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Thrips can wreak havoc on your plants

Just over a week ago, we hosted – alongside Manna soup kitchen – the 14th annual Tour de Farms. The tour was a leisurely bike ride through the neighborhoods of Durango, where we visited a school garden, a couple of backyard gardens and the Manna Garden in a span of about 3 miles. Fortunately, no one bonked, no one walked away with a yellow jersey (although everyone did ride away with a new T-shirt!), and there were no accusations of blood doping or illegal drafting.

But many of us rode away with new ideas on how to use containers for growing tomatoes; that watermelons are possible in our short season; and that my full Lycra riding suit may have been a bit overkill (just kidding – flip-flops and a Hawaiian shirt for me). It is also easy to forget, as we cruise by in our vehicles focusing on the road ahead, how many impressive landscapes there are scattered around town. I saw more front yards converted to edibles and xeric plants; more trees that are appropriate for our smaller urban lots; some amazing yard art; and even a couple of fairy gardens, which make everyone smile.

Unfortunately, I also saw the effects of one of our biggest home garden pests: thrips. If you have a fast-growing vine, like Virginia creeper or grapes, there is a good chance that you have seen increased damage caused by thrips over the past couple of years. They are a piercing-sucking insect, so every time they penetrate the leaf surface to reach the tasty “sap,” they create a point of injury. Do that a thousand times on each leaf, or leaflet, and you will start to see the plant go from green, to yellow, to brown, to crispy.

At this point in the year, there isn’t much you can do. However, you can make sure you rake up all leaf matter in the fall and don’t compost it, and if you have the issue on Virginia creeper, you can cut the whole thing back to 6 to 12 inches when it is dormant and start fresh next year. That is what I do, and knock on wood, I haven’t had a bad thrips problem and I get 20 to 30 feet of growth every year.

Next year if you see thrips, or the signs of thrips damage, try spinosad, a low-toxicity insecticide that is derived from a soil bacterium, and horticultural oil mixed together and sprayed on the leaves. According to the University of California-Davis, spinosad lasts one week or more and moves short distances into sprayed tissue to reach thrips feeding in protected plant parts. Spinosad can be toxic to certain natural enemies (e.g., predatory mites, syrphid fly larvae) and bees when sprayed and for about one day afterward, so do not apply spinosad to plants that are flowering.

Oh, and I almost forgot – my new installment at the end of random columns that I write: Plant of the month. For September, it is moon carrot (Sesli gummiferum). I love it. I was lucky enough to walk the Durango Public Library gardens last week with CSU Extension’s regional entomologist and she counted more than 25 different species of pollinators on one plant. It is a biennial, so don’t expect much in the way of flowers the first year, but once it gets established, it becomes a prolific bloomer throughout the summer months.

Darrin Parmenter is the director and horticulture agent of the La Plata County Extension Office. Reach him at darrin.parmenter@co.laplata.co.us or 382-6464.