A quick lesson in oak wilt, dealing with weeds
Q: I need a crash course in oak wilt. What types of oaks are most likely to be affected? How can I know if my trees are in danger? What precautions can I take, and who should I hire? When can I have them pruned?
A:
Those are excellent questions for anyone who loves oak trees. This fungal disease (Bretziella fagacearum) was first identified in the Upper Midwest in 1942. It has since been confirmed in more than two dozen states, from New England to Texas (eastern U.S.), and less than one year ago it was confirmed in Ontario.
The roughly 800 species of oaks are broken into two major categories. The red oak group (pointed lobes) is by far the more susceptible to this disease. Infected red oaks will not recover and are usually lost within a couple of months. The white oak group (rounded lobes) is more resistant. They are less likely to die. In fact, some do recover. But oak wilt is still of great concern.
Live oaks are in between. They are certainly susceptible, and oak wilt has done significant damage to our magnificent live oak population across much of our state.
There is a strong partnership between the Texas A&M Forest Service and the Forest Health Protection Branch of the U.S. Department of Agriculture Forest Service. Its highly informative website is https://texasoakwilt.org, and if you navigate through the tool bar to “Oak Wilt,” then “Identification,” you will see excellent photographs to help you know what it looks like.
The discoloration of leaves as conducting tissues are damaged is characteristic. They are evidence that it is time to call in help from an International Society of Arboriculture-certified arborist to confirm the diagnosis. Several other problems, including gas leaks, herbicide damage and normal late-winter leaf drop of live
oaks (going on now) can resemble oak wilt’s effects, and a certified arborist will know the proper steps to take.
Every gardener thinks of pruning their oak trees at some point. However, timing of that trimming is critical in dealing with oak wilt. The fungal mats that form beneath the bark of infected trees are produced in spring and early summer. Pruning must not be done between Feb. 1 and July 15. The acceptable pruning time runs from midsummer through fall, and all of winter until February.
The reason for that timing: Bark beetles involved with those mats can carry the fungus to exposed wounds on otherwise healthy trees. Take all precautions not to gouge oak trunks as you mow and trim grass, and coat all cuts larger than your thumb with some type of paint or
pruning sealant immediately after you finish pruning.
There are two other noteworthy precautions. Remove infected dead or dying oak timber as quickly as possible so it cannot serve as a source of spread to healthy trees. Do not leave it stacked as firewood. And if your trees are growing close together, talk to your arborist about whether root grafting could be a concern. It may be necessary to cut trenches between the trees that could be merging their roots so the fungal infection won’t be able to spread underground.
Q: I have these two types of weeds every year. I put preemergents down in late winter and 90 days later, then again in the fall, yet I still get these. Is there something I can put down that won't kill my St. Augustine?
A: The coarser grass is rescue grass. A fall preemergent applied the first week of September should prevent its germination. You didn’t specify when your fall treatment was made, so perhaps it was after that time. The materials Dimension, Halts or Balan should work on it.
This past fall and fall 2022 were very hot and very dry in early September. I suspect that some of the effectiveness of the preemergents was diminished by all the watering we had to do while it was still too hot for the weeds to be sprouting.
Your other weed appears to be annual bluegrass (Poa annua). The same three preemergents are labeled for its control, but there is research from several southern agricultural schools saying it is more difficult to control and appears to be developing some level of resistance. All I can suggest is
that you “stay tuned.” We can hope a new product will come into the market that will offer better prevention.
Q: What type of weed is this? It's an annoyance to have to pull it out. It's all over my yard.
A:
You would need flowers (the way plants are identified) and a good plant taxonomist to confirm the precise name for this. My dad and uncle were both PH.D. botanists with Texas A&M, but when you wrote me, you got a horticulturist (sorry about that).
However, from the practical standpoint, its name doesn’t matter at all, because any nongrassy plant can be controlled with a broad-leafed weedkiller spray.
Look for a product containing 2,4-D. That will be in the fine print on the “Contents” part of the label, and it also will probably show there are two other active ingredients mixed with it. Those two are active in the soil, which means you won’t want to apply it as a hose-end spray. Use a small spritzer bottle or a 2-gallon tank sprayer. Apply it directly to the weeds’ leaves to the point of full coverage without runoff, and you should start seeing results within a few days.