Weevil Damage to Rhododendrons?
F. W. Schadt
Jeffersonville, N. Y.
For several years, I have had rhododendrons that showed leaf damage in the form of notched edges. Neat little semi-circular bites out of the margin of many of the leaves. Some plants showed little if any disfigurement, but there were two or three that really looked disgraceful toward the end of the summer. The damage to the foliage increased each year, but principally to the same plants. All the reading I did on rhododendrons inevitably gave me the same answer-Black Vine or Strawberry Weevil.
The leaves of many of my plants looked identical to the pictures of weevil damage shown in every book or catalog having anything to do with rhododendrons. Every rhododendron grower, I talked to, almost condescendingly assured me that weevils were damaging my plants. The damages were so obviously caused by these long snouted pests that apparently I was lacking in even elemental knowledge to discuss the matter.
Mr. E. P. Breakev wrote in "The Handbook of Rhododendrons," "The rounded notches that one often finds cut in the margin of rhododendron leaves have doubtless (the italics mine) been made by Black Vine Weevils while feeding." At least five other authorities said the same thing in varying language.
Content for the time with the assurances of everyone, I laid poison bait and sprayed as directed, but of no avail.
I had read, of course, that weevils were nocturnal feeders, and so to the amusement, and finally, I think, suspicions of the neighbors, I would sneak up on the plants at all hours of the night trying to find the culprits that did the damage. Never was there one to be seen. I sifted the mulch around the plants-still no weevils.
Finally, last summer while nosing around the Curtis Nurseries, in Callicoon, New York, I bumped into Doctor L. L. Baumgartner, of the Horticulture Research Laboratory, of Croton Falls, New York, and in the course of our conversation, I casually mentioned my troubles and my nightly search for weevils. He smiled and remarked that he had had a similar experience with plants of a client of his and that his decision when first made was that weevils had caused the damage, but that subsequently, as all methods of control had failed, he had reached the conclusion that the damage had been caused by fungus. It was his opinion that what really happened was that fungus would attack the margin of the leaf, causing dead areas which went unnoticed until they would drop out, leaving a hole or indentation similar to insect bite and especially that of weevil. He suggested I spray with Capstan and watch the results. I did as he suggested, spraying the plant which was worse affected thoroughly and regularly, spraying a couple of other plants less thoroughly, and leaving some completely unattended. The results were convincing. For the first time in four years, the plant most affected had nearly unblemished leaves and each plant showed results in accordance with the amount of spraying.
Twice each day I would examine all the plants and actually watched the blighted areas develop on those which went unsprayed. Often in the morning, I would find notched leaves where the evening before there was a dead, but not markedly noticeable area.
I do not mean to even suggest that weevils do not do damage with which they are charged, and unquestionably, they probably are major pests. I just want to pass along my experience and would almost like to wager that much of the so-called weevil damage here in the northeast and northern middle Atlantic states is caused by fungus and not weevils. I am enclosing a few leaves from an unsprayed plant, so that you can see the damage I have written about.