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United States Department of Agriculture

Agricultural Research Service

Research Project: Production Management Research For Horticultural Crops in the Gulf South

Location: Southern Horticultural Research

Title: Timing of fungicide sprays to prevent azalea web blight symptoms

Authors
item Copes, Warren
item Hagan, Austin -
item Olive, John -

Submitted to: International Plant Propagators Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 10, 2012
Publication Date: May 7, 2012
Citation: Copes, W.E., Hagan, A., Olive, J. 2012. Timing of fungicide sprays to prevent azalea web blight symptoms. International Plant Propagators Proceedings. 61.

Interpretive Summary: Azalea web blight is an annual problem on some evergreen azalea cultivars grown in containerized nursery production in the southern and eastern United States. Several rules and scouting techniques were evaluated for timing of fungicides to control web blight development. Applying fungicides on a scheduled calendar date (around July 10 and August 1) provide the most consistent control over three years. Simple scouting methods did provide control some years, and would be effective for adjusting timing for a week earlier or later than the calendar date. The calendar date allows fungicide applications to be scheduled and the scouting allows additional ability to adjust for yearly differences in weather that affect web blight development.

Technical Abstract: Several fungicides will control web blight, but guidelines about when to spray have not been clearly understood. Previous research has shown that a maximum daily temperatures greater than 95°F and minimum daily temperatures less than 68°F slow web blight development, but weather conditions are not suitable for precise prediction of when rapid blight will develop. With three years of research at two locations (Poplarville, MS and Mobile, AL), applying fungicides on scheduled calendar dates (around July 10 and August 1) was the most reliable criterion for suppressing blight development on ‘Gumpo’ azalea. Scouting provides additional information to adjust fungicide timing due to yearly differences in weather and growing conditions that affect web blight development. Scouting should take about 10 minutes per block of plants of the same cultivar and age. Scouting is done by spreading branches so you can take a quick count of the number of dead leaves present in the inner canopy (not ones on the surface of the bark medium). By checking several blocks it will be obvious which blocks of plants have more advanced symptoms and when disease has advanced. This knowledge will allow fungicides to be applied a week or so earlier or later than the scheduled date, but should be used with caution because rapid blight can develop later in the same week plants were scouted.

Last Modified: 9/20/2014
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