Western flower thrips causes several kinds of damage to greenhouse plants. A white discoloration or streaking in leaves or petals is typical, often with tiny dark specks of their droppings. Foliage or flowers damaged early in growth are often distorted as they expand. Flowers that are severely injured may fail to open, turn brown or become severely stunted. Look for these symptoms and use yellow or blue sticky cards to detect thrips early. Thrips are quite tiny and like to feed or hide in flowers; to more easily detect them, tap blooms over a paper or blow lightly into open flowers them to draw the thrips out.