Sooty mold is usually what tips gardeners off that there’s an aphid issue. The mold is black, ugly and can slow down growth by blocking light to the leaves of plants. In general the mold itself is not a huge problem, but it’s definitely an indication that you have a problem with two intertwined insect buddies.
Once sooty mold shows up, you are behind in the game. The mold is caused by ants, who are farming aphids. I actually think the interdependence of these two very different little critters is pretty cool. But, I also have had some serious issues with them on my fruit trees. Specifically two persimmons and a peach tree. Although, it has been the persimmons that suffer the most.
My two persimmons are happy in my yard until the weather begins to really warm up around Mother’s Day. Then the ants start their dance with their aphid buddies and the health of the two persimmons goes down hill. A really cool experiment with photos of how aphids feed, (and how they use them in the lab to track transpiration) is here: bioninja
Ants farm aphids by placing them where the aphids can suck the most liquid from the tree leaves. They will place aphids all over the tree’s new growth and it will become a full on invasion quickly. Once the aphid’s piercing mouth parts go to work, they get a powerful push of sugary water from the phloem and the ants begin milking them. In return for the liquid that the ants receive (called honeydew) the ants defend the aphids. Both insects benefit from this arrangement, my trees do not.
The ants found a way under the wrap.
Birds, wasps, stingless bees and honey bees can also milk aphids for honeydew, but in my garden it’s mostly ants (including fire ants, which I never want in my yard!)
As the ants encourage and protect the aphids: the aphids excrete honeydew for the ants to feed on. As the aphids move, the honeydew collects on the leaves. Honeydew is sweet. Just like a hummingbird feeder will grow mold in the sugar water, honeydew’s sugar content feeds sooty mold. Your leaves will start to look black as the mold spreads across the surface.
In most plants, this isn’t that big of a deal. But in fruit trees, limiting sunlight will affect fruit development and harvest. If the tree affected is over pavement or cars, dripping honeydew and the resulting sooty mold is difficult to remove.
So, I’ve had this issue for a couple of years now. I know it’s coming when I start to see ants all over the trunks of my fruit trees. There are other ways to stop this issue, but I prefer to just stop the ant activity, and do it in a way that does not include spraying toxins on my tree. If I can stop the ants, I can just spray the leaves with a stream of water and knock off the aphids.
Enter the easy to use product called Tanglefoot. This is a jar of some gooey, sticky stuff! You also need a strip of weatherproof fabric, (I use this: link) to put the Tanglefoot on. The company that makes Tanglefoot recommends never applying this stuff directly to your tree’s bark. By the way, I don’t recommend the tanglefoot brand wrap. It isn’t rated well and doesn’t last.
All you need to do is wrap the fabric around the trunk and secure the end by tucking it tightly under the rest of the wrap (if you have a tree with deep cracks in the bark, they recommend wrapping the tree with a layer of cotton batting first.) Make sure that the end of the wrap is very secure. The Tanglefoot is so thick and sticky, that it can unravel your wrap as you’re applying it, if you aren’t careful.
It’s thick like hot caramel and kind of colored similarly. Definitely not edible, though!
Once you have the wrap in place, you can open the container of Tanglefoot. This stuff is seriously messy and not simple to remove. Use a disposable utensil for this. I found a plastic fork or knife worked well for application. This does pour, so watch the container while you are applying it or you’ll lose some over the side.
Wipe the Tanglefoot across the wrap in a thin layer. If you leave a thick layer, then it will run down the tree, especially when it gets hot out and the product becomes more fluid in the heat.
In an hour or so go back out and check the ant activity. If it hasn’t slowed down, you’ll know that they’ve found a way around it, probably in a crack in the bark, on the inside of the wrap. At this point it is messy to repair. I recommend running another layer of wrap and keeping it tight over the area they are using or stick a small piece of something fluffy like batting into the crack they’re using. This product only works if they can’t get around it, and they’ll spend hours trying to find a way.
Check again the next day. The ant activity should stop. If not, keep trying until you plug wherever they’re crossing.
The next thing you’ll want to do is look for the aphids. A strong stream of water from the hose should knock them off. But, there’s already aphids in the tree, so unless you spray with insecticide (which is really overkill) you will need to repeat the inspection, and spray the aphids off with water, throughout the growing season.
Or, you could be smart and put the Tanglefoot up before the season starts. I sprayed with dormant oil and copper during the winter. Dormant oil kills over wintering insects and their eggs. It would have been smarter to put the wrap up before I noticed the ants. Not everything goes as planned, unfortunately! So, at this point: the ants and aphids are already established.
The Tanglefoot will stop all crawling insects from getting into your trees, unless they have access into the canopy from something up against your tree (like a fence, building or another tree.)
I’m not noticing any ants on my pear, but there are roly pollies hiding in the cracks in the peeling bark (it’s been a very wet spring). I may get my hose end sprayer and fill it with neem oil and go around and hit my trees a couple of times before harvest. If there’s roly pollies (aka pill bugs or sow bugs) then there’s probably a lot of crawlers who’ve already made it up the pear, and that are hiding in the bark, that I just haven’t noticed yet. Tanglefoot won’t hurt, and since it’s an organic choice, I’d rather put some out preventatively rather than getting a surprise invasion of some sort that needs insecticide!
The company suggests removing excess Tanglefoot from objects with mineral spirits. They recommend removing it from hands with an orange based cleaner like “goo be gone” or baby oil, but using those takes some scrubbing. If you are a Melaleuca user, then I really recommend using their sol-u-mel cleaner. This worked really well on my hands and removing the excess that had dripped down the sides of the Tanglefoot jar.
Another good use for the Tanglefoot, is to apply it to brackets that you hang hummingbird feeders on. Ants always seem to find their way to the nectar. Even if the feeder has ant moats, my heat and wind dry those out. What people call a sugar ant down here, (they’re super tiny black ants named Monomorium minimum) always get inside the feeder and float around in there, contributing to the nectar going bad. I put some Tanglefoot on the bracket that holds the feeder and the ants won’t/can’t cross it. It’s a very permanent solution. I only have to apply it once a year. If the Tanglefoot gets gross and full of bugs, I get some Sol-u-mel, put it on a paper towel, wipe the area down and the ick comes right off. Then you reapply some more Tanglefoot and you’re good to go.
Tanglefoot is an old gardening product. It has been around for as long as it has, because it’s effective. Let me know if you use it, and what your tips are.