How to Protect your Garden from the Aphid, a Common Pest.
By Brad Sylvester
The aphid is a common garden pest that can weaken and kill your plants. They prefer soft new growth, especially if you use commercial fertilizers that make your plants grow very fast. This often results in lots and lots of lush, tender new leaves. Aphids will attack many common garden plants including squash and tomatoes. They secrete a chemical into the plant that can kill the area around each "bite" and result in stunted growth of new branches. They are also known to spread harmful viruses between plants. Aphids attack the plants by sucking the juices from the leaves, stems or blossoms. The juices they get from plants are so low in protein that they need to draw quite a bit from the plant in order to survive. The plant juices are however high in sugar and in order to survive the aphids pass this sugar out as waste. One sign of aphid infestation is a clear sticky residue of droplets on the leaves below them (or on the table surface beneath indoor potted plants). Ants love this sugar-rich residue and will often defend aphids from their natural predators in order to ensure their supply.
Aphids themselves are funny looking little green bugs. They are tiny at just about 1 millimeter in length. Their bodies, to me, resemble little water balloons filled with the liquids they have siphoned from the plants. They also can produce a winged variation when populations get too large or when continually exposed to threat. This helps them disperse the population to other plants. This is why I don't recommend manually washing them off the plant. You'll always miss a few, and the latest research shows that they give off an alarm chemical which increases the number of winged aphids from the next generation. More winged aphids means they can more easily spread throughout your garden and your yard. When I get time, I’ll add some photos here to help you identify them, for now just use a Google Image Search for aphids to see what they look like. They reproduce VERY quickly and just a few aphids can virtually cover a leaf in a day or two. Each adult aphid can produce 10 or more live young each day! Amazingly, no males are needed for this sort of reproduction. Males will only be born toward the end of the year, when the females need them in order to produce the eggs which will lie dormant over winter to hatch next years population.
The ususal recommendation is to manually wash them off of the infested plant with an insecticidal soap to prevent re-infestation. This is difficult and time-consuming and usually is only a delaying tactic. Some recommend spraying them off with a garden hose, but this again just knocks them down, many will survive and climb back up. Ladybugs eat aphids so they can be used as another weapon against them. No matter how you deal with aphids,maintaining a healthy population of ladybugs or lacewings is a good idea. Again, though, ladybugs will reduce the population of aphids, and may keep them under control, but will likely not eliminate the threat. Which brings us to the question of how can you best protect your vegetables from aphids?
Although aphids will attack a wide variety of plants, they do have preferences for certain types of plants. Knowing this allows us a simple and elegant way to protect our vegetables from these pests without resorting to artificial chemical interventions. To keep aphids off our vegetables all we have to do is provide them with something else that they’d rather eat. Fortunately, aphids seem to just love nasturtiums. The nasturtium is a leafy flowering plant that has plentiful brilliant orange flowers. The blossoms are edible for humans as well, and can be used in salads to make a really eye-catching presentation. Planting just a couple of nasturtiums in your vegetable garden is an organic and easy way to keep the aphids off your other vegetables while adding a bright splash of color to your garden. We tried this last year (2007) in our garden and it worked fantastically! We grew a few nasturtiums amongst our vegetables and we saw zero aphids on any of our vegetable plants while the nasturtiums had large numbers of them.
Final recommendation:
To protect your vegetables from aphids encourage healthy populations of ladybugs and other aphid-eating insects, and more importantly, grow nasturtiums among your vegetables. Space them every 10-15 feet apart to have coverage throughout the garden. Nasturtiums are easy to grow and you can find seeds at any local store that carries flower seeds. Pick a few blossoms, wash them carefully and use them in salads from time to time, especially if you’re having company!
Scientifically speaking:
This was our first year in this location so to be scientific about the effort, we can’t conclude definitively that the aphids would have been attracted to our garden if the nasturtiums were not there. And although we did not see even a single aphid on any of our vegetable plants, we did not thoroughly check every leaf of every pant to make sure that absolutely zero aphids were munching on any vegetable plant in our garden. We do know from our own experience that aphids can and do cause severe damage to vegetable plants. And we do know that despite large populations of aphids on the nasturtiums right smack dab in the middle of our vegetable gardens, no vegetable plant had any visible damage from aphids, nor even any obvious aphid populations on them at all. We would call this highly indicative of a successful intervention, especially when there is prior research from multiple sources documenting the aphid’s preference for nasturtiums. A proper scientific experiment would involve control plots without nasturtiums or leaving nasturtiums out of the same garden plot this year while planting the same varieties of vegetables and repeating these “with and without” scenarios enough times to get a statistically significant set of data which would show some correlation between the number of aphids found on vegetable plants and the presence or absence of interplanted nasturtiums. We could further document the yield and health of the vegetable plants against the presence of aphid populations on each plant to measure the ill effects of aphids each plant. Too much work for now, but if you want to try the experiment in your gardens, I’d love to hear (and post) your results. It is worth also noting that we also had nasturtiums nearby (about 50-75 feet from the garden) in window boxes and these plants showed no signs of aphids at all. That doesn’t prove, but indicates that the aphids were initially attracted to the garden and were not present only because we had nasturtiums there, but this is even shakier evidence from a scientific viewpoint since there are many other variables as well.
By the way:
Aphids are one reason we strongly recommend that you do NOT bring live plants or soil from the outdoor vegetable garden to your indoor garden. Without natural pests and other natural controls, aphids can get out of hand VERY quickly and ruin all your indoor plants!
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The words and photos found on this website are copyrighted (2007, 2008) with all rights reserved and may not be reproduced in any fashion without our express written permission. However, we will be liberal in granting that permission if you ask nicely, include acknowledgement of the source, and a link back to our website. The photos are our original property, if you’d like to use them for your own project, you must contact us for permission. They are also available in high resolution. brad@sylvangardens.com
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