I'm having a problem with several trees that has me stumped. I haven't yet bought the citrus disease book from the extension service so I'm hoping someone here can diagnose this.

Three trees: The first a Kimbrough satsuma on what I believe is trifoliate. The second a Sunburst tangerine on Swingle, the third a Ponkan on Swingle.

I've had some minor trouble with scale, aphids, the fire ants that feed off them, and this year grasshoppers in particular, but that is with all of my trees. I eliminated all but the hoppers with some summer weight oil. About mid-summer or so the Kimbrough I noticed was drooping and upon investigation I found the trunk bark was peeling off right at ground level and a few inches up the trunk. I dug the sand away a bit and the root bark seemed intact. It looked like the fire ants were attacking the bark, but they may have been after something else as they were also in the top of the tree with the aphids. I sprayed the tree which eliminitated the ants and the aphids, but it continued to dwindle, finally dying a month or so later.

About two months after that the Sunburst did the same thing, but more quickly. I did find some more aphids and ants in the top of the tree, but not a lot relative to what I'd found earlier. I sprayed all the trees again with summer weight oil and an insecticide (a Bayer product, but I can't recall the name offhand) to eliminate the hoppers as they were causing an unacceptable amount of damage. Same thing with the trunk bark from soil level to a couple of inches up the trunk being missing. The Ponkan was the same way but not showing any obvious signs of distress.

The ants, aphids, scale, and even the hoppers are gone, the second combined spraying of oil and insecticide eliminated them and the remaining trees are appearing healthier than they did before. The Ponkan still isn't showing any signs of distress even with the trunk bark damage. I'm really concerned about what killed the Sunburst and Kimbrough.

Any thoughts or idea?

.....Alan.

Hi Alan & welcome to the forum. My guess would be some type of fungus disease entering where the bark is open. Let me check my files when I get time later.


Here is some good info : http://aggie-horticulture.tamu.edu/citrus/l2313.htm

Perhaps Dr. Manners could help you out with this a bit more.

Hello AT, I dont have any way of looking at your tree but I do know from self experience that fire ants can kill a tree and it doesnt take them long to do it. I had a year old citsuma in my mini grove and I noticed it turning yellow. This was back in the summer... when I investigated, I found the fire ants had mounded around the little tree and had eaten all the bark away where they had mounded. This tree died and I then noticed my yuzu tree which was much larger seemed to be stressing. I checked around the base and sure enough those red devils were chewing away at that one too. The citsuma was a rooted cutting but the yuzu is grafted on trifoliate. They were eating a trifoliate tree! I loaded them down with some orthene 75 WP and that was the end of that. The yuzu tree trunk still shows damage where they were eating away. After that, I put orthene at the base of my entire grove. I will repeat this process next spring because we have fireants here almost like the locust hordes that devour crops. I wish I could ship them all back to South America. Like so many other imports they seem to thrive and prosper here in the good ol USA.

Stan,

Do you really think the fire ants were attacking your trees directly?

I'm asking because when the Kimbrough first started going south on me the ants had mounded up around the base, but I could not decide for sure if they were really attacking the tree or just happened to be there while whatever was really killing the tree was doing its thing.

They were around the bases of the other two trees as well, least around the Ponkan that's still alive.

Why would they attack the base of the tree like that?

.....Alan.

Following up my own post.

I've been thinking I had a disease problem with these trees, but now I see it may have been the fire ants directly causing the problem.

http://www.ipm.ucdavis.edu/PMG/r107300211.html
DAMAGE
These ants feed on honeydew excreted by soft scales, mealybugs, cottony cushion scales, whiteflies, and aphids. As part of this relationship, they also protect these insects from their natural enemies, thus interrupting biological control of the honeydew-producing pests. In the process of keeping most natural enemies away, they also protect other pests, such as California red scales, that profit from the lack of natural enemies. Fire ants feed on the twigs and bark of young trees, sometimes girdling the trees.

http://agnews.tamu.edu/dailynews/stories/ENTO/Oct2300a.htm
They are a big problem in citrus orchards because they swarm onto and sting unsuspecting citrus workers, and because the ants can kill young citrus trees. They get under freeze protection foam tree wraps, out of a grower's sight and can completely girdle a tree, which cuts off the nutrient flow.

I won't let them slide next Spring, I can tell you that.

.....Alan.

Very interesting. I have never had a problem with fire ants as my yard is treated twice a year with the 12 month dose of fire ant control granules. After reading this I did a little research and found this info http://agnews.tamu.edu/dailynews/stories/HORT/Jul3004b.htm

Bug Juice http://www.logfinish.com/items_detail.php?name=Bug+Juice&ItemID=11&CA=7&UID=2005122021160565.184.95.46

Alan, They were'nt attacking it.. They were eating it alive. When I found out what was going on, I took action right away. I wonder how the organic only folks deal with fireants? The orthene that I used around the base of my trees knocked out the ant population and I wasnt bothered with them the rest of the season. Problem is, they just move away for a little while and then they will be back. Using the pesticide was all I could do.
That is all that saved the yuzu from certain death. I could see where they had eaten whole sections of bark from the trifoliate rootstock. The bark was oozing out a sticky sap that they were feeding on. I guess thats why they find young citrus trees to their liking. They must be feeding on the sap. Glad we solved the mystery of the sudden death kimbrough.