Cause Botrytis gladiolorum, and possibly B. cinerea, fungi. They survive in soil as sclerotia and as mycelium on plant debris. The leaf and flower spot phase of the disease is most prevalent in northern Washington, where weather often favors fungal buildup on flowers and old foliage late in the season. High humidity and leaf wetness are needed for infection and sporulation. Usually, infection is too late to seriously interfere with the plant's growth and development; however, spores may wash down to the corms or spread to the corms during digging time to cause serious losses from corm rots. Latent infections may cause significant postharvest losses when in transit to market.
Symptoms A variety of leaf and flower spots. Leaves develop large, round-to-oval brown spots, smaller pale brown spots with red-brown margins, and very small rusty-brown spots that usually show on the leaf's exposed side. Flowers develop pale brown, then dark-brown spots on the flower stem. Soft rotting at bases of florets may follow heavy rain. At first, petals develop translucent water-soaked spots. As petal spots enlarge, dead tissue turns light brown. Under moist conditions the whole flower becomes slimy with rot.
Corm rot-tan to light brown rotted areas that are wet or spongy. Rot may start at the base and spread from the core through the corm or may start at any point on the corm.
Cultural control
- Cure corms as quickly as possible after digging. Best results are from curing 48 hr at 95°F, turning corms once after 24 hr and circulating the air at 200 cu ft/min. Results were good at lower temperatures, but more time was required. Hold corms for 5 days at 80°F and for 2 weeks at 70°F to cure corms to the same extent.
- Destroy all diseased corms as quickly as possible. Low storage temperature alone is not effective in preventing Botrytis rot.
- Space plants for good air circulation.
- Avoid overhead irrigation or any practice that keeps plants wet for extended periods of time.
- Rotate gladiolus beds each year.
- Remove and destroy diseased plant parts, especially fading blossoms.
Chemical control Best when used with cultural controls.
- Preplant control of corm rot. First sort out all diseased corms, then soak sound corms in fungicide solution for 20 to 30 min.
- 42-S Thiram at 1.5 pints/8 gal water. Group M3 fungicide. 24-hr reentry.
- Bonide Captan 50 WP at 0.5 to 1.25 Tbsp/gal water can be used in home gardens. H
- Captan 80 WDG at 0.25 lb/10 gal water. Group M4 fungicide.
- Foliar sprays for leaf and flower spot. Tank-mix and/or alternate materials from different groups with different modes of action to prevent building up resistant fungi. Limit the use of any one group during the growing seasons.
- Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Chipco 26019 FLO at 1 to 2.5 quarts /100 gal water. Group 2 fungicide. 12-hr reentry.
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Decree 50 WDG at 0.75 to 1.5 lb/100 gal water. Check for phytotoxicity before using. Group 17 fungicide. 12-hr reentry.
- Mancozeb-based products can be used as mixing partners and provide some protection. 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.
- Nu-Cop 50 DF at 1 lb/100 gal water. Group M1 fungicide. 48-hr reentry.
- Pageant at 12 to 18 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Thiophanate-methyl-based products. Tank-mix with another product. Group 1 fungicides. 12-hr reentry.
- Bonide Infuse Systemic Disease Control Lawn and Landscape at 3 lb/1,000 sq ft. Activate with 0.1 to 0.25 inches of water within 24 hr after application. H
- Cleary's 3336 EG at 12 to 16 oz/100 gal water.
- OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water.
Reference Magie, R.O. 1956. Gladiolus Botrytis control. Proceedings of the Florida State Horticultural Society. 69:337-343.