- 1). Look for discoloration. Insects that use piercing mouthparts to suck the sap from roses can leave yellow or brown dead spots in leaves or petals. These insects include whiteflies -- they look like very tiny white moths -- and spider mites, which are hard to see, but you'll likely notice the fine webbing they leave all over your plant. Aphids -- small, soft-bodied insects that range in color from green, pink, yellow or black -- can cause entire leaves to yellow and drop off the plant. They're usually seen feeding at points of new growth around leaves or buds. Leafhoppers look like very small grasshoppers and can cause white stippling on leaves.
- 2). Look for wilting. Wilting plants can be an indication of grub activity at the roots of the plants. Most grubs are white or cream and "C" shaped. They bore into roots and prevent water from getting to the rest of the plant. Severe infestations of sap-sucking insects can also cause wilting.
- 3). Look for malformed leaves or petals. Aphids, thrips -- or very small fly-like insects -- and leafhoppers feed on young growth of buds and leaves, causing deformity.
- 4). Look for honeydew or sooty mildew. Aphids and whiteflies excrete a sticky, shiny substance called honeydew, which attracts a black mold called sooty mold that causes leaves to turn black.
- 5). Look for large, circular or ragged holes in foliage. These indicate the presence of larger insects like caterpillars, beetles or leaf-cutter bees. Several species of caterpillars feed on rose bushes, but the most damaging is a small green caterpillar with a black head called a leafroller. They roll leaves together with silk and feed on leaves near this shelter. Several species of beetle attack rose bushes, as well. Among them are the brown June beetles and rose chafers, the metallic green rose leaf beetles, and the 12-spotted cucumber beetles, which are black with yellow spots.
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