I ordered six 2-3yr trees from FourWinds in the summer and one, a Golden Nugget Mandarin, arrived with a dozen green fruits. The branches were weighed down by the weight of the fruits, and on all of such branches the leaves seemed droopy also. I brought them inside in October, and in mid-November the mandarin fruits began turning orange and dropping off. They were still half green when they fell off, and tasted somewhat sour though still very much like an orange. I don't think they were quite ripe yet. A few weeks later, the leaves on the branches that bore fruit began to dry up. They have been falling off ever since and the tree has now lost about half of its leaves, almost entirely on the lower half where the fruits were. The branches that did not have fruit seem to be doing fine, although I have yet to see any new growth on this tree since it arrived. All of my other nine trees are doing very well and putting out new growth and flowers. Any idea what might be wrong with the mandarin?

I have the ten trees in a heated room ~55-72 degrees under timed grow lights. They also get a decent amount of sunlight from an east window but the window isn't huge.

.........."fell off, and tasted somewhat sour"..........
Mandarins on such a young tree are always sour to the taste. Your tree will begin to produce sweeter fruit after the age of 5 years. Each year thereafter, the fruit should keep improving in taste. It is common for a young mandarin trees to drop some fruit.

.........."leaves on the branches that bore fruit began to dry up"............
Without further information on the care of the tree, I am unable to ascertain why the leaves dried and dropped. However, I don'[t think their is a relationship between the fruit and leaves.

I will say that Four Winds Growers generally produces very high quality trees.

Millet

Unfortunately I think I found my answer. It seems that tree has a large mealybug infestation that I missed somehow. I found sticky residue on some of the other trees as well. Any recommendations? Insecticidal soap?

Yes, I like soap and water better than neems oil and water. The experts on here say neems oil only when you need the big guns so to speak. Seems you will get more leaf drop with oil.

I would recommend a horticultural oil called Ultra Fine. UltraFine can be purchased at most any garden center, or Home Depot. Ultra Fine is a very pure grade of horticultural oil. Non toxic to humans, and even qualifies as an "insecticide" in organic culture. Make a 1 percent blend of oil and 99 percent water. Works on mealy bug, aphid, white fly, mites, scale, plus works as a retardant for citrus leaf minor. Every grower should keep this in their supply chest. Works very well. My second choice would be soapy water. - Millet

I tried some store-bought insecticidal soap I use for my apple trees because I had it already mixed, but I do also have some horticultural oil. "All Seasons Horticultural Oil" from Bonide. Any experience with it? I already have it so I will try that if it is appropriate. A few of my trees are in full bloom right now so I'm hesitant to mess with them too much but I'd rather lose blooms than entire trees to pests.

I know nothing of Bonide horticultural oil, however i would *think* that it would be OK to use. If your tree is in bloom you will have to either wait until the blossoms fall, or carefully spot treat with a hand held adjustable spray bottle. One note of caution I failed to advise in my last post is, when spraying a citrus tree, spray ONLY in the early morning, or better yet, spray in the late after noon. NEVER spray the tree in the heat of the day. - Millet

I had sprayed in late afternoon but while blooms were still around and most of those blooms died off instead of holding fruit. The bugs are gone at least, and there are still a few fruits that have held. Not sure how well the mandarin will recover but it at least has not shown any more deterioration. Branches were rapidly wilting and browning but that has all stopped.

Thanks for the advice.