Can I grow lowquats from seed ? I already have a fruit-bearing lowquat in my yard and have had it for 30 years.
Yes, and this article will help you.
https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-seeds.htm
Treatment I used spectracide fungus control and malithk as well as been oil.
Can you include a photo? This will help me to better identify the issue. I do believe it to be a fungal infection, however, I would like to confirm.
The best, broad spectrum, method that I have found is wettable sulfur and dolomitic lime. This will take care of most tough infection, while keeping the soil free of toxicity.
This article will guide you on the care of Loquat: https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-fruit.htm
Been using malithon, neem oil and a fungus control spray...
This is a fungal infection. If none of those treatments are working, then you will find it difficult to find anything that will. It is likely an incurable infection.
The only thing that you can do is provide the perfect conditions to prolong its life. This article will help: https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-fruit.htm
I am in Central Queensland
It is likely that what you have is not a self fertile variety. Some are, but many require multiple trees to bear fruit.
They will also need annual fertilization to be productive.
This article will help: https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-fruit.htm
About six years ago, I planted two traditional loquat trees that my sister-in-law gave me from her yard. They look beautiful, have grown to about 12' in height BUT still bear no fruit. Why not?
Some some trees are more reluctant to bear fruit than others. If you are concerned about them, add fertilizers high in phosphorus and potassium to it. This article will help: https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-fruit.htm
Maybe my loquat tree doesn't get enough sun. We just had a big rain - it looks worse today. Is there some way I can save it?
It appears that the loquat foliage is completely browned out, and that is a dire sign. It is most likely due to water deficit during previous drought period. Or other negative factors, recent transplanting, root disturbance, gopher damage herbicide poisoning?
If due to drought stress, there is slight possibility that the rain, followed up with a watering program during dry periods, will allow it to revive. Give it a month to respond.
My loquat tree has been flowering but not bearing fruits. I only have one tree. Would I need another to help pollinate it to fruit?
Some cultivars are self-fertile, while other are not. This would depend on what you have. Another factor would be if the tree was seed grown, or bought as a grafted tree. If it is seed grown, then its fruit will not be like the parent tree's.
My guess is that you have a variety that is not self fertile. You may have to have a second tree. This article will be helpful: https://www.gardeningknowhow.com/edible/fruits/loquat/growing-loquat-fruit.htm