Influence of different dates of sowing on incidence of virus diseases of French bean.
French bean crop sown on 5th Sept. recorded lowest Bean common mosaic virus (BCMV) and Bean yellow mosaic virus (BYMV) disease incidences of 5.4 and 27.93 per cent, respectively. A relatively higher disease incidence of BCMV (7.3%) and BYMV (28.57%) was recorded in the crop sown on 20th Sept. The initial disease symptoms of BCMV and BYMV were observed within 7 and 28 days after sowing, respectively, under all the six sowing dates starting from 5th to 19th Nov. Aphid vector population build up in the crop sown early i.e., 5th Sept. was rather slow and maximum population of aphid (3.2) was recorded after 70 days when the crop reached almost maturity stage. As the sowing was delayed beyond 5th Sept. population build up was very rapid. Aphid vector population was found to be negatively correlated with maximum temperature when the crop was sown on 5th Sept. Also, aphid vector population was found to be negatively correlated with minimum temperature when the crop was sown on 20th Sept., 5th, 20th Oct 4th, 19th Nov. Correlation between incidence of BCMV and BYMV diseases with aphid vector population was found to be positively correlated for all six dates of sowing.