The cool, wet weather this past week has forced many to put transplanting on hold. As a result many transplants have been kept in greenhouses that have been tightly closed up. Unfortunately, closed greenhouses retain heat and humidity which can spell problems if left unchecked.
Remember, high relative humidity equals wet leaves which favor the development of fungal diseases such as Botrytis or bacterial diseases such as bacterial leaf spot. To avoid potential problems, do your best to vent out as much humidity as possible in the late afternoon and/or early morning. Turn on circular fans to promote air movement and finish watering earlier enough in the day so leaves have enough time to dry out before nightfall.
As a side note, stressed transplants where water and/or fertility have been withheld are also more prone to disease development. A light fertilizer application may go a long way in improving transplant health before setting in the field.