this my 1st time to plant a lemon tree , ive planted it since May

it grows well until the last month ive noticed that older leaves had yellow dry edges

leaves came wavy and curly , and last week ive seen some black spots on new leaf

also there are some springtails in the soil

i live in coastal city in saudi arabia

temp : appox. 40°C

humidity : 50-70%

watering every 3 days (watering can)

62 leaves

70 cm

full sun with green net cover

media : peatmoss

covered the soil with dead cucomber vines to retain moisture in the soil since our sunlight is too strong

it seems unhealthy :(

Diseases , causes & cures ?

-sorry for my poor english-