Tag Archives: Squash

Disease - Vegetable

Blossom End Rot

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UW Plant Disease Facts
 
Authors:   Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   02/28/2024
D-number:   D0022
 
Blossom end rot of tomato.
Blossom end rot of tomato.

What is blossom end rot? 

Blossom end rot is a physiological disorder of tomato in which the tissue of the blossom end of the fruit (the portion of the fruit opposite the stem) breaks down and rots, thus reducing yield.  Pepper, eggplant and vine crop (e.g., cucumber, pumpkin, squash, watermelon) fruits can also be affected.

What does blossom end rot look like? 

Blossom end rot often occurs on the first fruits formed on plants.  Initially, water-soaked spots (resembling small bruises) appear, most often on the bottoms of fruits.  On peppers these spots can resemble sunscald and can form on the sides of the fruits near the blossom end.  Spots enlarge, becoming dark brown to black, sunken and leathery.  Half the fruit may eventually be affected.  Sometimes, when a fruit is cut, the exterior will be sound, but the interior will be discolored and shrunken.  Often, bacteria and fungi invade the discolored areas, leading to further tissue decay.

What causes blossom end rot? 

Blossom end rot is caused by a lack of calcium in the fruit.  This lack of calcium may be due to low calcium levels in the soil.  More often however, there is plenty of calcium in the soil, but its availability for uptake and transport to fruits is impaired.  Drought stress, alternating soil moisture extremes, and damage to a plant’s roots all can inhibit calcium uptake, as can waterlogged or cold soils, and high concentrations of ammonium (NH4+), potassium (K+), and magnesium (Mg++) in soil.  Movement of calcium within plants depends on active transpiration (i.e., loss of water through above-ground plant parts).  Because leaves transpire more than fruits, calcium moves more easily into leaves where it remains.  Calcium is not later redistributed from leaves to fruits.  This preferential distribution of calcium to leaves can be made worse by over-fertilizing with nitrogen which promotes excessive production of leaves.  In addition, high relative humidity OR low relative humidity in combination with hot, windy weather can limit transpiration, thus preventing calcium from reaching fruits.

How can I control blossom end rot? 

Avoid conditions where there is too much or too little water.  Water evenly and mulch the soil to retain moisture during dry periods.  Avoid practices that would damage roots (e.g., cultivating too near plants thereby cutting roots).  Use nitrate (NO3–) rather than ammonium (NH4+) forms of nitrogen fertilizer.  DO NOT over-fertilize.  Have your soil tested periodically to determine if there is sufficient calcium in the soil.  If not, add calcium (e.g., bonemeal or lime).  Check the soil pH on a regular basis, particularly if you use lime as a calcium source.  Use of lime tends to increase soil pH.  A pH of about 6.5 is ideal for growing most vegetables.  Finally, grow vegetable varieties/cultivars that are tolerant of calcium deficiencies and less likely to show blossom end rot symptoms.

For more information on blossom end rot: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

© 2005-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Karen Delahaut, Kristin Gies, and Barb Larson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Vegetable

Bacterial Wilt of Cucurbits

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UW Plant Disease Facts

 

Authors:   José Pablo Soto-Arias*, UW-Madison Plant Pathology
Last Revised:   02/28/2024
D-number:   D0014

What is bacterial wilt? 

Bacterial wilt is a common and destructive disease that affects cucurbits (i.e., plants in the cucumber family), including economically important crops such as melon (Cucumis melo), cucumber (Cucumis sativus) and, to a lesser extent, squash and pumpkin (Cucurbita spp.).  This disease is distributed throughout the United States; and can be found anywhere that cucurbits are grown.

Sudden wilting and eventual death of melon, cucumber and squash plants can be due to bacterial wilt. (Photo courtesy of ISU-PIDC.)
Sudden wilting and eventual death of melon, cucumber and squash plants can be due to bacterial wilt. (Photo courtesy of ISU-PIDC.)

What does bacterial wilt look like? 

