Crown Gall control for Argyranthemum
DISEASE FASTFACTS

Introduction
Crown gall disease may affect many popular garden plants. For Argyranthemum, crown gall is not a devastating disease, but it will affect the salability of the crop. As this species of blooming plant becomes more interesting and more popular with gardeners, growers should be aware of the potential for infection by the disease and take steps to prevent it in production

Crown gall is caused by Agrobacterium tumefaciens, a common bacterium which lives in the soil on and around root surfaces. Agrobacterium requires a fresh wound in order to infect a plant and initiate gall formation. After entering a wound site, the bacterium transfer part of its DNA to a plant cell and integrates into the cell’s genome, leading to the production of tumor-like swellings called galls. Galls typically occur at the crown of the plant just above ground level, but they may also be found underground on roots or higher up on stems. Although galls usually do not cause serious damage to mature Argyranthemums, infected plants should be removed from the growing area and destroyed.

Symptoms

  • tumor-like overgrowths, or galls, on the crown, roots and/or stem
    •     galls are usually rounded, with an irregular, rough surface

Cultivar Susceptibility

  • all cultivars of Argyranthemum are susceptible to crown gall
  • Comet White is especially susceptible and should be handled with extra care

Environmental Factors Affecting Development

  • Humid, warm conditions, such as the propagation environment, promote the development and spread of crown gall
    • T    he propagation stage is when the crop is most susceptible to infection, so it’s best to avoid pinching Argyranthemums under propagation conditions
  • cool, dry conditions, with good air movement, suppress development of the disease

Control

  • start with clean cuttings
  • pre-plant sanitation of the rooting media, pots, growing area and tools is very important
    • use sterile, well aerated rooting media; if native soil or other non-sterile components are included in the rooting mix, steam to 190°F (85°C) for 30 minutes prior to filling pots
    • start with new pots, or sterilize used pots with bleach or other appropriate disinfectant
    • remove all plant debris, weeds and trash from the growing area prior to transplanting
    • keep pots elevated on benches if possible, or use ground cover to avoid direct contact between the pots and the ground
    • do not plant clean material in sites previously infested with the disease if disinfection is not possible
  • apply a copper-based fungicide within 48 hours after sticking the cuttings. Suggested chemicals include Camelot, Kocide, or Phyton 27. Consult labels for recommended rates.
  • a warm, wet propagation environment is perfect for the spread of bacteria so Argyranthemum should not be pinched in propagation.
  • avoid damaging roots and stems whenever handling the plants, especially when transplanting
  • use clean tools or hands when pruning or pinching, and disinfect regularly
  • prevent attack by soil insects which may cause root or stem damage (fungus gnat larvae, centipedes, earwigs, etc.)
  • scout regularly and rogue all infected plants
    • to avoid contaminating nearby plants, place infected plants in a plastic bag before removal and wash hands prior to continuing
  • apply a copper-based fungicide within 24 hours after pruning or pinching to help suppress infection
    • Camelot applied at labeled rates is effective and has not caused phytotoxicity when applied at weekly intervals
    • Kocide 2000 and Phyton 27 may also be effective
  • Maintain a cool and dry environment with good air movement
    • Avoid overhead irrigation, syringing and splashing water that favor the disease
  • The biological control agent, Agrobacterium radiobacter strain 84, produces an antibiotic and competes with A. tumefaciens for attachment to wound sites. It acts only as a preventative treatment and will not cure infections, so it is applied at a high population level to protect wound sites against invasion by A. tumefaciens.
    • A. radiobacter strain 84 is the active ingredient in the products Galltrol and Gallex


With proper sanitation, environment and precautionary measures, it is easy to produce a healthy, gall-free crop of beautiful Argyranthemums!

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