PREVALENCE AND MANAGEMENT OF STRIGA (Striga hermonthica L.) AND ITS EFFECT ON PRODUCTIVITY OF SORGHUM [Sorghum bicolor (L.) Moench] IN EASTERN ETHIOPIA

Abstract

Sorghum grows in a wide range of agro-ecologies most importantly in the drought prone areas and is the main staple food crop in eastern Ethiopia. However, Striga hermonthica is the major constraint to sorghum production in the Striga-stricken or invaded areas. Thus, this research was conducted with the specific objectives to: (1) investigate the prevalence and socio economic impact of Striga infestation in sorghum growing areas; (2) evaluate the effect of moisture conservation practices and cowpea intercropping with sorghum in reducing the infestation of Striga and increasing sorghum yield; (3) determine the effect of legumes intercropping and double cropping on Striga infestation, yield and yield related traits of sorghum; and (4) evaluate the combined effect of mineral NPS blended fertilizers and common bean intercropping on Striga infestation and the yield and yield components of sorghum in Hararghe, eastern Ethiopia. The field survey was conducted in six districts (Babile, Darolabu, Fedis, Gemechis, Habro and Kurfachalle) in 2019 and experiments were conducted during the 2019 and 2020 main cropping seasons. Random sampling was employed to collect the field and socio-economic data during the field survey. The experimental treatments were laid out in a randomized complete block design in factorial arrangement. Data on Striga counts per plot and per plant, awareness and impression of farmers, prevalence, management used, severity, sorghum growth and development parameters, Striga height, Striga capsule per plant, Striga biomass, and legumes development parameters were collected. The data were analyzed using IBM SPSS software version 20, SAS software version 9.0 and R-software version Rx64 4.1. The survey results showed that two Striga species, namely Striga hermonthica and Striga asiatica, were observed. However, Striga hermonthica was more prevalent than Striga asiatica in all the surveyed locations, and its occurrence differed among locations. The maximum level of Striga hermonthica occurrence was recorded at Kile-Bisidimo (92% Striga per m2 ), and less level of Striga occurrence was recorded at Homacho dayo (23% Striga per m2 ) in the assessed fields. Striga hermonthica resulted in an estimated yield reduction of 0 to 80% in the surveyed areas. This causes higher economic loss and incurs social instability in the region. The analysis of variance in experimental results showed the percentage of reduction in Striga infestation and XX yield increases highly and significantly differed among treatments (p≤0.001).The highest (4.1 t ha-1 ) yield of sorghum and the highest (90.3%) Striga reductions were obtained by use of tied ridges and cowpea intercropping between rows. The lowest (1.4 t ha-1 ) sorghum yield was obtained from the sole susceptible sorghum variety (Teshale) in the flat control plot with a high (80%) Striga infestation percentage.The intercropping of sorghum with cowpea significantly reduced Striga infestation by 73.9% as compared to sole planted sorghum (control). The highest (16 Striga plants per plot) mean number of Striga count per plot occurred in the control plot. The lowest (6 Striga per plot) number of Striga count was recorded from simultaneous cropping of sorghum-cowpea in single alternate row arrangements. The analysis of the data showed that the highest (3 t ha-1 ) sorghum yield and maximum (2262%) marginal rate of return was obtained from single alternate row arrangement of sorghum-cowpea in simultaneous intercropping. The study also confirmed that sorghum yield increased by 35.7% over the sole planted sorghum. The lowest (1) Striga count per plant and the lowest (2) per plot were also obtained from the combination of 50% common bean planted density and 100 kg NPS ha-1 blended fertilizer application, whereas the highest (5) Striga count per plant and highest (8) per plot were recorded from the sole planted susceptible sorghum variety (Teshale). Thus, the NPS fertilizer and common bean combination reduced Striga hermonthica infestation by 60%, supporting the host crop (sorghum). The highest (2.54 t ha-1 ) grain yield of sorghum was obtained from the combination of 50% common bean planted density and 100 kg NPS ha-1 blended fertilizer application, while the lowest (0.98 t ha-1 ) grain yield was recorded from the control plot. From this study, it could be concluded that Striga hermonthica is easily disseminated by different dispersal mechanisms and the major constraint of sorghum production. In low and inconsistent rainfall areas, moisture conservation, legumes intercropping and NPS blended fertilizer were essential for Striga management. The land equivalent ratio and the economic analysis of the system showed intercropping sorghum with legume crops contributed to yield advantage and land use efficiency. Therefore, it can be recommended that integrated management options be employed to reduce Striga infestation and maximize sorghum yield on sustainable basis.