Whiteflies

The upside to garden pests and diseases is getting to do a little amateur backyard science. Any excuse to mix up a martini, pull out the microscope and take a close look at things and we’re all over it. This week’s happy hour entomology comes thanks to a infestation of white flies living on the underside of our tree collards.

I believe the specific culprit pictured above is the greenhouse whitefly, Trialeurodes vaporariorum which, despite the name, does not only inhabit greenhouses. Moving the leaf around under the microscope revealed thousands of tiny eggs pictured on the right. These eggs hatch and pass through several stages on the way to the winged adults seen above. At all stages, whiteflies suck sap from the host plant (brassica family members like collards are a favorite) and exude honeydew. Some whitefly species are tended and protected by ants acting like miniature cattle ranchers in return for the sweet, sticky honeydew–yet another remarkable example of symbiosis among nature’s many cycles of interdependence.

Control of our whitefly interlopers was simple: we washed them off with a hose. If we had a huge row of collards we might have had a bigger problem on our hands, but biodiversity in our tiny backyard means that the whiteflys don’t have many other options for feeding. What we could have done better is to have kept a closer eye on our plants. Daily inspection of more sensitive vegetables is always a good idea, but something we’ve been lax about lately. Keeping intensively planted annual vegetable beds close to places of daily activity means being able to stay on top of pest and disease problems. Raised beds we recently installed by the front door are on the path of our early morning amble down to the street to pick up the newspaper. A quick glance is sometimes all that’s need to spot a problem.

Permaculturalist Bill Mollison and David Holmgren suggest conceiving of our living spaces in a series of concentric zones, numbered one through five, with the first zone being our house and kitchen gardens and the outer zones being less cultivated and more wild spaces. Mollison and Holmgren’s zones are easily miniaturized for small urban yards. Trees that don’t need much attention can go towards the back, the chickens a little closer and the vegetables and herbs can benefit from being close at hand.

For additional information on whiteflys see the Colorado State Extension service’s whitefly quick facts.

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2 Comments

  1. I get these whiteflies on my kale and broccoli – it’s usually telling me that my annual plant is nearing the end of its useful yield (they’re usually followed by lots of harlequin bugs – and some of those green inchworm types).

    Washing off whitefly works, but I recommend doing it in the morning on a hot day – because they like it really moist – so if you wash late in the day and it’s cool out, things stay pretty wet and you can end up fostering a niche that they like and will come right back to. If you can catch them when there are just a few, I just squish ‘em with my fingers. For greens, it’s very easy to just wash off a few right before eating that leaf.

  2. I need a sprau of soapy water, neem and nori and throughly sprayed the kale and the next morning all was well.

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