Tell me what's killing my plant!
June 12, 2010 11:00 AM   Subscribe

Can anyone identify these beasties that have killed my hydrangea?

One more pic here; sadly my iphone won't let me get a really good closeup.

A week or two ago, these things looked like larvae. Now they look more like a fungus, maybe--glued to the leaves and a little dried out and chalky around the edges.

I'm going to snip off the affected areas. I'd like to try to save the healthy part of the plant, but don't know whether to use a pesticide or fungicide or what.

posted by torticat to Home & Garden (8 answers total)
Best answer: It's a sap-sucking insect: Cottony cushion scale.

It's difficult to kill adult scale with insecticides though I have had good luck with systemics. The downside is systemics also kill the natural predators of scale but it's pretty clear from your pics that natural predators aren't doing their job.

Cut and discard dying stems, if the plant is small enough you can use rubbing alcohol on cotton swabs to dab at the scale (it kills them in the most satisfying, although time-consuming, way) and apply an insecticide to kill the larvae before they have a chance to develop their protective coating. You'll have to do several rounds of this over the next few months to get them all.
posted by jamaro at 11:07 AM on June 12, 2010 [3 favorites]

(You definitely want to deal with this quickly and decisively because this species of scale is mobile and spreads quickly: those white fluffy things are egg sacks each containing hundreds of eggs. Eww.)
posted by jamaro at 11:12 AM on June 12, 2010

Best answer: Insecticidal soaps or oils can kill these and now is the time of year to use them.
posted by TedW at 11:33 AM on June 12, 2010

Neem Oil
posted by X4ster at 11:44 AM on June 12, 2010

You may want to call a local nursery to see if they carry Ladybugs and if they eat this particular insect. FYI--I'm heading out to get some ladybugs for my yard and garden later today . . .
posted by 6:1 at 1:18 PM on June 12, 2010

You can always clip off a section of that, put it in a ziploc bag, and take it into your local nursery. They can grab a specific bottle off a shelf from their wall of chemicals that will take care of it, as well as educate you on application and future prevention.
posted by msbutah at 2:25 PM on June 12, 2010

i've had the best luck with neem oil for scale. Definitely better than with insecticidal oils that smother bugs- those often don't work on scale. Neem oil will be taken up by bugs as they are feeding on the plant, so you don't have to soak every single little critter down for it to be effective. Three times a month is usually enough to disrupt successive generations. Always spray anything early in the morning to prevent sunburn. Neem generally does not harm beneficials. It's also a fungicide, so it has multiple uses for gardeners. Make sure you get the real thing- some "neem" products marketed to gardeners don't have all the active constituents. I buy from Mountain Rose Herbs. (scroll down).

BTW, the hydrangea's not dead. Cut off all the crap and do not use any nitrogenous fertilizer until it recovers nicely. Too much nitrogen is a beacon to insect pests.
posted by oneirodynia at 6:38 PM on June 12, 2010

Response by poster: Thanks all!

I cut off all the dead parts and cleaned the scale off the rest of the leaves and stems with rubbing alcohol; then I treated the soil with systemic insecticide. Will get neem oil if the bugs reappear.

The pot actually holds two hydrangeas. One I cut down to the soil (it was completely brown and shriveled), and the other I pruned and cleaned.
posted by torticat at 7:32 PM on June 12, 2010

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