David Owens, Extension Entomologist, owensd@udel.edu
Congratulations to Grier Stayton for guessing this week’s challenge as a Fusarium stalk rot pathogen. Due to an oversight on my part, the online submission form still had the previous week’s Dectes photo up, so everyone who entered a Dectes answer will also be included in the end of season raffle.
From Dr. Alyssa Koehler:
Stalk rots have been quite widespread this season. There are multiple pathogens that can cause stalk rots. Giberella stalk rot is caused by the fungus Giberella zeae, also known by its asexual name, Fusarium gramineraum, that causes Fusarium Head Blight in wheat. (In older naming systems, many fungi have two names for different stages of their life cycle). Plants with Giberella stalk rot have a shredded pith, often with pink to red discoloration, and it is common for infected stalks to die prematurely. We have seen a number of plants over the past month with accelerated senescence due to various stalk rots (Figure 2). As you are riding in the combine, these are now often the lodged plants with snapped out tops. Giberella stalk rot can be separated from other stalk rots by the black specks called perithecia that form at the base of the plant (Figures 3 and 4). These specks house spores of the fungus and will overwinter in residue to be a source of inoculum for future corn and wheat crops. These structures are not embedded in tissue and can be easily removed with a fingernail. Red root rot is another disease common in our region that can cause red/pink stalk and root discoloration. Red root rot is caused by a different fungus, Phoma terrestris, that does not make perithecia.
Figure 1. Corn affected by stalk rot
Figure 2. Corn plant with accelerated senescence due to stalk rot
Figure 3. Perithecia at the base of a corn plant with Giberella Stalk Rot
Figure 4. Zoom in from last week’s Guess the Pest! image (Fig. 3), black structures (perithecia) at the base of a corn plant with Giberella Stalk Rot.