Spider Mites for Beginners

by Georgie Bever, Consulting Rosarian, Denver Rose Society

This is a 2020 AOM winner

Spider mites are not really spiders. Spiders have two parts to their body, and the mites only have one. But they are related. Think of a wolf and a Dachshund. Both are canines, but the Dachshund is quite different in looks, size and temperament. Spider mites would be the Dachshund. They are also related to ticks.

Many varieties of mites love it hot and dry, making a Colorado garden a perfect home for them.

Sometimes their web is so fine it is hard to see the filaments, but you can see leaves, twigs, and/or pine needles laying on top of the webbing as shown in the picture to the right.

There are many kinds of mites. The spider mites on roses are only one of many varieties. We call them “Spider Mites” because they excrete a web that reminds us of the spider and her web in the children’s book Charlotte’s Web. (No, they are not named from the book, but it is a good example of the webbing from a book most of us have read.)

Spider mites are so tiny, you must have excellent eyesight to be able to see them without magnification. It is much easier to see their webbing and damage to plants.

If you suspect spider mites on your rose leaves, clip off a leaf you suspect of being infested with mites. Place your thumb on the bottom of the leaf and your index finger on the top. Apply light pressure and pull the leaf though the closed fingers. If it leaves a rusty red- looking residue on your thumb, you have spider mites.

Your first line of defense with Spider Mites is a swift stream of water from your garden hose. Wash the bottom sides of the leaves on your roses. Use a strong stream on webbing seen in your garden. Use a heavy stream of water to wash the foundation of your house and other structures at least once a week.

Once you see webbing as shown to the right and below, you already have a heavy infestation of spider mites.

The next line of defense should be a solution of 1 part rubbing alcohol to an equal part of water in a tank sprayer. Add one drop of dish liquid to the tank and agitate. Spray the underside of the leaves plus any webbing you see. Check the foundation of your house and any outbuilding. Spray if necessary.

If all else fails, use a Miticide. NOT a broad-spectrum insect killer – a Miticide. Read the labels carefully. Many will say “Do not use if temperatures are above 80 degrees.” That doesn’t mean 80 degrees when you spray. It means if the high for the day will be 80 degrees or above. I strongly recommend against using Neem oil or any other product that is oil based (mineral of petroleum-based oils, too) any time after the middle of May. Our weather is just too hot, and our sun is too intense.

Remember, you have Consulting Rosarians and Master Rosarians in the DRS who you can call upon for help at any time. We are here to help you.

Photos by Georgie Beaver