Labeano - the initial advice that Jefe gave is good advice. His comment immediately above is also spot on. If you use a soil that is well aerated and primarily composed of ingredients that don't break down quickly (pine bark, Turface, crushed granite, perlite, pumice ....., it will be very difficult to over-water, a primary reason for gnat infestations. In addition, the slow decomposition of the organic component (pine bark) is unlikely to support much in the way of gnat numbers unless you work very hard at over-watering. A high % of fine organic components in the soil, especially those that decompose quickly, and organic fertilizers like fish/seaweed emulsion can also cause an explosion in soil borne pest populations (promotes algae growth, too). Mike also makes a good point. I would consider very carefully whether it is wise to use a "chemical garden bug killer on top of the soil", as was intimated upthread. It's probably best to accurately identify the actual pest, and then use the least offensive remedy that includes your pest in its net of effectiveness to bring the numbers of pests back to an acceptable level, or eliminate them. There are MANY chemicals that are used in outdoor applications that are wholly unsuited to, and too dangerous for, indoor use. Al

Probably fungun gnats. Whiteflies are not soil-dwelling. Fungus gnats lay their eggs on the soil. The larvae that hatch feed on algae and fungus in the soil, sometimes on plant roots. When mature, the adults emerge and fly around. They can be an indicator of overwatering, which encourages algae growth. Try to let the soil surface dry between waterings. You can also use the microbial pesticide called gnatrol which contains Bacillus thuringiensis v. israelensis.

Before we get to the problem you think you have, let me go to the real issues :-) Or you can ignore what I say and skip to the bottom two lines for thoughts on your leaf issue. Are you afraid to trim the low branches for some reason? Get those low branches off the tree, tie it to a stick for support, ALL the way up, not 12" from the ground only, lose the fruit and train it in a straight upward growth habit. I let my three grow to about 5 feet then snipped the top to force branching. Once it branches, let the branches get long say 3-4' tip prune them to force more branching cutting off branches that grow downward. This way you will be able to move around the tree and pick fruit easily as it matures. Carambola start life VERY scraggly and you need to help it get strong. In 4-5 years with help from you it will be strong and give you more fruit than you and your neighbors can eat. If you want fruit today, go to Publix :-) If trained properly you can let it keep fruit when it's strong enough to not break or deform under the weight of the fruit. That said, carambola are VERY disease resistant in so. Fla. and with your tree so low it's hard to tell if it's cat spray, yard spray, direct fertilizer burn or maybe something else spraying on it from say a neighbor, splashing from your roof or from your lawn mower debris landing on it. To me it looks like mineral oil spray burn. Have you sprayed it? Ever? The only foliar spray you may need is to cure chlorosis which is not life threatening to the tree, but foliar nutrients will not burn it. Look up chlorosis your tree does not have it. Trimming and thinning branches is a lifelong job. They will have LOTS of dead branches that need to be trimmed OFTEN so you can get up in it to harvest fruit by hand without poking yourself in the eyes with dead branches. Carambola fruits don't do well with fruit pickers that I have tried. Finally, the worst things that can happen to Carambola are drying out, chlorosis, a hard scale (seemingly harmless to the tree) that gets on the branches. Frankly they're hard to kill, I know I had a devil of a time killing a Bell two years ago rather than bringing in a stumper. About your custard apples, Are those new flushes? Anonnas get white fly (look under the leaves for them) and "maybe" scale but for the most part are also pretty disease resistant. Bottom line is, I suspect something airborne is causing those spots on both trees. OR it "could" be bacterial leaf spot. See: https://www.planetnatural.com/pest-problem-solver/plant-disease/bacterial-leaf-spot/

I tried to answer that question with research, Rosie. I found the quote that follows on The Green Blog, Green News from the UC Division of Agriculture and Natural Resources. Does it mean that it would work specifically on mite larvae? I do not know; remember that Tarsononemid mites are not "insects" but members of the Arachnid family. Mosquitoes are insects, as are flies. I keep coming back to information such as this: "Not every insecticide that kills roaches, spiders and ants will kill a mite. Even the pesticide sprays labeled for spraying mites will sometimes suppress the pest instead of killing it quickly. Products labeled for controlling mites usually have specific sites, locations or plants where they are allowed to be used." I would think in any case that alone, mosquito dunks would not be of any use in combating the adult mite population and so one would STILL need a miticide to treat the affected plants. But you could say that using this "tool" would certainly not do any harm. But would it help? I am doubtful. "Larvicides containing spores or metabolites of the bacterium Bacillus thuringiensis israelensis (Bti) (e.g., Mosquito Dunks, Mosquito Bits, Microbe-Lift, and other products) act as stomach poisons when ingested, killing larvae within a few days. Bti affects only fly larvae, so it won't harm predatory insects living in the pond or water feature. Another effective larvicide is the insect growth regulator (IGR) methoprene (e.g., Pre-strike Torpedos). IGRs interfere with larval molting and also take a few days to kill, but they have a broader spectrum of activity, affecting most juvenile insects and other arthropods that might be in the pond. Both Bti and methoprene are available as granules or pellets, remain effective for about a month, and as with all pesticides, should be used only according to label directions."