GRAIN AND 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 o n its yield stability. The effects of rust, caused by Puccinia substri ata 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. Treat ments imposed to vary disease severities in 1992 consisted of inoculat ion, control, and three fungicide applications il[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 appli cations. Early planting in 1992 resulted in crop maturation during ear ly development of the rust epidemic. Mean final disease severities ran ged from 0 to 33%. No differences among treatments for yield or 500 gr ain weight were detected. Late planting in 1993 was more conducive to rust development, and mean final severities ranged from 36% to 96%. Gr ain 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 rai n, and averaged 92% severity in plots receiving seven fungicide applic ations. Grain protein averaged 23.3% (233 g/kg) in 1994, and increased with rust severity. Indirect yield losses from lodging occurred in 19 93 and 1994 when final rust severity exceeded 90%. Regression equation s suggest that yield losses occur when disease severity exceeds 50%. U ntil resistant hybrids are available, grain losses may be avoided by p lanting the crop by early June.