Plant Pathology Infobytes

January 14, 1998
Handle Plant Pests With Dormant Season Sprays

Plant disease and insect pests have a nasty habit of hanging around on fruit and ornamental plants from one season to the next. An important first step in preparing for the coming growing season is through the application of a dormant season spray which will help clean-up some of these pests which are overwintering in your orchard and home landscape.

One of the best dormant spray materials for control of fruit diseases is liquid lime-sulfur. Used at recommended rates during the winter months, lime-sulfur very effectively wipes out fungus spores which overwinter on peach, plum and apple trees, grape vines, and other fruit crops.

Lime-sulfur is also recommended as a dormant spray as part of a control program for black spot, powdery mildew, and other rose diseases. As an eradication treatment for overwintering fungus spores, apply lime-sulfur before the buds begin to swell. Most formulations of lime-sulfur are approved as a dormant spray for other ornamental plants as well.

As an added plus, lime-sulfur dormant sprays are also effective for certain insects which attack fruit and ornamental plants. If a dormant oil is added to the lime-sulfur spray mixture, the combination is effective on such pests as scale and overwintering eggs of spider mites. Be sure to follow label directions relative to temperature when using a dormant oil.

Peach leaf curl is a good example of a disease where a single application of lime-sulfur applied during the dormant season provides excellent control. This fungus disease is frequently severe in Mississippi following wet springs and causes premature defoliation, thus seriously weakening trees. Control peach leaf curl by applying lime-sulfur after trees are fully dormant but before buds begin to swell in the spring.

A related disease on plums, referred to as plum pockets, is also reduced by lime-sulfur application in the dormant season. This disease shows up as small blisters on fruit shortly after fruit set. Blisters enlarge and soon the fruit becomes spongy. The young seed within the fruit stops development and the young plum becomes a hollow cavity, thus the name "plum pockets."

Black knot on plum and cherry is characterized by the production of elongated swellings or knots on the limbs of susceptible tissue. These corky outgrowths appear on twigs and small branches, where they may reach a foot or more in length. Newly formed knots are greenish and soft but become hard, black, and knotty with age.

The most effective control for black knot is to prune away all galls. However, a liquid lime-sulfur spray during dormancy will help control this disease and should be used along with canker removal.

Fireblight of apple and pear is a highly damaging bacterial disease that kills blossoms, fruiting spurs, entire branches and limbs, as well as trees during seasons when this disease is especially severe. The bacteria which cause the disease overwinter in fire blight cankers and spread to healthy tissues in the spring. Therefore, a dormant spray application of a copper fungicide (available under trade names such as Kocide, Bordeaux Mixture, and others) will help control this disease. Make sure that the brand of copper you purchase is cleared for use on apple and pear trees.

Dormant season fungicide applications can play an important role in your orchard and home landscape pest control program. Visit your local garden supply store and read labels on lime-sulfur and other fungicides for additional application information. If you have questions, please feel free to call or visit us at the County Extension Office County Extension Service Office.


Written by the late Dr. Frank Killebrew

A black line that separates the body text from footer information