How to control aphids in your home garden
No gardener exists that isn’t familiar with aphids. But few gardeners achieve effective control of these pests. I can help.
Important information about aphids: Aphids do best when temperatures increase, but humidity remains high – most often in the spring. They are phloem-feeders, meaning they use mouth parts to penetrate soft plant tissue and “drink” the phloem, or nutrient rich fluid that is the life-blood of the plant. They can reproduce asexually resulting in extreme population increases. A single female aphid can produce asexually for many generations resulting in thousands of clonal offspring. There are many different kids of aphids. Some aphid species create males in the autumn and undergo a sexual production period prior to overwintering. Some aphids feed on only one type of plant and are usually named after that plant. Other aphids can feed on thousands of different plants from different families. Aphids may be called different names in other parts of the world, but the damage from these insects is universal. It is considered the number one pest for crops in temperate regions across the globe.
Do you have aphids? Do you scout? (Regularly checking your plants, turning over leaves and seeing what’s there.) The first line of defense is finding them. If a plant was particularly damaged last season, check this season to see when you first find aphids and record the date. Look for new damage. As a gardener, you know to look for signs of stress, so you will no doubt find aphid damage – however, finding damage from aphids usually means the problem is out of control – we aim to avoid this. Other signs of aphids include:
Sheddings are the dropping of body parts, (often exoskeletons or wings) which are released at changes in an aphid’s life-stage. If you see these, it is probably in large amounts on a leaf or on the ground. Look immediately above this site and you will find aphids. What makes this easy to find is because sheddings are often sticky, so they stay where they fall. They are sticky because of the next sign:
Honeydew is the product of many phloem-feeders. They suck the sap from the plant and produce a sugary substance we call honeydew. Honeydew actually contributes to a plant’s decline by causing the buildup of molds and fungi. In my experience, seeing the shiny, wet looking leaf covered in honeydew is a sign the plant is close to death and the aphids are out of control. However, on some plants, catching this early can still lead to effective control. Honeydew is also a problem because it attracts….
Ants! Look for ants. If you see ants in your garden you must follow them and see what they are eating. It is very likely they will lead you to aphids. Yes, ants eat the honeydew that the aphids produce, which would be a good thing, except for the fact that ants will farm the aphids. No joke! When ants discover an aphid population they may stroke the feeding aphids with their antennae to excrete more honeydew. Furthermore, they are known to pick up fallen aphids and put them back on the plants to continue production. They have also been known to carry aphid eggs over winter to continue the farming in the spring. Many “natural” home remedies for aphids merely knock them off the plant. If you have ants, they will pick up the fallen and aphids and carry them back to the plant. Not only that, but ants will fight off aphid predators – so we often suggest stopping the ants as a method of aphid control.
Once we find aphids we mustn’t just panic and pick the damaged leaves, spray off the aphids, use a pesticide or pull the plants. Instead, look to see if you already have natural predators. Here is what to look for:
– Lady bugs and other beetles
– Aphid mummies
– Aphidoletes larva
Lady bugs are easy to identify. If you leave an aphid problem long enough, they will show up. They eat aphids, as do their larva. If you find many lady bugs in your garden you are likely in very good shape – unless all your plants are drooping and covered in honeydew.
Aphid mummies are parasitized aphids from a parasitic wasp in the aphidius family. They lay their egg inside the aphid, it dies, and the cycle continues. Finding one of these in your garden likely means there will be many.
Aphidoletes are predatory midges that prey on aphids. Adults will fly to infected areas, eat some aphids and lay their eggs. The larva will eat several aphids before falling to the ground to pupate and return as an adult. These are highly effective at control. You might see a cluster of midges flying around above your garden at dusk, or you might find the bright orange larva in and amongst (often under) a cluster of aphids. Aphidoletes tend to arrive later in the spring and try to play catch-up to aphid populations.
Check out this video for more on aphidoletes: https://www.youtube.com/watch?v=QN5dbWg9WBc&feature=share
Naturally, aphid populations will explode prior to the populations of predators meeting those numbers to control the aphids. Indeed, the goal of nature is to continue, so control as we may see it is never a goal of nature. But, if you see the predators, it means that the predator population is about to increase and you’re at the end of the aphid threat for that site. I can tell by looking at a population of aphids and the number of predators if that plant will survive. This is hard to tell without the experience and it is even more difficult to describe. So, it goes back to scouting. As you watch the aphid populations increase and the plant stress increase, you might be able to guess, when the predators arrive and you find they have established, whether they will control aphids on that plant to ensure its survival. They best thing you can do is to establish the predators into your garden earlier than they would normally arrive and thus achieving the control that you desire, whether it be by providing habitat or purchasing the biological pest control.
