Ants are eating Potato plants.

Asked June 4, 2020, 4:39 PM EDT

Hello; Ants are eating Potato plants.These are Black about 6 mm long ants. Several of them gather around the main stem of a plant and eat it making the stem narrow -looks like what beavers do to trees. They continue until the plan dies. So far they killed 4 plants. I tried soap and water, no effect. I put cinnamon on and around the stem, this kept them away for some hours but they came back and started eating the stem at a higher place. I know many believe ants don't eat potatoes, they put Aphids on plants but I am sure, I saw them and watched carefully there is no other insects. Any suggestions?

Montgomery County Maryland

11 Responses

Hi- could you please send photos- close-ups of the ants and the damaged stems? As you mention, ants will protect and herd aphids to secure the honeydew excreted by the aphids. Ants are decomposers; they collect and chew dead and decomposing plant material. They are not plant pests.

Can you see any aphids on your plants? It's possible that some type of insect pest is feeding on your potato stems at night, such as cutworms.

Thanks for fast response. I can't get a picture of ants, this morning I applied Cinamon that keeps them away. Attached are pictures -I know the quality is not good, but it is not easy to get pictures. I moved the soil away so the stem can be in picture. Also the red color is the cinamon. I looked many times I can not see any other insects. I had potatoes before and this is the first time I see this. Last year the same ants attacked my red Cabbage eating roots and stem, can I say these ants are "learning"?
By education I am a physicist so I believe "there is no impossible". I have observed very strange behavior of ants in my garden so I am OK to say what we knew about ants -and animals in general- may be Wrong. Please do tell me what else you need and I see if I can a picture of ants while eating the stem.

Based on your photos, we suggest cutting a few freshly wilted potato stems to see if a boring insect, such as potato tuberworm or wireworm, may be infesting your plants.

This is a fairly comprehensive NC State U. web page on potato insect pests. We have the same pests, with lifecycles a few weeks behind NC.

I looked at the site, I can not see any other insects. Also if I keep adding Cinnamon, to keep ants away, the plant comes back to life, does cinnamon effect any of those pests? If not then the problem must be the ant.

The ants are about 3 or 4 mm long how small are those pests, can I see them as I can see ants? Please explain more how/what should I look for, should I cut the main stem = kill the plant? No other parts of the plants are damaged. Also no other potato plants in the same area show any problems until I see ants on them. I attached new pictures. please advise.

Sorry I forgot to mention, I push the soil down to be able to take picture. Ants attache themselves to the Main stem right at the soil line. They do not bite anywhere else on the plants.

We suggested slicing open a potato stem to determine if there was another cause for the feeding injury and wilt symptom. This would require sacrificing an affected plant- pulling it out and cutting the stem vertically. Any potential boring insect larva would be visible to the unaided eye.

Although ants do not typically consume live plants it is certainly possible, as you've witnessed, that an ant population has taken a liking to your potato plants. There could be a lack of other, more commonly accessed foods.

Cinnamon oil is a low-risk insecticide used to repel insect pests. Pure cinnamon could possibly kill ants or other insects. Diatomaceous earth is another organic insecticide that can repel and control pest populations when sprinkled on the soil around plants and on plant parts requiring protection.

Thanks for detail explanation. One question, do I need to reapply Diatomaceous earth after each rain? In another words, would rain wash out the Diatomaceous earth and Cinnamon oil?

Probably not not necessary to re-apply after a light rain, but definitely after heavy rainfall.

I took out 2 of the dead plants. The stem upper part, up to where it was cut at soil level, was dry and hollow but lower part was solid, green and juicy. I could not see any insects inside the stem. The root was small and I found 5 small light red color worms in the soil between roots still alive. These are about 2 cm long and 3 mm thick with tiny antennas on the head and several legs in the front part of the body. These moved like centipede. They could not stand the sun, curled up and died fast. I don't think these are wireworm. I tried to get pictures but they are not clear. Digging the soil more, I found few small potatoes that look healthy with no visible damage. Also today I notice yellow edge area on otherwise healthy plants. I did not see any ants around stems. The "Insect.png" is a picture of what I found on my hand yesterday (before digging potatoes) when I came inside, I have no idea where did it come from. Please see attachments and let me know.

Update-2, 6/16/2020
Please see pictures, this is another plant. Included is one leaf that is danged, I found 1 ant on it, no other insects, no other damge anywhere on this plant.

Hi- we can't identify the insect on your hand. The 2 cm long insects you found are most likely some type of soil invertebrate, harmless to plants.

Thank you for the interesting and unique photo of ants clustered on the damaged potato stem. We had not seen this phenomenon before now.