White mold, or lettuce drop, caused by Sclerotinia sclerotiorum, can cause serious losses in lettuce and other susceptible crops if left uncontrolled. Disease development is favored by wet, humid conditions (especially in high tunnels and fields) with known histories of the disease.

White mold on lettuce. Notice the white fungal growth and black sclerotia developing on the base of the stem. The sclerotia can survive in the soil for up to 10 years.