post from friend: I live in zone 10b, and my mexican lime tree is in a container and is about 5 years old. In the past 10 days, I noticed some black slime like material. Upon closer inspection, the slime is due to decomposition of flowers. I have never seen anything like this before!
Some of the leaves near the slime spots have holes munched into them, which leads me to believe this might be a pest problem?
I trimmed the places where I couldn't clean out the black slime flowers, and sprayed the tree with BTU, but I'm not sure what kind of pest this is. The same pest also appears to be trying to move into a jade succulent that is adjacent to the lime planter. If anyone has experienced something similar before and knows what this problem may be, please let me know!
Other info of note: normally watered once a week with a hose, but rainy season started here and it has been raining pretty regularly since Thanksgiving. I fertilize it with a citrus fertilizer as directed. Pot is a half-wine barrel with drainage holes drilled into the bottom. It gets part sun (I know full sun would be more ideal, but we had to move 2 years ago and our new patio unfortunately doesn't get much sun...we have it in the sunniest spot).
im seriously just refreshing this page waiting for the answer. I know I came to the right online forum. I have so much faith in you guys. im positive someone on this planet knows what the hell is going on. im giddy with anticipation
I don't have a precise answer, but if these symptoms just began as the rainy season started, and the tree is in partial shade (on sunny days) and it's been cloudy a lot with rain, my hunch is it is some sort of bacterial or fungal thing, and not an insect.
"Study books and observe nature; if they do not agree, throw away the books." ~ William A. Albrecht
I won't say it's not sooty mold. This could be the link to the insect activity and the gooey blossoms. Here's a quote about sooty mold from a page about citrus problems from the university of california.
Sooty mold fungus: Most active in cool, moist conditions. Feeds on honeydew excreted by aphids, mealybugs, scale insects, and whiteflies. Sooty mold should be washed off leaves because it can reduce photosynthesis and tree productivity if prolonged. Cosmetically unappealing on fruit; usually no serious harm, but wash it off.
I see this a lot on our citrus during rainy periods, and it's just the petals decomposing where they're held in place by spiderwebs. It's not sooty mildew (we get plenty of that as well). Citrus flowers shed their petals after they've their dash, and since they have a fair bit of "stuff" in them they make great food for insects and microbial life on the ground...or up in the tree in this case.
If I look really closely at the photo, I can see the pistil of a flower at the top, and it is bright green and plump. This says to me that it may have been pollinated, is healthy, and when the rotting flower petals fall away there will be a little lime growing there. Nothing harmful or worrisome, but if it really bothers your friend they can squirt it gently with the hose and wash them off. I think the hole munching is coincidental.
That appears to me to be the result of citrus whitefly larva, which are not only tiny but also almost transparent (hard to see without some sort of magnification).
These larva attach themselves to the underside of citrus leaves and flower stems, they secrete a "honeydew" like substance and this is perfect food for sooty mold which can be found on flowers and leaves.
In your photo there are enough of these larva present that I can see them on the undersides of the leaf just below the lowest dead flower, it is probable that the larva did some migration to the flower stems since those would have more sap flowing to them than the leaves.
If you shake that tree and tiny white flies start fluttering around the tree, you have discovered the problem causer.
Citrus trees are notorious Nitrogen feeders so, to help the tree be healthy adding rhizobacteria so it can get to the root system is one of the best things you can do for any citrus or other fruit trees.
A spray down with a good aeratedcompost tea will also help the tree fight off any new attacks or diseases.
Since the tree is container bound it would be a good idea to lift it every two years and give it a root trimming so that there is room for root growth in the barrel half. (think bonsai root trimming)
container grown citrus can use up their soil nutrients in a single year when artificial fertilizers are being used.