Effect of Sowing Dates and Nitrogen Levels on Popula-tion of Okra Jassids (Amrasca biguttula biguttula Ishida)

Abstract

Okra (Abelmoschus esculentus L. (Moench) is one of the most important vegetable crops grown in Nepal. The crop is susceptible to various insect pests of which jassids (Amrasca biguttula biguttula Ishida.) is most predominant which reduces production and deteriorates seed quality of okra. A field study was conducted at Horticulture Farm, Agriculture and Forestry University, Rampur, Chitwan, Nepal to elucidate the effect of sowing date and nitrogen levels on the population and damage of jassids from April to September 2018. Three levels of nitrogen (100, 200 and 300 kg N ha-1) and five sowing dates (8th April, 20th April, 2nd May, 14th May and 26th May, 2018) were evaluated in randomized complete block design with three replications. Results indicated that the highest damage score was recorded in okra which was sown on 8th April (2.39) followed by 20th April (2.31) and 2nd May (1.26). The highest damage score of jassids was obtained with the use of nitrogen at the rate of 200 kg ha-1 (1.94) followed by 300 kg/ha (1.72) and 100 kg ha-1 (1.54). Mean population of jassids was maximum with okra sown on 20th April (29.91) and minimum with okra sown on 26th May (6.95). This study showed that late planting i.e. 26th May and applying low level of nitrogen i.e. 100 kg N ha- 1is an effective approach for reducing the jassids population and its damage in okra.

Impact of Nitrogen Levels and Planting Density on the Growth and Yield of Okra (Abelmoschus esculentus L. Moench)

“…Muenoke and Asiegbu, (1996) reported decreased pod yield per plant and yield components as population increased. Maximum fruit length, fruit weight, fruit number and yield per plant of the most extensive ranges have been recorded by various researchers (Singh, 1990;Weiner, 1990;Muenoke and Asiegbu, 1996;Ali, 1999;Anjum and Amjad, 1999;Olasantan, 2001;Kabura et al, 2002;Muenoke and Asiegbu, 2003;Manga and Mohammed, 2006;Salau and Makinde, 2015;Khanal at al., 2020;Adekya at al., 2020;Regmi et al, 2020;Verma et al, 2020). Increasing plant population may result in growth and yield decrease per plant due to inter-and intraspecific plant competition.…”

“…Nitrogen, phosphorus and potassium fertilizer applications increases vegetative growth, yield and quality characteristics (Verma et al, 1970;Singh, 1979;Hooda et al, 1980;Mani and Ramanathan, 1980;Fatokun and Chheda, 1981;Sherestha, 1983;Majanbu et al, 1985;Mishra and Pandy, 1987;Abusaleha and Shanmugavelu, 1988;Arora et al, 1991;Faraq and Damrany, 1994;Fondane and Bhatia, 1995;Haque and Jakhro, 1996;Katung et al, 1996;Anjum and Amjad, 1999;Khan et al, 2000;Amjad et al, 2002;Kabura et al, 2002;Mouneke and Asiegbu, 2003;Manga and Mohammed, 2006;Rahman and Akter, 2012: Khanal at al., 2020, Adekya at al., 2020, Regmi et al, 2020, Verma et al, 2020. Also, several researchers have reported linear increase in green pod yield of okra with the application of N from 56 to 150 kg/ha (Majanbu et al, 1985;Singh, 1995: Khanal at al., 2020Adekya at al., 2020, Regmi et al, 2020Verma et al, 2020). Firoz (2009) reported that the highest yield (16.73 t ha -1 ) was obtained after the application of 100 kg N ha -1 which was statistically identical to 120 kg N ha -1 .…”