Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/26/99
Contacts:
Paula Flynn, Extension Plant Pathology, (515) 294-0581
Elaine Edwards, Extension Communication Systems, (515)
294-5168
Yard and Garden Column for the Week Beginning April 30
Have a Healthy Vegetable Garden
by Paula Flynn
Extension plant pathologist
Iowa State University
Most people think about vegetables in terms of human health. Have you ever considered the health of your vegetable plants? Most vegetables face hazards from several types of pests; these include pathogens that cause disease (fungi, bacteria, viruses and nematodes) as well as insects, mites and weeds. Although problem organisms in the garden and environmental stresses cannot be avoided entirely, good yields can be achieved with proper planning before planting and careful attention to the plants afterward.
Know the needs of your plants and common problems.
Learn how to properly grow your plants. Healthy plants are
less likely to have disease problems than weak,
under-fertilized or over-fertilized and over-watered plants.
Learn the most common problems that are likely to occur on
the vegetables you grow. Accurate problem identification is
the first step in developing an effective control
program.
Rotate crops.
Control of vegetable disease problems in the home garden
should start before the seeds and plants are placed in the
ground. Keeping a record of the location of plant types
within the garden will help ensure a good rotation
program.
Rotation is important because certain disease organisms form resistant structures that enable them to survive for long periods in the soil or on diseased plant parts. For instance, the bacterium that causes black rot of cabbage may survive in plant residue for two years. The dry root rot fungus of beans, Fusarium, can survive for five years or longer in the absence of beans. By not planting the host plant in the same location for several years, pathogen numbers should decrease.
Remember that certain groups of plants need to be considered together. Cucurbits (cucumber, melons, squash and pumpkin) are susceptible to many of the same diseases. Tomato and potato plants are susceptible to similar diseases.
Use disease-resistant vegetable varieties.
A cheap and easy way to reduce disease loss is to plant
disease-resistant varieties. Many vegetable varieties are
available with resistance to one or more diseases. For
instance, tomato varieties resistant to Fusarium wilt and
Verticillium wilt are available for home gardens and are the
primary methods of reducing losses to these diseases. Pea
varieties are available that are resistant to powdery
mildew. No variety is resistant to all diseases. Some
catalogs list resistance information clearly. Others,
unfortunately, simply list a vegetable variety as being
"disease resistant," making it difficult to know what
specific disease the plant is protected against.
Inspect transplants for disease.
Planting diseased vegetable seedlings is a quick way to run
into trouble. Inspect transplants carefully, and buy only
vigorous-looking seedlings. Check the leaves for spots,
distorted shape or any unusual yellowing or browning. Also
examine stems and roots, if possible, for any symptoms of
discoloration or rot. Consider how the transplants have been
cared for. The cheapest plants may not always be the best
deal. Buy from a reputable source. Continue to inspect
plants throughout the season, so disease problems can be
spotted early.
Water plants in the morning.
Splashing water is one of the most common ways disease
organisms are spread. Many fungi and bacteria require a
certain period of wetness in order to infect leaf tissue.
Watering early in the day allows time for the leaves to dry
prior to the evening. Adequate spacing between plants will
help provide good air circulation and rapid drying of
leaves. Avoid too much water. Wet soils provide ideal
conditions for many of the root rot fungi. If soil drainage
is poor, you may want to consider raised beds to avoid
excess soil moisture. Finally, avoid fluctuations of too
little water and then too much. Blossom end rot of tomato is
an example of a problem that may develop when such moisture
fluctuations occur.
Control insects and weeds.
Certain insects, especially aphids and leafhoppers, may
transmit virus and bacterial diseases to healthy plants.
Perennial weeds can serve as overwintering spots for disease
organisms, especially viruses. Consequently, keeping weeds
and insects under control also may pay dividends in reduced
disease pressure.
Clean up garden at season's end.
Removing dead plants from the garden during the growing
season and in the fall will reduce the chance of pathogens
surviving over the winter. Fall tillage will bury and help
to speed up the breakdown of any remaining plant residue.
Weeds also should be removed because they can harbor
pathogens until spring.
Use chemical products wisely.
Some fungicides and bactericides are available for use when
cultural practices alone do not provide adequate disease
control. Before purchasing a product, check the container to
be sure it is approved for the plant and that it will
control the disease problem observed. Effective control is
dependent upon applying the proper rate at the proper time
and providing good coverage on the plant. Most fungicides
and bactericides are protectants, meaning that they must be
present on the plant part before the pathogen arrives.
Successful control of diseases can be achieved by using a combination of the methods described. However, don't expect a perfect garden. Plant pathogens are a part of nature. Some disease loss may be acceptable, especially when only minor blemishes result.
ml: isugarden
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