Sunday, June 28, 2009

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

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