I have income from foreign rental property I own.
I relocated to US in October 2017.
If I report as a resident - do I need to report the whole year foreign property income? or should I report only on the 3 month that i was a US resident?
It depends. If you are a citizen or green card holder then you are always a US resident and all of your worldwide income is reported. For certain citizens living abroad, there is a foreign earned income exclusion, which makes wage and self-employment income not taxable.
Your income from your rental may be considered unearned income as most often rental property is held for investment. Therefore, this investment income is taxable for US residents. Unless, you are in the rental real estate business, then the income may qualify for the exclusion.
If you are a non-resident then you would not be required to report your rental property income earned in a foreign country.