our transatlantic friends help us much with their experience, for though the species has swarmed during certain years on the elms in Paris and other large French cities, the French writers confess that they know no remedy. Indeed the insect is not so easily managed as the canker-worm, and has heretofore defied man's efforts to counteract its ravages. The similar larva of the grape-vine flea-beetle is brought to grief by a thorough dusting of the infested vines with dry lime, while an application of any mixture having Paris green as its basis, deals rapid death to the striped cucumber beetle. I would consequently advise your Virginia correspondent to dust his trees with lime by means of a perforated vessel attached to the end of a pole, or to syringe them thoroughly by means of a garden syringe, with water in which Paris green is stirred - one pound of the green to 15 or 20 gallons of water.
The proper proportion of green and water to be effectual will depend on the quality of the former, and should first be ascertained by a few experiments on a small scale. The first remedy will prove most expedient if the trees are small - the last, perhaps, if they are large.
They are oval, fixed on the small end, and arranged in rows along the ribs of the leaves. The larva which eats only the parenchyma of the leaves, descends when full grown, and enters the earth to transform; while the beetle hybernates under whatever shelter it can find. As preventative measures, therefore, I would advise a good sprinkling of lime on the ground under the infested trees, as soon as the larva is noticed on them, and a careful collecting and burning of all leaves and rubbish late in the fall of the year.