Cut off the infected branch and burn/squash the critter inside. Treat your tree with imidacloprid or other systemic to prevent further infestations, and try to remove other hosts for the borer.

Hi Phil, From your post, lots of woody growth, lots of borers and then fungal attack, pruning may help,but you are prolonging the agony of the Lemon. The costs and time factor, saw and dig out the butt if possible, drench the area with a good fungicide, back fill. If posible replace with a new improved version but a few meters from the old one, to try to stop any soil born nasties transfering to the new specimen. We all like to hang on to old faithful things, but there comes a time to say goodbye.Good luck, Peter r

This is what I found. My thoughts...if in doubt, DON'T USE IT! Butterflies often lay their eggs on plants, and when those eggs hatch the little caterpillars will stay and feed on the plant as they grow. Caterpillars can be controlled using a common organic insecticide known as Bacillus thuringiensis, or Bt. Bt is a naturally occurring bacteria that causes caterpillars to stop eating and die. There are several varieties of Bt that can be used, depending on the type of caterpillar you’re after, including one specific to Colorado potato beetle larvae and another for corn earworms. Bt is also effective against tomato hornworms, the little green worms that like broccoli and cabbage, and bagworms. Bt should be applied at 1-2 week intervals to kill succeeding generations of insects. Gardeners with butterfly gardens should avoid using Bt on their plants because it is harmful to butterfly caterpillars. However, Bt is completely harmless to pets and people. Diatomaceous earth is another natural insecticide that may be used on a variety of insects. Diatomaceous earth is a fine powder that feels like talc, but it is actually the fossilized skeletal remains of small aquatic critters called diatoms. It is completely harmless to people and pets, but when soft-bodied insects come in contact with it, the tiny sharp edges of the diatoms lacerate the insects, making them dehydrate and perish. Apply diatomaceous earth in the early morning or evening when the plants are wet with dew, which will make the powder stick to the surface of the leaves and doom the insects that walk through it. Diatomaceous earth can be used to control ants, aphids, beetle grubs, box-elder bugs, flea beetles, those nasty little earwigs and many more insects. It’s also safe to use on houseplants, and can even be sprinkled on the ground to control slugs. http://gardening-articles.com/controlling%20insects%20organically.htm Outdoor insects affected by Diatomaceous Earth include:- ants, caterpillars, cut worms, fleas, ticks, cockroaches, snails, slugs, spiders, termites, silver fish, lice, mites, flies, centipedes, earwigs, aphids, beetles, fruit flies, lemon tree borer, borers, thrips, pysllid etc.. http://www.greenurbanliving.co.nz/diatomaceous-earth-for-natural-insect-control/ And from the manufacturer: (look half way down where I bolded, italicized, and starred) While Red Lake Diatomaceous Earth works well to kill most crawling insects, there are a few species that DE is known to be especially effective against. These include: • Ants • Bedbugs • Fleas • Cockroaches • Silverfish • Flour Beetles • Darkling Beetles • Grain Beetles • Carpet Beetles • Colorado Potato Beetles • Caterpillars ******* • Earwigs • Centipedes • Millipedes • Sowbugs • Pillbugs • Spiders • Crickets • Slugs http://www.absorbentproductsltd.com/diatomaceous-earth-insect-list.html

Thanks Kelley! I'm still on the fence about how well my tree is doing but so far it doesn't look like there's any large infestations or obvious diseases. The only explanations would have to be root rot, lots of fungus gnat larvae, or not enough food for the tree. And I'm hoping it's not the root rot! With your mix, it might be due to the fact that each of those materials hold water very well. From all the research I've looked at online, vermiculite and perlite are usually recommended to be chosen for just one or the other in most soil mixes. Or a mix of both to equal 1 part. The only time I've seen a mix include both as separate parts was IVOrganics on YouTube but I didn't stay updated on how the tree fared. If your vermiculite was a larger, coarser type then it might be ok? I've read vermiculite tends to hold water very well due to absorption while perlite just gets wet on its surface. Is your lime also on that same mix? It probably is just the mix's drainage...I think an expert should give you a more informed opinion on your eureka. I've had my first lemon for only a month now. My advice would probably be to not listen to my advice lol