Northern red oak (Quercus rubra) is a Midwest native and is generally well adapted to growth across much of the region, but we get questions about dieback or ‘flagging’ on it fairly regularly. The two most common causes of twig dieback on this host are Kermes scale (Allokermes galliformis and A. kingii) and fungal canker/dieback[Read More…]
Tom Creswell
Contorted filbert is an ornamental cultivar of European Filbert, (Corylus avellana ‘Contorta’), grown for its twisted, gnarly stems. The plant is also sold under the name Harry Lauder’s Walking Stick. While it’s unique architecture can be impressive, it’s highly susceptible to a fungal canker that can cause extensive damage to the tree. Eastern filbert blight[Read More…]
First identified on coleus in the US in 2005, downy mildew has become an annual threat to production of this popular annual. The disease may be caused by the pathogens Peronospora lamii (also infects basil, as well as several species of Salvia and Lamium) or P. belbaharii (also infects basil). The symptoms may range from[Read More…]
Rhizomatous bearded iris (Iris x germanica) is a favorite early spring perennial; however, it is routinely troubled by a fungal leaf spot that tends to appear soon after flowering (Figure 1). These start as small wet-looking lesions that may quickly enlarge into larger spots with brownish edges, tan centers and yellow margins (Figure 2). When[Read More…]
Dianthus is a much-admired perennial, but occasionally it develops serious disease problems. The most dramatic of these is anthracnose, caused by the fungus Colletotrichum. The disease may spread rapidly on greenhouse benches or in landscape plantings of susceptible dianthus varieties. The old-fashioned ‘Sweet William’ varieties seem to tolerate this disease fairly well and may only[Read More…]
Leaf blotch, also called red spot and measles, is a common disease of peony caused by the fungus Graphiopsis chlorocephala (=Cladosporium paenoiae). The disease has multiple names because there are multiple symptoms. Lesion on leaves and stems can vary from tiny red spots (“measles”) to larger brown or purple blotches (Figures 1, 2 and 3).[Read More…]
Tubakia leaf spot, caused by the fungus Tubakia, is the disease we find more commonly on oak than any other. Throughout the world, there are 11 species of Tubakia known to infect oak, with Tubakia dryina (previously known as Actinopelte dryina) being the most commonly encountered species in our landscapes. Apple, ash, black gum, chestnut,[Read More…]
We often think of Phytophthora as mainly a root rot pathogen, but Phytophthora can also cause a bleeding trunk canker under the right conditions. The most commonly attacked trees we see in the diagnostic lab are American and European beech (Fagus spp.), and maples (Acer spp.); but this disease is also reported to occur on[Read More…]
This very slimy substance (Fig. 1) has many common names, was once classified as an algae but is now known as a Cyanobacterium. It is worse in areas that are frequently wet, such as low areas in lawns or on frequently irrigated golf courses (Fig. 2) or along walkways in nurseries where it can create[Read More…]
This spring the PPDL received several samples, calls and emails related to dying weeping cherry trees (Fig. 1, 2, 3). Reports of this phenomenon came from as far away as Missouri. Ornamental cherry trees (and related Prunus spp.) are susceptible to multiple problems, including southwest injury (Fig. 4) Botryosphaeria dieback/canker (Fig. 5), bacterial canker and[Read More…]
