There is no specific provision for interest under IGST Act, does this mean interest is not applicable for delay in payment of IGST

No, provision of Section 50 of the CGST Act has been made applicable to IGST Act vide miscellaneous provision contained in section 20 of the IGST Act.

(ICAI FAQ PUBLICATIONS 06-09-2017 TAX PAYMENTS, INTEREST, PENALTY AND OTHER AMOUNTS: FAQ NO. 36)