Written by: Kris Kremser
Shortly after spring pruning of your roses, the foliage will begin to emerge. In several weeks you’ll notice bud formation. Another year of rose growing is about to commence. Not long after your modern roses begin to unfold from their state of quiescence and your old garden roses from dormancy, an onslaught of pests is sure to follow.
As seasoned rosarians, we know this. We can set our watches to it! It is springtime in the rose garden. The first step to insect control is to identify the insects by the damage they do. Here, we will take a look at two insects that begin to affect roses early in the season……Aphids and Thrips.
Flower thrips (Frankliniella occidentalis of the order thysanoptera) are found in vegetable and flower gardens on practically all species. Whether it’s one thrips or ten thrips, the name is both singular and plural. Thrips are extremely tiny, slender insects with long narrow wings that range in color from white or yellowish to dark brown or black.
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It’s the damage that thrips incur on roses that is the concern. They mainly infest an unopened rosebud. In fact, the damage is often seen before the thrips. While all colored roses are subject to thrips infestations, it is the light colored roses where they are most easily seen. But, how do they get inside an unopened bud?
The female thrips makes a small slit into a bud then lays her eggs. The eggs hatch in a few days and the larvae begin to suck the plant fluids from the petals. When the petals open, if they open at all, the edges will be brown and discolored. A condition not to be confused with balling brought on by humid conditions.
To check for thrips, find a blossom and pull back the petals. If you see little slivers of yellow, crème or even brown or black scurrying about, these are thrips larvae sucking sap from the petals.
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Control of thrips is difficult but there are some things that you can do to ease the infestation. For instance, to help reduce the numbers of over wintering adults remove debris in the fall. Also, encourage natural predators such as ladybeetles and lacewing larvae to control the thrips population.
Treatment using an organophosphate such as orthene is an extremely effective control. You can also use Bonide’s ‘Eight’ and Bayer Insect Control. The mixtures should be directed at the bud. Be sure to follow all label directions.
Aphids are another early season pest quite familiar to rose growers. While there are various species of aphids that feed on roses, one species, Macrosiphum rosae, is the most predominant. Unlike thrips, aphids on roses may be a skosh more tolerable. In small numbers, aphids generally do little physical damage to your roses.
However, larger populations can become quite a nuisance and can even reduce the number of quality blooms. Aphids, also called plant lice, have piercing sucking mouthparts and cause damage by sucking the plant juice. They are usually found on stems, underneath leaves and on the flower buds.
A nasty by-product of aphids is the sticky honeydew substance they excrete. Honeydew is a sugary liquid made up mostly of unused plant sap. In time, this buildup causes a black fungus called sooty mold to form on the plant. In addition to being unattractive, sooty mold can interfere with photosynthesis and consequently retard the growth of the plant. It can also attract ants and wasps.
Aphid control is not a big deal but it would be wise to keep even minimal infestations in check because aphids reproduce extremely rapidly and can easily overrun the garden. If populations are nominal, lacewing larvae and ladybugs have voracious appetites for these pests.
In the absence of predators, insecticidal soaps work well or even a few strong blasts of water from the garden hose. Neem and horticultural oils will work using suffocation as a mode of action. Insecticides containing cyfluthrin (Bayer), permethrin (Bonide Eight), or pyrethrin will provide excellent control. Or, use any insecticide labeled for uses against aphids. Just follow the label directions for use.
So, as another rose growing season begins to rev up, so will the thrips and aphids that come along with it. And while these two insects are just the beginning of the parade of pests, it’s good to know that with today’s knowledge and technology we can combat them with great precision to build a rose garden with blooms that are the envy of the neighborhood or the exhibition table.
About Kris Kremser: He has been involved in gardening for most of his 55 years. He's been growing roses for about 20 years. Kris enjoys exhibiting roses for competition. As an American Rose Society consulting rosarian, he writes and teaches about rose culture in the Columbia, SC area. Kris is also a member of the Greater Columbia Rose Society, the South Carolina Rose Society and the American Horticulture Society.