AMARANTH PESTS ABUNDANCE AND DAMAGE LEVEL CORRELATES TO ENVIRONMENTAL TEMPERATURE REGIMES

Abstract

The grain amaranth, Amaranthus hypochondriacus (L.), is becoming an important crop worldwide due to its nutritional value. Various pests, among them the pigweed beetle, Hypolixus haerens, are the major biotic factors causing low yield of grain amaranth worldwide. It has been reported in the Latin America that the beetle causes high yield loss and plant stem breakage just before grain is harvested. The present study evaluated injury level of both foliar and stem damage pests on eight varieties of A. hypochondriacus, namely KAM 201, Kisii Brown, KSC, Kisii White, KAM 114, KAM 105, KAM 106 and KAM 115 during two seasons of production at Katumani and Kiboko in the low midland regions of Kenya. Both bollworm and leaf miner larvae were found to be the common foliar pests, although they caused no significant (P>0.05) yield loss in A. hypochondriacus varieties at the two sites. Stem tunnel length of beetle H. haerens correlated to environmental temperature where the hotter Kiboko site had highest stem damage. The same hotter Kiboko site of low midlands five (LM5) was drier (43.7 ± 15.9 mm, 28 ± 2°C) than the cooler Katumani zone of low midlands four (LM4), which was relatively wetter (57.1 ± 13.8 mm, 24 ± 2°C). Highly significant (P<0.05) yield resulted in chemical treated plots than in control ones for most varieties. Beetle stem tunnel length inversely correlated with yield of most varieties punctuated by climatic conditions. The stem damage levels at the cooler zone were lower by 35%, 42% and 47% in comparison to those from the hotter zone (LM5). The wetter and cooler zone (LM4) had lower stem damage and subsequently 5-9 times higher grain yield than the hotter zone LM5. In conclusion, considerations of the environmental factors in each agro-ecological zone would lead to right timing of insecticide spray for management of the pests of grain amaranth to prevent yield loss.