IDT has found that a significant amount of primers with hetero- or homo-dimers with a Delta G value of -9 kcal/mole can cause problems in your PCR reaction. This value is mainly a guideline to use when designing PCR primers. Ideally the Delta G values for your primers are more positive than -9 kca/mole, however it is not guaranteed that you will experience problems for primers with Delta G values more negative than this.
Essentially the more negative the Delta G value of a secondary structure, the more likely it is that you will experience problems with your PCR assay.
The maximum delta g refers to the energy needed to break apart a fully complementary set of oligos. The delta g values above each self-dimer refers to the amount of energy needed to break apart that particular self dimer. If the delta g for the self dimer is more negative than -9kcal/mol, or if it is more than 10-30% of the maximum delta g, you should consider redesigning the oligo because the self dimer could interfere with your reaction.
IDT