The first photo does appear to show an infection stage of Hypoxylon, but can't be certain. We suggest you have a certified arborist with experience in diagnostics assess the tree in person. (Consulting arborists, for example, aren't necessarily affiliated with a tree company, so would be less likely to recommend taking actions that are not necessary. Given the amount of canopy death already present, though, it's likely an arborist will recommend removing the tree for safety, or at least doing lots of pruning.) Taking samples for lab testing would likely entail carving out infected portions of the trunk/branches itself since tissue samples usually need to come from the zone of active infection adjacent to healthy tissues, not cuttings further out into the canopy, but a visual confirmation of symptoms might be sufficient for diagnosis in this case. There is no cure or treatment for Hypoxylon, though the fungus tends to only cause damage to trees once the tree becomes stressed (even if symptoms of that stress are not yet obvious), such as from drought (which most of Maryland had last year), overly-wet or injured roots, girdling roots, and similar environmental triggers in the root zone. Given that stress is a precursor to most tree decline, it would be expected that what affects one tree in a cluster or row would potentially affect others, especially once a pathogen takes advantage of the situation and begins disease on one of them.

As noted in our Why Oak Trees are Declining or Dying page (plus its included links) and our Browning and Defoliation of White Oaks page (which can also apply to red oaks, the group Willow Oak belongs to), a range of environmental factors can contribute to chronic or acute tree stress and the development of disease. If any of the others have girdling roots, for example, due to planting too deep originally or over-mulching, an arborist can help to expose and correct them using tools like an air spade. It can be expensive to operate one, but it can be worth the cost if it corrects a problem that can kill a tree in the future.

A laboratory soil test might also help to narrow-down contributing factors impacting root health if the soil surrounding the trees is either too alkaline (pH too high, particularly if the turfgrass has lime applied periodically) or has high "salt" levels (such as from the minerals used in any ice-melting products used on the street and/or sidewalk, which doesn't necessarily have to involve sodium per se). Lowering pH to an acidic level preferred by the oaks is fairly simple, but correcting any excessive salts may be harder, though both processes can take a few months.

Miri

Hi Miri,

Thanks for the information. 

I planned on doing a soil test because that area suffers from compaction, which I know is a key factor in this. I would also like to have samples from the tree tested as well. Can you provide me with information as to where to send samples to be tested from trees? 

You can inquire with UMD's plant diagnostic laboratory to ask about how to send in samples and if she thinks anything can be diagnosed from twig cuttings on a tree with suspected Hypoxylon. UMD doesn't have a soil testing lab, but we do have a short list of regional labs as suggestions on that linked page.

Miri