| Cause: The fungus Erysiphe polygoni affects only
Beta spp. The disease has been widespread in several western
states since 1974. Fungal spores may blow in from overwintering sources. Overwintered
infected seed beets may also be sources of infections. The fungus tolerates
a wide range of environmental conditions. |
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Symptoms: Small, discrete, white patches on both leaf surfaces.
Patches coalesce until white mycelium and spores cover the entire leaf.
Leaves later become yellow, then purplish brown, and finally necrotic. |
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Chemical control: Begin applying when mildew is first observed.
If necessary, repeat application to maintain 10% or lower leaf area diseased
through the growing season. Sulfur dust provides superior control to liquid
applications and is the preferred treatment. Research in south-central Idaho
indicates it is economically feasible to apply sulfur to fields developing
initial powdery mildew infections up to 5 weeks before harvest (or about
September 1 in that area).
- Gem at 6
to 7 oz/A at 10- to 14-day intervals. Do not apply more than 21 oz/A/season
or within 21 days of harvest. For resistance management, do not apply more
than three times a season; alternate with a labeled, non-QoI
- Headline
at 9 to 12 fl oz/A at 14-day intervals. Do not apply more than twice sequentially
before alternating with a nonstrobilurin fungicide. Begin applications before
disease develops. Do not use silicone-base adjuvants. Do not exceed four applications
per season. Preharvest interval 7 days. 12-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.
- Kumulus
DF at 10-20 lb/A. 24-hr reentry.
- Laredo EC
at 8 fl oz in at least 10 gal water/A (aerial application) or 20 gal water/A
(ground application) or SLN OR-010017. Do not apply more than 48 fl oz/A/year.
24-hr reentry.
- Quadris
Flowable at 9.2 to 15.4 fl oz/A on a 5 to 7 day interval. Do not apply more
than 2.88 qt /A or make more than 6 applications per season. Do not apply
more than 1 application before rotating with fungicides that have a different
mode of action for resistant management. May be applied the day of harvest.
4-hr reentry.
- Sulfur dusts
give better coverage than liquid formulations.
- Sulfur
Flowable 6 (52% sulfur) at 0.66 gal/A at 18-day intervals. 24-hr reentry.
- Thiolux
Dry FlowableMicronized Sulfur (80% sulfur) at 5 to 10 lb/A at 10- to 30-day
intervals. 24-hr reentry.
- Sulfur
Dust (80% sulfur) - 20-30 lb/A each application.
- Topsin M
WSB at 0.5 lb/A at 14-day intervals. Do not use alone; use another nonbenzimidazole
fungicide with TOPSIN M WSB for disease resistance management. Resistant strains
can persist for many years. Do not apply within 21 days of harvest. 12-hr
reentry.
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Biological control:
- AQ10 biofungicide
is a fungal hyperparasite (Ampelomyces quisqualis) on the powdery mildew
fungus. Use 0.5 to 1 oz/A plus a mineral-oil-based or silicone-based surfactant
at 7- to 14-day intervals with a minimum of two sequential applications.
Apply in early morning or late evening when humidity is highest to ensure
maximum germination of AQ10. Ineffective when powdery mildew is present
on 3% or more foliage. AQ10 can be applied up to and on the day of harvest.
Not compatible with some chemicals such as sulfur, dithiocarbamates, potassium
salts of fatty acids, and strobilurins. 4-hr reentry.
|
References:
- Whitney,
E.D., and J.E. Duffus. 1986. Compendium of Beet Diseases and Insects. St.
Paul, MN: APS Press.
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| Content
edited by: John Gallian and Cynthia M. Ocamb on May 16, 2003 |
