The gnat problem sounds like over-watering; the 'chunk out of the stem' issue sounds like a damping off/ fungal disease issue due to over-watering, with the resident insect being more of an opportunist than an agent of cause.

It's hard to say what to do because we don't know if the plant has a single or multiple stems. It wouldn't hurt to formulate a plan that will allow you to make sure you have the basics covered well enough that you can restore normal root function and root health, because w/o a healthy root system, a healthy plant is out of reach. Start by making sure the plant actually NEEDS water before you irrigate. Keep the plant warm, in good light, and keep the humidity well north of 40% in the room where the plant resides, as long as that presents no condensation issues.

The Bayer 3-in-1 for Insect, Disease, and Mite Control is a good product, but you can't spray it indoors, even though it's approved for use on houseplants. It has a systemic insecticide (imidicloprid) and a systemic fungicide (tebuconazole), so it should rid you of the insect and help with any fungal infections. Like most fungicides, it's more effective used prophylactically than as a fixative. Pure, cold-pressed neem oil does have some good insecticidal properties, but lacks anything like instant knockdown. The pure, cold-pressed products have some fungicidal properties as well, but it's unlikely neem oil will be able to fix the problem you described. If the plant is in advanced stages of root rot such that the stem tissue is that compromised, it might be too late - no way to tell from afar.

Al

There are 4 more stems with multiple leaves on each. They appeared to be healthy and I watered every 10 to 14 days I also have the Natria insecticidal soap. The stem is reduced to half of its circumference. Should I replant by getting rid of old dirt and cutting away bad section and rooting in water.The other stems do not appear to be infected at this time. I am going to have to do something because I put the plant in plastic bag and bugs are flying out
so I doubled the bag awaiting advice on which would be my best approach.
Thank You

It is a good idea to change the soil. Chinese evergreens need a free draining potting mix, and not too large pots, as they have quite a shallow root system. If you let the soil dry up between each watering, you should be able to keep the gnat problem at bay. (It should not be bone dry, however, but not wet.)

Reed - your user info doesn't offer anything about where you live, which can be an important consideration when offering advice.

When you water, it should be at the time your plant needs water. That means just before the plant starts to experience drought stress or at about the time the soil seems dry to the touch. Until you get used to when that is, use a wood dowel rod sharpened in a pencil sharpener, pushed deep into the pot to determine whether the plant needs watering. If the tip of the 'tell stick' comes out damp or dark looking - wait to water.

Where you live sort of determines whether it's a good idea to repot now. If you have cold winters and the plant isn't in immediate danger of dying, it's better to wait until summer - the best time to repot - around Father's Day. If the plant IS in immediate jeopardy from root rot, you might need to bite the bullet and repot anyway. The loss of 1 stem doesn't mean the loss of the plant, but id the issue has arisen due to root disease problems, acting might rise to the necessary level io2 save the plant. Lift the plant from the pot, inspect the roots, and see if they look dark/slimy or smell other than like fresh earth. These conditions ask for a pruning of roots back to sound tissue and a repot, because it's unlikely the issue will resolve itself w/o intervention.

Plants with shallow root systems where they naturally occur don't need special consideration when it comes to pot size or depth. If the soil is well-aerated, the roots will happily colonize the entire soil mass from top to bottom, even if the pot was 10 ft deep. It's just the nature of growing in pots vs growing in the earth. A very large % of the general rules that apply to growing in the earth DO NOT apply to growing in containers, with the reciprocal also being true.

Also, appropriate pot size is determined primarily by soil choice. It's more critical to be careful about over-potting when using soils with excessive water retention than when using soils that hold little or no perched water. With a high quality soil that holds all of it's water inside of soil particles vs large fractions of water in the spaces between particles, you can plant the tiniest seedling in a 100 gallon container (if that was your wish) w/o experiencing ill effects. The size of the root mass has some effect on pot size, but that effect is pretty much limited to how large the container must be to accommodate the unpruned, untended roots. Root systems that are well maintained can remain very healthy in very small containers and a small fraction of the soil volume needed to accommodate the unmanaged root mass.

For clear advice re what to do about the bugs, you'll need to identify them to us.

Al

Sorry for lack of info. I live in Brooklyn, NY I took the plant out of the pot which was double potted and water was trapped in bottom and the dirt was soaking wet. The roots were rapped around the bottom looking healthy.I emptied the water and the dirt just fell away which allowed me to add new soil I did not water. I will wait for awhile. The leaves are starting to point upward. I thank everyone for there ideas.

How is your plant doing, Reed?

Sorry for the delay in response. I changed the soil, let it dry out and now the plant is doing fine. I'm paying attention not to over water again. Thanks