Growing Concerns 595: Sap dripping pine, plant poisoning plants

Late Fall!

Sap dripping from pine is a sticky subject


Dear Janet,

We have a Michigan Pine tree in front of our home. It was planted about 30 years ago by the previous owner.

Our neighbor alerted us to some white seepage at various spots on the trunk and limbs. Also, when we had a windstorm this fall many pine cones came down and he pointed out that they, too , were coated.

We want to have the tree looked at but are not sure how to proceed.


Dear E.M.,

Michigan's State Tree is the white pine, Pinus strobus. It has long, soft needles in clusters of five. Like most trees in its family, it pushes out sap as a defensive move.

Pine resin is an effective insecticide and fungicide. It can kill or slow the growth of an invading insect or fungus spore.

Sap's not only a chemical shield but can be a physical deterrent. It can forcefully flood an area to eject insect larvae. It seals holes as  it hardens, shutting out wood-eaters and pathogens.

There may be tip boring insects attacking the new buds on your tree, or trying to enter the wood through wounds made by hail or poor pruning. Sap sucking birds may have made holes in the trunk that the tree is trying to seal. Squirrel-bitten twigs may be dripping sap. A fungus may be growing in cracks at bases of storm-bent limbs. There are other possibilities. Any of them may be serious enough to warrant treatment or might be minor ills an otherwise healthy tree can deal with.

So you're right to seek an examination by an arborist -- a tree care specialist who can diagnose and help treat problems.

Check "Tree Care" in a phone directory for a company which employs a certified arborist. Call to ask where the arborist's certification was obtained -- organizations like the International Society of Arboriculture and National Arborist Association require that individuals have extensive education and experience to earn certification, and continue their schooling to keep the endorsement. Some organizations maintain their own referral lists, too. For instance, at, select "Find a Certified Arborist", enter your zip code and obtain a listing.

An arborist may have a landscape technology certificate from a Community College or a horticulture degree from a University. These are all good starts.

Next, do what you would if you were hiring someone to remodel or repair your home. Ask for references, then follow up to learn about the experience others have had in working with this individual.

I go one step further before hiring a specialist, which is to talk to someone who knows about the work I'm looking to hire done. From my brother the carpenter, for instance, I can get a question or two to ask to test a potential cabinet-maker's knowledge and skill. For pine tree care, you've checked with me and can ask, "Why might sap be dripping from my pine tree?" At least some of what you hear should be what I've already told you!

Short reports

Grow all plant-poisoning plants in one place?

This is what O.L. proposes, after reading here that some otherwise-desirable plants such as sunflowers, mums, yarrows and black walnut trees are allelopaths. Such plants are capable of stunting and killing other plants that share their root space.

It won't work, O.L. These plants share a survival strategy but they don't all use the same chemical to do their killing. So they each get along differently with various plant species, including each other. A killer like buckthorn that can live with black walnut, another allelopath, may die under the influence of toxins from sunflowers, barley or rye grass.

Another consideration is that we haven't identified all the allelopaths yet. Nor do we know which plants may or may not be able to tolerate a specific killer's presence.

It's a fascinating and important field. To stay abreast, use the Internet or your local library to follow references to "allelopath" in the latest scientific publications.

Does construction damage kill red oaks more quickly than white oaks?

C.R. and others asked for clarification after reading this in my November 13 column. Answer: No. Construction damage makes no distinction between oaks.

Oaks in the red oak group (red-, scarlet-, black- and pin oak) are killed more quickly than oaks in the white oak group (white-, burr-, swamp- and English oak) by the oak wilt fungus that was the topic of my November 13 column.


Green thumbs up

to the brilliant red fruit on cotoneaster and barberry bushes. A little color goes a long way in December!


Green thumbs down

to tiny, dry, white flecks on the needles of a pine, so noticeable now. These scale insects will begin a new round of needle-sucking in spring. In some cases they can weaken and disfigure the plant. Although you can't kill them now, you can mark your April, 2005 calendar to further evaluate and treat the problem if necessary.


 Originally published 12/4/04