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Disease Management Strategies
Tillage (especially fall tillage) helps control diseases by
reducing the amount of inoculum (pathogen structures) that
survives the winter. Rotating fields to different crop families
each year also helps control diseases by preventing the buildup
of certain plant pathogens in the soil. Summary of Cultural
Management Strategies for Disease provides tillage and crop
rotation recommendations. A general rule is that you should
not rotate a field to a crop in the same botanical family.
Unfortunately, there are several kinds of soilborne diseases
that are unaffected by rotation. The first group of these
diseases is caused by pathogens that produce resilient
survival structures that can withstand the effects of time and
nonhost crops. Two such diseases are Fusarium wilt, and
root-knot nematode.
Another group of diseases unaffected by crop rotation has a
broad host range, so they can survive indefinitely on many
host crop and weed species. Examples include Sclerotinia,
Rhizoctonia, and Verticillium diseases.
In addition, root-knot nematode can cause disease in multiple
vegetable plant families (cucurbits, tomato, carrot, and many
more) along with some field crops and even weeds.
The third group of diseases unaffected by rotation overwinter
in Gulf Coast states, and then spread north by wind during the
growing season. Examples include sweet corn rust and
downy mildew of cucurbits.
In addition, certain viruses spread by highly motile insects
(such as aphids), so rotation does not reduce these diseases
either. Since the pathogen does not overwinter locally in the
field, survival in residue is not a factor.
Consider all options before making management decisions.
Rotation is a good general practice that improves or
maintains good soil tilth. Tillage (especially fall tillage) often
is not in accord with recommended soil management and
conservation practices. If you practice no-till or reduced
tillage, you will need to be even more vigilant with other
strategies in order to reduce your risk of disease.
Two publications that may be useful for no-till or reduced
tillage growers are Building Soils for Better Crops:
Sustainable Soil Management and Managing Cover Crops
Profitably, both available from the Sustainable Agriculture
Research & Education (SARE) Learning Center, sare.org.
Water and Humidity Management
Many bacterial and fungal pathogens thrive in wet conditions.
Certain soilborne pathogens such as Phytophthora and
Pythium species are favored by wet soils with poor drainage.
Avoid planting into sites with known drainage problems.
Improve drainage, and consider using raised beds.
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Many leaf spot and fruit rot diseases are favored by high
humidity and wet plant surfaces. Using drip irrigation instead
of overhead irrigation will reduce leaf wetness. If you use
overhead irrigation, irrigate in the morning so that plant
surfaces dry before nighttime. Avoid overhead irrigation in
the evening.
Reduce plant density to allow better airflow and sunlight to
penetrate, which will decrease leaf wetness and humidity.
With certain crops (such as tomato) appropriate staking or
trellising will also increase airflow. Reducing weed pressure
in and along the sides of the crop can also improve airflow.
Align rows to maximize airflow and sun exposure.
In greenhouses and high tunnels, use passive ventilation
and/or fans to reduce humidity. See Transplant Production for
details about water and humidity management in that setting.
Avoid working wet fields.
Scouting and Sanitation
Depending on the disease and the size of your operation, you
can and should rouge (remove) infected plants. For example,
there are no treatments for viral diseases, so you should
remove infected plants to reduce the spread to other plants.
Bacterial canker of tomato is another disease where you
should rogue out the infected plants and several neighboring
plants. Flag the area and come back to check for further
spread. Culls should be removed far from the field.
In greenhouse situations, remove the trash frequently, and
always keep lids on trash cans to prevent pathogens (and
insects) from building up in discarded plant materials. For
some crops (such as tomato) stakes and trellises can harbor
certain bacteria from one crop to the next. So always use new
stakes, or at minimum disinfest them. Disinfest tools
frequently, such as at the end of rows. Avoid working fields
under wet conditions.
Other Cultural Practices
Insects (such as thrips, aphids, cucumber beetles, and others)
spread numerous diseases, so cultural practices that reduce
the insects will reduce the risk of diseases. The comments for
the Summary of Cultural Management Strategies for Disease
table lists some of these practices. See the Insect
Management Strategies section for guidelines about cultural
controls to reduce insects that may spread diseases.
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