Bald cypress, a deciduous conifer, sheds its needle-like leaves in early fall after the foliage turns tan, cinnamon, and deep orange. We noticed fall-colored needles in bald cypress trees grown in a nursery in western Kentucky last May (Figures 1 & 2). The symptoms looked like nutrient deficiency at first, but as we looked closely we noticed irregular red spots. Nothing could be seen with naked eyes, but under a stereoscope in the laboratory we found many tiny creatures that were identified as eriophyid mites.
Conditions Favoring Rust Mites
Bald cypress rust mite (Epitrimerus taxodii) is species-specific, hence it will not attack other host species nearby. High temperatures in late spring, as well as high humidity, trigger a rapid increase of overwintered eriophyid mite populations. Bald cypress rust mites feed and live freely on the surface of the bald cypress needles.
Identifying an Infestation
They are clear-white or light-orange colored mites with a worm or cigar shape (Figure 3) that occasionally have their bodies covered with a white wax (Figure 4). A large number of molted skins (exuviae) are left on the affected foliage (Figure 5) as product of mite development; and after high populations migrate to healthy leaves. This may be the easiest sign of infestation to find.
Rust mites feed by rasping the epidermal cells to suck their contents. The needles initially turn yellow, and they later turn brown and reddish as the damage progresses. Nursery trees with obvious mineral deficiency showed severe damage (Figure 1). Landscape bald cypresses (Figure 6) grown in UK Research and Education Center in Princeton showed mild discoloration that was hardly noticeable at a distance in early summer. The presence of bald cypress rust mite is usually not detected unless there is considerable damage. Bald cypress rust mite monitoring is especially recommended for small plants to avoid severe injury and economic losses in nurseries. To detect rust mites, it is necessary to use 10X or higher power handheld magnifier.
Eriophyid mites can be controlled with thorough spray coverage using miticides, such as abamectin. Once the mite population is controlled, plants might recover by developing new green foliage (Figure 7). Horticultural oil can cause injury to bald cypress, therefore it should be avoided. Please read the insecticide label for the proper use and rates. For more information, consult your county Extension agent.
By Zenaida Viloria, Extension Associate; Virginia Travis, Horticulture Technician; Raul Villanueva, Extension Entomologist; and Winston Dunwell, Extension Horticulturist