The Plant Lady

Fusarium Species and Their Diseases

• General:
  • Widespread fungus that affects a wide range of crops. Each species of Fusarium attacks a particular crop.
  • For more information and treatment of fungal diseases in general, see my article, "Fungal Diseases"
  • Fungus that is most common in heavy or wet soils but can be in any soil, even in seed trays.
  • usually introduced on infected seedlings or plants but may also be present in the soil
  • VGPS-210: The fungi attack and destroy plant roots and then spread into the plant's vascular system near the crown, blocking the flow of water from roots to stems and leaves. The first symptom of Fusarium often is wilting of the foliage on one side of the plant
  • may persist in plant debris and may also be capable of remaining viable in the soil for several years
• Diseases:
  • Aster Wilt (Fusarium oxysporum f. sp. callistephi)
    • Symptoms:
      • rapid wilting of the plant, often followed by death
      • stem base blackens and shrinks inward
      • faint, furry, pale pink or white fungal growth may develop
    • Control:
      • promptly remove and dispose of infected plants and the soil in the vicinity of the roots.
      • Use a fresh site for future plantings of asters and plant only healthy-looking stock.
      • discard any with dead roots or damaged stem bases
      • avoid planting asters on heavy soils, or improve soil texture before planting.
      • grow resistant cultivars
  • Cabbage Yellows
    • Plants Affected:
      • infects only plants in the cabbage family
    • Symptoms:
      • VGPS-211: become dull green and look lifeless; stems and leaves warp or curl. Lower leaves turn yellow and may die and drop off the plants. Cut stems show brown discoloration
    • Treatment:
      • VGPS-211: No treatment, but if the weather cools off and soil temperatures drop, the plants may rebound and produce a decent harvest
  • Foot & Root Rots (or Basal Rot)
    • Symptoms:
      • deterioration of basal stem tissues causes the upper parts of the plant to wilt, discolor and die back
      • soft-stemmed plants, especially seedlings and cuttings, are commonly affected, but most annual, biennial, and herbaceous perennial plants may show symproms
      • Tomatoes, cucumbers, and melons are frequently affected
      • the tissues at the stem base may darken, atrophy, become discolored (usually darkening), and occasionally soften
      • root rot may occur simultaneously
      • sometimes called basal rot
    • Control
      • no cure for infected plants, but you can prevent the spread of the fungus
      • prevent spread by promptly removing infected plants, along witht he soil mix or soil around their roots
      • hygienic cultivation techniques, including the use of sterilized media, clean trays, pots & tools, even water
  • Fusarium Wilt (most commonly caused by F. oxysporum)
    • Plants Affected:
      • Most vegetable crops
      • Beans
      • Eggplant
      • Okra
      • Passionfruits (may be serious in some subtropical areas)
      • Peas
      • Pepper
      • Potato
      • Sweet Peas (Lathyrus odoratus)
      • Tomato (Fusarium oxysporum f. sp. lycopersici)
    • Symptoms:
      • soft-stemmed plants wilt, either in part or in their entirelty
      • in carnations (dianthus), the flowers fade prematurely and the leaves wilt and discolor.
      • woodier-stemmed plants may retain their overall shape, but foliage on affected stems wilts and withers
      • internal staining of the vascular tissue may occure and is usually brown or black
      • death almost always follows, either rapidly or over several seasons, depending on the plant affected
      • cool, damp conditions may encourage very pale pink or white, slightly fluffy fungal growth from the infected tissues
      • symptoms are very similar to those caused by drought; dry soil may encourage rapid wilt symtoms, but they do not recover permanently when watered
      • symptoms are also very similar to Squash Bug infection, but gray or brown insects will be present, typically in the interior of the plant, under leaves, and on fruit
      • BBGS-114: fungal infection of vascular tissues; very similar to verticillium wilt; leaves and stems turn yellowish. Plants wilt and have a brown discoloration inside the stems. Plant growth is stunted and yields are reduced
      • TWM-63: this is the first thing to suspect when tomato leaves start to yellow from the bottom of the plant up.
      • AHSEG-646: Black pathces develop on stems and foliage; they are sometimes covered with a white or pale pink fungal growth. Roots turn black and die
      • AHSEG-653: if cut longitudinally in the early stages of degeneration they may show a central, vascular column of brown discoloration
      • VGPS-210: occurs in hot weather, and plants often show no symptoms until they are close to maturity. Verticillium wilt, which causes similar symptoms, tends to occur in cool, wet weather, such as late spring. Lower leaves wilt. Frequently all leaves on one side of the plant will wilt. Yellow patches may show up on leaves; leaves may die. Beet & Swiss chard leaves will curl inward; potato and tomato leaves curl under. Dark lesions appear on lower stems in half lengthwise to reveal reddish brown or black streaks inside. On vining crops such as sweet potatoes and squash, the first symptom often is yellowing and wilting of the older leaves. Other times, vines wilt without showing any other symptoms first. Vines may be stunted or die completely.
    • Cause:
      • the fungi partially or completely block the vascular tissues, usually by gumlike formations
      • damage creating open wounds when spores are in the vicinity can make plant more susceptible
      • non-sterile pruning shears or other tools; infected root material; infested soil.
      • BBGS-114: fungus lives in the soil and infects plants through the roots; fungus develops in hot dry weather
      • TWM-63: soil-borne fungus that can survive for a decade or more in dormant stages. It enters the plant through roots and invades its water distribution network.
