The experiments were conducted for three years on ‚€œINSECT PESTS OF CANOLA (BRASSICA SPP.) AND THEIR MANAGEMENT‚€Ě. The role of resistant varieties, impact of predators for the control of aphids, role of insecticides and plant washing with tap water were integrated with the objective to find the impact of these factors on aphid population in Brassica crop. Eight varieties of Brassica juncea (Raya), three Brassica campestris (Sarson) and nine of Brassica napus (Canola) were included in the study (Appendix 1.pag 52). The role of weather factors was also measured by processing the data into simple correlation and multiple linear regression analysis. The results are summarized as under:
B. napus (var. Bubul-98) was found susceptible variety as compare to B. campestris (var. Peeli Sarson).
The varieties ranked in descending order during preliminary screening trial was Bubul-98 > RBN-3057 > RBN-3255 > RBN-03041 > Rain Bow > RBN-03075 > Zafar-2000 > Gobhi Sarson (DGL) > RBN-03033 > Km- 158 > Poorbi Raya> RL-18 > Khanpur Raya > KJ-147 > RBJ-02-19 > RBJ-3031 > RBJ-2050 > KJ-151 > RBJ-3041 > RBJ-02-7 > Bhuri Sarson > Toria > and Peeli Sarson. .
Second week of February provided a suitable environment for the propogation of aphid population (136.47 per 10 cm inflorescence) followed by third week of February (134.33 per 10 cm inflorescence).
The results recorded during 2000-2001 crop season revealed significant difference among dates of observation between aphid species, among Brassica varieties and in their interaction. Lipaphis erysimi (Kalt) (mustard aphid) (Homoptera: Aphididae) was found dominant over Brevicoryne brassicae (Linn.) (Cabbage aphid) (Homoptera: Aphididae).
Bubul 98 found to be a susceptible variety.
Peeli Sarson and Toria (B. juncea) showed maximum population of Coccinella septempunctata (Linn.) (Coleopera; Coccinellidae) whereas Bubul-98 showed maximum individuals of Chrysoperla carnea (Stephen) (Hymenoptera; Braconidae, Aphidiinae) Maximum population of C. septempunctata and C. carnea was observed on. Peeli Sarson and Bulbul-98 respectively on February 26, 2002.
The population of predators on cumulative basis showed positive and significant correlation with the L. erysimi and B. brassicae.
On cumulative basis of both the study years, Bubul-98 (B. napus) showed maximum host plant susceptibility Indices (HPSI) i.e., 20.32 % while Khanpur ray a (B. juncea) showed minimum HPSI i.e., 14.40 %.
The impact of temperature and rainfall on the population of aphid species viz, L. erysimi and B. brassicae was negative but non-significant, whereas relative humidity showed positive and non-significant correlation with both the species individually as well as on cumulative basis. Multiple linear regression analysis showed 60.2 % contribution in population fluctuation of aphids when all the weather factors were computed together.
The role of all the weather factors on the population of C. septempunctata and C. carnea was non significant individually as well as on cumulative basis.
Amongst various insectcides viz., imidachloprid 200SL, acetamiprid 20., SP, carbosulfan 20EC, thiomethoxam 25WP and methomyl(monomyl carbamate) 40 SP @ 370 ml, 198 g, 741 ml, 60 g and 560 g per hectare respectively, methomyl proved to be the most effective resulted in maximum reduction in aphids density at all the post treatment intervals. The effect of different insecticides was equal statistically at 7 days after spray but their longevity was varied with the passage of time.
Various control methods viz., blank spray @ 315 kPa, release of C. septempunctata (50 grubs/plot), C. Carnea (1000 eggs/plot) individually and collectivelly blank spray with release of both predators and spray of methomyl 40SP (@ 560 g/ha) were applied once when population level reached to Economic Threshold Level (ETL). The results revealed that methomyl was the most effective treatment resulting in significantly maximum control of aphids till seven days after treatment followed by the plant washing with tap water with release of both predators. Blank spray with tap water gave satisfactory control of the pest till 48 hours after application but it did not show good control of aphid. The efficiency of the predators when released individually or collectively was increased as the releasing period was prolonged.
Different treatments were applied for the control of aphids resulted in significant increase in plant height, number of branches per plant, number of pods per plant, number of grains per pod and grain yield. Methomyl was significantly better as compared to other treatments and gave 6.00, 28.45, 20.35, 29.48 and 21.23 % increase over control followed by blank spray with release of C. septempunctata and C. carnea together with 4.63, 17.92, 15.71, 17.64 and 12.89 % increase in plant height, number of branches per plant, number of pods per plant, number of grains per pod and grain yield, respectively.
Besides aphids, other insect pests of canola (mentioned on page 7) are minor in southern Punjab Pakistan and need control occasionally. Therefore, emphasis was given to manage the aphids in the present dissertation.