By now, the emerald ash borer (EAB) invasion is an old story for landscapes and forests in the Midwest. Since EAB was first found in North America in 2002 more millions of ash trees than we can know have died and this tiny insect continues to kill ash in an ever widening zone that currently…Read more about Fungal Decay of Ash Trees[Read More]
Tom Creswell
Yews are widely used as foundation plantings in many areas and are valued for their dark, evergreen foliage. The most widely used landscape yews are Japanese yew (Taxus cuspidata) and Taxus x media hybrids, such as Hicksii or Wardii Yew. While few diseases and insects attack yew, there are a few problems to watch for….Read more about What’s Killing My Yews? Top Problems and How to Prevent Them[Read More]
Cool, cloudy weather with frequent rainfall and high humidity provides ideal conditions for the development of several diseases, including downy mildew. The fungus-like pathogens that cause downy mildew are commonly known as ‘water molds’ and are classified as oomycetes. Many types of plants are susceptible to downy mildew diseases, including sunflowers, grapevines, impatiens, other ornamentals,…Read more about Watch for Downy Mildew on Roses and Brambles caused by Peronospora sparsa[Read More]
These oak trees are showing the symptoms of smooth patch (Figures 1, 2, 3). This condition is the result of a fungal infection that is restricted to the outer bark, causing it to slough off. The bark layer remaining is smoother and lighter in color than uninfected, normal bark. Patches can vary from a few…Read more about Smooth Patch of Oak[Read More]
Dieback and canker diseases caused by Botryosphaeria, Sphaeropsis, Diplodia and other closely related fungal pathogens are exceptionally common on woody landscape plants. This group of diseases are often referred to collectively as Botryosphaeria diseases and this article will follow that convention to discuss them as a group. Examine any mature oak tree long enough and…Read more about Botryosphaeria Dieback and Canker[Read More]
Rocky Mountain juniper, Juniperus scopulorum, has gained some popularity in Midwest landscapes due to cold and drought tolerance, and to the availability of several upright columnar varieties with attractive blue color, including ‘Skyrocket’ and ‘Wichita Blue’. Like many other junipers, J. scopulorum may suffer dieback of small branches and twigs caused by the fungal pathogens…Read more about A Triple Threat to Rocky Mountain Juniper: Cytospora, Diplodia and Botryosphaeria[Read More]
A new invasive insect of concern has been identified in the state of Georgia. In August of 2023, Georgia’s Department of Agriculture, along with the USDA, confirmed the presence of the yellow-legged hornet, Vespa velutina, outside of the city of Savannah. To date, this is the only confirmed identification of this insect in the United…Read more about New Invasive Predator of Honeybees[Read More]
Creeping phlox (Phlox subulata) has been a reliable mainstay in home landscapes for generations. This spring-blooming perennial is also known by a string of other common names, including flowering moss, moss phlox, moss pink, rock phlox, and thrift (not to be confused with sea thrift which is Armeria maritma). Creeping phlox is native to a…Read more about Anthracnose on Creeping Phlox[Read More]
Each spring the PPDL receives several samples of oak trees showing curled, twisted, stunted and/or generally ratty looking leaves. When there are holes in the leaves or leaf edges are missing tissue, we add another symptom name to the mix: tatters. Distorted new growth and tatters are most common on white oaks and may occasionally…Read more about Oak Leaf Tatters – a spring ritual[Read More]
Rose rosette disease is a severe problem for rose growers and occurs widely throughout many rose growing regions of the US, especially from the mid-South into the Midwest. The problem was described on roses in the early 1940s but actual cause of the disease remained murky until the pathogen was identified as a virus in…Read more about Rose Rosette[Read More]
Rust diseases produce some of the most dramatic symptoms and signs we see on woody plants in the landscape. These fungi live up to the name of ‘rust’ diseases because the spore structures they produce on the plant are generally bright orange, as shown by these examples: Cedar-apple rust (https://purduelandscapereport.org//article/orange-koosh-galls-on-eastern-red-cedar/), Hollyhock rust (https://purduelandscapereport.org//article/jolly-hollyhock-rust/) and Buckthorn…Read more about Cedar Quince Rust[Read More]
I enjoy gardening and take pride in the variety of flowers my wife and I manage to squeeze into a few beds each Summer. This year an interesting zinnia caught my eye and ended up in our back-yard garden. After fending off rabbits early in the season a new threat emerged in July: bacterial spots…Read more about Zinnia Bacterial Spot[Read More]
Brittle cinders and burnt crusts usually bring to mind bad baking experiments, but in this case they are common names for a highly destructive wood rot fungus: Kretzschmaria deusta. The names derive from the charcoal-like fungal fruiting structure (the stroma), where spores are produced (Figure 1). Most wood decay fungi can be classified as…Read more about Kretzschmaria Basal Canker: Fast Path to Tree Failure[Read More]
Arborvitae (Thuja spp.) fulfill several crucial roles in the landscape, especially windbreaks and screens (Fig. 1). Their relatively fast growth habit, wide variety of available forms, and inexpensive price point make them one of the most common conifers in the Midwest landscape. Due to the ubiquitous use of arborvitae, and their perceived problems, the Green…Read more about Stop Making These Arborvitae Mistakes! Common transplant problems of arborvitae.[Read More]
If you have ever seen gooey neon orange branches on trees and shrubs you may have been observing a phenomenon commonly known by the very scientific name of ‘orange goo’. Appearing in cool, wet weather during spring sap flow, the goo is caused by fungi, bacteria and yeast colonizing tree sap, especially where an injury…Read more about Orange Goo – Dramatic but Harmless.[Read More]
When we see round holes in the bark of a tree we often think the cause might be due to wood boring insects or bark beetles. However, that is not always the case. Small holes arranged in neat, uniform rows and columns on the trunks of trees or woody shrubs are usually caused by sapsuckers,…Read more about Rows and Rows of Holes[Read More]
One of the most common diseases found on boxwoods is Volutella blight and dieback, caused by the fungi Pseudonectria foliicola and P. buxi. Both fungi are considered weak pathogens, always around but not causing much damage until plants are injured or stressed, rarely infecting otherwise healthy plants. Volutella blight alone usually doesn’t kill boxwoods, but…Read more about Volutella Blight and Dieback of Boxwood[Read More]
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 about Oak Kermes Scale and Fungal Dieback: A One-Two punch for Northern Red Oak[Read More]
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 about Contorted Filbert: A Gnarly Problem Plant[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 about Coleus Downy Mildew[Read More]