The most distinctive symptom exhibited by a plant with bacterial wilt is wilting and ultimately death.  These symptoms are a consequence of the blockage of water movement inside of the plant.  Symptoms appear first on leaves of a single runner (vine).  Leaves may develop chlorotic (i.e., yellow) and necrotic (i.e., dead) areas as the disease progresses.  Symptoms typically develop rapidly along individual runners, and eventually, the plant’s crown is affected, resulting in the entire plant dying.  To determine if a symptomatic plant has bacterial wilt, cut a wilted vine near the base of the plant.  Next cut a section from this vine and look for sticky threads to form between the two vine sections as you slowly pull them apart.  The presence of these sticky threads is diagnostic.  This technique works best for cucumbers and melon, but less well for squash and pumpkins.

Where does bacterial wilt come from? 

Bacterial wilt of cucurbits is caused by the bacterium Erwinia tracheiphila.  This bacterium is moved from plant to plant by two insects: the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabrotica undecimpunctata).  See University of Wisconsin Garden Facts XHT1092, Cucumber Beetles, for details on these insects  The bacterium primarily overwinters in the guts of adult beetles, and is released when beetles feed on healthy cucurbit plants and excrete contaminated frass (i.e., feces) onto fresh feeding wounds.  E. tracheiphila has been found in association with wild cucurbits and other plants such as goldenrods (Solidago nemoralis and S. altissima), Johnson grass (Sorghum halepense) and even corn (Zea mays).  However, most of these plants never show wilt symptoms, and none are considered an important reservoir for the bacterium.

How do I save a plant with bacterial wilt? 

Bacterial wilt cannot be controlled once a plant is infected.  In particular, chemical sprays are not effective for control once plants show symptoms.  If you find bacterial wilt in your garden, immediately remove infected plants, and dispose of them by burning (where allowed by law) or burying them.  DO NOT compost infected plants.  Prompt removal and disposal of infected plants is important not only because they serve as a source of E. tracheiphila, but because they attract more cucumber beetles, thus increasing the risk of spread of the bacterium to other, healthy plants.

How do I avoid problems with bacterial wilt in the future?  

Management of bacterial wilt relies on control of cucumber beetles to prevent infection.  Target non-chemical and chemical control methods to protect plants at the beginning of the growing season when plants are more attractive to cucumber beetles.  Use mechanical barriers, such as row covers, to protect plants from cucumber beetle feeding.  Also, inspect cucurbits on a regular basis for cucumber beetles and their damage (two to three times per week early in the season, and weekly thereafter).  When cucumber beetle numbers are high (more than 20 per plant), spray plants with an appropriate insecticide (see UW Garden Facts XHT1092 for recommended insecticides).  Be sure to read and follow all label instructions of the insecticide(s) that you select to ensure that you use the insecticide(s) in the safest and most effective manner possible.  Cucurbit varieties resistant to bacterial wilt are not currently available.  However, some cucurbits such as watermelons and pickling cucumbers tend to be less attractive to cucumber beetles and thus tend to have fewer problems with bacterial wilt.  These crops can be used as alternatives to more susceptible cucurbit species.

For more information on bacterial wilt of cucurbits: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

© 2013-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Kimberly Cowles, Amanda Gevens, Kristin Krokowski, Jenna Lind, Dan O’Neil, Isael Rubio-Salaz ar and Tom Wilson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Herbaceous Ornamental, Disease - Vegetable

Bacterial Soft Rot

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UW Plant Disease Facts

 

Authors:   Tobias Lunt*, UW-Madison Plant Pathology
Last Revised:   02/28/2024
D-number:   D0010

What is bacterial soft rot? 

Bacterial soft rot describes a group of diseases that cause more crop loss worldwide than any other bacterial disease.  Bacterial soft rots damage succulent plant parts such as fruits, tubers, stems and bulbs of plants in nearly every plant family.  Soft rots commonly affect vegetables such as potato, carrot, tomato, cucurbits (e.g., cucumbers, melons, squash, pumpkins), and cruciferous crops (e.g., cabbage, cauliflower, bok choy).  These diseases can occur on crops in the field as well as on harvested crops in storage.  Rot can occur over a wide temperature range (with the worst decay between 70 and 80°F) and is particularly severe when oxygen is limited.

