What IQ does my child have to have in order to have a learning disability?

Not defined by IQ. The concept of a learning disability implies a child has an IQ in a normal range but has a decreased ability to handle a specified learning process compaired to age equivalent kids. This can be weakness in reading, math, memory for sequences, etc.. Individualized test can detect strengths & weaknesses and are the starting point for deciding how to help them. Low IQ implies weakness in everything.
Not related. IQ and learning disabilities are not related. Learning disability refers to a lack of a specific skill. While the subtests of standardized IQ tests such as the WISC-IV may be low and consistent with a particular learning disability, all of the subtests may be in the average range and a child may still have a disability related to reading, math, executive function etc.
IQ Disability. The iq test is the cornerstone of any psychological test battery. Depending on how the psychologist diagnoses learning disorders, usually we look for discrepancies between iq and academic abilities (iq > academics) in order to start thinking about whether a learning disability exists. There is no "cookbook" recipe for doing so.
Average to above avg. Learning disabilities are defined as unexpected difficulties learning in a child with an average to above average iq. A significant discrepancy between iq & achievement scores on standardized tests used to determine eligilibility for "special ed." now it is determined by a student's lack of adequate "response to intervention" when educational help is provided over a specific time.