University of Vermont
Department of Plant and Soil Science

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COMMON VEGETABLE DISEASES

Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont

Blossom end rot, early blight, and powdery mildew are some of the common vegetable diseases that you might find in our region.   

Blossom end rot begins as a water-soaked spot near the blossom end of the fruit.  This spot (lesion) soon enlarges and turns dark, just as the green fruit is beginning to ripen.  This lesion may become leathery and crack, with other diseases then taking hold.

Blossom end rot sounds like a disease caused by an infection, but it is not.  Rather, it is caused by a calcium deficiency, often associated with too little water or drought.  It often occurs after rapid growth early in the season, followed by hot and dry weather, or conditions alternating between the two.  This physiological “disease” is most common on the earliest to set fruits, plants put out early into cold soil, or plants spaced too close together.

Blossom end rot is often prevented by:
--keeping soils uniformly moist, and deeply watered during drought.  Using mulches can help.
--avoiding root damage by not cultivating too close to plants,
--using fertilizers in subsequent years early in the season that are high in phosphorus and low in nitrogen, and
--spraying plants early in the season, especially after heavy rains, with a dilute calcium chloride solution. Mix one level tablespoon of calcium chloride (as used in making pickles) into one gallon of water.

Another disease that attacks stems, leaves and fruit of tomatoes, but also those of potatoes and eggplant, is early blight.  This disease is caused by either of two fungi, beginning as circular or irregularly shaped spots one-quarter to one-half inch in diameter.  If these spots have a yellow halo on the outside and concentric lines inside, they are likely from the Alternaria fungus.  This fungus also can cause sunken, dark areas (cankers) in stems.  Infected fruit have sunken, dark, leathery spots on the stem end.

If the leaf spots are gray with dark centers, they are likely from the Septoria leaf spot fungus.  This fungus also may infect stems.  Although fruit aren’t attacked, they may be burned by the sun (sunscald) from infected leaves dropping off. 

Ways to minimize or prevent early blight include:
--selecting resistant varieties,
--growing tomatoes in a different part of the garden each year,
--watering early in the morning if overhead watering, to allow leaves to dry during the day, and
--using a fungicide labeled for this disease.  If using such a chemical, read and follow all label directions for best control, and for your safety and that of the environment.

Powdery mildew can attack many plants, but is most commonly seen on cucurbits such as squash and pumpkins.   High humidity promotes this disease, but it does not require rain to spread, as do many diseases.  In fact, rain may help to prevent the spread of the disease spores (microscopic structures which spread such diseases).  Often the spores don’t last over winter in the north, but blow in from southern areas.  Once infected, a single leaf can produce tens of millions of spores.

Symptoms are a quite visible white spotting or growth on leaves, eventually causing them to turn yellow, then brown, and finally die.  Methods to control this disease include:
--choosing resistant varieties,
--planting in areas with good air circulation, and
--using appropriate fungicides. Again, to use these properly, read and follow label directions.

More on these and other vegetable diseases and how to control them can be found online from the University of Massachusetts Extension (ag.umass.edu/vegetable/fact-sheets/diseases).

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