Thursday, December 9, 2010

Rhododendrons - Part 4

Rhododendron 'Sapho'

Another day of rhododendrons. Today I'm going to talk about some of the insects that could bother your plants. I'll repeat what I said before - we've never had any of these on our large plantings, so don't expect them and don't be scared off from growing rhododendrons because there might be something that might bother them. I just wanted people to be aware of the possibilities and how to take care of them.
Weevils are listed as a common problem. Maybe in other parts of the country. I don't know of any weevils that bother anything here. A common one on rhododendrons (to the extent that any are common) is a small black beetle about 1/4 of an inch long. They don't appear until warm weather and then they do all of their eating at night, so you may not see them, just the holes in the edges of the leaves. These won't kill your plant, just make it not quite so pretty. Orthene is rcommended to control them, but it might not be totally effective, since they may lay eggs before they start eating for the season.
Aphids may also appear on your plants. They will like to feed on tender new shoots. Orthene or Malathion will control them, but there are also other, less chemical means. A number of beneficial insects predate aphids or if the infestation is tiny, you can just pick them off or squish them.
Scale insects may appear on the bark. These suck on the bark and exude a sticky substance that turns the stems black. This is the sort of thing that also attracts aphids.

Rhododendron calendulaceum (azalea)

Caterpillars might also like to feed on newly emerging foliage. They don't seem to bother mature foliage, so as with the previous pests, you just need to keep an eye on the new growth.

Spider Mites and White Flies both feed on the undersides of the leaves. These, luckily aren't pests we see much in the garden. We have more trouble with these in the greenhouse in the winter. Spider Mites will turn the leaves a mottled brown green color. The White Flies will leave white spots where they have been sucking. Malathion will take care of both of them.

Slugs and snails can occasionally be a problem, but because of the thickness of the leaves, this isn't something you have to worry about much. Just like in hostas, those with thick leaves are not so attractive to the little slimy pests.

Rhododendron catawbiense boursault

This pretty much takes care of the planting and care of rhododendrons and azaleas. This afternoon, when I was looking for something else, I came across an older book with a chapter on the history of rhododendrons. To finish up the week, I'll share some of the more interesting parts with you tomorrow.

No comments: