Those aren’t early Halloween decorations in the trees

[ratings]

They’re a harbinger of fall and not a welcome one, but those webs you see consuming the tips of branches at roadside or in your yard are, fortunately, not cause for major concern even if they do seem to be more prevalent in some areas this year.

Steven Mann, a certified arborist and owner of SJM Arboricultural Consulting, gets calls about these nests from concerned property owners in late summer and early fall asking what’s eating their trees and what they can do about it.

The nests are built by a native insect, fall webworm (Hyphantria cunea). Natural population fluctuations can make them more noticeable, but the nests cause only seasonal, aesthetic damage that most trees will be able to recover from.

“From time to time, conditions are good for them to propagate. We did see them earlier this year – they don’t usually show up until September but there have been tents as early as the first or second week of August,” says Mann. “This summer’s high temperatures have sped up incubation of the eggs and they’ve hatched earlier than they do normally.”

What’s a concerned tree lover to do? The common advice of arborists is: nothing.

Pruning would remove more foliage than the insect would remove. If people can bear with the look of it, it’s best to leave them.Arborist Steven Mann, SJM Arboricultural Consulting

Fall webworm is a type of tiger moth. Its caterpillar is sometimes confused with the eastern tent caterpillar which spins its nests in late spring and early summer in the forks of branches, rather than at their tips like their fall cousins. This timing bodes well for trees, even in years when there are many nests. Fall webworm has the misfortune of being a late season insect, explains Mann. Their populations can be controlled by cool nights and sometimes frost, in addition to natural predators.

The caterpillars use their nest as a shelter and feeding is often confined to that habitat – they don’t leave often and when they do they tend to retreat fairly quickly. That behaviour doesn’t cause massive defoliation, unlike gypsy moths which are an invasive species that feeds on the entire canopy of a tree.

“Even if a tree has heavy nesting, it doesn’t lose a ton of foliage and it loses it toward the end of the season when the leaves turn fall colours and drop off anyhow,” says Mann. “The impact is pretty minor.”

Those features – late-season nesting and contained defoliation – make intervention largely unnecessary. However, some property owners can be tempted to prune their trees as a control measure, a move Mann cautions against.

“Pruning would remove more foliage than the insect would remove. If people can bear with the look of it, it’s best to leave them. They’ll moult into an adult, fly away and lay eggs elsewhere. You may not get them back the next year.”

It’s good when people are concerned – it shows that they care about trees and want to help them.

Of larger concern this fall is overall tree vigor. Dry summers are stressful for trees and watchful property owners may see signs of it in the coming month. “You might see deciduous trees turning fall colours earlier than normal this year – that’s a sign of stress – and the colours won’t linger as long.” So you could see an early, pronounced, and short-lived fall show this season.

Coniferous trees aren’t immune to the stress of a dry summer either. The moniker ‘evergreen’ is a bit misleading – conifers don’t keep their needles forever. They have a natural cycle of shedding or dropping their needles, but with a dry summer that needle drop can be heavier – expect to see your hemlocks and white pines lose more than usual this year. Natural needle drop occurs with inner needles, though – if you’re seeing needles at the tips dying, it’s time to call an arborist. Sooner rather than later.

Visible signs of damage to your trees are often the result of something that actually occurred much earlier. It can be frustrating for arborists but most of us don’t have the training to notice smaller signs that there’s a problem. So when you first notice an issue, make the call. “It’s good when people are concerned – it shows that they care about trees and want to help them.”

What are you concerned about with your trees?