Hardiness and Notes on the Rhododendron Bud Moth
By Joseph B. Gable, Stewartstown, Penna.
On page 47 of the January Bulletin, Dr. Overstreet of Eugene, Oregon, describes a worm which eats the flower buds of his rhododendrons. He states that he has seen no description of this pest and shows two photos of it. (Fig. 7 and Fig. 8).
We have a pest here which if not the same is very similar and neither have I found any reference to it in our rhododendron books. We call it a 'bud moth' locally where it is very common to abundant in some seasons. It is probably endemic for it is to be found here on our native Azalea nudiflora everywhere. And in this part of York Co. this azalea is the most common undershrub in our forests.
This 'bud moth' starts its bud eating activities very early in spring. I have found them with the head inside the bud in warm spells in February and in the same position frozen hard in zero freezes so I surmise that the eggs may be laid in autumn. Whether they are laid on the bud or where I do not know. It may be very destructive in some seasons. Very early spraying with lead arsenate or any stomach insecticide is necessary, so early that one seldom gets it done. I have wondered if they were sprayed in fall with lead arsenate in something like 'Wilt-pruf' if it would hold long enough to get them. It should be noted that after the larva have their heads in the hole-they may enter the bud completely when small or when the bud is large enough-it may be difficult to get the poison into the area where it feeds. After the new foliage has started growth these same worms seem to feed on it too to some extent and should be easily poisoned but by then the buds are killed. Often they do not eat all the flower buds and the truss appears as though it had been partially winter killed when it opens only a few flowers.
We know nothing more of the life history of this pest than the above or how much of the eastern U.S. it may infest. Of course it always prefers the prize plant in one's garden. The only good thing I can say is that it is generally not abundant and when it is abundant is mostly localized to small spots of the planting.
I think a really severe winter of continued cold inhibits their activity to some extent but in the Northwest with its milder winters I could envision very unpleasant possibilities. And there is the chance that the Dr. and I are describing different bugs?
Again the results of the hardiness tests of evergreen azaleas on page 40 differ considerably with our experience of many years here with our plants in the open.
Again, on page 15-17 of the A.R.S. Quarterly, January 1959 regarding the descriptions of R. yakushimanum, the two plants I have so labeled are easily separated from R. degronianum, makinoi and the like in foliage but my R. yakushimanum always loses its buds and the foliage is injured in our winters. Which probably makes it a true R. yakushimanum?
My prize plant of this group of rhododendrons is R. adenopodum - or correctly - one plant of this species which seems to outdo its kinsmen. This superior seedling of adenopodum was one of my finest plants but was badly broken by snow in March 1958.
Hybrids of this group of rhododendrons with others of the R. ponticum, and R. fortunei series have produced nothing of enough worth to carry on with me. Perhaps they will mate better with R. griersonianum and R. haematodes to give us some hardy dwarfs.