Stumped is not something we often admit to being. As a new horticulture agent, I am still delighted when I get a chance to learn something.
Recently, myself and others in my area, began to notice a fuzzy white growth on Ruellia simplex, a ubiquitous though invasive and not recommended landscape plant. It’s been particularly rainy, hot, humid and the problem is showing up in all manner of managed landscapes, so naturally we assumed (since fungi make up about 85% of all plant diseases) that we were looking at a potential fungal pathogen of Ruellia spp.
After some deft detective work by our Florida Friendly Program Coordinator Susan Griffith, we stumbled upon an older blog by one of our since retired UF/IFAS Extension Agents, Doug Caldwell (known to us as Doug Bug) about a tiny but mighty mite.
Turns out that the white fuzzy growth on the Ruellia is a growth known as erineum and is caused by an eriophyid mite. These microscopic mites cause the plants to respond with abnormal ‘velvet galls’ on the surface of the leaves and stems. This growth does not typically result in long term health problems for the plants and will generally clear up as the weather shifts in the fall. One potential upside to an infestation of these mites is that they act as a food source for beneficial predatory mites, increasing their populations in the overall environment.
Have you got a question about strange fuzzy or otherwise abnormal growth on your plants? Submit your photos/questions here and we will get back to you!
Even if we get stumped, we have a wealth of resources and love the opportunity to learn!