Witchweed Management by Sorghum‐Sudangrass Seed Size and Stage of Harvest

Abstract

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 ✕ 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.

Push-Pull: Chemical Ecology-Based Integrated Pest Management Technology

“…Striga infests >40 % of arable land in SSA (Lagoke et al 1991) and causes yield losses of up to 100 %. Striga is so ingeniously adapted to its environment and host plants (Bebawi and Metwali 1991) that it will germinate only in response to specific chemical cues present in host root ex-udates or certain non-host plants (Parker and Riches 1993;Yoder 1999). Seeds can remain dormant but viable in the soil for >10 years.…”

Assessment of Different Legumes for the Control of Striga hermonthica in Maize and Sorghum

“…Striga weakens the host, wounding its outer root tissues and absorbing its supply of moisture, photosynthates, and minerals (Tenebe and Kamara, 2002), and is so ingeniously adapted to its environment (Bebawi and Metwali, 1991) and integrated with the host that it will only germinate in response to specific chemical cues present in root exudates of its hosts or certain nonhost plants (Yoder, 1999; Parker and Riches, 1993). It also causes “phytotoxic” effects within days of attachment to its hosts (Frost et al, 1997; Gurney et al, 1999), whose underlying mechanism has not yet been elucidated (Gurney et al, 2006).…”

Influence of annual forages on weed dynamics in a cropping system

“…For example, sorghum-sudangrass (Sorghum bicolor [L.] Moench × Sorghum sudanese [Piper] Stapf) has been reported to control johnsongrass (Sorghum halepense [L.] Pers.) (Forney et al 1985) and witchweed (Striga hermonthica [Del] Benth) (Bebawi and Mutwali 1991). Siemens (1963), in a summary of a long-term crop rotation study at Indian Head, SK, indicated that a 1-yr green manure crop in a 3-yr rotation reduced wild oat dockage in spring wheat grain crops relative to continuous wheat or wheat-fallow systems.…”