Our vineyards are currently being sprayed with CuSO4 (Copper Sulphate), while the grapes are still pea-sized. This is done before the grapes become too big and the bunches become too 'tight'. Copper Sulphate prevents fungal growth on the inside of the bunch, therefore preventing the inner grapes of the bunch from rotting. This time of the year, after each rainfall, when it starts heating up again, powdery mildew can become a problem, so we normally spray after rain as a preventative measure.