      • AHSEG-646: Various species of the microscopic fungus Fusarium, which are present in the soil or on plant debris, or are sometimes seedborne; they may also be introduced on new stock. They will build up in the soil when the same type of plant is grown in the same site year after year.
    • Control:
      • remove infected plants promptly
      • remove soil or soil mix from the immediate vicinity of the roots
      • do not grow the same or closely related plants on the site again, or at least for a minimum of 5 years
      • BBGS-115: crop rotation is important, as well as the planting of resistant varieties where available. Practice a 4-year rotation plan for okra
      • AHSEG-646: There is no cure for affected plants. Remove them and the soil in their vicinity, and destroy the plants. Avoid growing susceptible plants in the area. Propagate only from healthy stock; if possible, grow resistant cultivars
      • VGPS-211: no treatment, but if the plants are near maturity, harvest what you can before uprooting the infected crop debris. If the plants are young and symptoms are mild, you can try to nurse the crop through by watering regularly. Otherwise, remove infested crop residues from the garden, taking care not to spread the debris while you work. Discard or destroy this debris; if you compost it, be sure not to apply that compost in your vegetable garden or you'll end up spreading the fungi throughout your garden. It's okay to apply the compost to ornamentals because Fusarium fungi are so host-specific. Solarizing infected beds during the hottest part of the summer will help to reduce the levels of Fusarium fungi.
      • VGPS-211: next time you plant, adjust soil pH to 6.5 to 7.0 several weeks before planting. Planting resistant and tolerant varieties is the best defense when you know that your soil contains Fusarium fungi. Be sure to buy certified disease-free seed potatoes. Always handle plants carefully to avoid creating wounds. Mulch to keep sol cool and moist, and add compost to boost beneficial soil microorganisms.
      • VGPS-211: Crop Rotation: Fusarium spores can persist so long in soil -- up to 15 years -- that you cant' rid your garden of Fusarium by rotating crops. However, since each crop family or individual crop is attacked by a different species of Fusarium, practicing crop rotation will help to prevent a continual buildup of Fusarium fungi in your garden. Plan a 4-year rotation (or longer) if possible.
  • Gladiolus Corm Rot (Fusarium oxysporum f. sp. gladioli)
    • Symptoms:
      • concentric brown markings develop on the corm, usually at its base and while in storage
      • crocuses and bulbous irises may also be affected
      • the corm dries out, becoming mummified but not developing fungal growth
      • if plants grow from infected corms, the foliage shows yellow flecing and later striping toward the tips of the outer leaves
      • the discoloration spreads downward, and the leaves turn brown and die
      • roots of affected corms blacken and may die back
    • Cause:
      • the fungus usually enters the plant through the basal plate or roots of the corm
    • Control:
      • dispose of plants showing foliage symptoms
      • check all corms throuroughly before storing in a cool, dry place and again at the end of storage before replanting
      • dry plants off after lifting and dip corms in a fungicide solution or treat them with sulfur dust
      • plant on a fresh site each year
  • Narcissus Basal Rot (Fusarium oxysproum f. sp. narcissi) - Daffodils
    • Symptoms:
      • bulb discolors and rots, spreading upward through the inner scales, turning them chocolate brown
      • a pale pink fungal growth may develop on the basal plante and among the affected scales
      • bulbs in storage turn uniformly brown, dry out, and become mummified
      • those in the ground usually rot off completely, and by the end of the season there may be no trace of them
      • leaf symptoms on growing bulbs include yellowing, stunting, and sparse foliage
      • most damaging during or following hot summers
      • AHSEG-654: After about one month in storage, the basal plate of the bulb becomes soft and brown, then rots. The deterioration spreads to the inner scales, which turn dark brown, and a pale pink, fluffy fungal growth may then appear between the scales and on the basal plate. The bulb gradually dries out and becomes mummified. Bulbs that become infected in the ground may, if not lifted, rot away in the soil. In some cases, foliage symptoms of yellowing and wilting occur first.
    • Causes:
      • infection occurs at the basal plate (the flattened area at the base of the bulb)
      • persists in the soil and on infected bulbs in storage
      • AHSEG-654: the soilborne fungus infects bulbs through the basal plate; the fungus is encouraged by high soil temperatures. If the infected bulb is not lifted, it may infect adjacent bulbs. Stored bulbs that are infected but do not show symptoms also act as a source of infection when planted
    • Control:
      • dip bulbs in a fungicide solution, before summer temperatures are at their highest, and within 48 hours of the bulbs being lifted
      • dust with sulfur
      • early planting in autumn
      • AHSEG-654: check bulbs for signs of disease before storing, and discard any that are damaged.
  • Snow Mold
    • Plants affected:
      • AHSEG-657: Lawns, particularly those that contain a high proportion of annual bluegrass (Poa annua)
    • Symptoms:
      • AHSEG-657: patches of grass become yellow and die, often merging to form large areas. in damp weather, a white fungal growth appears, causing the grass blades to stick together. it is most prevalent in late winter and early spring, especially on areas of grass that have been waled on while snow covered
    • Cause:
      • AHSEG-657: principally the fungus Fusarium nivale, which is encouraged by poor aeration and the overuse of nitrogen fertilizers
    • Control:
      • AHSEG-657: Regularly aerate and scarify the lawn. Use winter-hardy grass species. Avoid using high-nitrogen fertilizers in late summer to early fall and rake thoroughly after mowing to prevent building up a water-holding mat. Cut grass short in late fall.
  • Turf Drought
    • Fusarium can blight drought-stressed turf during a 2- to 3-day period of high night temperatures (over 75 degrees F) and high humidity
• Sources: