Fruit Rots of Pickling and Slicing Cucumbers
Vegetable Disease Information Note 1 (VDIN-001)
Gerald J. Holmes, Extension Plant Pathologist
Fruit rots, caused by soil-borne fungi or bacteria, are major diseases
of pickling and slicing cucumbers in North Carolina and the southeastern
United States. Their occurrence is unpredictable because of changes in
weather and soil conditions. Losses occur in the field and often continue
after harvest. An integrated plant disease control program is necessary
to reduce losses from these rots. Each step provides an increment of aid
in managing fruit rots of cucumbers.
Drainage. Use cultural practices which will reduce standing water,
humidity, and improve field drainage. Land leveling will reduce standing
water. Slightly sloped beds and fields are recommended for good drainage.
Select fields with a sandy loam soil that will provide good drainage.
Land Preparation. Plow so that the top 2 to 4 inches of soil is
completely turned under (see control section Information
Note 9). Disking or similar tools that mix the top few inches of soil
will not reduce inoculum levels and subsequent disease. If hardpan layers
are present and cause slow drainage in soil, use a chisel plow during
Plant Density. Plant populations should be limited to between 20,000
and 25,000 plants per acre for river bottomland and about 25,000 plants
for sandy, well-drained soils. Consider the vine habits of the cultivar;
a dense canopy usually results in more fruit rot because it promotes conditions
that are conducive to disease. Slightly higher plant populations can be
utilized if a sparse-canopy cultivar is chosen. The timing and method
of irrigation should be such that long periods of excess moisture on the
soil surface are minimized. For example, one inch of water on a weekly
cycle is preferred to half an inch on a 3- to 4-day cycle. High humidity
and moisture favor fruit rots and should be considered when devising the
Rotation. Rotate cucumber with grasses or small grains. Intensively
cropping cucumbers on the same fields will encourage fruit rots and other
diseases. The longer the rotation out of cucumbers, the better.
Fertilization. Excess nitrogen fertilizer promotes lush growth
of vines, creating a dense canopy of succulent tissue. This type of rank
growth provides conditions conducive to disease development. For this
reason, over fertilization should be avoided.
Fungicides. Azoxystrobin (Quadris), chlorothalonil (Bravo) and
thiophanate-methyl (Topsin M) are labeled for control of belly rot. Products
containing mefenoxam (Ridomil Gold) provide some protection from cottony
leak (Pythium rot). These fungicides will give disappointing results under
heavy disease pressure (consult table
6-18 in NC Agricultural Chemicals Manual for fungicide efficacy ratings).
1. Chilling injury.
control strategies. Harvested fruit should be kept as dry and cool
as possible. Harvested cucumbers in containers will generate heat. Thus,
these containers should be kept out of the sun and ventilated with fans
when there is no wind. Fruit should not be washed until ready for processing
or brining. If they must be washed, add 50 ppm of chlorine in the wash
water. Harvesting and handling fruit in a manner to minimize bruising
or wounding will reduce losses. If fresh fruit needs to be transported
long distances, it should be kept at 45 to 50 degrees F and transported
as rapidly as possible. Chilling injury will result if fruit is held at
temperatures below 45 degrees (Figure 1).
Occurrence and Importance. Belly rot (soil rot, Rhizoctonia rot)
is one of the most common fruit rots of cucumbers in North Carolina. Losses
vary from year to year with a loss of 5 to 10 percent in warm, humid weather.
Fruit becomes infected where they contact the soil in the field. Fruit
that are apparently healthy, but have already been infected, can develop
severe symptoms within 24 hours.
Cause. Belly rot is caused by the cosmopolitan soil-inhabiting
fungus Rhizoctonia solani.
2. Water-soaked decay caused by R. solani.
Figure 3. Water-soaked areas turn scabby and cracked.
Very small cucumbers show yellowish-brown superficial discoloration. Large
fruit have dark brown water-soaked decay most often on the side of the
fruit in contact with the soil (Figure 2). If the lesion is allowed to
dry (just a few hours) the watersoaked areas turn scabby and cracked (Figure
Disease Development. The fruit can develop symptoms 24 hours after
coming in contact with the fungus and the entire fruit can rot in 72 hours.
Temperatures below 50 degrees F retard disease development during transit
Occurrence and importance. Cottony leak (Pythium fruit rot) causes
serious losses of cucumber in North Carolina and other southeastern states.
Infection occurs in the field and decay progresses rapidly. Losses occur
during wet weather over a wide range of temperatures. Often it is worse
after a drought. The Pythium species, which cause this disease,
remain in the soil and
attack a number of different host plants.
Figure 4. Pythium sp. growing on cucumber fruit.
The first symptoms on the fruit are soft, dark green, water soaked lesions
or spots. Later, as it penetrates the tissues of the fruit, water is liberated
in large quantities. In the humid atmosphere of the vine canopy (or the
containers used during transit) a very luxuriant, white, cottony fungal
growth completely covers the fruit (Figure 4). The cottony growth may
become flattened and matted over the fruit.
Disease Development. Pythium is spread by microscopic, swimming
spores or by contact between diseased and healthy fruit tissues. Visible
wounds are not necessary for entry to the fruit. Temperatures below 60
degrees F retard Pythium growth and rot is slowed considerably.
Cucumbers should be cooled to and held at that temperature until processed.
with a specific problem, contact your local North
Carolina Cooperative Extension Service
This disease is characterized by sunken lesions colored by salmon or pink
spore masses, and is caused by the fungus Colletotrichum orbiculare.
This occurs only when anthracnose susceptible cultivars are planted. For
more information on anthracnose see Plant
Pathology Information Note No. 11.
Caused by the fungus Cladosporium cucumerium, this disease
is characterized by small grayish, slightly sunken spots on the fruit.
Usually this disease occurs only in the mountains of western North Carolina
on susceptible cultivars.
Black Rot (Gummy stem blight)
Caused by the fungus Didymella bryoniae, small water-soaked spots
develop that gradually enlarge and darken. Despite the fact that this
is a serious foliar disease of cucumber in North Carolina, very little
loss occurs due to fruit rot. See Plant
Pathology Information Note No. 8 for more information.
Bacterial Spot (Angular leaf spot)
This disease is caused
by bacterium Pseudomonas syringae pv. lachrymans, and causes
minute, circular water-soaked lesions that later become sunken and chalky-white
in color. This fruit rot phase is rarely seen and losses are very low.
Most modern cultivars possess good resistance to this disease.
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by North Carolina Cooperative Extension Service. Distributed in furtherance
of the Acts of Congress of May 8 and June 30, 1914. Employment and program
opportunities are offered to all people regardless of race, color, national
origin, sex, age, or disability. North Carolina State University at
Raleigh, North Carolina, A&T State University, U.S. Department of Agriculture,
and local governments cooperating.
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 chemcial 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