I have a Ponkin mandarin that is in the 3rd growing season since I planted it. The first year it numerous fruits which I thinned to about a dozen. They were doing fine until hurricane Ivan which knocked off all of the fruit. There were no blooms the second year, (I understand mandarins can be alternate year producers), but now that the new growth has come out and I do not see any blooms I am beginning to get concerned that I am doing something wrong.
In addition to the fact that the tree is not bearing, I have noticed that there are quite a few dead stems at the ends of the branches. There are also black spots (1-2 inches long) along some of the otherwise green stems of 1-2 yr old wood. Could that be the cause? If so what is it and how do I eliminate the problem?
Here are some pictures of the tree and stems. I would really like to know what is causing this. New stems starting from the bottom of the tree appear to be growing fine, but some of this year's new growth on the upper (older limbs) has died.
Looks/sounds like maybe Citrus Root Rot (Phytophora spp.) See if this site helps at all: http://edis.ifas.ufl.edu/CH087
Thanks for the link, but I am not sure that fits. We did have a very wet year last year, but soil here is sandy and drains fast. No sign of damage on the trunk, but most damage appears on limbs that are less than 1/2 inch in diameter. These lesions start as a black spot in the middle of otherwise green stems. The close up of the stem in the second picture shows where one of those spots started (where the stem turns from green to black). Earlier this year that was a relatively healthy limb, now it is essentially dead from that spot on. This may still be the fungus you mentioned, if not it may be another fungus that is controlable by the systemic fungicides mentioned in the link, so I will try to find those fungicides and use them.
Careful using systemic fungicides on Citrus as most systemic chemicals will also be present in the fruits as well.
How long will the fungicide last-- there is no fruit this year. Also, should I cut all the infected limbs off below any sign of disease?
Most systemic chemicals wont last more than a couple months in the plant, but still be careful in what you use to make sure that it wont persist in the plant or the soil for a longer duration. If the disease is a root contracted disease, which it seems like it is, then pruning the dead branch tips will not help to prevent the fungus from spreading as it does its damage in the cambium layer of the crown of the plant. Also be sure that the systemic fungicide you use is one that is absorbed by the root system.
Also I'm not 100% positive that the damage is from a root contracted fungus, or any fungus for that matter, so you may want to research the problem further before you take any action.
That plant looks like it had some major frost damage. Citrus that are activley growing & get a quick freeze will split the bark. Many times it causes quite a bit of branch die back. I would cut it back a few inches below the bad spots & keep a close eye on it.
I have a few questions for you. About when do you see the infection spread from a black spot as you call it to when the outer portion of the branch dies back to live growth? Are you losing entire limbs? Can you show a photo of the trunk of this tree? Do you have an idea as to what this Mandarin was grafted onto? If it was grafted or budded was it supposed to be a dwarf, a semi-dwarf or a standard tree? Sometime read the description of Hendersonula Branch Wilt from this link below and go from there. Plant Disease Publications, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona Jim
In response to the frost damage, we did have some frost, but the lowest temp was 29 and that was in Feb.--The tree should have been acclimated, however we had had a warm Jan. It may be the cause of some of the damage, especially to smaller limbs, but I saw splitting only on one limb and I do not think that explains the black spots. As to the question of how fast it progresses, the first post was 3 weeks ago. At that time the limb you see in the closeup had a black spot that was about 1 in long where you see the limb turn from black to green. Beyond that point the limb was still greem and trying to grow. As you can see the limb is pretty much dead from that point on, although some of the leaves are still green. At this point I have cut all infected limbs below the lowest sign. Most of the cut limbs were small, but several were the size you see in the closeup and were cut back about 2/3 of the way. The tree was grafted. It was bought from a grower in So. Lousianna about 3 years ago. I do not think it is a dwarf, but have no idea what the rootstock was. I will read the link you suggested and post a picture of the trunk later. Thanks for all of the responses, I am new to citrus, but have been gardening for years.
The Hendersonula Wilt seems to fit the discription. The link to mechanical damage may also be significant since we had so many hurricanes last year. Here are a couple pictures of the trunk and graft.
I would not be overly concerned about being new to Citrus, even some of us that have been around these plants for years still learning something new all of the time. You gave me enough clues to think that a branch wilt might be affecting this tree. Mother Nature hits the tree hard and weakens the tree and then we get hit with an invader that causes us more trouble. I can see the canker pretty easily which brought me to Hendersonula Branch Wilt. If you want to be more certain of the disease and how to treat for it then you may want to contact your nearest County office of your IFAS Extension through the University of Florida and see what they recommend for treatment aside from pruning off the infected areas back to live wood and a little ways beyond. A standard prune here for Bacterial Canker of Stone Fruits and Pomes is to make our cut no less than a foot back towards the base of the tree from where the lesion or the last visible gummosis can be seen. The less exposed growth of your tree appears to be okay for the most part aside from a scrape I see but the remnants of the fallen leaves on the ground is what I expected to see, especially with the canker and the resulting dieback I see from the branches. University of Florida IFAS Extension Jim
