COMMON VEGETABLE DISEASES
Dr. Leonard Perry, Extension Professor
University of Vermont
Blossom end rot, early blight, and powdery mildew are some of the common vegetable diseases you might find in our region.
Blossom end rot begins as a water-soaked spot near the blossom end of the fruit, as described in a University of Vermont Extension leaflet. 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 anhydrous calcium chloride in one gallon of water.
Another disease which attacks stems, leaves and fruit of tomatoes, but also those of potatoes and eggplant, is early blight. According to a University of New Hampshire Extension leaflet, this disease is caused by either of two fungi, beginning as circular or irregularly shaped spots ¼ to ½ inch in diameter. If these spots have a yellow halo on the outside and concentric lines inside, they are likely from the fungus Alternaria. This fungus can also 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 fungus Septoria. This fungus may also 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 using 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 prevent the spread of the disease spores (microscopic structures which spread such diseases), according to a University of Maine Extension leaflet. 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 proper use of appropriate fungicides.
More on these and other diseases, pests, and controls for New England can be found at an extensive online website (ProNewEngland.org).
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