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Those Darned Aphids!


by Kristina Hughes, Clear Creek County Master Gardener
Lime tree- Photo by Kristina Hughes
For those of us who like to let our houseplants spend time in the great outdoors during the warm months, there are many benefits. My plants love being outside in a protected location and they reward me with vigorous growth and rich blooms. Those benefits come with a price, however, and I have paid a price.

My lime tree in particular seems to attract aphids, which isn’t a problem when the plant is outside. Aphids are a favorite food of many birds and predatory insects. Aphids are an important food source for beneficial insects such as lady beetles (especially their larvae) and green lacewing larvae (see photo below). Some people recommend allowing small numbers of aphids to be part of a garden ecosystem, to support healthy populations of the predatory beneficials that love to eat aphids.

My lime tree does fine when it’s outside in the summer. But a couple of years ago, right around this time of year, the aphid eggs hatched. Since I don’t have a house full of beneficial insects (as much as I love them when they are outside) the aphids quickly got out of control. Honeydew was spattered thickly on the floor of my conservatory and the plant was crawling with, infested with, aphids.

I worked my way through the control options for aphids, starting with the least aggressive method. I took the plant into the shower and sprayed it down, knocking the bugs off the plant. I’ve used this method with satisfactory results on plants outside in the garden, where there are natural enemies to help. Inside, however, it only worked for a short time. Then they were back. When I couldn’t stand them anymore, I took the plant back into the shower. And I went around and around. 
Green lacewing larvae- These are good guys (Bugwood.org) 

Next, I tried insecticidal soap. It worked for a little bit longer, but I still ended up with lots of accumulated honeydew and lots of creepy, crawly aphids on my plant. Again, if I had had beneficial insects working with me, the soap probably would’ve been sufficient. But as I indicated earlier, I love beneficials which are outside my house. I personally don’t want to release more insects intomy house.

I needed another approach. I clearly wasn’t reaching all of the nooks and crannies on my plant where the aphids were hiding. I consulted my references and decided to use a systemic insecticide. I followed the directions carefully and, most importantly, I kept the plant indoors out of reach of pollinators for several months while the insecticide was moving through the plant. Gradually the aphids started to disappear and eventually they were all gone. They have not returned. But I had to keep my lime tree inside all season and I would prefer to be able to put it outside.

Horticultural oil worked really well for the aphid problem I had on my honeysuckle (see my blog from January 17, 2018- http://coloradomountaingardener.blogspot.com/2018/01/aphids-on-my-honeysuckles.html). So this year I have a new plan. I will put the lime tree outside to enjoy the increased sunlight and fresh air. When I bring it in at the end of the season, I will apply horticultural oil to smother the aphid eggs. I am hopeful this approach will allow both me and my plant to be happier, but also keep the aphids out of the house!

For more information on how to control aphids indoors see:
Managing Houseplant Pests, Factsheet 5.595 from CSU Extension https://extension.colostate.edu/topic-areas/insects/managing-houseplant-pests-5-595/

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