Grain & oil crops - Pearl millet grain yield loss from rust infection

Pearl millet [Pennisetum glaucum (L.) R. Br.] has potential as a feed grain crop in the USA, but acceptance by growers will depend in part on its yield stability. The effects of rust, caused by Puccinia substriata var. indica, on grain yield of the pearl millet hybrid 'Tift 23DA(1)E x Tift 8677' were evaluated at Tifton, GA from 1992 to 1994. Treatments imposed to vary disease severities in 1992 consisted of inoculation, control, and three fungicide applications (chlorothalonil[2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile], 720 @ 0.46 oz/gal [3.6 ml/L]). Treatments in 1993 consisted of a control and one or three fungicide applications. Treatments in 1994 were control, two, four, or seven fungicide applications. Early planting in 1992 resulted in crop maturation during early development of the rust epidemic. Mean final disease severities ranged from 0 to 33%. No differences among treatments for yield or 500 grain weight were detected. Late planting in 1993 was more conducive to rust development, and mean final severities ranged from 36% to 96%. Grain yield and 500 grain weight of the control were reduced by 76% and 41%, respectively, of those yield components measured from plots with three fungicide applications. Protein concentration of grain averaged 10.8% (108 g/kg) and did not differ among treatments in 1993. Rust was severe in 1994 as a result of late planting coupled with frequent rain, and averaged 92% severity in plots receiving seven fungicide applications. Grain protein averaged 23.3% (233 g/kg) in 1994, and increased with rust severity. Indirect yield losses from lodging occurred in 1993 and 1994 when final rust severity exceeded 90%. Regression equations suggest that yield losses occur when disease severity exceeds 50%. Until resistant hybrids are available, grain losses may be avoided by planting the crop by early June.