What categories of control are commonly used for scale insects on ornamental shrubs?

• A. Crop rotation and intercropping.
• B. Watering frequency and fertilizer type.
• C. Horticultural oil and systemic insecticides.
• D. Pruning only.

Answer: (C)

Controlling scale insects on ornamental shrubs relies on products that act directly on the insects, either by suffocating them or by delivering the active ingredient through the plant. Horticultural oil coats the insects and blocks their openings, smothering scale at various life stages, including crawlers and eggs, when applied properly and under suitable conditions. Systemic insecticides are taken up by the plant and reach feeding scale insects as they insert their mouthparts, making them effective for infestations that are hard to reach with surface sprays.

Other approaches like crop rotation and intercropping are not practical primary controls for scale insects on established ornamental shrubs in landscapes. Adjusting watering and fertilizer affects plant vigor but does not directly eradicate scale insects. Pruning can help reduce some visible individuals, but it doesn’t reliably eliminate eggs or hidden populations, so it’s not as consistent a control strategy as the combination of oils and systemic insecticides.