Bacterial soft rots cause the collapse of plant parts such as potato tubers. (Photo courtesy of the UW-Madison/Extension Plant Disease Diagnostics Clinic)
Bacterial soft rots cause the collapse of plant parts such as potato tubers. (Photo courtesy of the UW-Madison/Extension Plant Disease Diagnostics Clinic)

What does bacterial soft rot look like? 

Soft rot bacteria degrade pectate molecules that bind plant cells together, thus causing plant structure to fall apart.  Woody tissues are not susceptible.  Initially, bacterial soft rots cause water-soaked spots.  These spots enlarge over time and become sunken and soft.  Interior tissues beneath the spots become mushy and discolored, with the discoloration ranging anywhere from cream to black.  Seepage from affected areas is common.  Soft rots are known for a strong, disagreeable odor that accompanies the breakdown of plant tissue.

Where does bacterial soft rot come from? 

Soft rots are caused by several bacteria, most commonly species of Pectobacterium [particularly Pectobacterium carotovorum (previously called Erwinia carotovora)], Dickeya species [particularly Dickeya dadantii (previously called Erwinia chrysanthemi)], and certain species of Pseudomonas, Bacillus and Clostridium.  These bacteria can enter plants through wounds caused by tools, insects, and severe weather such as hail, as well as through natural openings.  The bacteria can be spread from plant to plant by insects, on contaminated tools, or by movement of infested plant debris, soil, or contaminated water.  Bacterial soft rots tend to be more of a problem during wet weather and can be more severe when plants lack sufficient calcium.

How do I save a plant with bacterial soft rot? 

Once soft rot bacteria have infected plant tissue, there are no treatments.  Immediately remove and discard infected plants or plant parts.  DO NOT bury or compost this material.

How do I avoid problems with bacterial soft rot in the future?  

Avoiding wet conditions is key for managing soft rot.  Plant vegetables in well- drained soils, and control watering times and amounts, making sure plants are watered adequately (but not excessively) and uniformly.  DO NOT crowd plants; wider spacing will promote more rapid drying of plants and soil.  Make sure that soil fertility (particularly soil calcium) is optimal for the vegetables that you are growing based on a soil nutrient test.  Add calcium (e.g., bone meal) at planting as needed.

Use soft rot-resistant vegetables in rotation with susceptible vegetables.  Corn, snap beans and beets are vegetables that are not considered susceptible to soft rot.  When growing broccoli, avoid varieties with flat/concave heads that trap moisture and promote soft rot.  Instead, select varieties with domed heads where water readily drains away.

Avoid damaging vegetables when weeding and during harvest.  Minimize any handling of soft-rotted plants, but if you must handle such plants (e.g., to remove them from the garden), wash your hands afterwards with soap and water.  Decontaminate garden tools before and after use by treating them for at least 30 seconds with 10% bleach or preferably (because of its less corrosive properties), 70% alcohol.  Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol.  Also, keep insects that can wound vegetables such as cabbage maggot under control (see University of Wisconsin Garden Facts XHT1030, Cabbage Maggot, for details).

Harvest only during dry conditions.  Closely inspect vegetables from infected gardens that will go into long-term storage, and be sure not to store any diseased vegetables.  Cure vegetables where appropriate prior to storage.  Store vegetables in a cool, dry, well-aerated place to suppress bacterial growth.

At the end of the growing season, remove any infested plant debris remaining in your garden, and destroy the material by burning (where allowed by local ordinance) or landfilling it.  If soft rot is a serious, recurring problem in an area in your garden, DO NOT grow susceptible crops in that area for a minimum of three years.

For more information on bacterial soft rot: 

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

© 2013-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Breann Bender, Amy Charkowski, Mary Pelzer, Scott Reuss, Isael Rubio – Salazar and Mary Thurber for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.