Oak gall ruining our tree

[Your Letters 2]

Janet/Steve,

We have an infestation of jumping oak gall on our white oak in the back.  I have read the MSUextension report and other botanical articles and they say don't do anything.  My husband and I are watching while it destroys our small oak tree, Any suggestions, my insecticidal husband wants to deluge with insecticide, but everything I read says its too late, just work on the health of the tree. 

 

Please help!

[Janet Macunovich 32]

We understand the distress of watching a young tree in trouble. Even now that we've watched lots of little trees do their thing and realized that nothing is more capable, more tough or more resilient than a well planted young tree, we still feel our protective instincts rise when pests appear.

 

That's accurate and practical advice you've read in the Extenson bulletins. You can do some things that may curtail the infestation, although  insecticides in late spring or summer are not on that list. However, if you do those things keep one thing straight. The tree doesn't need your help. What you do, you do to make yourself feel better.

 

The dead and galled spots on the foliage develop where tiny wasp larvae are feeding within the leaf. This damage is purely cosmetic. It is entirely within the tree's tolerance level. Most galled leaves remain functional. Even when the damage to a given leaf is extensive enough that the tree "decides" to shed it, that's no big loss. Leaves are important but also entirely expendable and replaceable.

 

Consider this: A leaf is simply a sun-powered food factory. A single leaf can produce enough starch to fuel its own needs, sustain its share of the tree's woody parts and roots, create an entire shoot with multiple leaves for the next growing season plus sock away some starch in nearby woody cells as insurance against calamity. No kidding. A plant grows on this energy. It can get by, can hold its place on even 50% of that power. Remove half a plant's leaves, or remove all of its leaves half way through the growing season, or remove half of every leaf, and the plant will still come out of that growing season with a net gain.

 

(Very recently, two baby hornbeams we planted were visited by a fawn within 12 hours of planting. That baby deer nipped off every leaf it could reach, which was over half the total foliage. The trees, now protected by odoriferous repellent, are pushing out new foliage on every bare twig.)

 

How much of its total leaf surface has your tree lost? It's not a matter of how many leaves are damaged but how much of the total is no longer green. With a spot on every leaf, it may still be 80-90% green, with plenty left to keep the tree going -- and growing, as well. Even if it loses 100% of its leaf surface to a pest that occurs only early in the year -- as this gall wasp, for instance -- it has time to produce a whole new set.

 

Here's an ironic twist: Your concern may be greater because your oak is NOT in big trouble. If the damage is really heavy a tree will usually "say" to itself, "Well, that's it for those leaves, then" and drop them all, and start over. But when the damage isn't enough to warrant giving up on that investment, the tree hangs onto them. It looks awful and we worry.

 

The best thing you can do is to pick up and burn or pick up and hot-compost all its fallen leaves.That's to help end the gall wasps' current run. They are always around but usually only prolific for a year or two. Fire, or the 140°F heat of an active compost pile will kill gall wasp pupae inside the leaf. Next spring there won't be so many emerging gall wasps. That means fewer eggs deposited on the oak buds to reboot the cycle.

 

One catch: Since the gall wasp does fly, those that emerge from oaks elsewhere in your neighborhood may visit your tree. So picking up and disposing of galled leaves is effective around an isolated oak, less so in an oak-filled community.

 

As for insecticides, which are not recommended by any Extension for controlling this problem, don't waste your time and money on those now. All the gall wasps in the world are currently inside- and protected by the oak's leaves from chemicals that kill on contact. They're about finished feeding for the year, too, so chemicals that soak into and make the leaf toxic are also ineffective. So the gall makers are untouchable, chemical-wise, until they emerge to lay eggs on the leaf buds shortly before the oak's budbreak next spring. Even then it would require multiple, exquisitely timed insecticide applications to catch the adults and kill the young as they exit the eggs, before they burrow into the leaves.

 

So it's a cosmetic problem, not life threatening, and chemical solutions are problematic. Thus the experts advise allowing the natural cycle. Stay out of it while the gall wasps have their "boom" -- a year or two of big numbers. That allows their natural predators to multiply and bring about the bust that follows.

 

Extension bulletins are great resources but even so there are some that are outdated or that differ, so we always do double check. In this case, most speak with one voice. Here's Missouri Botanical Garden backing up Michigan State:

http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/other/galls/jumping-oak-galls.aspx

[Your Letters 2]

Since we're speaking of galls:

For the first time, our neighbor's Accolade Elm, about 20' tall, has galls or maybe a scale or other infestation on the leaves. Hope this photo shows them well enough to identify them.

 

 

Not sure if we should spray something or use a systemic, or just relax and sell tickets to other interested gardeners. Otherwise the tree is quite healthy. - Thanks! - D.T. -

 

[Janet Macunovich 32]

That's actually a leaf gall - a mite living within the leaf -- as opposed to a scale insect living on the twig or foliage. My guess would be it's elm leaf gall Eriophyes ulmi... We hope you did relax and sell tickets, because it's not life threatening and probably won't be an ongoing problem. The eriophyiid mites are a class of gall-causing mites that are rarely ever worth trying to control. Maybe worth fighting if they infest seedling nursery stock...

 

Some people say of elms that, like locusts and cherries, it's not WHEN something will show up to infest them but "which one this year" of the many insects that evolved with them. These tree species are fast growing and resilient so they can and do host a lot of life.

 

If you'd like to check into the elm leaf gall situation, here are some places worth looking:

 

Image shows Eriophyes ulmi before galls become pink:

http://www.extension.umn.edu/garden/diagnose/plant/deciduous/elm/leavesprojections.html

The page above leads to this page with management advice, summed up as "none usually required":

http://www.extension.umn.edu/garden/insects/find/insect-and-mite-galls/

Re there are no very effectve controls:

http://hyg.ipm.illinois.edu/pastpest/200409e.html

Some general gall info

http://msue.anr.msu.edu/news/not_all_galls_are_created_equal_in_the_plant_world