Landcape - Current Diseases in the Landscape

The following is information on current diseases in the landscape from Bob Mulrooney, Extension Plant Pathologist, UD.

This is turning out to be an exciting year for plant pathologists--diseases springing up everywhere (pun intended). Look for scab, frog-eye leafspot and cedar-apple rust (bright orange lesions) on susceptible crabapple cultivars. Frogeye or Phyllosticta leafspot on red maple, silver maple and boxelder (irregular tan spots withred-brown margins--a minor disease rarely requiring control). Anthracnose, booming due to the cool wet weather can be found on sycamore, ash (same fungus causes anthracnose on Chinese fringe tree--look for curled, deformed leaves or leaflets and brown necrotic areas), even on oak leaves in the understory (producing large brown blotches and small irregularly shaped spots). Each host has its own specific anthracnose fungus. These diseases are usually not serious enough to warrant fungicide control.

Landscape and Nursery - Cedar-Apple Rust

The follwing is information and pictures of cedar apple rust on eastern red cedar.

CEDAR-APPLE RUST GALLS.

The round woody galls on twigs and branches of eastern red cedar have been observed in Delaware. During wet weather these woody galls produce orange-red gelatinous spore horns with spores that infect apple and crabapple leaves. The best control on cedar is to prune out the galls to the extent possible.

Cedar apple rust gall on Eastern red cedar. Photo by Daniel H. Brown, USDA Forest Service, Bugwood.org.

Telial-stage horns of the cedar-apple rust pathogen. Photo by Joseph O'Brien, USDA Forest Service, Bugwood.org.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Landscape and Nursery - Know Your Plant Diseases: Rusts

the following are pictures of three rust diseases found on woody plants in landscapes and nurseries. The first four pictures are of ash rust, the next two of cedar-apple rust, the last four pictures are of cedar-quince rust.

Ash rust

Ash rust

Ash rust

Ash rust



Cedar Apple Rust



Cedar-Quince Rust

Cedar-Quince Rust

Photos by Bob Mulrooney, extension plant pathologist, UD.

Landscape - Spring Diseases

Periodic rainy days and nights have been occurring recently in Delaware. Wet weather leading to prolonged leaf wetness as new foliage is emerging is very favorable for many landscape tree diseases. Symptoms of scab, rust, and anthracnose diseases are already beginning to appear in many landscapes.

Apple scab. Unsprayed, susceptible flowering crabapples and some backyard apples are already showing symptoms of leaf infections by the scab fungus, Venturia inaequalis. Long (15-18 hours) periods of leaf wetness are were favorable for new apple scab infections in. If trees were not already infected, expect symptoms developing from recent infections to appear in 10-12 days.

Cedar apple rust and cedar quince rust. The causal fungi, Gymnosporangium juniperi-virginianae and Gymnosporangium clavipes are still active on infected cedar trees. Symptoms on flowering crabapple and apple are already visible in some locations.

Fire blight (Erwinia amylovora). The primary infection season on flowering pears and crabapples and backyard apples and pears is over since most blooms have dropped flower petals by now. Depending on location, landscapes in Delaware were exposed to one or two fire blight primary infection periods based on favorable weather conditions this spring. If fire blight infections occurred earlier this season, symptoms in the fruiting spurs should be visible now. Look for blossom blight symptoms in the form of blackened, dead fruitlets in the fruit spurs throughout the tree. If there are not too many of them, infected clusters can be broken out by hand. Shoot blight symptoms, if they are going to occur, will appear in the coming weeks.

Anthracnose diseases. Where cool, rainy weather has prevailed, it is likely that sycamore (Apiognomonia veneta), oak (Apiognomonia quercina), maple (Discula sp. or Kabatiella apocrypta), and dogwood (Discula destructiva) anthracnose diseases will be active.

Adapted for Delaware from "SPRINGTIME DISEASES IN THE LANDSCAPE" By John Hartman in the May 5, 2008 edition of the Kentucky Pest News from the University of Kentucky College of Agriculture.

Landscape and Nursery - Rusts on Junipers

The following is information on two common rusts that affect Junipers in Delaware.

CEDAR-QUINCE RUST caused by the fungus Gymnosporangium clavipes. The orange-red swellings on the twigs will be very evident. This fungus infects groundcover junipers, Juniperus horizontalis, Juniperus scopulorum, and several others as well. On this host the swellings are often undetected and can persist for years. The galls are perennial on juniper and should be pruned out if possible. The alternate host is hawthorn, serviceberry, and several other rosaceous plants and causes deformed fruit and green twig dieback.

Cedar-quince rust on Juniper. Photo from the University of Massachusetts Extension.

CEDAR-APPLE RUST. Be on the lookout as well for the round woody galls on twigs and branches of eastern red cedar, Juniperus virginiana. During wet weather orange-red spore horns emerge. These gelatinous appendages produce the spores that infect apple and crabapple leaves at this time of the year. The best control on cedar is to prune out the galls to the extent that is practical. These cedar-apple rust galls can be pretty spectacular for fungi-philes.

Cedar-apple rust on juniper. Photo from the University of Nebraska, Lincoln, Plant Pathology

Information from Bob Mulrooney, Extension Plant Pathologist, UD.