Questions on: Spidermites
Ron Smith, Horticulturist, NDSU Extension Service
Q: I live in central South Dakota. We are in a very dry area and are seeing a lot of spider mites on our spruce and cedar trees. What can we do before there is some damage to our trees? Some are large, older trees and some are newly planted. I know that a good rain would do the trick, but donít think it will happen in the near future. Is there a chemical that I can use, such as malathion? (e-mail reference)
A: If you can, hit the trees with a hard spray of water from a garden hose or a pressure sprayer. If you have a family member who belongs to the volunteer fire department, get the tank truck and use that to blast the mites. I used to be a volunteer fireman and used the tanker for such purposes. Of course, that assumes there was no fire that needed putting out! Orthene is an insecticide that will provide some mite control, but entomologists tell me that using any chemicals to control them results in a resistance buildup that takes place quite quickly. With water, that doesn't happen.
A: Those are spider mites that are showing up on your plants. Control them with sprays of Insecticidal soap, making sure to get the undersides of the leaves and the leaf axils.
Q. I have noticed spider mites on a pointed ivy houseplant and the morning glory that is covering all the walls of our deck. I sprayed it with Ortho Isotox with a pressure sprayer to get under the leaves twice, a week apart.
Two weeks later the morning glory was 40 percent yellow and losing leaves, and all my flowers around the deck were about wiped out.
I sprayed the morning glory again with ivory dish soap, diluted, three nights in a row, as well as the ground area.
Still, the leaves continue to be sucked of all life and drop. Also, my ivy inside is infested again. I had used Shult 2, Instant Pyrethrin, and it had worked for awhile. Is something other than spider mites?
Also enclosed are branches from a nice bush next to the deck that is also infested. It must also be sensitive to the spray used. The brown spots weren't there earlier. It was a beautiful light green in June.
Lastly, we have 10 to 12 large (30 to 40 year old) cottonwood trees on our end of the block. The last week of August they dropped about a third of their leaves all at once. Was it the shift from three weeks of cold back to hot weather? Are they infested also? The leaves are spotty, but there is no "web" underneath.
This has been very discouraging so any assistance or advice would be greatly appreciated. (Aberdeen, S.D.)
A. I will give you an "A" for effort and for a partially correct diagnosis.
It looks as if you have some high salts in your soil or water supply, or poor drainage in the areas where you have been growing your plants. I suggest a good fall clean up after killing frosts and then incorporate generous amounts of peat moss to improve drainage. Soils in your area are typically high in pH, and the peat, especially if it is sphagnum, will help to lower it.
Morning glories are usually a piece of cake to grow and are often included in kids' garden kits.
You are obviously a very vigilant person and while that is generally good, don't overdo it.
Yes, the poplars will abscise their leaves following wide temperature and moisture swings.
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