Environmental factor influence on foliar and stem pests of grain amaranth in low midlands agro-ecological zones of Kenya: Correct timing for effective pest management

The pigweed beetle Hypolixus haerens Boheman has been cited as a major insect pest of grain amaranth worldwide. A study to evaluate injury level of both foliar and stem damage pests in Kenya revealed that the stem beetle H. haerens caused higher stem damage in the hotter zone (26-30 ºC) than the cooler zone (22-26 ºC) in the low midlands zones of Kenya. Eight varieties of Amaranthus hypochondriacus (L.) were evaluated during the two seasons study.  The hotter zone of low midlands five (LM5) was drier (43.7 ± 15.9mm) than the cooler zone of low midlands four (LM4) which was relatively wetter (57.1 ± 13.8mm). Beetle stem tunnel length was inversely correlated to yield. The stem damage levels at the cooler zone were lower by 35, 42 and 47% in comparison to those from the hotter zone (LM5). Foliar damage level did not reflect direct grain loss. No variety was found resistant to H. haerens stem injury from the eight accessions evaluated. The wetter and cooler zone (LM4) was found to influence lower stem damage and subsequently 5-9 times higher grain yield than the hotter zone. In conclusion, considerations of the environmental factors in each agro-ecological zone would lead to right time of insecticide spray for management of the pests of grain amaranth to prevent yield loss.