If the cost of the mosquito control program for any year exceeds the estimated cost and if the program funds become exhausted, then the board of supervisors may transfer from the general county fund, sufficient money to complete the program for such year. Such board may borrow money for such purpose by issuance of its note, said note and interest thereon to be paid on or before April 15th of the following year, and such board may levy a tax on the taxable property in the county sufficient to produce funds to pay said note and interest thereon.