Abstract

The parasitic weed species Striga asiatica (L.) Kuntze is one of the major constraints in maize production in Malawi. The effects of metalachlor (as Dual^TMMagnum 960 EC), a pre-emergence herbicide, with 69N:21:P₂O₅:4S kg ha^-1 and without fertilizer application, on maize growth and Striga suppression, were investigated at 5 sites in 2000/’01 season and 6 sites in 2001/’02. The use of metalachlor at 2.2 kg ha^-1 gave no considerable phytotoxic effects on maize plants. Application of metalachlor significantly suppressed Striga emergence across all sites in 200/’01 and not in 2001/’02. Metalachlor application increased yields from 1448 to 1793 kg ha^-1 in 2000/’01, and from 1677 to 2077 kg ha^-1 in 2001/’02. On the overall, the use of fertilizer was superior to herbicide use in increasing maize yields. Yields were generally low as, in most cases, sites withStriga are low in productivity. Due to this association between poor site productivity and Striga, an integrated approach which tackles both problems is suggested. For example, rotation with legumes is strongly recommended not only to reduce Strigaseeds in the soil, but to improve fertility. The increased productivity in subsequent years would then allow sufficient yields to cover other inputs such as herbicides, fertilizer and improved seed.

Key words:  Witchweed, Zea mays L., metalachlor, on-farm fertilizer responses.