Oak leaf blister is caused by the fungus Taphrina caerulescens. Infections occur as buds swell and open during wet, spring conditions. Leaf blister symptoms usually appear within several weeks following infection as 1/4-1/2 inch circular, light green bulges on the top surface of leaves.(Fig 1) From the underside, the affected areas are sunken or depressed. These distortions may cause leaf bending or curling of narrow-leaved oak species. Some insect galls may resemble symptoms of oak leaf blister at first glance. (Fig 2) Upon closer inspection, the insect gall is a solid mass of leaf tissue as opposed to the distorted leaf blister caused by Taphrina. As the blisters age, they become dry, brown spots; severely diseased leaves may drop prematurely. (Fig 3.) Although this disease is quite conspicuous, it does not seriously harm healthy trees and control with fungicides is not usually recommended.
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…]
Volutella leaf blight and stem canker of pachysandra
Volutella stem and leaf blight caused by the fungal pathogen Volutella pachysandricola can cause major damage to Pachysandra, destroying large areas in a bed. (Fig 1) Infected leaves first develop tan or brown blotches with dark brown margins, which expand, often with concentric lighter and darker target-like zones. (Figs 2a,b) Stem and stolon cankers appear as water-soaked diseased areas, turn brown, shrivel and often girdle the stem. causing stem dieback. (Figs 3a,b) Orangish spore masses develop in the cankered areas and the underside of infected leaves. (Fig 4) Volutella blight of pachysandra is often associated with plant stresses such as recent transplanting, exposure to bright sunlight, scale insects, and winter damage. Normally this disease does little damage to vigorous plants, thus providing good growing conditions is the most important control measure. Unfortunately, a dense planting bed of pachysandra is the desired horticultural outcome, thus thinning the planting to allow better[Read More…]
Fungicide Costs
Fungal diseases of ornamentals will always be a limitation to profitable plant production and management—how significant that limitation is in your hands. Fungicides are effective in reducing the risk of loss– in numbers, in quality and in terms of aesthetics. However, fungicide costs in terms of product cost, number of applications and labor need to be evaluated against the benefits their use provides. It is important to keep in mind that these costs and benefits vary between greenhouse, nursery and landscape use; in the case of greenhouse and nursery, these costs are also weighed against plant (commodity) prices. That said, there are several effective, and cost-effective fungicides available for each type of user, keeping in mind that what is effective and cost-effective for one may not be effective for another. For example, a pathogen like Rhizoctonia infects plants in the greenhouse, nursery, turf, and landscape! What is best for one[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…]
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…]
