Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Gladiolus

  • Gladiolus spp.
  • Disease (causal agent) Symptoms Survival of pathogen and effect of environment Comments on control
    Botrytis disease * (Botrytis blight, Neck rot, Corm disease)
    (Botrytis gladiolorum, B. cinerea)
    Tiny brown leaf spots develop; spots may expand or coalesce. Brown water-soaked spots appear on flower petals. Basal stem infections (neck rot) may penetrate corm; corm decay may continue in cold storage. Fuzzy gray fungus spores may form on decayed tissues. Black seedlike sclerotia may form on underground parts. In corms and on crop refuse. Spores are airborne. Favored by moist conditions and low temperatures (50° to 70°F). Complete control program essential in coastal areas: cure and treat corms as outlined at end of this section; protect foliage with chlorothalonil, iprodione, mancozeb, or thiophanate-methyl. After harvest and before packing, spray flower spikes with a fungicide.
    Fusarium yellows
    (Fusarium oxysporum f. sp. gladioli)
    Leaves tend to turn downward, yellow progressively, and die prematurely. Brown rot of corms begins in basal plate and core, and extends upward into the leaf bases via vascular strands. Corms may rot in ground or while in storage. Cultivars vary in symptoms and susceptibility. Infection without obvious symptoms is common. In diseased corms and in infested soil for many years. Favored by temperatures of 70°F or above. Plant disease-free corms in clean soil, or grow resistant cultivars. Hot water treatment of cormels eliminates the fungus from infected stocks. Cure and treat corms as outlined at end of this section. Fumigate infested soil with chloropicrin or a chloropicrin combination. Disease is less severe if soil pH is 6.6 to 7.0 and 80 to 90% of nitrogen is the nitrate form.
    Penicillium corm rot
    (Penicillium gladioli)
    A firm brown corm rot develops in storage; frequently in association with other corm rots. If conditions are moist, greenish blue spore masses appear over rotted areas. On corms and corm debris and as spores on storage-room equipment. Rot develops rapidly when humidity is high. Cure and treat corms as outlined at end of this section.
    Rhizoctonia neck rot
    (Rhizoctonia solani)
    Stem below ground and husks at harvest appear shredded. Brown fungus strands (mycelium) visible with a hand lens. Common soilborne fungus with wide host range. Favored by warm, wet conditions. Corm dips help control the fungus. Treat soil with PCNB before planting. Sprays of iprodione or thiophanate-methyl should reduce spread of the fungus down the row.
    Rust
    (Uromyces transversalis)
    First seen as small yellowish spots that later break out of leaves, stems, and sometimes flowers, forming pustules with yellow-orange spores. May also include yellowish-brown (uredinia) or blackish-brown (telia) pustules. Besides Gladiolus species, other hosts include other members of the Iris family: Crocosmia, Tritonia, and Watsonia. Spores can contaminate corms, rhizomes and bulbs. Spores can be blown long distances by wind. Only accept corms and plants from known clean sources. Prevent introduction into nursery by careful regular monitoring.
    Scab
    (Pseudomonas gladioli pv. gladioli)
    Mainly seen on corms as irregular or round sunken brown spots with a shiny, brittle, varnishlike material (bacterial exudate) on the surface. On corms and in soil refuse for 2 years. Favored by heavy, wet soils and warm weather. Encouraged by heavy nitrogen fertilization. Rotate every 3 years. Control measures for other diseases usually take care of scab. Control chewing insects in the soil.
    Stemphylium leaf spot
    (Stemphylium spp.)
    Small round or angular yellow spots with a red dot in the center appear on green parts of plants. Spots are larger on some cultivars. Cultivars differ in susceptibility. Carried over on gladiolus foliage and refuse. Favored by warm, wet weather, especially sprinkler irrigation and rain. Spray mancozeb at 10- to 14-day intervals. Plow under gladiolus crop residues.  
    Stromatinia rot
    (Stromatinia gladioli)
    Leaves yellow and die. Leaf sheaths rot at soil level (neck rot). Rotted tissues appear shredded. Numerous, very small black fungus resting structures (sclerotia) are imbedded in dead tissue. Corm lesions are dark brown and sunken with raised margins. On diseased corms and in soil for 10 years or more. Favored by wet soil. Cure and treat corms as outlined at end of this section. Use uninfested or chemically treated land. Fumigate soil with chloropicrin or a chloropicrin combination.
    * For additional information, see section on Key Diseases.
     
