European Asparagus Aphid

Asparagus is one of those crops that requires a lot of patience.

​We eat the immature shoots of new plants that emerge from the roots of the previous year’s growth. To ensure the longevity and production of your asparagus plants, you need to restrain yourself from harvesting new shoots for the first 2 or 3 years to allow for adequate root development. If you can wait, you will be rewarded with 20-30 years of production. That is, of course, unless your plants become infested with the European asparagus aphid!

European asparagus aphids

European asparagus aphid description

Native to Eastern Europe and the Mediterranean region, European asparagus aphids (Brachycorynella asparagi) were first seen in the U.S. in 1969. They are now found throughout North America. Similar to the over 4,000 other varieties of aphid, the asparagus aphid is a tiny (1 mm), soft-bodied, powdery greenish-blue or grayish-green, pear-shaped insect with a pair of cornicles at the tail end of the abdomen. You can think of cornicles as tailpipes that spew a waxy substance in retaliation to attack. Some aphid varieties feature chromed-out monster truck cornicles, but the asparagus aphid is far more subtle and inconspicuous. It has short antennae and a relatively long cauda. The cauda is a tail-like appendage used to fling honeydew away from the insect’s body as it is excreted.

Ants and aphids

Ants are big fans of the honeydew excreted by aphids. So much so that ants will fight off aphid predators, groom aphids, and, I suspect, they might even bring aphids a latte every now and then, to keep them producing. It was the number of ants on my asparagus plants that drew my attention.

I planted my asparagus bed last fall using 1-year old crowns. Most of the crowns made it through our nonexistent winter and our scorching summer, but the ants were a clear indication that something was wrong. Closer inspection showed small, shiny black globules, which turned out to be egg clusters. I also noticed flat gray, oval bodies of immature aphids, upright green bodies of wingless adult females, and black winged adult males. The European asparagus aphid life cycle was in full swing in my asparagus patch and I should have noticed it a lot sooner. (That’s what happens when you go to Burning Man for three weeks at the height of the growing and harvesting season!)
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Aphid controls

One of the most common methods of controlling aphids is to use short, powerful bursts of water to displace the bugs from their host. This can work pretty well in most cases and it beats the heck out of using pesticides, which tend to kill off beneficial insects (predators and pollinators) along with the Bad Guys. Unfortunately, asparagus aphids damage your plants in a rather unique way that makes hoses an inadequate treatment. In addition to sucking sap from plant veins, these little buggers inject a toxin that reprograms the way the plant grows!

This reprogramming causes the spaces between leaves and twigs ("internodes") to become shorter, creating a tufted appearance called bonsai growth. This increases the number of the aphids’ favorite feeding sites. It can also delay bud break the next spring (which is struggle enough in our winter-less region). New shoots then emerge all at once, thinner and smaller than normal, draining the root system of desperately needed nutrients.

So, what’s an asparagus-loving gardener to do?

1. Identify the problem. Carefully and regularly monitor your plants for signs of damage or infestation. This let’s you know what you’re up against. Remember, finding out sooner is better than learning too late.
2. Know thy enemy. Female aphids hatch from eggs hidden in the soil anytime temperatures are warm enough, generally April to October, and they do not need males to reproduce!
3. Find a weak link in their life cycle. Asparagus aphids lay microscopic egg clusters that look like shiny black blobs to the naked eye. Eventually, those eggs fall from the plant and overwinter in the soil. Armed with this information, you can remove and destroy (burn) any infested stems before the eggs have a chance to overwinter hidden in the soil.
4. Promote natural predators. While garden supply stores are happy to sell biological controls, your best bet is to simply avoid using pesticides and to include plantings that attract and provide for beneficial bugs. Most beneficial adult parasitic wasps eat nectar and pollen from plants with shallow flowers, such as fennel, dill, yarrow, parsley, cilantro, mint, cosmos, marigolds, sunflower and chrysanthemums. These adults will then lay their eggs in soft-bodied garden pests, which will then hatch and, well, you get the picture.

​​So, go check on your asparagus plants and let me know what you see!