- Author: Help Desk Team
Aphids can be a scourge in the garden. There are over 4,000 species of aphids in the world, but fortunately only(!) about 250 species are attracted to the plants we grow in our gardens and landscapes.
Aphids are small, slow-moving insects that come in a variety of colors—green, yellow, brown, red, or black. They sometimes match the color of the plant they feed on, but not always. They have long legs and antennae, and usually have a pair of cornicles (tube-like structures) sticking out of their hind end. No other insects have cornicles. Some adult aphids have wings—this can occur when populations are high or during spring and fall—that can allow them to disperse to other plants.
Aphid reproduction is interesting. Adult females can give birth to up to 12 live offspring each day without mating. During warm weather, many aphid species can grow from newborn nymph to reproductive adult in a week. No wonder it seems like they appear overnight.
Aphids are attracted to plants on which they can feed. Plants that are actively growing are prime targets. Right now, these include plants in our winter gardens such as kale and broccoli and landscape plants such as roses, but also the many winter weeds growing abundantly in many neighborhoods.
Aphids have sucking mouth parts, somewhat like little straws. They use them to suck sap (which is a plant's sugar source). What they excrete is commonly referred to as ‘honeydew' which contains sugar and is therefore sticky. Ants are attracted to this honeydew and will actively “farm” the aphids and protect them against natural predators.
Many plants, especially trees and shrubs, can survive just fine with low to moderate numbers of leaf-feeding aphids. Damage can occur with larger populations. Yellowing leaves and stunted growth are common.
Aphids can also transmit viruses from plant to plant on many vegetable crops and ornamental plants. Symptoms can include mottled, yellow, or curled leaves, along with stunted growth.
Controlling aphids
Understanding their life cycle is key to their management. By checking plants twice a week while they are growing rapidly, you can catch infestations early. With small populations of wingless aphids, hosing them off with a strong stream of water works well. Once off the plants, aphids are unlikely to be able to return. You can also prune out the most infested parts. Make sure you also remove nearby weeds that can serve as a reservoir of new infestations.
Natural enemies are important for aphid control. Parasitic wasps lay eggs inside live aphids, causing them to turn into mummies. You can recognize these by light-colored aphid bodies with circular holes on top where the wasp has emerged. Lady beetles (especially the larvae), syrphid fly larvae, and green lacewings are voracious eaters of aphids. See this website: https://ipm.ucanr.edu/natural-enemies/
If spraying with water is not effective enough, insecticidal soaps and oils are the best choices for most situations. Oils include petroleum-based horticultural oils or plant-derived oils such as neem or canola oil. These products kill primarily by smothering the aphid, so thorough coverage of infested foliage is required. Soaps and oils kill only those aphids present on the day they are sprayed, so applications may need to be repeated. Although these products can kill some natural enemies that are present on the plant and hit by the spray, they don't leave a toxic residue.
It is easier to manage aphids earlier in an infestation than later when populations are high. Some aphids cause leaves to curl around them, protecting them from sprays and beneficial insects.
Prevention
- When you purchase new plants, inspect them carefully.
- Don't over-fertilize. Excess fertilizers, especially too much nitrogen, can stimulate plants to put out lush new growth that will entice aphids to set up home.
- Excessive pruning can also stimulate plants to put out attractive new growth.
- Use a row cover, especially on seedlings and new plants. This will keep out aphids but also protect from other pests.
- Control ants that can protect aphids.
For more information, check these websites:
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7404.html#TABLE1
https://ipm.ucanr.edu/QT/aphidscard.html
Help Desk of the UC Master Gardeners of Contra Costa County (SEH)
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: ccmg@ucanr.edu, 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.
Advice for the Home Gardener from the Contra Costa Master Gardener Help Desk
Client's Brussels Sprouts “Problem”
photo: Kepplerworld.com
Response and Advice from the CCMG Help Desk:
Thanks for the GREAT picture! You have an "aphid" infestation. Brussels sprouts are in the Brassica family, and this is a very common ailment for that family of vegetables. Most plants can tolerate some aphid infestation but yours has reached a moderate level so you will want to take action.
Management options:
- Often a forceful spray of water directly on the aphids will knock them off, once they have fallen to the ground most will not be able to climb back up on the plant. Use the water jet option first as it is the least invasive.
- The second action you could employ would be to use a water-soap solution, this would be an insecticidal soap available at any nursery. They are sold in ready to use formulas and in concentrates which must be mixed with water before use. Make sure to follow the directions on the package if you purchase a concentrate.
- For more stubborn infestations you can use a Neem Oil application. Again use the water jet first and then treat any remaining aphids with the Neem Oil.
These products kill primarily by smothering the aphid, so you will need to make sure you cover the infested foliage well, targeting both the top and underside of the leaves. Soaps and oils kill only the aphids present on the day they are sprayed, so you will need to monitor the plant regularly and repeat the application as needed. Keep in mind that any active spray will also kill beneficial insects so spray only when you need to and only the minimum amount you need to get the job done.
The following link is to the UC Davis IPM web site's Pest Note on aphids, it will help you understand the life cycle, good cultural care practices and management options. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7404.html
The good news is you can get this pest under control with some diligence on your part.
Thanks again for contacting us and enjoy those Brussels sprouts.
Contra Costa Master Gardeners Help Desk
Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/
