Root Rots of Green Beans and Lima Beans
Vegetable Disease Information Note 7 (VDIN-007)
Charles W Averre, Extension Plant Pathologist
damping-off, and seed rots are major diseases of green beans and lima
beans in some years and in some soils. These diseases are caused by a
complex of soil-borne fungi; they are not seed-borne. These diseases tend
to be spotty in fields, and their occurrence is unpredictable. On the
average, two crops out of five are likely to be affected. In some locations
it is possible to have a complete loss of stand in a field and then to
reseed and have no problem. This variation is due to changes in weather
and soil conditions.
A total plant
disease control program is necessary to reduce losses from these soil-borne
diseases. Some practices will reduce the intensity and the likelihood
of occurrence of these diseases.
no resistant varieties, though some may be more tolerant than others.
Crop rotation is of little value since the fungi are widespread and survive
in soils for a long time.
Root Rot, or Dry Root Rot, is the most common and important root rot of
beans in North Carolina. Green bean is the main host but lima bean, southern
pea, and garden pea are also affected. It occurs mostly in hot weather
in acid and poorly fertilized soils. The disease tends to be evenly distributed
over a field.
is caused by the fungus Fusarium solani f. sp. phaseoli.
The fungus can live in the soil several years in the absence of beans.
usually occurs when the seed germinate and the fungus penetrates the hypocotyl.
A slightly reddish discoloration on the taproot occurs as early as 1 week
after the plant emerges and gradually increases in intensity and extent.
It may also occur in streaks that extend to the soil line. The red color
may change to a dark brown and the lesions frequently crack longitudinally.
The small lateral roots are usually killed, and clusters of roots may
develop above the lesions and just below the soil line. Losses with this
disease are usually more severe than the other root rots.
bean culture may result in a buildup of the fungus in soil, long-term
rotations (4 to 5 years) with nonleguminous crops reduce the severity
of the disease. No suitable resistant varieties exist; but some varieties
are more tolerant than others. Subsoiling to break up hardpans and bed
shaping to improve drainage help to control the disease. Shallow cultivation
reduces injury to the root system. Nematodes must be controlled.
Rhizoctonia root rot vary greatly from year to year with a loss of 5 to
10 percent are not unusual. This condition is more prevalent in warm weather;
however, it is likely to be found under cooler conditions than those favorable
for Fusarium root rot.
is caused by the cosmopolitan soil-inhabiting fungus, Rhizoctonia solani.
root rot, damping-off, stem rot, or hollow stem can cause serious losses
on beans throughout North Carolina. Infection is often very rapid; it
is apt to occur during wet weather, either hot or cold. The fungi which
produce this disease remain in the soil for several years and attack a
number of different crop plants.
exhibit seed rot, damping-off, and root rot symptoms due to many other
which causes Sclerotinia wilt or white mold also causes a stem rot under
certain conditions. The disease frequently occurs after a period of warm,
humid weather. It can be recognized by the white fungus growth and large
(2 to 5 mm) black bodies (sclerotia) in the pith of the stem.
root and stem rot is caused by the fungus Sclerotium rolfsii and
is a hot weather disease. It causes a rot at the base of plants. It can
be easily recognized by the white fungus growth and numerous seed-like
bodies (sclerotia) that form around the base of the plant. See Vegetable
Disease Information Note No. 9.
blight is a root rot disease caused by the fungus Macrophomina phaseoli.
It often starts as a dark, sunken lesion at the base of the cotyledon
and may extend into the roots. The plants may easily break off when cultivated
or are blown by strong wind.
injury causes stem or root rot when excess fertilizer comes in contact
with plants. The greatest damage occurs when the fertilizer is placed
in the row and the seed is planted at the same time or soon there after.
Careless placement of sidedressing may also result in injury. See Vegetable
Disease Information Note No. 10.
that injure roots or beans may cause symptoms that may be confused with
the parasitic diseases. Examples of these include: mechanical injury,
excessive water, and insect (e.g. lesser cornstalk borer) or pest injury.
agricultural chemicals must be used exactly as stated on the label of
North Carolina Cooperative Extension Service
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of specific chemicals are based upon information on the manufacturer's
label and performance in a limited number of trials. Because environmental
conditions and methods of application by growers may vary widely, performance
of the chemical will not always conform to the safety and pest control
standards indicated by experimental data. All recommendations for pesticide
use were legal at the time of publication, but the status of registration
and use patterns are subject to change by actions of state and federal
regulatory agencies. 06/91/1000
North Carolina Cooperative Extension Service
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