A group of samples of several varieties of blue holly (Ilex x meservae) arrived in the lab from a commercial nursery in late January with a common problem, yellowing and rapidly dropping leaves and general poor growth (Fig. 1). After ruling out disease and insects on the foliage we next checked the root systems. After washing away most of the soil we started to see areas of black roots (Fig. 2, 3 and 4), especially at the root tips (Fig. 5). Microscopic examination of roots confirmed the suspicion that the plants had black root rot (BRR), caused by the fungus Thielaviopsis basicola. The distinctive black segmented spores (chlamydospores) make it easy to identify in the lab (Fig. 6 and 7) The fungus usually begins by only rotting scattered roots throughout the root system. As it spreads it can cause significant root loss and stunting of susceptible host plants. The pathogen[Read More…]
PPDL Case Study #1: White Fungi on Crabapple Branch
Purdue’s Plant and Pest Diagnostic Lab (PPDL) receives more than 2000 samples for diagnosis each year. We’ll highlight some of the more interesting cases in the Purdue Landscape Report in brief case studies like this. PPDL Case Study #1: White Fungi on Crabapple Branch Earlier this year a landscaper submitted several photos of a crabapple he had been treating for apple scab and borers. He noticed white, fan-shaped fungi growing on the bark of a still-living branch (Fig. 1). At first glance this is surprising because most fungal fruiting bodies arise from dead wood. After obtaining additional photos showing the fungus close up (Fig. 2) we could identify it as Schizophyllum commune, which is reported to occur on hundreds of species of trees and is one of the most common fungi found on wood. S. commune is a sap rot (a.k.a. canker-rot) fungus; a wound invader that spreads from an[Read More…]