    Virus or viruslike disease Symptoms Host range and natural spread Comments on control
    Grassy top
    (Aster yellows phytoplasma *)
    Current season infection results in early maturity, small corms, and arrested root development. Next year, the corms produce numerous thin, weak shoots—grassy top. Flowers produced by grassy top plants are green. Leafhoppers. Many kinds of plants, including some weeds. Destroy infected plants.
    Mild mosaic
    (Bean yellow mosaic virus)
    A faint leaf mottle and sometimes a pencil-stripe color break of blossoms. Disease is common in nearly all gladiolus cultivars but symptoms are more severe in some cultivars. Blossoms may fail to open all the way. Aphids. Mechanically transmitted by harvesting tools. Legumes (beans, peas, vetch). Propagate from selected disease-free plants grown in isolated areas.
    Ringspot
    (Tobacco ringspot virus,
    Tomato ringspot virus)
    Yellow or white ring patterns and blotches on leaves. Nematodes. Mechanically transmitted by harvesting tools. Many kinds of plants, including weeds. Destroy infected plants.
    White break
    (Cucumber mosaic virus)
    White streaking or flecking of leaves and a white blotch or color break in petals. Flowers sometimes fail to open completely or shrivel prematurely. Aphids. Corm-propagated. Sometimes transmitted by harvesting tools. Cucurbits (melons, cucumber, squash), peppers, tomatoes, nandina, and hundreds of other hosts. Propagate from selected disease-free plants grown in isolated areas. Rogue infected plants at flowering time or as soon as virus symptoms appears. Control aphids.
    Gladiolus are also susceptible to Septoria leafspot (Septoria gladioli) and leaf smut (Urocystis gladiolicola), which are rare diseases in California. Curvularia leafspot (Curvularia lunata) appears occasionally as a neck rot, particularly in cormel stocks.
     
    CARING FOR CORMS
      The major gladiolus pathogens can be carried on the surface of or inside corms. To control the pathogens, it is essential to correctly cure, store, and dip corms before planting.
    Curing: Immediately after digging, place corms in shallow trays in storage rooms maintained at 95°F (35°C) and 80% relative humidity. Use fans to circulate air through and around corms. When old corms break off easily, usually after 6 to 8 days, clean the new corms. Return corms to storage at 95°F and 80% relative humidity for 4 more days.
    Storage: Store cured corms at 40°F and 70 to 80% relative humidity. In mild climates, clean corms can be replanted if Fusarium yellows is not a problem.
    Preplant dip: Before planting, dip corms in iprodione or thiabendazole plus 4 to 6 fluid ounces of wetting agent/100 gal water. The water should be at a temperature of 80° to 90°F. Allow corms to dry before planting.
    Sanitation: Maintain sanitary storage facilities. Burn all gladiolus refuse. Steam treat or disinfect trays, tools, and the like.
    Hot water treatment of cormels: (1) Select sound, hard, fully dormant corms grown in warm soil and harvested before cold weather. Cure as outlined. (2) Presoak corms for 2 days in water when the air temperature is 60° to 80°F. Discard any corms that float. (3) Immerse 30 minutes in water heated to 131°F. (4) Cool immediately with clean, cold water. (5) Dry thoroughly and quickly in warm air or sunshine. (6) Dust with a fungicide and store at 40°F and 70 to 80% relative humidity.
    Text Updated: 11/20