My car is covered with a sticky substance because I parked it under a tree dripping with gummy, tacky goop.
Many believe the tree is oozing sap, but it’s not. It’s actually much grosser than that. It’s actually the secretions of zillions of aphids that are feeding on the poor tree. As the aphids suck out the tree’s juices, they excrete a sticky and smelly substance called honeydew. This sweet gummy stuff attracts ants, which ‘farm’ or ‘milk’ the aphids for their honeydew by stroking the aphid’s abdomen. Probably too much information for you there – sorry.
The honeydew also attracts a fungus called Black Sooty Mould. It looks like the name implies - black soot - and it covers the leaves. It doesn’t cause too much harm to the plant other than blocking out the sunlight. It’s the aphids that are the problem.
Symptoms first appear on the foliage as they become coated with this thick, glossy and clear honeydew from the feeding aphids. It soon coats all the leaves, dripping onto anything below. It covers sidewalks, cars, plants and anything or anyone that lingers too long.
Which Trees Are Susceptible
Some trees are really prone to aphid infestations, but it does depend on the type of tree, the climate, the tree’s health as well as its maintenance. For example, lindens, also known as Lime trees, are grown extensively in England, but don’t seem to suffer like the ones grown in British Columbia. The lindens grown here in BC, are predominantly the Little Leaf Lindens (Tilia cordata) and they are savaged by aphids. I was impressed with a perfectly healthy huge Silver Pendant Lime tree (Tilia tomentosa 'Petiolaris') at the Jephson Garden, Leamington Spa in England. Was it the tree variety, the climate, the soil or superior maintenance? I think it was a combo of all those factors.
Meanwhile, back at home in my neighbour’s adjoining front yard, her variegated tulip tree, Liriodendeon tulipifera 'Aureomarginata', is dripping a fine mist of stickiness on everything below it. It’s adjacent to my driveway and I warn people not to park near it. All the plants at its feet including a rhododendron, star magnolia, rose and spirea are covered with the sticky stuff. It sucks – or should I say, the aphids do.
At the beginning of the growing season, this tree is in good health with no aphids in sight. You’d think that the aphids would be feasting on the new succulent growth, but alas they are not. Is this due to the tree having adequate water? It could be. As summer heat and lack of rain takes over, all plants including trees suffer. This lowers a plant’s resistance, which results in insects honing in on the weakened tree.
What to do
First off, keep trees watered during the summer. Soak the soil to about 12 inches to beyond the drip line (where the canopy ends), once a month. Lay a hose on good trickle for about half an hour a couple of times a week. Avoid watering at the base of the trunk as it may cause the trunk to rot.
Keep moisture in the soil by applying a 3 inch layer mulch under the tree on top of the soil, pass the canopy (dripline). Avoid placing it against the tree trunk to prevent rotting. If it the tree is planted in the lawn, it is not going to do as well as compared to having its own bed with mulch.
Spraying huge trees with any kind of anything is impossible and very impractical. If the tree is small enough to coat it thoroughly, soap and water is effective, but you must reapply in 7 days to kill their offspring. Fun time.
Another control is dormant oil applying in January or February just before the tree buds out. A dormant oil, lime sulfur combination is an effective control for overwintering insects and diseases. Follow the directions to the letter and go for complete coverage. This is a relatively low toxic method that is often used for organic pest control.
If you have an aphid infested tree, inspect it closely for ladybugs before spraying with anything, including soap and water as it will kill them too.
Ladybugs take many forms so be aware of the different stages in their life-cycle: eggs, larva, pupa and adults. The larva and pupa look nothing like the adults. The larva are shaped like an alligator while the pupa resemble bird droppings.
There are lots of ladybugs, their larva and pupa on my neighbour’s tulip tree. They were doing a happy dance as they feasted away. Spraying is not an option as I know these beneficial insects are doing the job for me.
My lesson is learned though as I can’t control the aphids so I’ve just got to remember to look up before parking!
Here are some of my previous blog postings. They cover a wide range of topics from bugs to my botanical excursions and conventions. Click on whichever interests you on the titles below for easy navigation.