Archives: Diseases

All are caused by all the same organism, Botryosphaeria obtuse, but the common names refer to the different stages of the disease. This disease can attack many kinds of trees and shrubs, not just apple trees, especially when wood is weak or dying. For example in grapes, it is known as dead arm. The Frog … Read more

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A bacterial disease, fireblight affects only members of the rose family. The infection enters through the blossoms, then spreads by pollenizing insects and splashing water from rain or sprinklers. Fire-blight is favored by temperatures above 60°F and high humidity caused by rain, dew, fog, or irrigation. The bacteria survive in blighted twigs and cankers.

Each of the many fungi causing downy mildew attack a narrow range of hosts. Spread by wind, rain, and infected seeds, these fungi all require wet conditions, and most must also have cool temperatures (the exception is downy mildew of cucurbits, which can germinate at temperatures as high as 90°F). 

Present in almost all soils, the various organisms referred to as damping-off fungi can kill seedlings sometimes even before they emerge, and rot potato seed pieces. Healthy seedlings resist infection, though, and plants generally become less vulnerable with age. Over-watering and poor air circulation foster the growth of damping-off fungi, and plants are more susceptible … Read more

Circular brown spots begin occurring on the older, lower leaves in late June and July. The leaves begin to turn bright yellow, orange or red with dark small spots and fall off the tree. As the summer progresses, many infected trees will have dropped all but their newest leaves. Fungicide treatments should be started in … Read more

Spread by wind and rain, this fungal disease enters the blossoms of fruit trees, then moves down the twigs. It survives on infected twigs and on mummies (shriveled fruit) to reinfect the tree the following year.

Late blight is caused by crops that are left in the ground from the previous year’s harvest, in cull piles, soil or infected volunteer plants and can spread rapidly in warm and wet conditions on new crops. This can have devastating effects by destroying entire crops. Target: Mainly potatoes and tomatoes but may spread to … Read more

Early blight (sometimes called target spot) is a fungal disease that most often affects tomatoes and potatoes. It starts by causing distortion of the new growth, followed by brown or black spots. Gradually the whole plant withers, yellows and dies.