until the lawn dries out and actually by that it is the soil beneath the lawn, grass roots and crowns can decline, decay and rot without a lot anyone can do. plants can for a brief period stand having the soil saturated, but without oxygen in the soil, functions within the plant begin to fail. Tomatoes suffer from several foliar diseases besides the rots that can occur below the soil line. Use disease resistant varieties, plant on a slightly soils or raised beds to avoid the moisture.