Landscape - Current Diseases

The following is information on current diseases being found in Delaware landscapes.

Late season leafspots are present on many landscape plants. Septoria leafspot is being seen on many dogwoods including C. sericea, amomum, and florida. Look for grayish angular spots on the leaves. Sometimes they can look like anthracnose but we generally don't see anthracnose here in the fall. Again no controls are needed. Leaf blotch on horsechestnut is another foliage disease that is causing some premature defoliation. Look for the large brown blotches with yellow borders that follow the major veins. Usually it does not affect the health of the tree either.

Leaf blotch on horsechestnut. Photo by Fabio Stergulc, Università di Udine, Bugwood.org

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Landscape - Powdery Mildew on Dogwood

It is powdery mildew season for dogwoods in the landscape. The following are some control recommendations.

Disease management. Powdery mildew can be confronted by using cultural practices, planting resistant dogwoods, and by using fungicides.

Avoid cultural practices that stimulate succulent growth and encourage powdery mildew. These include applying nitrogen fertilizer, pruning heavily, and irrigating excessively.

Use good cultural practices such as mulching over the root system, pruning out dead branches, and providing good air movement and light penetration by judicious pruning of nearby vegetation.

Plant dogwood species and cultivars resistant to powdery mildew.

Susceptible: All Cornus florida, seedling wild types (but individuals vary in susceptibility) and most C. florida cultivars.

Intermediate susceptibility: C. florida ‘Cherokee Brave’ and cultivars of the C. florida x C. kousa hybrids.

Resistant: Four powdery mildew resistant C. florida cultivars have been developed by the Tennessee Agricultural Experiment Station and are available in the nursery trade. They include ‘Jean’s Appalachian Snow’, ‘Karen’s Appalachian Blush’, ‘Kay’s Appalachian Mist’, and ‘Appalachian Joy’. Also resistant: Cultivars of C. kousa, oriental dogwood.

Immune: Cornelian cherry dogwood, C. mas.

If fungicides are to be used, determine which trees in the landscape are most susceptible so that applications are not made unnecessarily. Those trees most at risk for powdery mildew disease then can be considered for preventive fungicide applications. Most fungicides are capable of stopping the progress of powdery mildew infections fairly quickly, but none will restore already discolored or damaged leaf tissues. Good control can be obtained with as few as four fungicide applications made three weeks apart. Begin applications by early June. Delayed application can still help protect some leaves.

Effective fungicides include:
azoxystrobin (Heritage)
fenarimol (Rubigan)
myclobutanil (Eagle, Immunox, Procoz Hoist)
propiconazol (Banner Maxx, Procon-Z, Procoz Fathom, Propensity)
thiophanate-methyl (Cleary’s 3336)
triadimefon (Bayleton, Strike)

Powdery mildew fungicides requiring more frequent applications to be effective include:
neem oil (Triact)
potassium bicarbonate (Bonide Remedy, FirstStep, Kaligreen, Milstop)
paraffinic oil (Sunspray UF Oil)

When using fungicides for powdery mildew management, be sure that dogwoods are listed on the label and carefully follow all label directions.

Information from an article by John Hartman in the current edition of the Kentucky Pest News http://www.uky.edu/Ag/kpn/kpn_09/pn_090623.html

Landscape - Spot Anthracnose on Dogwood.

The following is information on spot anthracnose of Dogwood. You may see this disease on dogwoods in flower at this time.

SPOT ANTHRACNOSE on the petals (bracts) of flowering dogwood was identified on a sample from Sussex County. This fungus produces very small (1/8 in.) spots with purple red borders. Spots can be numerous and during wet weather spread to leaves. This disease is mostly cosmetic but can be controlled with Daconil (chlorothalonil), myclobutanil (Eagle, Immunox), Heritage, Cleary's 3336 (thiophanate-methyl) and other labeled fungicides.

Spot anthracnose on dogwood flower petals. Photo from the Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org.

Information from Bob Mulrooney, Extension Plant Pathologist, UD

Landscape and Nursery - Rutgers Dogwood Breeding Program - Starlight Dogwood

I recently attended the Northeast branch meetings of the American Society for Horticultural Science at Rutgers University in NJ. There was a great presentation on the breeding programs at Rutgers in the ornamentals area. The following is another new release from the Dogwood breeding program that you all should watch for in the future from nurseries.

Starlight®
Cornus x ‘KN4-43’U.S. Plant Patent No. PP 16,283

Cornus x ‘KN4-43’ Starlight® is an advanced interspecific hybrid of Cornus kousa and C. nuttallii, which exhibits the vigorous nature and the floral display of large, white bracts of plants of C. nuttallii and the dark, glossy green foliage and disease and insect resistance of plants of C. kousa.

