Seed treatments (a drench after planting, hard and powder coats, as well as priming and planting wet and dry) were tested as cost effective procedures for preventing Striga (witchweed) damage, even in the most heavily infested soils. The use of maize mutants with acetolactate synthase target site resistances available should allow application of the high levels of herbicide needed to effect season-long control. Various salts of imazapyr, a herbicide previously shown to have the least phytotoxicity and the longest persistence, were tested in screenhouse experiments and the magnesium salt proved optimal and was used for most of the field experiments. Two field experiments, one each during the long rains (March-July) and short rains (October- January) were initiated at Kibos in Kenya to determine the optimal formulation and methodology of seed dressing for effective Striga hermonthica control on two maize hybrids with different ALS target site resistances. Seeds were dressed with various rates of magnesium imazapyr and planted when either wet or dry. These treatments were compared with the conventional method of post emergence application, and with drench- dressing of seed in each planting hole with a herbicide solution. Maize seeds treated with imazapyr and planted wet, resulted in significantly reduced plant stand 6 weeks after planting when compared to other treatments, but only during the long rains. Emerged Striga on untreated maize increased from 6 to 12 weeks after planting and started to fall thereafter as maize roots begin to die. There was hardly any Striga emergence for three months after planting on with primed maize seeds even at very low doses. The few Striga plants that emerged and flowered by 12 weeks after planting formed no seed by harvest during both seasons. During the short rains, all treatments except for the controls and hills with 15 g a.i./ha imazapyr application had less than one Striga stalk with flowers and capsules per m2 at 12 weeks after planting. Striga was almost completely suppressed when seed was coated with 30 and 45 g a.i. imazapyr/ha in a commercial fungicide-insecticide seed dust or polyvinyl pyrilidone. Maize seeds treated and planted dry, produced greater maize yield than those planted wet. Seeds treated and planted dry yielded more compared to untreated. Treating seeds with 11 and 14 g. a.i./ha imazapyr and planting them dry, gave 5T/ha, which was 25% higher than the untreated. Applying imazapyr in hills gave higher yield than post emergence application. Since very few Striga plants reach flowering in treated plots, herbicide treatment coupled with other cultural Striga control methods such as hand pulling escapes will go along way in containing and eventually reducing Striga in small scale farms in Africa. Such methods are needed to control Striga in the heavily infested soils of Africa, both as stop-gap until genetic resistance in crops becomes available, and to lower the seed bank levels as most genetic resistance fails at high infestation levels.

Conservation Agriculture Program

English

0103|AL Maize Program|R98-99CIMPU|AGRIS 0102|AJ|3

Jose Juan Caballero

INT2340

CIMMYT Staff Publications Collection