Control of Ants in Garden - Knowledgebase Question

Long Beach, NY
Question by crbauer
June 16, 1999
I read your Q&A about the use of spray with oil and/or paste. How often should you spray with the oil or apply the paste? Will too much of either harm the vegetables?

Answer from NGA
June 16, 1999


I think the answer you are referring to is this one: The ants you see may not be doing any harm themselves,
but if you look more closely, you may see that they are
hanging out with aphids, which are tiny insects that feed in
masses on plant parts. They are sometimes called plant lice
(this give you an ideaas to their size!); they are small, oval
insects that congregate on new growth. Some ants actually
feed on the waste product of aphids, called honeydew,
because it is very sweet. If you can control the primary
problem--usually aphids--you might just control the ants as
well. If there are no aphids present, then look closely to see if
the ants are causing any damage. Most often they prey on
other insects or feed on plant sap that is already leaking from
wounds caused by other insects or physical damage.I have
used two things successfully when dealing with ants. The first
is a homemade bug spray: 1 gallon water, 1/2 tsp. eucalyptus
oil, 1 tbsp. vegetable oil, 1 tbsp. dishwashing liquid. Combine
all ingredients and shake well. Pour liquid into a spray bottle.
When applying shake often to keep components evenly
distributed. This "potion" works well on ants and aphids in
particular (cats don't like it much either). The second remedy
should be kept out of the reach of children and pets: Make a
paste out of boric acid powder and sweetened condensed
milk. Add powder and condensed milk until you have a
consistency somewhat like fudge. Roll into small balls and
place balls where ants are a problem. The ants will carry the
bait back to their nest where they share it with other ants
who ingest it and die. When using this remedy outside place
the balls in a sheltered area where the rain won't melt the bait
and in such a way that children and pets can't get to them.
There is also an inedible herb called Tansy which works well
as an ant (and other insect) repellent, try planting a few in the
vegetable garden. It is an attractive flower, the flower heads
are often used in dried flower arrangements. Tansy is
available from Burpee at 1-800-888-1447. Remember though,
it is not an edible herb.

It is my understanding that the "paste" is rolled into balls and placed as a bait, it is not applied to the plants and so should not contact the plants at all. Using bait can take a while to show results because the ants must carry it back to the nest where it must be eaten and will ultimately kill them. You would need to replenish the bait if the ants shoud deplete the supply. Be very careful to keep the bait away from children and pets.

The spray, in contrast, should act as a contact insecticide to kill aphids and thus repel ants because it removes their food supply; it would be applied only when aphids are present, and would possibly require followup applications to disturb subsequent generations of aphids. Overuse or use on plants sensitive to the ingredients could possibly hurt the plants. It is always a good idea to test any spray on a sample leaf or two and wait a few days to see if there are any negative effects on the plant. Routine washing of the vegetables should remove the oil and soapy residue.

You could also use a strong spray of water from the hose to disturb the aphids (repeat as needed) or a commercially produced insecticidal soap as per the label instructions. In my experience the water method works quite well.

Disturbing or removing the aphids would reduce the ant population on the plants IF that is why the ants are there in the first place. If the ants are not there in search of aphids, then you would need to address the ants specifically. In addition to baits, some gardeners report success by pouring boiling water into the holes or ant hills.

Since ants generally do not harm plants, the occasional ant should not be cause for concern. However, if you are experiencing a severe ant infestation, you might want to contact your County Extension (454-0900) for more specific control suggestions.

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