Efficacy of Imazapyr Herbicide Seed Dressing on Maize (Zea mays L.) in the Control of Witchweed [Striga asiatica (L.) Kuntze] and the Evaluation of CIMMYT Imazapyr Resistant Maize Hybrids for Agronomic iv Performance.

Abstract

The parasitic weed Striga asiatica (L.) Kuntze is one of the major constraints in maize production in Zimbabwe. Studies were conducted in the 2010 and 2011 rainy season to evaluate the effects of imazapyr seed dressing on Striga suppression and grain yield at Henderson Research Station, CIMMYT Harare and Muzarabani. Imazapyr was applied at 30 g/25kg of maize seed. A pot experiment was conducted at Henderson Research Station to find the effect of seed dressing with imazapyr on S. asiatica infestation. The experiment was a factorial design with five untreated imazapyr resistant maize lines and five treated lines. The lines used were J437-27, J437-29, J437-30, J450-2, and J450-3. Field experiments were conducted at CIMMYT-Harare and Muzarabani sites to evaluate the imazapyr resistant maize lines for agronomic performance. There were significant differences (P<0.05) among the imazapyr resistant (I.R) maize lines in Striga suppression. The treated hybrids showed suppressive effects of imazapyr on Striga. There were no significant differences among the treated plots due to the delay in Striga emergence. Field trials conducted at CIMMYT showed that if the StrigAway maize is grown in a field not infested with Striga the hybrids will perform to the same standard as other improved maize varieties and the farmer will not have the benefit of imazapyr seed dressing in the absence of Striga infestation. Analysis of variance showed highly significant differences (P<0.05) among the lines. The best performing hybrids were J450-2 and J437-29 with an average yield of 7t/ha while the lowest yielder among the hybrids recorded was J437-30 with an average yield of 5.8t/ha. There was highly significant difference in response to Maize Streak Virus disease infection. The line J450- 2 had the highest MSV score showing it had least resistance to MSV and J437-30 had the lowest MSV score indicating that it is the most tolerant hybrid. The line J437-29 had the least score for grey leaf spot of 1.7 among treated lines while line J450-2 had the least score for grey leaf spot among the untreated lines. Line J437-27 had the least score of 2.5 for leaf rust among the treated lines. The line J450-2 had the least score of 1.2 for ear rot (Sternocapella maydis) among both treated and untreated lines. Overall the results for grain yields and disease infection at CIMMYT-Harare and Muzarabani showed that the lines J450-2 and J450-3 have the best potential and are recommended for further screening in field trials. At Muzarabani, maize grain yield were significantly different among the hybrids at (P<0.05). However J450-3 had a higher yield with the least obtained from treated J437-29 with a yield of 4.5t/ha.