C - Chemicals

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Lime Sulphur and Dormant Oil Spraying
By The Garden Commando

Every year, around February or March, people begin to wonder when they should spray their fruit and ornamental trees. The instructions on the kits usually tell you that the spraying must be undertaken when you know you are going to have two dry days and nights, and that the temperature will remain above freezing. On the other hand, we are told that we must apply this spray before the buds actually break. Quite a conundrum.

Horticultural experts suggest that you can use the dormant oil from after the first deep freeze (so that plants are dormant) up to just prior to the buds breaking. ("Breaking" means when the outer bud case opens, revealing tender new growth inside.)

Because the weather varies so greatly from day to day, it is difficult to predict when you are going to be able to pick precisely the right time, so you have to do the best you can.

If a mild spell is predicted at some surprising time, like January or February, and the forecast suggests that we are going get a warm air mass moving in for a few days - then this is a great time to get out the hose, the hose-end sprayer, and load it up with the Lime-sulphur and Dormant oil. 

There may still be snow on the ground, and you may be wearing heavy boots, but as long as the temperature outdoors is above freezing, and you can manipulate the hose,  you can apply the spray. In conclusion therefore, you can spray Lime Sulphur and Dormant oil pretty well at any time during the dormant period - providing you get two days of dry, preferably sunny, above-freezing weather.

Applying the dormant oil mix can be messy, and it smells awful.  While you are spraying, wear an old rain cape over your outer clothing (or just use a garbage bag with holes for head and arms), and disposable rubber gloves, When you are finished,  you will be able to remove all the outer gear and stuff it in a garbage bag before you come inside. (Hint: Try to avoid neighbours when wearing this outfit.)

You should spray your target trees and shrubs to "run off". This means that you start at the top, and keep spraying until the mix is running down the branches and dripping off.

The Lime Sulphur mix helps to combat fungus diseases such as black spot; the dormant oil ibn which it is suspended smothers overwintering insects eggs, such as those of scale, and aphid and thrips.

Spraying with the Dormant Oil mix does not completely prevent pest and disease problems from occurring in your trees and shrubs, but it certainly drastically reduces the occurrence. This means that you will have fewer pest and disease related problems during the growing season.


The following texts were used to obtain information and references to validate the process analysis provided in this text.

Name of Author  Name of book or Text  Publisher and Year 
Hawthorne, Ross Gardening from the Ground Up Wilson Laboratories Inc. Dundas, 
Ontario, Canada. 1989 
Ridell, Jack 
Switzer, Clay 
Insect and Disease Control in the Home 
Ministry of Agriculture and Food. 
Toronto, Canada. 1988

This page was updated December 28/99 

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