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The trouble with thrips: They’re as annoying to gardeners as is possible

  • Author: Jeff Lowenfels
    | Alaska gardening
  • Updated: August 7
  • Published August 7

Thrips, photographed here on a dahlia, have been found in large numbers in Southcentral and Southeast Alaska this year.

It happens to all of us sooner or later: You think you have the perfect gladiola or sweat pea blooming, so you decide to harvest and bring some of your beauties indoors for bragging rights. Then you discover that your flowers are being attacked by what look like tiny, black, thread-like worms and you brought them into the house!

Upon closer examination, those wiggling animals turn out to be thrips. They cling to their flowers — and leaves — as they suck out juices for nourishment.

Cling? Does that suggest you can shake them off? I hope not. They have a mouthpart that literally acts like a hook or a large mouth claw. The thrip digs into whatever is being attacked and sets this anchor like a snagger on the Kenai going after a red. This is why the insect is so difficult to dislodge. You can try to dislodge them with a strong jet of water, but it might tear apart your blooms.

Oh, did I mention thrips like vegetables, too? Onions, carrots and the flowers of zucchini and other squashes and even beans. Persistent critters, too. They just don't give up.

Thrips hang about in gangs, which is why you see so many of them. It is as if they want to be as annoying as possible. The adults have wings, which make them even more annoying. Females lay 80 eggs at a time and the sap-sucking larvae go through a few stages before they fall to the ground and pupate. When the adult emerges, the cycle is repeated — up to 12 times a year. Aghhhh. And heat only speeds up the process, which only needs 15 to 20 days in the summer.

To top it off, thrips love light-colored flower petals, white and yellows in particular. They also carry diseases, making them a double-whammy. Gee, not much fun here unless you are into keying insects. If that is the case, however, you might be able to actually discover the exact kind you have attacking your gardens. (There is a very interesting website, which will guide you in an identification quest.)

To get rid of them, experts say, clean up grasses and weeds around your plants. Is that really advice people give? So silly; we have lawns surrounding our flower beds for the most part. And, how does a thrip know a weed from a desired peony? Well, so much for us, huh? Chances are, we are going to have to deal with them in other ways.

The first thing is thrips are attracted to blue sticky traps which you can buy or make (coating blue oaktag or blue cardboard with cooking oil). Early use will help you monitor their presence. Knock plants in their vicinity and try to attract the disturbed insects.

You can also start to control thrips by knocking them off those flowers that can sustain a hard spray of cold water as noted. There is actually a hose end tool that helps, called The Bug Blaster. A good adjustable spray nozzle will do just fine. Sometimes just running cut flowers under a faucet for a while will help.

There are organic pesticides you can try. Anything with Beauveria bassiana, a fungus, neem oil or a bacteria called spinosad will help, but honestly, thrips are really hard to control. Make sure to get under leaves and make sure to cover stem-flower junctions which is where they like to congregate when they are not out in plain sight.

Finally, some readers always question my insistence on using mulches on bare soils and assume that is where these critters hide all winter and thus survive. Well, thrips do like mulches, but they like green, living material, so once things are dead, you can use them as a mulch with confidence, with the exception being onion leaves, which trips like dead or alive. I doubt you have so many of them, so don’t worry.

It is time to acknowledge as gardeners that we are going to continue to see increases in pest numbers and new pests. This is just one of the reasons we have to get control of ourselves and thus our climate warming.

Global warming. It is time to acknowledge as gardeners that we are going to continue to see increases in pest numbers and new pests. This is just one of the reasons we have to get control of ourselves and thus our climate warming.

Jeff’s Alaska garden calendar

The 9th Annual Anchorage Invasive Weed Smackdown: 10 a.m.-1:30 p.m. Saturday at Valley of the Moon Park. This year’s target is European bird cherry at that location. Volunteers needed!

Butter and eggs: Only you can prevent increasing the invasive nature of this weed. Pick and destroy.

Anchorage Master Gardener Training: 5-8 p.m. Mondays through Dec. 9 in the Loussac Library Learning Commons. The fee is $300. Gina Dionne, a master gardener who works for Extension there, will teach the session. Registration at http://bit.ly/AK_MG19. $100 rebate for completing 40 hours of volunteering.

Master Gardener Late season plant sale: 10 a.m.-3 p.m. Aug. 10. Lots of perennials, many of which you won’t be able to buy in the stores, and some garden art. There will also be three classes for people to participate in, starting at 10:30 a.m., 11:30 a.m. and 12:30 p.m. Benny Benson parking lot across from the Alaska Botanical garden.







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