It looks like frost cracks to me, which is caused by the bark warming up on a sunny winter day and then being exposed to rapid freezing at night. It's mostly always on the South or West side a tree, so if this damage is on one of those sides, I'd bet that's it. It's possible it's something else which has caused the damage(like mower or weed eater damage down low which caused the areas above to die), but either way the damage has been done. The fungus growing out of the middle part is just taking advantage of the exposed dead wood and is most likely not the cause. I'd clean all the lose bark and debris off(breaking the bark off with your fingers usually works and a good spray with the hose cleans most debris off) all the damaged, cracked areas, and then assess how much damage has occurred. At least one or two people on this forum suggest painting a copper based fungicide on the damaged area just to prevent fungus from destroying the heartwood(structurally important for the stability of the tree, but not living tissue), but don't use any tree sealers or paints. If this damage is relatively old(like last year) and the tree is healthy you should see a line of what may look like swollen growth around the edges of the damage, which is the tree growing over the damage(a good sign). If it's newer damage or the tree isn't healthy, then you won't see this area. No matter what, all you can do now, other than keeping the damaged area clean of debris and lose dead bark is keeping the tree as stress free as you can. This usually is just watering during any dry times, like when it hasn't rained in a week or so. Nothing else you can do other than that and waiting.

Hi Karen03, is hard to make a diagnosis with out knowing the exact growing conditions ie how much direct sun/day, how often do you water plants, is your plant growing in potting mix or garden soil do you have pets which use that part of garden? etc., Your dahlia plants look to me as though they have root damage hence the foliage is dying off as a response to lack of nutrient & water getting to the leaf ? A similar effect can be the result of magnesium or other element deficiency causing breakdown of green chlorophyll organs with in leaf. Over use of lime etc. can cause this. I would take plant out of soil (if in pot) & examine roots to see that they are healthy first though if in garden soil, would check drainage in garden first, if ok then cut the top 1/3 of plant foliage off to reduce stress on roots, hopefully new growth will make up for lost foliage soon after. Good luck allan

Daisy, I took Dave's advice and threw the plant away. I also took part of it to my local nursery in a plastic bag. The nursery is staffed by professional horticulturists. I opened the bag to show him the leaves and he yelled "NO, don't open that!" (didn't want it to spread if it was viral). Then he stared through the bag and said he thought it was cucumber mosaic virus. I personally think it was affected by herbicide, but will never know. I had another one in a similar situation which I stuck into a pot away from all the other tomatoes and today, finally, after a really good bout of rain, it grew at least 4" and looks like it's going to produce. So, I will probably never know for sure, but I think it was herbicide. My lack of sun issue persists but with the sun higher and stronger now, growth is occurring! I have learned a lot this year and am sure I have a ton yet to learn about tomatoes. My next house will have a good plot with full sun exposure for gardening! This is getting to be an expensive hobby! :-) Good luck with yours.

tuscanlover - Thanks for the kind words. I wish your daughter the best with her 6 year old. They are learning so much today about Autism and how to work with it in the schools. It is so much better now then it was when my son was a student and they didn't know what the heck was wrong with him. And the general public is more aware and less likely to stare or make rude comments like they use to (though some people will never learn). I am sorry to hear about your move and the loss of your and DH's job, house and all. That is really tough to face at 55. My dad went through a similar thing when he was in his late 40's. In 1961 he was transferred by his company from Mass. to Illinois. He moved the whole family, bought a new house and less then a year later they closed that division. It was a very tough time for everyone. My mom missed her family terribly and we almost moved back to Mass. But then my dad changed careers completely and became a stock broker and made more money then he ever would have at his old job. He left my mother very well off when he died in 1987. And she still is very well taken care of by what he left behind. So when I see the grey clouds, I try to find the silver lining. As to whether I am still sane or not, my DH might debate you on that fact. ;>) Clare