The effect of imazapyr - resistant maize (Zea mays L.) plant density under bean intercrop on witchweed (Striga hermonthiea (Del.) Benth), maize and bean yield

Abstract

Maize (Zea mays L.) is one of the most important crops in East Africa serving both as a staple food and cash crop to millions of people. As a vegetable, it is produced either as green maize cobs, sweet com or baby com. Maize yields under farmers' conditions especially in the Lake Victoria Basin average 1.3 t ha-1 which is less than 25% of the potential yield. This is attributed to several factors; the greatest be"-i'ng Striga (Striga hermonthica) which is a parasitic weed attacking several crops in the grass family. A medium term technological breakthrough in form of a herbicide (imazapyr) resistant maize variety could help reduce seedbank in the soil. The main objective was to evaluate .the seasonal performance of imazapyr-resistant (IR) maize at different plant densities under bean intercrop on Striga weed and crop growth. The study was conducted for two seasons on a Striga-free field at Maseno University and on a Striga infested farmer's field in Maseno Division of Kisumu West District. The experiment was laid out as a Split plot design in three replicates with maize variety as the main plot factor at three levels (treated IR maize, untreated IR maize and WH505/H516 as commercial check varieties) and maize density as the sub-plot factor at three levels (44,444 plants ha-1, 66,666 plants ha·1 and 88,888 plants ha"). Data was collected on Striga seed count, days to first Striga emergence, crop stand, Striga incidence, Striga biomass, days to 50% flowering of the crop, crop biomass, and finally on maize and bean yield components. Data was subjected to Analysis of Variance (ANOV A) at 5% using SAS computer software to test for significant differences between treatments and means separated using the Least Significant Difference (LSD). The effect of IR maize plant density on Striga seed bank was not established due to the plot sizes which could not withstand Striga seed invasion from external sources. Treated IR maize delayed Striga attachment on maize thus . suppressing Striga parasitism and any late Striga attachments had little or no parasitic effect. Increasing the plant density of treated IR maize up to 88,888 plants ha-1 led to an increase in maize yield up to 3.48 t ha-1 and this high density can still be intercropped with two rows of beans between the maize rows translating into increased returns per unit area. Treated IR maize should be planted in Striga infested fields at 75cm x 15cm with two rows of bean intercrop 15cm away from the maize rows spaced at 45cm x 15cm.