Spider Mite Rose AttackBy Diana Wind, RD (wind)
July 8, 2010
Unlike insects, which have antennae, wings and six legs, spiders, scorpions, ticks and adult spider mites are wingless and have eight legs. Classified in Phylum Arthropoda and Class Arachnida, spider mites, in particular, lead a terrestrial life and have a short life span.
When spider mites mate, they can produce 100-plus offspring; from egg to adult only takes 3 weeks. I get the creeps just having to write about this, but imagine the 100 offspring mating and having 100 more offspring each? Now the colony has suddenly increased to 10,000 spider mites. When the 10,000 mate, it could bring the mite army up to a frightening 1,000,000! No wonder our poor shrub rose looked just about dead by the time I noticed what was going on. My mission became clear: in order to fight this new enemy, I had to learn more about them.
What are Spider Mites?
Mite species include two-spotted spider mites (Tetranychus urticae), cyclamen mites (Phytonemus pallidus), citrus rust mites (Phyllocoptruta oleivora), Southern red mites (Oligonychus ilicis) and spruce spider mites (Oligonychus ununguis). Not all mites are pests to reckon with; many mite species are beneficial, such as the predacious Galendromus occidentalis, Amblyseius californicus, Neoseiulus fallacis and Phytoseiulus persimilis. The latter, for example, are used in the control of spider mites on commercial strawberry crops.
I did not want to take a close look at our rose enemy under magnification to verify its identity, but I imagine it was the Two-Spotted Spider Mite, which typically is the culprit in rose attacks. This arachnid is very tiny, less than 0.002 inch (0.4mm long), greenish yellow in color, with two spots on its abdomen.
Common to Roses
Our beautiful pink shrub rose was in full bloom and healthy. In what seemed like a period of just days, the top half appeared to be covered with clear wrap, and the entire bush seemed to have received the kiss of death. Upon closer examination, I noticed that the leaves were covered with a silky mesh of finely spun webs from a severe infestation of spider mites. On the tops of some webs what appeared to look like a pile of saw dust was actually thousands of chomping spider mites, sucking the life and nutrients out of our once vibrant rose, changing its color from healthy green to a stippled greenish yellow, all yellow, then dead. All that remained after being stripped clean from the attack were leafless thorny stems. This meant war!
The Fight's On
I knew we had to act fast, or the entire rose would never have a chance at recovery. Using an insecticide with miticide activity would have some effectiveness, but too strong a product would not be a good solution because it would wipe out natural predators such as damsel bugs and lacewings. Spider mites are known to develop resistance to miticides too. Neem oil was a solution recommended to me by a fellow Dave's Gardener, I had to look up what it was.
Neem contains an oil extract from the Azadirachta indica, a 40-foot (12m) tall tree, native to parts of South Asia. Neem acts as a botanical pesticide, effective in fighting against spider mites. I decided to try the spray along with the following:
#1 Put on heavy gloves made just for rose pruning and grab a pair of pruners. Also bring over a heavy duty plastic trash bag.
#2 Cut back and remove the most infested branches; tightly close up and dispose of the plastic trash bag.
#3 Spray the plant all over with a forceful spray of water. This will wash away more of the mites.
#4 Use organic controls or a pesticide made just for killing spider mites. I'm a big fan of organic gardening - our property is even certified for wildlife. In an attempt to save the plant, I resorted to using a Neem oil spray. There is no guarantee the rose will survive either, especially in severe infestations. For us, time will tell - we hope our rose makes it.
According to University of California Pest Management program, organic biological controls would include releases of predatory mites, lacewings and sprays of rosemary oil, or organic PMS stylet oil.
#5 Repeat steps 3 to 4 every week as needed to control new born mites.
What else do Spider Mites Attack?
Some plants are more prone to spider mites than others. And weather can affect an outbreak too. After spider mites survive the winter in eggs laid on the underside of leaves, they hatch and thrive in hot, dry environments. Two-spotted spider mites attack other plants too, including trees, vegetable crops, soybeans, dry beans and ornamentals. Rain keep them somewhat in check; lack of rain results in greater damage.
If and when you get a severe spider mite attack (I wish you never do), this article is intended to help you win the fight!
 University of California Pest Management Guidelines, How to Manage Pests, Accessed June 20, 2010.
Spider Mites and Soybeans, University of Minnesota Extension
Azadirachta indica: One Tree's Arsenal Against Pests by Kirk Howatt, Colorado State University
Cool weather mites: Southern Red Mite and Spruce Spider Mite by S. Bambara and Steven Frank, NC Cooperative Extension