P&PDL Picture of the Week for
January 17, 2011

White Mold of Tomatoes

Dan Egel, Extension Plant Pathologist, Southwestern Purdue Agricultural Center, Purdue University

This disease can affect tomatoes anywhere they are grown, however, white mold is especially common where tomatoes are grown year after year in a greenhouse or high tunnel.  The first symptom that tomato growers will likely notice is that affected plants will begin to wilt (Figure 1).  Upon closer inspection, the stem of the plant has become ‘woody’ (the disease is sometimes known as timber rot) and irregular, hard, black structures about the size of a pea are seen outside or inside the stem (Figure 2). 

White mold prefers cool weather, perhaps explaining why the disease often affects tomatoes grown in a greenhouse during the cool portion of the year.  Infection begins when the fungal spores arrive on the dead or dying petals of a tomato flower.  Under the proper conditions, the fungus will then grow into the tomato plant and cause a stem lesion and perhaps fruit infection.  It is the stem lesion that may cause the entire plant to wilt. 

There is no host resistance to white mold of tomato.  Growers should prune tomatoes to encourage good air circulation, a factor that will slow white mold infection.  The white mold fungus may cause disease on a great number of hosts, but growers should especially avoid rotations with tomato, peppers, potato and snap beans.  Commercial growers should consult the Midwest Vegetable Production Guide for Commercial Growers 2011 for more information including a biological control for this disease. 

Click image to enlarge

Wilt on tomato plant

Figure 1

Closeup of white mold on tomato stem

Figure 2

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service