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…]
Taphrina Leaf Curl on Ornamental Flowering Peaches and Nectarines
There may still be time to protect Prunus spp. from Taphrina leaf curl. Do you remember seeing red, curled, distorted, leaves on Prunus spp. last year and wondering what might have caused this symptom? Taphrina leaf curl, a fungal disease that survives in bark and bud scales, infects peaches and nectarines as well as ornamental flowering species of Prunus. The symptoms of Taphrina leaf curl are very distinctive (Figure 1) and thus you definitely would have noticed this fungal disease if it was present in Prunus spp. last year. Infected leaves are severely puckered, distorted, thickened and reddish-to purple in color. (Figure 2) Premature leaf drop may also occur. A single, thorough, preventative fungicide application is recommended during dormancy (after leaf drop in late fall but prior to bud swell in early spring before green leaf tips are first visible). Several fungicides are recommended for dormant applications. Check the Midwest[Read More…]
Blue Spruce Update
Colorado blue spruce is not native to Indiana (no spruce is!), and it often suffers from environmental stresses such as drought, excessive heat, humidity, and compacted or heavy clay soils—making it an already poor choice for our landscape. If that weren’t enough, it also suffers from needle cast diseases. Needle cast is a generic term that refers to foliar diseases of coniferous plants that result in the defoliation (“casting off”) of needles. Needle casts vary by host, and severity is dependent upon the age of infected needles. Of all the foliar diseases affecting woody landscape plants and shrubs, needle casts are the most serious for the simple reason that coniferous plants do not have the ability to refoliate, or produce a second flush of needles from defoliated stems. Rhizosphaera needle cast is a fungal disease, caused by Rhizosphaera kalkhoffii that attacks the needles of Colorado blue spruce in the spring,[Read More…]
Damping-off of seeds and seedlings
This is the time of year when growers begin planting seed—whether you are child planting a few seeds in Dixie cup for a school project, home tomato growers, or professional horticulturists. Unfortunately, one problem you may share in common is damping-off. Damping-off describes the death of seeds or seedlings and includes all of the following phenomena: Seeds that rot before they germinate, the newly emerging root (radicle) or shoot (cotyledons) of the seedling rots before emergence, or stems of seedlings (cotyledon) are attacked near the soil line, causing the young plants to collapse. Damping-off is caused by several fungi, including Botrytis spp and Rhizoctonia solani, and fungal-like organisms such as Pythium spp. and Phytophthora spp. These microbes are found in practically all soils and pose a large threat to plant propagation. Almost all species of plants can be infected, and these organisms also cause new cuttings to rot, as well.[Read More…]
