Cause Stemphylium botryosum (sexual Pleospora tarda) a fungus that overwinters in affected leaves and other plant debris. The disease is favored by warm wet conditions.
Symptoms Small, pale yellow spots, translucent, with reddish brown centers. Severe spotting may kill leaves. The reduced leaf surface on severely affected plants may result in smaller corms.
Cultural control
- Rake up and burn leaves in fall.
- Isolate more susceptible cultivars from the main planting.
- Avoid overhead watering that keeps plants wet for extended periods of time.
Chemical control Use as foliar sprays.
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Daconil Weather Stik at 1.38 pints/100 gal. Group M5 fungicide. 12-hr reentry.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker. Reduce the rate to 0.75 lb/100 gal water for flower spikes.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- Monterey Liqui-Cop at 3 Tbsp/gal water. H
- Ortho MAX Garden Disease Control at 2 teaspoons/gal water. H
- Ortho Rose & Flower Disease Control at 2 fl oz/gal water. Group 3 fungicide. H
- Postiva at 10 to 28 fl oz/100 gal water. Group 3 + 7 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Ziram 76 DF at 1.5 to 2 lb/100 gal water. Group M3 fungicide. 48-hr reentry.
Reference Nelson, R. and Mooar, M. 1952. Life history of the Stemphylium that causes red leaf spot of gladiolus. Phytopathology 42:363-366.