A public notice said the emergency temporary closure will be from 8pm to 5.30am and will last for a maximum of 21 days.
It is anticipated the roadworks will be finished on Monday (January 31).
The public notice said: “The road closure is required for the safety of the public and workforce while West Sussex County Council undertakes Overnight Road Closure from the junctions with London Road to Brighton Road to undertake removal of ash dieback.”
“Access for emergency service vehicles and pedestrians will be maintained at all times during the closure,” it added.
An alternative route will be signposted at the site but people can also visit one.network for more details.
For more information about the closure ring 01243 642105.