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…]
Boxwood Blight – Be on the Look-Out
Boxwoods losing leaves should not be ignored!! Check them carefully for tell-tale symptoms of boxwood blight, a serious fungal disease that causes rapid defoliation and dieback (Fig. 1). The fungus that causes boxwood blight can infect all above ground portions of the shrub. The first symptoms of the disease are dark leaf spots (Fig. 2 ) that progress to twig blight and rapid defoliation (Fig. 3) and eventual death of the plant if it goes undetected (Fig 4). The narrow black streaks (cankers) that develop on green stems (Fig. 5), are a unique symptom that differentiates boxwood blight from other boxwood diseases. During periods of high humidity, white, fuzzy masses that consist of numerous clumps of spores will emerge from these black stem cankers (Fig. 6) as well as on the underside of leaf spots. The spores can be observed on infected stems and leaves with a hand lens. These[Read More…]
Opportunistic canker pathogens
Diseases that affect the twigs, branches, and the main trunk of a tree are referred to as cankers or blights. Cankers appear as a general sunken area of darkened tissue on the twigs or branches, often surrounding a branch stub (Fig. 1). Canker diseases can be a serious problem in the landscape when they are not properly managed, and even when they are. All woody plants can be infected by canker pathogens. Many canker pathogens produce fruiting bodies, which contain sacs of spores (asci or conidia) that forcibly release the spores when the conditions are right. These pustules are easy to find on the surface of the canker (Figure 2). As the canker grows, the twig or branch may become girdled, causing the wilting and death of the leaves past the point of infection on the tree. On stone fruit, this can cause gummosis, too (Fig. 3). What causes[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…]
Cultural Plus Chemical=A good weed control combo in landscape beds
This article, and many others, will be presented at the 2018 Purdue Turf and Landscape Field Day on July 10th. Registration is open and available online: https://www.mrtf.org/event/turf-and-landscape-field-day/?event_date=2018-07-10 Here is the lineup for the field day. A cultural weed control method is one that involves steps to reduce or eliminate weeds via maintenance techniques. In landscapes, the most common type of cultural control is mulching. Mulching provides many benefits in the landscape, including moisture retention, temperature consistency of the root zone, improvement of soil structure, addition of organic matter, aesthetics, and, perhaps most important, a significant reduction in weeds. Mulch prevents weeds a couple of different ways. Many weed species require sunlight for germination to occur. By shading the soil beneath the mulch, weed seeds that require sunlight will not begin to germinate. The other way that mulch prevents weeds from germinating is by providing large air spaces (macropores) between the pieces[Read More…]
Kingdom Fungi
Fungi are a unique group of organisms—so unique that they are put into a separate category called a ‘Kingdom’. In Kingdom Fungi, some members cause rust, scab, powdery mildew, leaf spots and blights (to name but a few!). When these fungi are ‘out of control’ many people turn to fungicides. What are fungicides and how do they work? We have a video that explains this: https://www.youtube.com/watch?v=eNiqROUtpgo Fungicides are used to stop fungi from attacking plants, not after you see the damage. Anyone who has grown roses knows how Japanese beetles damage plants. But do you know how powdery mildews infect and damage plants. Find out here: https://www.youtube.com/watch?v=eNiqROUtpgo Fungicides are best used as part of an integrated strategy that looks to improve how the plant looks or yields. Why use fungicides? Fungicides are used to protect plants when integrated management can’t do the job to the degree needed to produce[Read More…]
Red Band (Dothistroma) Needle Blight
The Purdue Plant and Pest Diagnostic Lab (PPDL) recently received samples of Mugo Pine and Spruce that exhibited reddish-brown bands on needles of lower branches (Figs 1 & 2). Microscopic examination of needles confirmed the presence of Dothistroma,(Fig 3) a fungus that causes red band needle blight. Needles infected with Dothistroma first exhibit dark green bands on the needles that are quickly replaced with brown or reddish brown lesions. Only the base of the needle will remain green, with the remaining portion tan or brown. (Fig 4) Infection is typically more severe in the lower portion of the canopy nearest the ground. (Figs 5 & 6) In late Fall, black fruiting bodies (Fig 7) appear on needles and mature to release spores the following Spring and Summer. The spores are spread by wind and rain and can infect needles throughout the growing season. New needles are susceptible once they emerge[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…]
Begonia Bacteria Brouhaha
Xanthomonas is both an unfortunate, but regular occurrence in the greenhouse industry. Despite the efforts from numerous companies to supply ‘clean plants’, Xanthomonas (and other bacterial pathogens) regularly slip through. This year, it came in on begonia. The pathogen. Xanthomonas is a genus of yellow colored bacteria that infect many species of plants (approximately 400!), causing spots and blights on leaves and stems (Fig. 1). The strain Xanthomonas axonopodis pv.begonia (formerly known as X. campestris pv. begonia) is specific to begonias, and does not readily spread to other plant genera. The abbreviation ‘pv.’ is short for ‘pathovar’, which is defined as a bacterial strain that is distinguished from other Xanthomonas axonopodis strains based upon the host plant it is pathogenic to). Begonias of all species are vulnerable to this pathovar, along with creeping saxifrage (Saxifrage stolonifera). On many crops the disease cycle of Xanthomonas spp. often begins with contaminated seeds, but outbreaks in begonia[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…]
