What pest is known to cause significant damage to ornamental plants?

Scales are known to cause significant damage to ornamental plants due to their feeding habits. These pests attach themselves to various parts of the plant, including stems and leaves, and feed on the plant's sap. As scales suck out the vital nutrients, they weaken the plant, leading to stunted growth, leaf yellowing, and a potential decline in overall health. In severe infestations, the presence of scales can lead to leaf drop and even plant death, making them particularly detrimental to ornamental plants.

In contrast, while fungus gnats can be a nuisance and can cause some damage, especially in moist conditions, they primarily affect seedlings and young plants rather than established ornamentals. Thrips, though they can damage leaves and flowers by feeding on them, usually cause localized problems rather than widespread damage to entire plants. Aphids are also sap-sucking pests that can stress plants, but they are generally less severe in their impact compared to scales, particularly on more mature ornamental plants that are better able to withstand some level of pest pressure.