Background: These boxwoods from a commercial nursery in Central Florida were showing signs of yellowing with the leaves progressing to a coffee-like brown color. Eventually, they would die back. The problem was widespread, affecting half of their liners. The issue was first noticed about 2-3 weeks ago and seemed to affect the plants in the open air more than those under shade.
Diagnosis: After culturing a sample of the plant tissue, we determined that the root cause of the illness was rhizoctonia. Rhizoctonia is a soil-borne fungus that is not uncommon in Central Florida. Along with the damage to the leaves, infected plants may be slower to put on spring growth than unaffected ones. There may be root discoloration and the bark may come off easily.
Treatment: We recommended this grower apply thiophanate methyl, a common fungicide, as soil drench to treat this current infection. Rhizoctonia, like most root rots, favors a continually moist environment with warm soil temperatures, so long-term we recommend taking steps to reduce prolonged soil saturation in the warmer months by paying closer attention to irrigation cycles.
“Just Rolled into the Clinic” is an ongoing series of interesting issues from the commercial plant clinic at the UF/IFAS Mid-Florida Research and Education Center.