By Gaye Hammond, Houston Rose Society
We’ve gotten a lot of calls this year about “aliens” taking over rose bushes in gardens in Harris, Montgomery, and Galveston Counties. While chilli thrips (Scirtothrips dorsalis) are not aliens, they were, until recent years, foreign to North America. The first reported case of chilli thrips in Texas occurred in 2005 on store shelves in McAllen. The chilli thrips took over their pepper plants! The next outbreak occurred in Houston, and we have had confirmed sightings of the pest every year since 2006.
The good news is that chilli thrips can be controlled. In Harris County where the pest has been correctly identified and effective control methods implemented, populations were eliminated in the first growing season and did not return to the garden the following year. The bad news –— more often than not — is that chilli thrips damage is not correctly identified resulting in a population explosion, which gets rapidly out of control and hard to eliminate. Also challenging is the fact that many pesticides that work on other critters do not work on chilli thrips. So not only do you have to correctly identify the pest, but you have to use the right products to get rid of them.
Chilli thrips appear along the Gulf Coast in May and take up residence until September. The first plant to be affected in this area is the Indian Hawthorne. From there they move from plant group to plant group feeding on any plant species with new growth. Roses are a favorite host because roses have new growth from spring until winter. Chilli thrips were worse last year than ever before, and it is believed that the reason is due to extreme heat in the summer followed by an almost non-existent winter. Chilli thrips are heat-loving bugs.
Unlike Western Flower Thrips that cause unsightly browning of rose petals, chilli thrips feed on leaves and stems and have the ability to decimate a plant. They have rasping, cutting mouthparts that work like little saws, splitting open green plant tissue so that they can suck the juice out of the leaves. Their favorite feeding sites are the tender maroon-colored new growths and where leaflets attach to the stem. In these tight locations, they feed until there is no more juice in the plant tissue and then move on to another spot on the plant. As the leaf continues to develop, scars form at the feeding site and depending on the level of feeding leaves may be distorted or not look like a leaf at all.
Copies of the Chilli Thrips National Plant Alert as well as photographs of chilli thrips damage taken of roses in our area are included on our website, www.houstonrose.org. Correct identification of the pest is critical. Once the presence of chilli thrips is confirmed, the following steps will help you get the problem under control:
- Cut off all parts of the plant that have evidence of damage.
- Bag the trimmings, tightly tie up the bags and send them to the landfill. Do not compost the infected plant parts.
- Begin a spray rotation with a product proven to control chilli thrips.
- Rotate the selection of chemical treatments in order to avoid the pest becoming resistant to the treatment. It is advisable to continue treatment applications for at least 6 weeks.
- Watch the plants for repeat symptoms of pest feeding. As symptoms reoccur – repeat the process.
Products shown to be effective on chilli thrips are spray products containing spinosad as the active ingredient. Spinosad-containing products have the lowest environmental impact on beneficial insects. Some products containing spinosad that I have used to control chilli thrips are Conserve and Fertilome Bagworm & Caterpillar Spray. Also effective for chilli thrips are products containing acephate. Acephates are indiscriminate pesticides in that they kill everything they come in contact with. So if you foster bees and butterflies, applications of acephates will negatively impact those beneficial insects. It is smart to time your spray applications around mid-morning when it is less likely that the beneficial insects are in residence.
If you had chilli thrips during the growing season, consider applying a dormant oil spray in December or January. Dormant oil sprays are petroleum-based products that smother pest larvae and eggs that may be overwintering in the plant. There are two products currently being tested on chilli thrips that are showing a lot of promise. For commercial applications, Suffoil-X, a spray oil emulsion has been tested by Texas AgriLife Extension and is currently being tested by Dr. Allen Owings at Louisiana State University’s Hammond Research Center. The society’s good friend and supporter, Mark Chamblee of Chamblee’s Rose Nursery has been using Suffoil-X on his greenhouse roses all year and claims “this is one of the most exciting products I have used in a very long time!” Suffoil-X is made by BioWorks, Inc.
Similar in composition, Saf-T-Cide by Monterey is sold in pints and is available at The Arbor Gate in Tomball. Both products work as fungicide, insecticide and miticide and their mode of action is to suffocate eggs, larvae and nymphs of insects/mites as well as adults of soft-bodied insects.
Unlike heavy petroleum-based insecticides, the emulsion process of Suffoil-X greatly reduces the chance of phytoxcity (leaf burn) and improves its effectiveness. That said, it is not advisable to apply either of these products during periods of drought or when plants exhibit moisture stress.
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