Aphids-Behind enemy lines

Aphids are a true terror when it comes to green housing. These small soft bodied bugs can tear through a crop in a very short period if they are not managed correctly. There is several strategies for containing infestations as a small number of aphids does minimal damage.


The first line of defence would be preventative measures, this would include:

· Keeping the aphids out via air tight structures (sprung structure), bug nets on louvers and the like. This can be tough to do no matter how sealed the building is mother nature always seems to find her way in.

· Ipm (integrated pest management) – IPM is the practice of using beneficial bugs to “defend” your crop. Some of aphids natural predators are: Ladybugs (colder climate), & beneficial wasps (warmer climate)

· Lady bugs eat aphids – as many as 50 per day

· Parasitic wasps don’t eat aphids, what they do is lay an egg inside the aphid and the larvae eats its way out

· Keeping vigilant and doing regular inspections of your crops is important for knowing what biology is taking place within your greenhouse – yellow sticky pads can be good indicators for what bugs are present in your greenhouse.

Spraying for aphids-

If infestations do get away on you beneficial bugs will not be effective enough to contain the invasion. Active measures must be taken. Removal of large plants with many aphids may be required. I have found the time it takes to spray larger plants and the amount of spray it takes is uneconomical.

After the removal of the larger most infested plants, it is time to do a thorough spray of the crop. There are many different sprays and the like you can use. I like to use more organic soaps and oils.

· Cold pressed virgin neem oil – is my go to. The active ingredient “azadirachtin” is non-toxic and does a number on aphids. It can be toxic to fish so if you have fish present use caution not to get it in the water. I use a mixture of neem oil and dawn dish soap. (neem oil has anti-feeding properties and the soap helps it mix in the water.

· Canola oil + dish soap – this is another very effective combination against aphids. If you live in Canada neem oil may not be readily available. (I get mine on amazon – its not cheap) So a good alternative, the combination works together to “stick” or encase the bug in the mixture which suffocates the insect.

· There are other options I have not used as much: Pyrethrin – “pyganic” (organic), “Mycotrol/Botanigaurd”, “Azamax”- concentrated azadirachtin.

· Always follow the label and do a test spray on a small number of plants rather than the entire crop at once.

· Diversifying your spray type is important as some pests can build up immunity to certain sprays.

· Sometimes all you need is a cold blast of water to knock the little guys off the plants.

Spray Times-

Spraying soaps and oils should never be done in the heat of the sun as it can make it difficult for the plants to transpire, basically suffocating them. Spraying either very early morning or just before the sun goes down is the best way to keep them out of the sun while wet.


1. Managing pests on younger plants can be a very effective way to prevent outbreaks later.

2. Get yourself a backpack sprayer or something motorized. It is well worth the investment just in the time it will save you. You will also be able to do a better job then with a spray bottle for instance.

3. Sacrificial plants such as eggplants can be used to establish beneficial bugs saving you money from the bug sales man. This is especially important in leafy greens – greenhouses where beneficials are the toughest to establish.

4. Aphids produce a sticky “honeydew” that ants feed on. Ants will actually protect aphids from predators and even carry aphids to nearby plants.

How many hours per week do you think should be spent on pest management ? Is it possible to run a greenhouse and never have to use any sort of pesticide?

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Alberta, Canada