Midwest Vegetable Guide - 2022 - 46

Disease Management Strategies
Disease Management
Strategies
Reviewed by Dan Egel - September 2021
Plant diseases are caused by a wide variety of microbial
pathogens (including fungi, bacteria, viruses, and nematodes).
For a plant disease to occur, three components must be
present:
1. The pathogen
2. A susceptible host (the plant)
3. An environment conducive to disease.
In addition, insects spread some diseases, which makes them
a fourth component of the disease cycle. Disease
management strategies target one or more of those these
factors to prevent and/or reduce the risk of disease. The
sections below provide a broad overview of general
management strategies. The crop-by-crop chapters go into
much more detail for each disease.
Disease Diagnosis
Before making any management decisions, always make sure
to correctly diagnose your problem first. Accurate diagnoses
can save time and money because some diseases look alike
but have very different management strategies.
Different pathogens have different modes of both survival
and spread. Therefore, certain management practices will
work for some diseases but may have no effect on others.
Furthermore, disease control materials are usually effective
against only a subgroup of specific diseases. For example,
fungicides will have no effect on viruses.
Moreover, even among the various fungi, some materials may
be effective against certain diseases but not others. In
particular, the pathogens Pythium, Phytophthora, and the
causal agents of downy mildews that we often discuss as
fungi are not true fungi, they are in a different group of
organisms called oomycetes. Many materials effective
against true fungi are not effective for those organisms, and
vice versa.
For example, numerous materials used to manage downy
mildew will have no effect or a negligible effect on powdery
mildew, and vice versa. A root disease may require very
different management compared to a leaf spot or fruit disease.
Moreover, there are several plant health issues that mimic
plant diseases (including environmental stress, nutritional
problems, herbicide injuries, air pollution, and others). These
are known as abiotic disorders.
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Unwittingly treating a nutrient deficiency with pesticides
wastes time and money, and does not solve the underlying
condition. Submitting samples to a diagnostic laboratory is
the best way to ensure the correct diagnosis. For a list of labs
and instructions on how to submit plants, see the State
Contact Information table.
Healthy Plant Material
Contaminated seed or transplants can introduce diseases, so
saving vegetable seeds for next year's crop is not
recommended unless you are trained and equipped to handle
seed sanitation. You should not save seeds when a seedborne
disease has been active. The Summary of Cultural
Management Strategies for Disease table lists some diseases
that may be transmitted by seed to transplants.
Whether you purchase transplants or produce them yourself,
you should read Transplant Production to better understand
transplant health. Be certain to inspect seedlings regularly.
Examine the foliage and remove a few plants from the pots to
inspect the roots. If you purchase transplants, keep newlyarrived
materials away from other plants and the production
area for a few days to prevent spread if a problem is found.
Talk to your supplier and ask questions about how the reduce
disease risk. If a you suspect a disease on received plants,
take photos and contact a diagnostic laboratory, and continue
to keep the plants separate. Keep good records of where
plants are sourced from so that you can contact the supplier if
a problem arises.
Disease-Resistant Varieties
Whenever possible, use varieties resistant to diseases. Some
varieties may not be completely resistant to particular
diseases; however, incomplete or partial resistance may be
available. Some seed catalogs may refer to tolerance. The
Summary of Cultural Management Strategies for Disease
table presents information about the availability of resistant
varieties.
For certain vegetables (such as tomatoes) there are rootstocks
available with resistance to some soilborne pathogens. A
resistant rootstock may be an option if you have a history of a
known soilborne disease but wish to grow a tomato scion
variety that is susceptible.
Tillage and Crop Rotation
If a disease pathogen survives from year-to-year in crop
residue or soil, then crop rotation and fall tillage are very
effective factors in disease management. The pathogens are
unable to survive once the crop residue decomposes.
Midwest Veg Guide 2022
Midwest Vegetable Guide - 2022

Table of Contents for the Digital Edition of Midwest Vegetable Guide - 2022
