Predicting crop growth and aphid incidence in Brassica under semi-arid environment

A field experiment was conducted in the sandy loam soils to predict crop gr owth parameters and aphid incidence in Brassica using spectral reflectance and meteorological data. Three Brassica oilseed species, viz 'BO 54' (Brass ica napus L.), 'Pusa Bold' Indian mustard (Brassica juncea L.) and 'T 9' to ria (Brassica campestris L.) were sown on three dates at 14-day intervals s tarting from third week of October to create different photo-thermal enviro nments during crop growth period. The intercepted photosynthetically active radiation and 4 spectral indices, viz (Infra red / red ratio, normalized d ifference, greenness index and brightness index) were derived to correlate plant growth parameters with these indices. The intercepted photosynthetica lly active radiation was found to be well correlated with biomass with the correlation coefficient varying from 0.71 to 0.92 in different cultivars an d sowing dates. It was found from correlation study among different spectra l and plant growth parameters that there was strong relationship (at 5% lev el of significance) between infra red / red ratio, normalized difference an d leaf area index for all the 3 Brassica cultivars. On the other hand, the brightness and greenness indices were more closely correlated (at 5% level of significance) with above ground biomass as compared to infrared / red ra tio and normalized difference. Model regression equations were also derived to forecast aphid incidence in Brassica with most significant weather vari ables. The aphid populations were found to be correlated with maximum tempe rature, minimum temperature and afternoon relative humidity with the correl ation coefficient's varying from 0.67 to 0.90 for different cultivars and s owing dates.