Full Length Research Paper

Imazapyr (herbicide) seed dressing increases yield, suppresses Striga asiatica and has seed depletion role in maize (Zea mays L.) in Malawi

V. H. Kabambe^1,3*, F. Kanampiu² and A. Ngwira¹

¹Chitedze Research Station, P.O. Box 158, Lilongwe, Malawi.

²CIMMYT, P.O. Box 25171, Nairobi, Kenya.

³Bunda College of Agriculture, P. O. Box 219, Lilongwe, Malawi.

*Corresponding author. E-mail: kabambev@yahoo.com.

Accepted 11 July, 2008

The parasitic weed species, Striga asiatica (L.) Kuntze, also known as witchweed, is one of the major constraints in maize production in Malawi. Most of the control measures do not protect a current crop from damage. In 1998/99 season, a trial was initiated at Chitedze Research Station under artificial infection, to evaluate the effects of seed dressing with imazapyr (an acetolactate synthase {ALS} inhibiting herbicide) using three seed treatment methods (coating, priming or drenching) and three herbicide rates (15, 30 and 45 g active ingredient ha^-1) on  S. asiatica suppression, maize growth and yield. The maize hybrid IntA/IntB//Pioneer325irMZ98F2, bearing target site resistance to imazapyr (IR maize), was used as test crop. In the subsequent season, normal or non-IR maize was planted on the same plots of 1998/99, to assess the residual or spill-over effects on Striga emergence, maize growth and yield. In the first season, results showed that imazapyr seed dressing suppressed (P < 0.05) Striga emergence to < 1.0 plant m^-2, compared to 4.8 plants m^-2 in untreated plots at 69 days after planting (DAP). At 86 DAP, use of imazapyr suppressed (P < 0.05) Striga emergence to  > 6.7 plants m^-2 compared to 14.7 plants m^-2 in untreated control. At 106 DAP, the number of Striga that flowered in untreated plots was 6.2 plants m^-2, compared to < 1.0 in all treated plots. The use of imazapyr gave   no significant (P > 0.05) yield differences. In the subsequent season, imazapyr treatments gave no residual or spill-over effects on maize growth and yield (P > 0.05. There were significant (P < 0.05) effects on Striga emergence similar to the first season. The results therefore suggest that the use of ALS inhibiting herbicides not only suppresses Striga emergence, but also has a seed depletion role in integrated management of Striga without any spill-over or, herbicide injury in subsequent unprotected maize. This technology would be simple for farmers to adopt.

Key words: Witchweed, imidazolinone, Zea mays (L.), imazapyr rates, seed dressing.