Symptoms and Signs
Cut out, or more correctly 'early-cut out', is when a large percentage of plants senesce and die after the first flush of pods, usually beginning about 80 days after planting. The most common aboveground symptoms are early leaf senescence and defoliation. No new leaves or blooms occur at the buds, which may turn brown and abort.
Comments on the Disease
Cut out should be considered a complex of symptoms rather than a specific disease. It can be caused by pathogens, a physiological response, or both. It eliminates the possibility of continued pod production, thereby shortening the season and potentially reducing yields by about 15 or more cwt (hundredweight) per acre. A combination of a strong first set, bean variety, soil pathogens, and environmental factors seem to trigger the expression of cut out.
The soil pathogens F. oxysporum f. sp. tracheiphilum (Fusarium wilt), F. solani (Fusarium root rot), or Thielaviopsis basicola may cause early senescence (aging and deterioration) of beans. Infections by these pathogens can be differentiated by symptoms. Fusarium wilt causes discoloration in the vascular system that extends from the roots into the aboveground stems and petioles. Fusarium solani causes rust-colored lesions on roots. Thielaviopsis root lesions are dark brown-black. Other pathogens that occur less frequently on roots of plants exhibiting early cut out are Macrophomina phaseolina, and Phytophthora drechsleri.
Cut out appears to be more severe in fields with soil compaction or water stress (too much or too little), especially during times of reproductive growth. In fields where cut out was known to be caused by Fusarium wilt, choose a wilt-resistant variety. If cut out is caused by F. solani or Thielaviopsis, crop rotation may help prevent the increase of these pathogens in the soil.