Lime Sulphur Spray on Roses in the Summer

Lime Sulfur

• Lime sulfur is a mixture of sulfur and calcium hydroxide. It is typically available as a spray. Once applied to a plant, the sulfur kills bacteria and fungi on contact. Adding lime to the mixture reduces sulfur’s potency, minimizing injury to foliage. The University of Nebraska states that the greater the lime amount, the less toxic the mixture to the plant.

Pest Control

• Powdery mildew, rust and botrytis blight are a few rose diseases. Signs of powdery mildew include curling leaves that turn purple. The giveaway symptom is a white coating on leaves and stems. Orange powder on foliage indicates rust infection. Botrytis blight is a fungus that results in gray lesions near flowers and prevents blooms from opening. Lime sulfur application is effective against these and other diseases.

Timing

• Lime sulfur is often referred to as a dormant fungicide. Sources suggest that gardeners apply this mixture after leaf drop in the fall or early spring. A fall application on roses following pruning targets overwintering fungi spores. The dormant timing also prevents foliage injury to your rose bush. However, this mixture is still suitable during the summer, especially if your roses are infected.

Warnings

• Lime sulfur is effective against disease, but it burns foliage and can injure the gardener. Take care when handling. Lime sulfur is absorbed through the skin and is harmful to the eyes. For summer applications to roses and other plants, spray during cool conditions in the morning or evening. According to Purdue University, lime sulfur is damaging to plants after temperatures reach 80 degrees Fahrenheit. For dormant applications, apply when the temperature is above freezing. Plants do not fare well if treated with lime sulfur and horticultural oil within a month’s time.