Spraying fruit trees in the winter will kill insect eggs and small larvae when the pests are most vulnerable. According to Oregon State University, some fruit trees may require several sprayings during the dormant season of winter. While applying sprays is important, another factor is just as crucial to the fruit trees' health: keeping the area around the base of the tree free from debris and leaves. Material laying around the tree will harbor many pests and could promote disease.
Apply dormant oil spray to the fruit tree after all leaves have fallen. Mix the oil according to the label directions on the container. Spray the tree in the morning hours when temperatures are expected to rise above freezing during the day. Freezing temperatures can force the oil into the bark, causing damage to the trunk of the fruit tree.
Treat the fruit tree with a fungicide, such as a lime-sulfur concentrate, during the midwinter months between December and January. The lime-sulfur will aid in controlling bacterial diseases as well. Use the label directions for proper mixing strengths.
Spray all stone-type fruit trees--cherries, peaches and plums--with a fixed copper solution. Wait at least six weeks before applying the copper spray to stone fruit trees if you used the sulfur spray in midwinter.
Paint the trunks of young trees with a white latex paint mixed half strength with water. The white reflective surface will reduce trunk cracking and keep insects from the small crevices.