Many of you know I rely on dormant-season spraying to prevent insect and disease problems in the spring. This helps me cut down on less effective pesticide and fungicide treatments later in the year. I mainly use two treatments: horticultural oil while trees are dormant, and lime sulfur in early spring when buds start to swell. The oil targets insects that overwinter, while the lime sulfur helps control fungal growth. Timing depends on the weather, and I make sure to leave several weeks between the two sprays. Now that winter is ending and spring is still a few weeks away, it’s a great time to use horticultural oil. In Virginia, I spray all my trees. When I lived in Houston, it was more challenging because conifers need to be truly dormant for lime sulfur, and with winter temperatures often in the 60s and 70s, they never really went dormant. If you live in a warm climate like that, skip the lime sulfur on conifers and only use it on trees that lose their leaves in winter.
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