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…]
Bacterial Leaf Scorch of Oak: Lab Confirmation Necessary
Bacterial leaf scorch (BLS) on oak is a systemic disease caused by the bacterium Xylella fastidiosa (Xf) (Fig 1). The bacteria live in the xylem vessels (water conducting elements) and restrict water flow. Xf is transmitted from tree to tree by xylem-feeding insects such as leafhoppers and treehoppers. Numerous woody hosts are susceptible to various strains of Xf . Symptoms of bacterial leaf scorch may vary somewhat between oak species. On pin oaks, scorching appears along the leaf margins and progresses inward toward the mid-vein (Fig 2). There is often a yellowish margin between the scorched leaf tissue and green tissue. On other red oaks, the scorch typically appears at the leaf tip and progresses up the leaf towards the petiole (Fig 3). Branches with leaves that appear to be healthy may be interspersed on the same tree amidst branches with scorched, diseased leaves (Fig 4). Leaf scorch and premature[Read More…]
Tubakia Leaf Spot on Oak—A Yearly Event
Tubakia leaf spot, a fungal disease, infects all species of oak. However, oaks in the red oak group such as black, red and pin oak, appear to be most susceptible. Symptoms on oak include small to large dark brown or reddish-brown spots or blotches. (Figs 1,2,3) Spotting that occurs on leaf veins may cause large extended areas of dead leaf tissue along the veins (Fig 4). Marginal leaf scorch may also be seen to contain lesions of Tubakia (Fig 5). If trees are heavily infected with Tubakia leaf spot, premature defoliation may occur, however, the disease usually develops so late in the season that overall health of the tree is not affected. Fungicide sprays are not recommended. Cultural practices include maintaining good tree vigor by watering during drought stress periods and fertilizing trees appropriately. A type of anthracnose known as spot anthracnose, may also be present on leaves infected with[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…]
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…]
