Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2002
Publication Date: N/A
Interpretive Summary: Sorgum ergot, a new fungal disease in the United States causes major losses in yield and grain quality, especially in hybrid seed production fields. As a result, it is important to develop good and cost-effective means of controlling the disease. One of the methods for controlling sorghum ergot is the use of fungicides. At present, Tilt is the fungicide registered for use in the United States. However, this fungicide could be less effective if it is used continuously. Therefore, we tested 14 fungicides to see if they could prevent the reproductive units (called spores) from germinating, and also to see how effective these fungicides are in preventing the fungus from growing in the sorghum plant. Our studies have shown that most of the fungicides (Penncozeb, Manzate, Topsin M, Tilt, and Flint) could prevent most of the spores from germinating; however, only few fungicides Tilt, Folicur, Bayleton, and Quadris were effective in preventing the fungus from growing on the sorghum head. These studies have demonstrated that farmers might be able to use different fungicides in the future to protect their sorghum crops from this disease. In addition, by using different fungicides in rotation with Tilt, we can avoid any resistance development in the fungus. This in turn will lead to higher sorghum yields and profits for growers in the United States.
Technical Abstract: Commericial formulations of 14 fungicides representing seven chemical classes were assessed in vitro and in vivo for activity against Claviceps africana, causal agent of sorghum ergot. All the fungicides markedly reduced spore germination in vitro on water agar, with EC50 values (based on active ingredient) that ranged from <0.04 ug ml**-1 for Penncozeb, Manzate, Topsin M, Tilt, and Flint, to 0.60 ug ml**-1 for Nova. Fungicides were tested on plants by spraying them on flowering panicles of a male-sterile line, ATx623, and then spraying panicles with a suspension of conidia immediately following drying of the fungicide. In greenhouse trials and in the 2000 field evaluation, a single application of Tilt, Folicur, Bayleton, Nova or Quadris at a rate of 25 ug ml**-1 suppressed ergot by 91-100%. In the 2001 field evaluation, Folicur, Tilt, and Quadris provided 97, 74, and 60% ergot control, respectively. Ergot control was greater when fungicides were applied at a rate of 25 ug ml**-1 than at a rate of 5 ug ml**-1. Generally, the triazole and strobilurin classes of fungicide were more effective in controlling ergot than other classes. At the two rates used in this study, the duration of protection using a single application was short. In general, ergot severity increased between 7 and 10 d after inoculation. These results showed that in vitro fungicide screening by measuring spore germination inhibition was not a good predictor of performance in the field. Results from the field trials suggest that control, particularly under high disease pressure, requires either higher fungicide rates or multiple applications.