| Hosts:
Peppermint and spearmints. |
| 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. |
| Symptoms
: Gray, powdery fungus growth on leaves, then leaves yellow and drop. |
Cultural control
:
- Clean plowing to cover all
stubble reduces disease incidence and severity.
|
Chemical control
:
- 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 3-week intervals as necessary to cover new growth or until
growth ceases in fall. Applying elemental sulfur increases 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
below.
- Microthiol Special (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 (80% sulfur)
at 4 to 6 lb/A. Do not apply within 30 days of harvest. 24-hr reentry.
- JMS Stylet-Oil at 1-2 gal/A.
Do not spray if temperature is below 50°F, above 90°F or when plants
are under heat or moisture stress. Do not spray when foliage is wet. Good
coverage is essential. 4-hr reentry.
- Kaligreen (82% potassium bicarbonate)
at 2.5 to 3 lb/A on a 7-10 day interval. Might be used to supplement a normal
program when powdery mildew is first observed. May be applied up to the day
before harvest. 4-hr reentry.
- Quadris Flowable at 6.2 to
15.4 fl oz/A at 10- to 14-day intervals. Do not apply more than three times/A/year.
Do not exceed 1.44 quarts/A/season. For resistance management, do not apply
more than twice consecutively before rotating to a labeled nonstrobilurin.
May be applied up to 7 days before harvest on mint for oil, may be applied
the day of harvest on fresh mint. 4-hr reentry.
- Rally 40W at 4 to 5 oz/A
on a 14 to 21 day interval. Do not apply more than 15 oz/A per year. Do not
apply within 30 days of harvest. 24-hr reentry.
|
| Content edited by
: Cynthia M. Ocamb on May 15, 2003 |
