Ask the Gardener

The mystery of 'snow' on a pyracantha

CorrespondentNovember 9, 2012 

COURTESY OF L.A. JACKSON

I was trimming my pyracantha and discovered a white fungus on almost every stem. It resembled the fake snow we used to spray on Christmas trees when I was a kid. What is it, and how do I treat it?

Ted Wilburn

Charlotte

I almost suspected that your problem was powdery mildew, a fungal disease that can coat the foliage of some pyracanthas with its white-ish blanket of bad news, but your “fake snow” comment nailed it for me.

You’re dealing with woolly aphids. This is a type of aphid that coats itself with a protective covering of white, waxy threads, giving the appearance of chunky, clumpy mini-mounds of – in your words – fake snow.

So, how can you prevent these little beasties from camping out on your pyracantha? They can be dislodged with a strong stream of water – and some folks also scrub the affected parts of the plant with a used toothbrush, just for good measure.

There are, however, chemical alternatives. Horticultural oil or insecticidal soap are both effective, garden-friendly solutions, and since aphids do their damage by sucking the juices out of plants, a systemic insecticide that contains imidacloprid as the active ingredient will also do the trick.

If you do decide to go the systemic insecticide route, wait until next spring to apply it, and only after your pyracantha’s flowers have faded, to keep from harming pollinating insects.

Hyacinth bean vine

My neighbor wanted to give me a vine that had flat, curved, bright purple pods, but neither he nor I know what it is. He says it really takes off no matter where he plants it. I just do not want to plant an invasive vine. It looks great, and if it is not invasive, I may take a cutting.

Michael Pearson

Raleigh

What your neighbor wants to pass along is hyacinth bean ( Dolichos lablab), a vine from the tropics that can stretch to more than 15 feet long – meaning it is a good candidate to cover a ratty-looking fence, soften the lines of a tall trellis or provide quick shade cover to combat the heat of summer. Clusters of fragrant, white, pink or light purple sweet pea-like blossoms will begin lacing this ornamental vine by midsummer, attracting hummingbirds, bees and butterflies. These pretty flowers are then joined by the additional visual treat of flat bean pods shamelessly flaunting themselves in a screaming, electric purple not seen since the days of disco.

Although hyacinth bean is a perennial in Zone 9 and farther south, in this area, it is grown as an annual. As far as it being invasive, well, if you consider a plant crawling 15 feet into your garden invasive, it is, but it is not the next kudzu getting ready to gobble up the South. It is a fast grower, but it won’t readily escape the garden. Need proof? This is an heirloom vine that has been a favorite in Southern gardens since Colonial days, which has been plenty of time for this vine to show a mean streak – if it had one.

Don’t bother taking cuttings – the beans will easily sprout when planted in the spring. Fall is the time to harvest hyacinth beans. To be sure the beans are ready for picking and storage over winter, only go for pods that have withered, dried and turned a light grayish-brown. Beans still in their flashy purple pods haven’t fully matured.

L.A. Jackson is the former editor of Carolina Gardener Magazine. Send your garden questions, including the city where you garden, to: askthegardener@newsobserver.com.

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