Earlier I mentioned recording when you discover aphids in your garden. The reason for this is to time your biological control intervention, such as the purchase of aphidoletes, for the same time as the aphids naturally arrive. As mentioned, one such intervention is adding aphidoletes Aphidemyza (aphidoletes). You can find commercially available aphidoletes many places, but most important is to find fresh, non-refrigerated aphidoletes. If this standard is kept, aphidoletes can be released at lower temperatures and withstand greater temperature swings, and their ability to search is exponentially greater – compared to the same bugs packaged at an earlier date. This means you need to buy less for your garden. (So paying more for fresh can result in saving you money.) Always follow the release instructions on the package, but fresh aphidoletes should be able to be released in only one (or maybe a couple) points, as their vigorous searching abilities will take them to all corners of the yard, intentionally keeping away from each other (which they see as competition). This means its simple for you to apply, and while you may see aphids after, they will never be at disaster levels and will likely already be accompanied by the aphidoletes. Lady bugs, and similar beetles are a tough topic. While they are commercially available, I often recommend against them. One reason is that (like most beetles) they feed on a huge variety of other bugs. And, being winged, means they may leave your yard immediately to follow the smell of some preferable food elsewhere. The other factor is that they are extremely expensive for companies to rear. This has resulted in the majority of the product coming from collecting wild beetles. In the southwest US and Mexico these beetles overwinter in large groups. Some merchants shovel them up, throw them in a bucket and sell them to you. This is causing extreme hardship on their natural populations and in their ecological balance. Other predators are already displacing them. One such predator is harmonia (larger, yellower beetle), which you could buy. But it is likely better to promote their overwintering in your yard with bug houses than to buy them. Another such solution is to purchase aphidius. However, unless you match the commercially available aphidius rearing food to your own aphid, it is sometimes useless. For example, if the aphidius is raised on a diet of green aphid, you mustn’t expect it to solve your potato aphid problem, as they may not be physically capable of attacking them. Having a garden that is purely organic for several seasons and providing companion plants and perennial bushes throughout your garden will promote the regular existence of aphidius, and other than buying a few mid-season to give your garden a healthy boost, it is likely not commercially viable.
I won’t touch on chemical sprays because that is a huge “hell-no!” Except under one very extreme situation: you’re facing total crop failure and the livelihoods of you and your family depend on the crops salvation. Then and only then should it be considered. (But don’t expect it to work next year, as you will likely be facing chemical resistance.) Many people share the idea of using a water spray to knock the aphids down or some sort of “natural” pest deterrent or soap. It might be a good idea to save a rose just before it blooms, but remember this: all bugs are good and serve a purpose – except maybe mosquitos! (Kidding) – any mechanical or chemical knock down will also affect the predators. So it is best to let the bugs battle it out.
Finally, avoid the use of chemical fertilizers. A common mistake is to fertilize a stressed plant. Aphids, feeding on the plant are attracted to the nitrogen in the phloem. Giving the plant a shot of nitrogen will make the plant tastier to the bugs and will attract more. Ideally, plants are grown in natural soil, best suited for the plant, with regularly applied natural compost to aid in a balanced uptake of nutrients and all the other health-benefits associated with bacteria and other micro organisms. This healthy soil helps the plant fight aphids.
Therefore, fighting the seasonal attack of aphids is best done with biological control. As with all biological control the trick is to apply the predators early in the season. It is rarely possible and never cost effective to try and chase an infestation with biologicals. Early detection and a preventative approach is your best method. Good gardening practices, like crop rotation, intensive planting, composting and being organic will all aid in the health and number or aphid predators, and will make your plants healthier and more able to coexist with a small number of aphids. Now that you are armed with the ability to identify the problem and apply solutions, I am sure you’ll have a much more favorable relationship with aphids in the garden.
My gardening efforts take place in a very different environment (8900 ft elevation in central colorado), but content like this is certainly relevant. Thanks.
That is certainly a unique environment. I would imagine Spring comes hard and fast up there. I would love to hear more about gardening there.
Rather oddly, spring moves slow at our elevation (http://betweenurbanandwild.com/change-of-seasons/the-slowest-season/). The short season and extreme climate make for tough going in the garden…although the bigger problems are inevitably caused by this gardener’s distractability. If you’re interested, you can find my garden-themed writings here: http://betweenurbanandwild.com/category/gardening/
Thanks! I will.