Quad City Times, IA
07-02-06
Webby stuff is evidence of spider mites
By Alma Gaul
Q: There’s some kind of web-like material on the bottom side of my plant leaves,
and some of the foliage is getting yellow. What is this? — Various, Quad-Cities
A: You may have an infestation of spider mites, which were particularly bad last
year because hot, dry weather favors their growth. Rainfall washes the plantfeeding insects out of vegetation, but without that they stay and multiply.
Spider mites really like euonymous (burning bush) and spruce and pine trees.
Mites won’t kill a plant outright, but with repeated and heavy infestations, they
can stress a plant to the point that it dies, Iowa State University Scott County
Extension horticulturist Duane Gissel says. Spider mites use their mouthparts to
remove plant fluids and chlorophyll (green pigment), which results in foliage
appearing bronze or brownish.
Spider mites are tiny and difficult to see with the naked eye. A convenient
detection technique is to hold a sheet of white paper under a branch and then
shake or tap the branch against the paper. The mites, if present, will show up as
tiny, slow-moving specks on the paper.
One of the first things you can do to control mites, especially if the infestation is
light, is to give your plant a strong hosing with water. A forceful stream will
dislodge mites. Repeat three or four times on consecutive days.
If your infestation is heavy particularly on conifers, or on a plant near conifers you
may want to use a pesticide, although Gissel urges caution. Pesticides will kill
beneficial bugs as well as the mites.
Sprays available include insecticidal soap, horticulture oil (summer rate),
malathion, Isotox and Orthene, according to Dr. Donald Lewis, entomologist at
Iowa State University, Ames. Use according to label directions.