Controlling Ants & Aphids On Fruit Trees

black aphids on underside of cherry tree leaf
black aphids on underside of cherry tree leaf

Introduction

There can be little more upsetting for a gardener than seeing a beloved fruit tree covered with ants and aphids (black, green, or white). An aphid attack is pretty common, but the presence of ants can make the aphid attack much more severe as the ants effectively farm the aphids and protect them from predators. It is the aphids that do the damage to a fruit tree, sucking out the sap and damaging the leaves. Once a tree is infested, removing the aphids can be a thankless task.

Possible ways of removing aphids from fruit trees are as follows:

  • Stopping the ants climbing up and down the tree to farm the aphids (see below) – if you can stop the ants this should alleviate much of the problem
  • Use a garden hose to try and blast off the aphids
  • Use a spray bottle filled with soapy water, or garlic infused water, combined with rubbing off the aphids by hand
  • Squash the aphids with gardening gloves
  • Start early – action at the first sign of attack can save much work later

It is frequently cited that companion planting around a fruit tree with onions, chives, and mint can help avoid an aphid problem. This may be true, but it is not something I have found successful in my personal experience.

Watch the video below, or continue scrolling to read the video transcript.

Step By Step Video

YouTube Video

Video Transcript

Aphids on fruit trees can be a big problem, especially for young trees that can become overwhelmed. I have a cherry tree, a plum tree, and an apple tree, and all have been affected by aphids over the years.

This video describes how I control aphids on my fruit trees. There are a number of techniques for doing this, but what I show in this video is what works for me.

The first sign of an aphid problem is usually the leaves starting to curl. This happens when aphids cluster on the underside of the leaves, sucking out the sap. This damages the leaves, and will eventually cause them to blacken. If left unchecked, a young tree may be left without any healthy leaves. Unfortunately, natural predators to aphids like ladybirds, will not, by themselves, be able to control an aphid attack, as aphids multiply so quickly.

My approach to controlling aphids on fruit trees is to control the ants that farm them. In my experience, a severe aphid attack is nearly always caused by ants. Ants like to farm aphids, as aphids excrete a sweet liquid called honeydew. Indeed, ants are not the only insect to like honeydew. Often, bees will visit a fruit tree experiencing an aphid attack too, which is another early sign of an aphid problem. Ants protect aphids from predators, and carry the aphids all over the tree helping them multiply.

My solution is simple. I stop ants being able to move from their nest on the ground up and down the tree trunk. To do this, I use tree grease. The great thing about tree grease is that it can be pushed into ridges in the bark, providing no route for ants to climb and descend a tree. When tree grease is first applied, ants are confused, and search hurriedly to find a way through the grease. This is a great test of whether the tree grease forms an impenetrable barrier.

I find the easiest way of applying tree grease is to use a putty knife, or similar flat bladed tool. If a tree is supported by stakes or poles, these will also need to have to tree grease applied to them too. Use the tool to create a ring around the trunk of the tree approximately two inches wide, pushing the tree grease into the bark. Aside from making it easy to apply the tree grease, a putty knife is also easy to clean, by wiping away any grease on the knife using some kitchen paper. This is far easier than cleaning a paint brush.

For the application to be successful, it is essential that there is no alternative way up for the ants to get to the leaves. An example of how determined, and resourceful, ants are, is how they managed to climb onto the cherry tree in my garden. From my cherry tree, I had run lengths of bird scare tape to canes to help keep birds off the fruit. Unknown to me, my rosemary bush next to the cherry tree had grown taller, and started to touch the bird scare tape. Ants had worked this out, climbing the rosemary bush, and then somehow balancing and walking across the tape to get to the cherry tree. I was amazed by this, as the tape is designed to blow around like a flag in the wind, yet somehow the ants made it across. To stop this, I pruned back the rosemary bush, and removed the bird scare tape. Problem solved.

I have found by controlling the ants, at least ninety percent of the problem of aphids is reduced. It seems to bring the tree back into equilibrium, so that natural predators like ladybirds can keep aphids under control.

However, for young trees, I also deal with the remaining aphids on the leaves. This is easy to do, by mixing a little washing up liquid with water in a spray bottle. I spray all the leaves affected by aphids, gently rubbing away the aphids as I go. The rubbing is important to ensure that all the aphids are covered by soapy liquid, and to wash them off the tree. The next day I come back to check whether any aphids remain, and if necessary, reapply.

An alternative to spraying is to use a water jet to dislodge aphids. This is effective, and faster than spraying, but I find there is a risk of accidentally knocking off any developing fruit, and missing some aphids.


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