Hosta Virus X (HVX) is not a new problem, however, it’s not as prevalent as it was nearly a decade ago because growers have gotten better about recognizing the disease and removing infected plants from their nurseries. The most common symptoms include mottled, light or dark green discolorations along leaf veins (Fig 1). HVX may also be expressed as green and yellow mottling of the leaf blades, puckering, circular discolored areas or twisted leaves. The appearance of symptoms varies widely by cultivar and the color of foliage (Fig 2, 3). HVX is not vectored by insects. It is transmitted from plant to plant by contact with infected sap through such activities as dividing or trimming. It doesn’t spread nearly as easily as Tobacco mosaic virus but care should still be taken to disinfest contaminated tools to avoid spread to healthy hosta. Management: Send samples to a diagnostic lab when HVX is[Read More…]
Gray leaf spot/blight of Hakone Grass
Hakone grass (Hakonechloa macra), also known as Japanese forest grass, is often used for massing in beds in where a low maintenance ground cover is needed in semi-shaded areas. The graceful arching stems along with the availability of gold or white striped variegated cultivars make it an attractive option. There are few reports of disease problems on Hakone grass but one problem seems to show up with some regularity in both nurseries and landscape beds: gray leaf spot and blight, caused by the fungus Magnaporthe (= Pyricularia). Fig 1 and 2: Hakone grass in a landscape bed with gray leaf spot. Reports of this problem from studies done in Ohio indicate that blight found on hakone grass is caused by the same fungus that causes gray leaf spot on perennial ryegrass and fescue. Gray leaf spot on perennial ryegrass is a widespread problem in the Midwest, especially on golf course[Read More…]
Woody Ornamentals Summary 2018
A look back at the past year may help us be alert to problems ahead. Here’s a summary of the most common problems received in the diagnostic lab on woody ornamentals in 2018. As is typical for most years there were more non-disease (abiotic) problems than infectious (biotic) diseases found on PPDL lab samples in 2018 (see Table 1). These abiotic problems include aggregate counts of everything from poor planting practices to soil conditions and environmental factors. The table also shows the most frequently diagnosed infectious disease problem was Botryosphaeria dieback or canker, which was found across a range of hardwood trees and shrubs including: Maple, Magnolia, Crabapple, Redbud and Oak. The most commonly submitted leaf disease was Tubakia leaf spot on oaks, which is usually more severe on the red oak group. We also had our first recorded samples of Bur oak blight (Tubakia iowensis) on Bur oak and[Read More…]
Boxwood blight found in Indiana
The DNR Division of Entomology & Plant Pathology has discovered that a shipment of boxwood plants infected with boxwood blight was shipped to Indiana in May. This is important because boxwood blight (Calonectria pseudonaviculata) is a fungal disease that infests members of the popular Buxaceae family, and is often transported through the nursery trade. Hosts include Buxus (boxwood), Pachysandra (Japanese spurge) and Sarcococca (sweetbox). In total, 23 stores in Indiana received infected material in early spring (particularly “Graham Blandy” cultivar), and it’s possible that members of the public inadvertently purchased some plants. The fungus, which can lay dormant in drier conditions, can be found on all above-ground portions of the plant and presents itself as dark leaf spots. It causes rapid defoliation, which typically starts on the bottom of the plant and moves toward the top. This fungal pathogen can move through sporulation in water and from dropped leaves. As[Read More…]
Oak Wilt in Indiana
Oak wilt has been found in most counties in Indiana and is one of the most serious threats to the health of oak trees in the Midwest, especially those in the red oak / black oak group. The disease is caused by the fungus Ceratocystis fagacearum and is spread from tree to tree by sap feeding beetles and by natural root grafts between trees. Beetles carry spores of the fungus from infected trees to fresh wounds leading to infections in the canopy. Root of oaks of the same species nearby normally join as grafts when they grow together, providing the other means of spread from one infected tree to other nearby oaks. Trees in the red oak and black oak group are highly susceptible. When infected early in the summer red oaks usually wilt rapidly, show extensive summer leaf drop and may die by fall, or spring of the year[Read More…]
Tar Spot on Maple
Getting calls from panicked customers about black spots on maple leaves? You’re probably not alone, because now is the time when people start to notice maple tar spot. Every summer we get questions about black spots on maple leaves that look like tar. These spots are not actually “tar” on maple, but are rather a fungal disease known as tar spot. These photos show a range of symptoms presented by this disease. Tar spots on maples are caused by fungi in the genus Rhytisma. The most common species are Rhytisma acerinum and R. punctatum. Symptoms first appear in late spring or early summer as infected leaves develop light green or yellow-green spots. During mid to late summer these produce black tar-like raised structures on the upper surface of leaves within the yellow spots. R. acerinum causes larger spots that are 0.5 to 2 cm in diameter; R.punctatum causes many small[Read More…]
Top Arborvitae Aggravations
Arborvitae varieties (Thuja spp.) provide some of our most beautiful and versatile evergreens for landscapes, with an extensive selection of sizes and types. Unless they get proper care, they also give us some frustrating failures. Here is my list of the most frequently encountered ‘Arborvitae Aggravations’, based on the samples and questions we get in the PPDL; in no particular order. Transplant stress: Transplant stress is a normal result of planting or moving any tree or large shrub but it is frequently more serious for conifers like arborvitae. If the plant has dried out at any point before transplant the stress and browning of foliage will be much worse. Don’t keep root systems soggy wet but do make sure they stay evenly moist until planting. During the first summer be especially vigilant about watering. Keep soil evenly moist and make sure water penetrates into the full root zone. After establishment[Read More…]
Tulip Fire
The recent jump from Winter to Summer (with 2-3 days of Spring somewhere in there) got folks out looking at Tulips in full bloom now in northern Indiana. The only thing marring the view in one local planting was an outbreak of tulip fire, caused by the fungus Botrytis tulipae. The disease first shows up as small spots on the leaves (Fig. 1) or flowers (Fig. 2) or may cause stem collapse (Fig. 3). Under favorable conditions blighting can be extensive and give the appearance that the plant has been burned, hence the name tulip fire (Fig. 4). There are dozens of species of Botrytis which attack thousands of types of plants but B. tulipae has a particular affinity for tulips and is found around the world. When Botrytis infections kill whole leaves the outer bulb scales and roots of the plant may become infected. The fungus then forms small[Read More…]
PPDL Case Study #2: Sickly blue holly
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…]
