The image above is a before and after I lost control of the aphid infestation. No, those spots in the right image aren’t dew or moisture, they’re all aphids in various stages of their lifecycle. Ever since I first turned everything on in the green house, I’ve had a small amount of ladybugs cohabitating with me. When I saw the first aphids, I introduced 1200 more to try to curb the issue, but soon learned that ladybug larvae are what really do most of the damage to aphids. At this point I am just throwing predatory insects at my problem willy nilly. Rather than spraying or doing something manual for the aphids, I just let the ladybugs do their jobs.
At first they seemed to be helping, until they weren’t. I decided to take some time and do some reading and learned that it only takes a week from when an aphid hatches to when it can reproduce. Each aphid can produce around 5 new aphids a day for the next month. As you can imagine this exponential growth is why my ladybugs were quickly overwhelmed. I then decided on a few courses of action.
- I started spraying the really bad spots with a diluted neem oil solution.
- Once it started to get sunny, I turned the fans off and baked them. Aphids are soft bodied insects and can’t tolerate temps above 90F for very long and the greenhouse can get over 110F with the ventilation turned off even in late winter if the sun is out.
- I pulled way back on feeding my fish. This dropped my nitrates down to almost 0. Aphids are drawn to nitrate sources and thrive upon them.
- I hung up yellow sticky traps. The flying adult aphids are drawn to the color yellow and this helped slow the spread to other plants.
We started with ladybugs which are very good predators of aphids and I hoped that they would start reproducing with the over abundance of food. While the ladybugs did eventually reproduce in numbers, it took while for them to mate and decide to lay eggs (around 3 weeks or so). By this time there were thousands of prolific aphids that could not be stopped.
Failures aside, watching the lady bugs do their thing was super interesting. In the pictures above you can see their full lifecycle the cluster of yellow eggs the females lay, the larvae crawling around looking all menacing, and finally the pupae stage after which they emerge as juvenile ladybugs.
Ladybugs are generally carnivorous, but they will drink nectar from flowers or a mix that’s sprayed on a surface. Their favorite food are aphids, but will eat pretty much any small insect like thrips and spider mites as well. Ladybugs start to get lethargic as the temperature gets cooler and will eventually go into a type of hibernation when it’s cold enough. If you have ladybugs in your greenhouse during cold periods, don’t throw out the dead looking ones, they’re probably still alive!
I also purchased green lacewing eggs and praying mantis egg pods. Both of these are a step above ladybugs when it comes to consuming aphids. The pray mantis’ were my nuclear option as they would have eaten everything crawling around including the ladybugs. Each pod can contain 50-200 mantis nymphs. I don’t have much insight into either of these insects at the moment because I only had a few lacewings hatch and I’m still waiting for the praying mantis’ to hatch. I purchased lacewing eggs in rice hulls and I really didn’t see many larvae emerge, but I did see a couple.
Baking the buggers
On the occasional sunny day in late February, the greenhouse can reach temperatures around 100F even when it’s 25F outside. I occasionally turned off the ventilation and let it heat up. This severely weakened the flightless adults and caused the flying adults to fly up and gather on the clear roof panels of the greenhouse in an attempt to cool off. I was then able to use a shop vac to vacuum them up which really help knock down their ability to spread to other plants. The heat also made the flightless aphids gather at the top of the plants where I could further vacuum those up and it gathered them for the for an easy meal for the ladybug larvae.
By the time I slowed the aphid infestation to a crawl, my plants were ruined. They were covered in honeydew (sticky sweet aphid poo) and beginning to mold and decay. There were also piles of aphid nymph molts that I had no chance of removing from all the sticky surfaces. We ended up having to remove all the plants and clean everything.
As you can see it was starting to get really disgusting. This is just what the rafts looked like let alone how much was on all the plants. My father in law and I scrubbed and scrubbed and eventually we returned the room to normal.
I still kept the sticky traps up for a bit to catch any stragglers and I had to squirt a few aphids off the new plants for 2 days or so. I haven’t seen any since. Mission accomplished.