Help for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Gardener's Request: Thank you for contacting the UC Master Gardener Program Help Desk about the ant pests in your recently installed raised bed vegetable garden. First off, welcome to the community of backyard vegetable gardeners. I hope you enjoy it as much as I do.
You've raised two questions—how to get rid of the ants which have moved into your garden bed and what to do about the ants that are crawling all over the Swiss chard where small black insect pests are also present… I'll start with the question about eliminating the ant colony from the garden bed and will then address the question relating to your Swiss chard.
MGCC Help Desk Response:
Eliminating the Ant Colony: It's not surprising that the ants have taken up residency in your garden bed. I'll bet you made it a fairly hospitable locale for ant colonies when you readied it for planting winter vegetables and herbs. It's a good idea to try to get the ants under control now before the colony expands further. Here's a link to a University of California website that has a significant amount of information about ants and how to manage them: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html.
For your vegetable garden, I suggest that you focus on the use of bait stations. To find information on the use of baits in the referenced UC website, scroll down the page until you come to the section heading “MANAGEMENT” and then scroll a bit further to find the heading “Baits”. The bait stations contain a pesticide that attracts the ants because they consider it a food source. The ants carry the bait back to their nest where other ants also feed on it. The bait doesn't immediately kill the ants, but over a few days, the ants that consume the baits will die, eventually wiping out the colony.
As noted in the referenced Pestnote on ants, the baits can be purchased in several forms. The easiest ones to find are the small plastic bait traps or ant stakes sold at nurseries and hardware/home supply stores. But as noted in the Pestnote, using a refillable bait trap filled with liquid bait may be more effective, particularly when you will need to use the bait long enough to wipe out an entire colony. You may need to use an online source to purchase the refillable bait station and the liquid bait to fill it.
For the vegetable garden, you will probably want to use boric acid (borate or various forms of sodium borate) as the bait. Boric acid is effective to kill most kinds of ants. The Pestnote referenced above includes a table listing products by their brand names that contain boric acid or other forms of borate as the active ingredient.
- As noted in this UC website, the risks to the environment, water quality, honey bees and people and other mammals that are associated with the use of borate products are all fairly low, which would make it a good choice to use in the vegetable garden. http://ipm.ucanr.edu/TOOLS/PNAI/pnaishow.php?id=16.
- Be careful when you fill and place the bait trap so that you don't spill the liquid baits on growing vegetables and plants. But with such care, it should be fine to use in your garden.
The Swiss Chard Problem. You mentioned that the ants are galloping up and down the stems of the chard and that you have also noticed some type of insect pest that looks like small black dots on the chard. We believe that the small black insect pests that you are noticing on the chard are likely aphids. Aphids feed on plants by piercing the leaves with a piercing mouthpart and sucking sugary plant fluids from the leaves. As they feed, the aphids exude a sticky, sweet substance known as honeydew. Ants love to feed on the honeydew and that is likely what has attracted the ants to the Swiss chard.
Here's a link to UC's Pestnote about aphids: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html. As you'll see in the Pestnote, a number of beneficial insects such as the lady beetle and various types of parasitic wasps can be a big help in controlling aphid populations. Because the ants want to protect the honeydew food source, they are known to attack the beneficial insects to prevent them have destroying the aphids. So, to get rid of the aphids, you'll need to get rid of the ants. As you'll see, for garden plants such as yours, the aphids Pestnote recommends the use of ant baits to manage the ant problem.
Since it will take a while to eliminate that ant colony using baits, in the meantime you may want to use some water sprays to wash the aphids, ants and honeydew off the Swiss chard. As noted in the aphids Pestnote, most dislodged aphids won't be able to return to the plant, and their honeydew will be washed off as well. Use a spray bottle or a spray attachment attached to a hose and use a strong enough blast of water to dislodge the aphids. Using water sprays early in the day allows plants to dry off during the warmer daytime hours which will make them less susceptible to fungal diseases.
We hope that this information is helpful and that you're able to enjoy a good crop of winter veggies and get rid of the ant colony before it's time to plant your next crops. You're welcome to contact us again if you have further questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (TKL)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.