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| Peppermint (Mentha spp.) -- Powdery Mildew |
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| Hosts: Peppermint and spearmints.
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| Cause:
A fungus, Erysiphe cichoracearum, which overwinters on mint, stubble, and many wild hosts. It is seldom serious enough on peppermint to warrant control measures; however, it is very destructive on Scotch spearmint. Interactions with some herbicides increase susceptibility to this disease.
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| Symptoms:
Gray, powdery fungus growth on leaves, then leaves yellow and drop. |
Cultural
control: - Plowing to cover all stubble reduces disease incidence and severity.
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Chemical
control:
- Headline at 9 to 12 fl oz/A prior to disease development on 7- to 14-day intervals. Do not make more than two (2) application of Headline or other Group 11 fungicide before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 14 days. 12-hr reentry.
- JMS Stylet Oil at 1 to 2 gal/A. Do not spray if temperature is below 50°F, above 90°F or when plants are under heat or moisture stress. 4-hr reentry.
- Kaligreen at 2.5 to 3 lb/A on 7- to 10-day intervals. Might supplement a normal program when powdery mildew is first observed. May be applied up to the day before harvest.
4-hr reentry.
- Quadris at 6 to 15.5 fl oz/A on 7- to 10-day intervals. Do not apply more than two (2) foliar application of Quadris or other Group 11 fungicide before alternating with a different mode of action. May be applied up to 7 days before harvest for processed mint and on the day of harvest for fresh mint. 4-hr reentry.
- Quilt at 14 fl oz/A. Apply when plants are 2 to 4 inches high or when conditions become favorable for disease development. Make a second application 14 days later. Do not apply within 30 days for harvest. 12-hr reentry.
- Rally 40W at 4 to 5 oz/A on 14- to 21-day intervals. Do not apply within 30 days of harvest. 24-hr reentry.
- Sulfur products. On Scotch spearmint, use wettable or flowable sulfur when plants are 5 to 6 inches tall or when the fungus first appears. Repeat application twice more at 3-week intervals. After harvest, repeat when mildew first appears or at four- to five-leaf stage; repeat at 30-day intervals as necessary to cover new growth or until growth stops in fall. Applying elemental sulfur in-creases sulfide concentration in mint oil; the length of time between sulfur application and harvest is more important than sulfur rates. Growers should have minimal problems with mint sulfide if they follow the rates and preharvest application interval as follows.
- Microthiol Disperss (80% sulfur) at 4 to 6 lb/A. Do not apply within 30 days of harvest. Do not apply if temperatures will exceed 90°F within 3 days after application. Do not use within 2 weeks of an oil treatment.
24-hr reentry.
- Thiolux Jet (80% sulfur) at 4 to 6 lb/A. Do not apply within 30 days of harvest. 24-hr reentry.
- Tilt at 4 fl oz/A. Apply when plants are 2 to 4 inches high or when conditions become favorable for disease development. Make a second application 14 days later. Do not apply within 30 days for
harvest. 12-hr reentry.
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| Content edited by:
Cynthia M. Ocamb on
January 1, 2009 |
