Page 82 - AG 7-2011 Revised 2016

PLANT DISEASE MANAGEMENT
Gary King, Ph.D. Plant Pathology
Diagnosis of plant disease is a crucial first step in picking a strategy for disease
management. Signs and symptoms are keys to diagnose the plant diseases. With a hand
lens, shovel, pocket knife, notebook and an open mind, you may be able to identify many
diseases. Asking the right questions about the history of the plants may provide pertinent
information to identify a cause or at least more clues.
The main plant disease control strategies are:

1) Use plants that are resistant to disease.
2) Use disease-free plant materials (seed, bulbs, cuttings, plugs, transplants, sod, etc.), as
well as pathogen-free soil, amendments and other materials.
3) Use sanitation and exclusion to keep pathogens away from susceptible plants.
Regulatory restrictions and quarantines including inspections at border entry points
may prohibit importation of certain plants or materials that may carry pathogens to
un-infested areas. Sanitation also includes removal and disposal of infected branches
or plant debris and may require cleaning and disinfestations of tools and boots or just
simply washing your hands.
4) Eradicate susceptible hosts. This was demonstrated in a drastic and expensive, but
necessary effort to control bacterial canker in Florida and other southern states, where
3 million citrus trees were destroyed. Usually, this may be done on a much smaller
scale in nurseries where specific problems can be stopped quickly by alert and well
educated pest control professionals. Sometimes, eradication efforts focus on the
alternate hosts of the disease, such as weeds that invade your plantings or in non-crop
areas near, upwind or uphill from your plants.
5) Rotate the types of plants to ones that are not susceptible.
6) Maintain optimum cultural conditions that favor the plant by providing vigorous growth.
Grow plants at times of the year when it’s best for them and worst for the pathogen.
Use proper irrigation, fertilizing, spacing, pruning, etc. Provide conditions that are
unfavorable for the pathogen when possible. Use drip irrigation methods that do not
splash water and spread bacterial diseases. Time irrigations for mornings, rather than
early evenings when plants may remain excessively wet for too long and conducive
to infection. Remove weeds that increase the wet, poorly ventilated conditions that
encourage infection around plants.
7) Protect your plants with the proper disease prevention chemicals, such as bactericide,
fungicide, and nematocide ahead of when the disease will be expected and they may
be much more effective. Some of these chemicals have some therapeutic, “curative,”
abilities. Do not count on this to permanently save the plants and your rear end, since
the chemicals may dissipate between applications, especially on perennial plants.
Small pieces of pathogen usually will survive somewhere on the plant and re-emerge.
Fumigants may substantially eliminate pathogens from soil or mixes, prior to planting.
Insecticides may prevent or reduce vectors of viruses and phytoplasmas, so fewer
infections result. Herbicides may be strategically used to kill parasitic plants that infect
your plantings, and doing so may stop another source of transmission of viruses or
phytoplasmas. Herbicides may also reduce the amount of weed vegetation around the
host plants, increase ventilation, and reduce the wet conditions that favor infection.

76