Thrips and their larvae are fond of light-colored blossoms, scraping at flower petals and sometimes leaves
Photo courtesy of Scot Nelson
These tiny (less than 1/25 inch), nearly invisible 4-winged flies damage roses by sucking their fluids, particularly on petals.
Thrips, also known as thunderflies, may become a serious problem in hot summers. Untreated, they will reproduce very fast and build large populations.
First signs of infestation are, that petal edges turn brown and blooms may be awful discolored when they open.
Rose buds will fail to open and leaves mottled and malformed with severe infestation.
Thunderflies are not specific for roses, and often move from other garden plants to roses. Preventing this pest is a matter of garden maintenance. Removing plant debris from the ground will reduce the possibility for the pest to lay their eggs.
Many beneficial insects love to eat thunderflies, especially lacewings. To attract them to your rose garden, plant some Beneficial Bug Wildflowers. Beneficial insects will keep pest infestation to a minimum.
Check your plants regularly for damage, and if thunderflies are suspected, use a magnifying glass to spot them. Best is to take some suspected flowers, shake them over a white sheet of paper and, if there is an infestation, you will see tiny, fast-moving brown insects on it.
Once the pest is identified, you have to take action immediately.
Once the insect pests are inside the rose petalage, insecticides cannot reach them. Take the following measures to control the pest:
For severe infestation, a chemical treatment with, for example, Orthos’s Thrip control, can be used as a last resource.
If you have a chronic,
every year returning problem with thunderflies, use a systemic insecticide in early spring and periodically repeat the
application for the rest of the growing season as directed.