Baldcypress rust mite is evident now on Baldcypress trees in Delaware. The following is more information.
Baldcypress rust mite (BCRM). Even with the wet spring, Taxodium foliage may be showing the russetting, bronzing, distortion, and premature leaf drop that are telltale symptoms of BCRM damage. Look for the white cast skins of these microscopic yellowish-brown with a hand lens. BCRM overwinters as mated females in bark cracks and buds of baldcypress. After bud break, females migrate to needles and lay eggs. Populations build up rapidly in warm weather and typically peak in late July to Mid-August. BCRM feed until about needle drop in mid-October, when they re-position for overwintering. Use funnel sampling to scout for BCRM and other spider/rust mites.
No need to manage BCRM in the landscape, if premature browning and leaf drop is tolerable. Treatment is warranted in container and field nurseries. Several natural enemies feed on BCRM-predatory mites, predatory thrips, and spider mite destroyers (a small lady beetle - Stethorus spp.) are a few. We found that populations of BCRM were best managed using 1250 GDD or petal fall of Kousa dogwood as early indicators. We're past that now…
2% (v:v) horticultural oil the best chemical control for BCRM. While several other researchers have noted phytotoxicity from its use on baldcypress, our mid-season oil applications have reduced BCRM without burn and may provide lecanium scale crawler control as well. Attempts to manage BCRM in the dormant stage with oil applications actually INCREASED mite populations during that season and should be avoided. Avid (abamectin) or Forbid (spiromesifen) are other miticidal choices for later in the season, but will harm some natural enemies. Many newer selective miticides such as Hexygon and Floramite have NO EFFECT on rust mites, so check the label.
Information from Casey Sclar, IPM Coordinator, Longwood Gardens