In California they need all the sun they can get.
Trying to grow a lychee in England, especially when winter is coming is tough.
Take your lychee and repot it. Water it heavily once and bag it up with a clear plastic bag, try to create some humidity for it. The longan looks like it will drop all it's leaves but should survive. In terms of stressed out plants, yellow leaves that drop are usually a better sign than dried crispy leaves.
I don't see how the vinegar can hurt the lychee plant.
Wind Burn: The most common and natural reason for the distortion of lychee leaves is none else than Windburn. As your lychee tree flushes new growth, the newly grown leaves are too sensitive and tender to stand the strong wind.
Even a very moderate wind of less than mph can damage these bushfelling.clubted Reading Time: 7 mins. Anthracnose attacks both leaves and fruit of the lychee tree. However, fruit of the lychee variety 'Mauritius' is more susceptible to anthracnose than is the fruit of the 'Brewster' variety.
The lychee fruit is susceptible to anthracnose infection from blossom until the fruit is half-grown. Most of the decay on mature lychee fruit is from latent infection when the fruit is small. Lychee is a tree. The fruit is eaten as a food and used for medicine. People take lychee for cough, fever, pain, to invigorate the body, and to promote urination.
In foods, lychee fruit is peeled.