Corry Evans had bundled in a debut goal for the Tigers after 51 minutes following Harte's mix-up with goalkeeper Adam Federici.
But the former Leeds defender made up for his error on 80 minutes, slamming home the spot-kick after Tigers keeper Brad Guzan brought down Shane Long.
Pearson said "It was an ugly game and for whatever reason today collectively we didn't perform. In the first half we laboured and it's hard to put your finger on why.
"At half-time we made a change and dealt with the conditions and their style much better.
"It was disappointing to concede the penalty but if I am honest it was a fair result. It would be wrong of me to suggest Reading didn't deserve something from it."