Effects of Sowing Date on Sunflower (Helianthus annuus) Damage by Pachnoda interrupta (Coleoptera: Scarabaeidae) and an Economic Threshold Levels for Its Management at Maiduguri, Sudan Savannah Ecological Zone of Nigeria

Pachnoda interrupta is one of the head-infesting insect pests of sunflower in Maiduguri. Two separate field experiment(one each for sowing date effect and threshold level) were conducted to investigate the influence of sowing date on damage and yield loss by P. interrupta on sunflower and the economic threshold level for its control in Maiduguri. The result for influence of sowing date experiment shows that percentage incidence of infestation was highly significant on sunflower sown on the 5th July than other planting date except that of 26th July. Significantly lower damage was recorded on sunflower sown on 19th July than those on the 5th and grain yield loss was also significantly higher on 26th July sowings than all other dates. The results for economic threshold level experiment indicated that 2.38 and 2.36 beetles/head were the economic threshold level for flowing and milky grain stage respectively and there was a 1:4.9 cost: benefit ratio/ ha. This means that there is a 20% return for every unit of inputs. The result implies that 19th of July is the best planting date to reduce infestations, damage and yield loss from P. interrupta in Maiduguri and artificial control measures should be initiated when there are 1.9 to 2.0 beetles/plant.