Careful cultural management of field crops has become imperative in countries where chemical measures are not economically feasible. The occurrence of the endemic parasitic witchweed [Striga hermonthica (Del.) Benth] in production fields of sorghum-sundangrass hybrid [Sorghum bicolor (L.) Moench X S. sudanense Stapf. cv. Piper], Pioneer brand hybrid 988 (coded P988), is one example that requires such procedures. Study objectives were to relate: (i) P988 seed size (large and small) to witchweed germination, P988 root and shoot length, and weight and (ii) P988 seed size and harvest growth stage to P988 greenchop yield and sucrose content at three initial and subsequent P988 harvests at boot stage, late bloom stage, and maturity in witchweed-infested fields. Seedlings of P988 grown from small seed had significantly shorter shoots but longer roots compared to those from large seed. Witchweed germination was not signficiantly affected by seed size of P988 but was postively correlated to P988 root length and root dry weight. Seed size of P988 had no significant effect on forage greenchop yield and forage sucrose of P988 at all harvests. Delaying initial harvest of P988 increased witchweed shoot dry weight with time and equated total yields, but reduced the quality of greenchop at late bloom and maturity. Delaying second and third harvests of P988 to maturity significantly increased greenchop yield of P988. Forage sucrose at maturity stage of second and third harvests exceeded forage sucrose at maturity of first harvest by 106 and 60%, respectively. Witchweed shoot dry weight was positively correlated with forage sucrose of P988. Growing small seeded P988 reduced witchweed incidence and sustained P988 yields when combined with harvesting at the boot stage on first harvest and at maturity of later harvests on witchweed-infested soils.
