Strange yellow substance in wood

[plantnewbie24]

I have waxleaf privet shrubs (ligustrum) that have been struggling with various ailments (leaf spot, witches broom) and are rather sickly. During pruning today, I noticed something that hadn't caught my eye before. Some of the thicker branches I removed had a strange yellow substance inside the wood. The first piece came from a shrub suffering from witches broom and it's the sickest shrub, so I feared this could indicate extensive disease (more than I expected). But the second piece in the picture came from the healthiest shrub and it had even more yellow streaking. So now I'm wondering if this is normal (?) or another symptom of my existing problems, or (heaven forbid) a sign of some other unrelated disease/problem. Does anyone know? Pictures below.

 

[Marck]

Greetings, welcome to the Forums.

I've found no reference to Waxleaf Privet (Ligustrum japonicum) having yellow-staining wood. There are various wood fungi that can stain wood various colours. It's an effect known as spalting. I'm not sure which fungus might do this to Ligustrum.
Would it be possible to see photos of the leaves with the leaf spots on them?

 

[plantnewbie24]

Thanks for the reply. Below is an example of the leaf spot which I believe is a fungus. I also included a second photo showing the "witch's broom" (brown clusters and tiny leaf shoots are chacteristic) infestation which I believe to be a separate issue caused by mites, but not certain. To date, I've tried treating the leaf spot with Immunox (myclobutanil) - to no effect, and now I'm trying Daconil (chlorothalonil). For the witch's broom (thinking mites are the cause), I've tried horticulture oil which maybe helped a little but not enough, and now I'm trying BioAdvanced (imidacloprid). I just started Daconil/BioAdvanced a week ago, so it's too early to tell if they are helping. If you have any ideas on the yellow staining or even better treatments for the leaf spot & witch's broom, I'd greatly appreciate it. These bushes are very sick and I'm worried I'll lose them soon if I can't get a handle on these issues.

 

[Marck]

The leaf spots apppear to be a symptom of an ascomycete fungus, Cercospora, or perhaps Pseudocercospora. They are known to be resistant to many fungicides.

The Witches Broom is very interesting.
Peacock mites (Tuckerella parviformis) are mentioned as a cause of witches broom galls on Ligustrum japonicum.

However the stem knot fungus (Sphaeropsis tumefasciens) is also known to cause similar damage, on Ligustrum, in Florida.
It's best known as a Citrus disease but i can infect a number of other hosts. Wood discoloration is mentioned as a symptom, though no mention is made of a bright yellow color. The color might vary with different hosts... If it is Sphaeropsis tumefasciens, sterilizing pruning tools between cuts is crucial.

Here is the article from the University of Florida, IFAS Extension. it discusses both Tuckerella mites and Sphaeropis tumefasciens on Privet (Ligustrum). https://edis.ifas.ufl.edu/pdf/IN/IN131000.pdf

 

[plantnewbie24]

Thank you for the information & the article link. That's the first mention I'd read about wood discoloration being due to sphaeropsis tumefasciens - I was about to say that this gives me hope that this could be the cause and not a new/unrelated issue, except I've read that this fungus is basically uncurable other than to prune back as far as possible until there is no discoloration of the wood. And unfortunately, I did a test on one of those yellowing branches in the original picture and trimmed it back further almost all the way to the trunk, and the yellowing never stopped. And strangely, one of the shrubs with no apparent witch's broom issues still showed very yellowed wood (one of the branches from the first picture). Perhaps the fungus spreads through the trunk and wood first before reaching the leaves, so it could be working its way up still? If this is the case, I fear all of my shrubs could be totally infected and it sounds like there may be nothing I can do for them. Is it your understanding as well that there is no treatment for spaeropsis besides pruning?

 

[Marck]

Pruning and sterilizing between each cut, does seem the best option for dealing with the Witches broom.

I don't know which fungicides would be effective on Sphaeropsis tumifasciens and I'm still not certain that is the cause or the entire cause of what you are seeing. That bright yellow wood staining is remarkable. I would have thought there would be some description of it.

 

[DirtMechanic]

Go for systemic fungicides. Clearys 3336 and agri-fos to name a couple. Even if they are not precise or super close to curative they will produce a less conducive environment internally. This would serve in a positive way as the plant fights back. Imidacloprids are systemic pesticides. Nicotine basically. The "new or neo" neonicotinoids. Lol same old really. Chew some tobacco and spit on the plants.

 

[plantnewbie24]

Thanks for the suggestion. I previously tried spraying the shrubs (5+ topical sprays over a few months) with Immunox which I think is considered a systemic, but it didn't seem to produce any positive results on any of the issues (both leaf spot or the witches broom). If the reason for this is resistance to the active ingredient Myclobutanil in Immunox, do you think one of the suggestions would be better than another - Clearys 3336 (Thiophanate-methyl?) or Agri-fos (Phosphorous Acid) or perhaps another systemic fungicide? Are some of these more effective against resistant fungus (or perhaps significantly different than myclobutanil) that would make them a better candidate to try next over another?

 

[Marck]

For less toxic residue and lower toxicity to non-target organisms, Phosphonate fungicides, such as Agri-fos, are a better fungicide than most, but I don't think there is any evidence it works on Sphaeropsis tumifaciens, so it could be a waste of time and money.

Another concern I have with applying fungicides ineffectually or imprecisely, is that there is the possibility of killing beneficial fungi, and other organisms, which may have all sorts of beneficial effects, such as keeping the pathogenic fungi in check.

That is a hypothetical generality, and might not be the case here, but there are so many micro-organisms and ecological relationships that we don't fully understand. It's hard to prove a negative, but who knows what is out there that might parasitize or out-compete the pathogens, if we give them a chance.

 

[DirtMechanic]

Last year was wet here. Tracking local moisture averages is liable to produce a certain predictability in the presentation of the following onset of damaging or aggressive fungi. There will never be a good way to get ahead of the curve because you cannot know what you do not know. Local historical knowledge becomes increasingly important. Yet the slow respiration especially of larger plants requires a preplan or you become reactive to damages of a variety of types. Most assuredly you try for the educated guess or are dealing with stopping observable damage after the fact and the years it can take to recover. No good answers its seems to me.