Plants of this hybrid grow very vigorously and become erect, uniformly wide, and densely branched and foliaged. They have reached heights of over 8.8 meters tall and spreads of over 7 meters in diameter in 30 years. One-year liners of this hybrid propagated in Oregon by budding are nearly twice the size of one-year liners of C. kousa as the hybrid liners typically are 1.2 meters in height and are very stout.

Starlight® hybrid plants are vegetatively hardy in USDA Plant Hardiness Map Zone 6a (-5o to -10oF.) and exhibit good floral display in areas of USDA Plant Hardiness Map Zone 7a (+5o to 0o F.). No insect or disease problems have been observed during the twenty-eight years the original F1 interspecific hybrid seedling has been tested in the field.

This hybrid of Cornus kousa x C. nuttallii (‘KN4-43’, Starlight®), along with ‘KN30-8’ Venus®, are the first two cultivars of Rutgers University’s Jersey Star™ series of hybrid dogwood (C. kousa x C. nuttallii) to be released from the Woody Ornamentals breeding Program at Cook College and the New Jersey Agricultural Experiment Station. Others will be released to the nursery industry soon.

For more information visit the website http://agproducts.rutgers.edu/starlight.html

Rutgers Dogwood Breeding Program - Venus Dogwood

I recently attended the Northeast branch meetings of the American Society for Horticultural Science at Rutgers University in NJ. There was a great presentation on the breeding programs at Rutgers in the ornamentals area. The following is a new release from the Dogwood breeding program that you all should watch for in the future from nurseries.

Cornus x ‘KN30-8’ Venus®
U.S. Plant Patent No.PP 16,309

Cornus x ‘KN-30-8’ Venus® is an advanced generation interspecific hybrid involving germplasm of Cornus kousa and C. nuttallii. Plants of this hybrid are distinguished by their exceptionally large, white floral bracts, superior winter hardiness, good tolerance of drought conditions, and high resistance to the incitants of Powdery Mildew and Dogwood Anthracnose.

Venus grows very vigorously as a dense tree branched low to ground with upright branches which form a rounded head wider than tall. Heights of 5.48 meters and a spread of 6.55 meters have been reached in 20 years.

The original seedling (age 20 years) has been field tested for 18 years and has been completely winter-hardy in USDA Plant Hardiness Map Zone 6a.

Hybridized by Dr. Elwin Orton in the Woody Ornamentals Breeding Program at Rutgers' Cook College and and the New Jersey Agricultural Experiment Station, the Venus® dogwood is one of the end products of a schedule of interspecific hybridization of plants of Cornus kousa x C. nuttallii initiated in May, 1973. Cornus nuttallii is native to limited areas of the Pacific Northwest and Western United States.

With some plants reaching a height of 70 to 75 feet in areas of the Columbia River Gorge, C. nuttallii is the giant of the large bracted dogwoods. Due to the absence of any report that plants of C. kousa and C. nuttallii were cross fertile, the challenge was to produce interspecific hybrids that possess the desirable traits of both species and would grow well over a wide range of soil and climatic conditions.

Many different plants of C. kousa were hybridized with plants of C. nuttalli in 1973. A limited number of seeds were produced and they germinated in the spring of 1974. Most of the seedlings flowered after seven to nine years, and in 1983, a superior F1 seedling selection was hybridized with a plant of C. kousa ‘Rosea’. Subsequently, the “best” among the progeny from this cross was propagated and plants distributed to cooperators in New Jersey, Tennessee and Oregon for intensive evaluation.

A plant patent is pending under the cultivar name ‘KN30-8’ and the plants will be marketed under the trademark Venus®.

From the Rutgers University website. Go to this site for more information http://agproducts.rutgers.edu/venus.html

Ornamentals Hotline Disease Pictures for Issue 22, August 24, 2007

Mushrooms growing on Mulch

Photo from University of Cincinatti, Clermont College, Biology

Slime mold on mulch

Photo from University of Tennesee Plant Pathology

Slime mold on mulch

Photo by Peggy Sellers, Purdue University

Birds nest fungus

Photo from Department of Plant Pathology, Washington State University

Stinkhorn mushroom Clathrus spp

Photo by Paul A. Mistretta, USDA Forest Service, Bugwood.org

Dog stinkhorn fungus Mutinus caninus

Photo by Chris Evans, River to River CWMA, Bugwood.org

Stinkhorn mushroom Linderia columnata

Photo by David J. Moorhead, University of Georgia, Bugwood.org

Septoria Leaf Spot on Cornus florida

Photo from Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

Septoria Leaf Spot on Cornus

Photo from Online Guide to Plant Disease Control, Oregon State University

http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=1279