Hickory tree issue

Question: I have a mature tree I believe is a bitternut hickory. In the last couple of weeks it has been shedding leaves and the canopy is not as full as it should be. I picked up some of the leaves and they show some weird growth at the base. Photos of the leaves and the tree itself are attached. The tree has been healthy to date. The only issue I see is where it lost a limb, which could have introduced rot.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 01, 2023, 10:38 AM EDT
response: This appears to probably be a petiole gall which is usually caused by a type of insect called phylloxera (Ohio State) which is similar to an aphid or adelgid. From Purdue University: https://extension.entm.purdue.edu/publications/E-56.pdf Maybe the galls have either already opened and dried a bit or could be just slightly different from what we are seeing in photos. Virginia Tech has a fact sheet that explain when they open and dry they get the black appearance. These are probably from last year. In any case, they are naturally occurring and shouldn't require a control since it is a mature tree. Many times, insect populations rise and fall and once the predators for these find out where they are, the symptoms will diminish. The falling leaves can be concerning, but usually the tree can recover and they most likely won't cause extensive harm. We would tend to caution you from using any insecticide, whether it be a foliar spray or systemic (the Malathion that is mentioned in VT info is not necessary since this is a large tree). Hickory are a food source to a number of native insects and pollinators like the rare to see Luna Moth.  Should you have further concerns with this, please feel free to reach out again.  Emily

responder: The Question Asker Replied June 01, 2023, 12:48 PM EDT
response: Hello Emily, Thanks for the information.I'm relieved to hear there will probably be no long-term damage from the infestation. If it's OK I have another question related to this tree: do these bitternut hickories or their nuts inhibit the growth of plants under them? I actually have pretty robust growth of wood poppies, heucheras etc. but it has always been very difficult to grow grass. That area is certainly shady but does get some sun. I've even tried switching to a clover lawn but the clover doesn't seem to grow. Three different lawn care companies have worked on it, tested the soil etc. to no avail. I only do organic gardening so maybe that's the issue. I've converted more than half the lawn to woodland beds but I'd like to have a bit of open area. Best regards, Leah

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied June 02, 2023, 1:57 PM EDT
response: Hello Leah,  Hickory is related to Walnut, and they both produce a compound called juglone that is suspected of negatively impacting the growth and survival of certain plants sensitive to its presence. Between the two, Walnut produces more juglone than Hickory, which is why juglone-resistant plant lists tend to focus on Walnut. Having said that, the science is undecided as to whether juglone is really a major factor in plant decline when certain species are lost to dieback or failure when planted under a Walnut (or Hickory, but we don't hear about this issue often).  Still, lawn grasses are not very shade-tolerant, so any mature tree shade will cause them to thin-out and decline over time. Competition with the tree's roots will also reduce grass vigor; the trees will have the competitive advantage. Comparatively few grass species can handle a decent amount of shade, and they are not the types used for lawns but instead more decorative kind that reach a couple feet high or so by midsummer. Even though you mention that some sun reaches that area, turfgrass really needs full sun (6+ hours of direct light in summer) to thrive and remain lush. For these and ecological reasons we recommend that gardeners use lawn alternatives around shade trees, plus any other area where lawn's tolerance of foot traffic is not needed or where growing conditions don't suit the health of the grass. It sounds like you are already doing this, but perhaps expanding the non-turf areas would be simplest.  One grassy look-alike for semi-shade is Sedge (Carex), and if you're interested you can explore the recently-released publication by Mt Cuba Center (a Delaware public native plant garden) to find out which species might work best for your needs. Note that there is a discussion of mowing tolerance in the article, but mowing is not at all necessary for the health of the sedge, and most are better off without it. Another shade-tolerant grass-like plant, though non-native, is Mondo Grass (Ophiopogon). (Despite its name, it's not a true grass.) Slower-growing than its Liriope cousins that we would not recommend using, it can gradually form a solid lawn-like colony as it spreads. A dwarf variety exists that stays about half the height of the typical form, which results in a low-cut lawn look over time. Mowing is not needed so aside from monitoring for watering needs as with any planting, it's as low-maintenance as the sedge would be.  Clover is not very shade-tolerant, and we don't recommend a solid clover "lawn" as it goes dormant in winter (leaving exposed soil for weed seeds or erosion). If mixing clover into an existing lawn, Microclover is the particular dwarf variant of regular white clover that we suggest is used so it doesn't take over. The PDF publication linked at the bottom of that page goes into more detail about how to set up a mixed microclover-turf lawn.  If you wish to keep the existing lawn (which we're assuming is fescue and not zoysia, since their care differs) essentially unchanged but just improve its appearance, then the best approach is to perform annual autumn overseeding, fertilizing two to three times a year based on the results of a laboratory soil test (one test every three years, more-or-less, is sufficient), and periodically irrigating the lawn to reduce stress on the roots if the weather remains dry during its active growing season. For example, many areas of Maryland are currently experiencing abnormally dry or droughty conditions from our lower rainfall so far this year. Feeling the soil about six inches down and water well if the soil is somewhat dry to the touch at that depth; if damp when sampled instead, then watering may not be needed yet. One soaking per week in hot, dry stretches of weather is often sufficient as a guideline.  Miri