Home gardeners grow roses because of the color, fragrance and beauty they add to the landscape or garden. However, rosebushes are susceptible to insect infestations that damage their blooms as well as foliage. Although there are a variety of white insects that attacked roses, the most common are thrips, rose scales and leafhoppers.
Thrips are small insects, measuring 0.5 to 1.2 mm in length, that can be difficult to spot without the aid of a magnifying glass. Chilli thrips, the type often found on rosebushes, are white or pale yellow in color and multiply rapidly. The rose scale, another pest that plagues roses, is pale white in color, round and measures 1/10 inch in diameter. Male rose scales are bright white and have an elongated body shape. Leafhoppers, also common in rosebushes, are wedge-shaped winged insects. Feeding on roses with their piercing mouthparts, leafhoppers remove sap and plant juices from rose leaves.
Chilli thrips cause damage to flowers, leaves and stems above the soil line. They punch holes in the plant surfaces and extract plant tissue by sucking it out. This pest prefers to feed on succulent, tender new plant tissue and causes leaves to turn brown or black in color. Roses infested with chilli thrips appear distorted, become stunted and suffer from premature defoliation. Thrips usually are found on roses during periods of very dry weather.The rose scale is often visible on host plants and looks like small, white round patches. Rose scales start at the bottom of the stems and work their way upward. Rosebushes with heavy infestations of this scale insect can look completely white because the insects attach themselves to all surfaces of the plant. The appearance and vigor of the rosebush is compromised by the presence of rose scales. Leafhoppers feed on the undersides of rose leaves causing them to develop a stippled appearance. Infested plants also can have off-color leaves and leaf bronzing.
Chilli thrips are a food source for a variety of predatory insects, such as syrphid flies, mirid bugs, predatory mites and the insidious flower bug. There are also a number of parasitic nematodes that feed on thrips, keeping them under control. If predatory insects are present in your garden and feeding on thrips, avoid applying insecticide as it will kill the predatory insects as well as the thrips. If you have rose scales on your rosebush, prune out infested branches and destroy them. Keep your garden free from weeds to avoid re-infestation. Yellow sticky traps are a good way to trap leafhoppers and avoid the use of chemical controls. Place these traps amidst the infested rosebushes to capture leafhoppers. Spraying your rosebushes with a hard stream of water twice each week can eliminate leafhoppers. This process is known as syringing and it knocks insects from the plant, keeping their numbers low.
Heavy infestations of thrips often require chemical control methods to eliminate this pest. According to the University of Florida IFAS Extension, there are several insecticides available for thrip control. Choose an insecticide with active ingredients such as abamectin, imidacloprid or novaluron for best results. These products are available in foliar sprays. Always follow the directions on the product label for best results. There are currently no insecticidal sprays recommended for the treatment of rose scales. Applying insecticidal soaps are often effective in eliminating leafhoppers on roses. Be sure to completely saturate the tops of roses, as well as the undersides of leaves to kill all adults and developing nymphs.
- University of Florida: Pests Of Roses In Florida: Gary W. Knox; Russell F. Mizell III
- University of Florida: Chilli Thrips (Castor Thrips, Assam Thrips, Yellow Tea Thrips, Strawberry Thrips): D.R Seal; W. Klassan
- National Gardening Association: White Bugs On Roses
- Ohio State University: Brambles: Production Management And Marketing Bulletin: Chapter 4 Insects And Mites
- University of Florida: Pests Of Roses In Florida; Gary W. Knox; Russel F. Mizell III
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