Studies on Phenology, Germination Ecology and Control of Some Important Weeds of Wheat

Abstract

Phenology: 1. Studies on various phenological events viz., germination, span of vegetative growth, flowering, fruit formation, seed dispersal and seed dormancy of life cycles of nine weed species from irrigated wheat fields of Lahore and six weed species from rain-fed (barani) wheat fields of village Maldeo-Dina, District Jhelum were carried out. 2. Initiation of germination and span of germination period is highly variable in different weeds. Amongst weeds of irrigated wheat fields germination in Convolvulus arvensis, Medicago, denticulate, Melilotus parviflora, Fumaria indica, and Senebiera didyma starts by the middle of October while in the case of Phalaris minor, Lathyrus aphaca, Chenopodium album and Anagallis arvensis, it is initiated by the middle of November. In all the cases germination is completed around mid-January. 3. Amongst weeds of barani wheat fields, Convolvulus arvensis and Asphodelus tenufolius start germination in early October, Fumaria indica and Vicia sativa in November, Anagallis arvensis in early December while it is delayed till early February in the case of Trigonella Polycerate. By the end of December germination is complete in all the above weeds of barani wheat fields except A. arvensis and T. polycerate where it is completed in January and March respectively. In general, weeds of irrigated wheat fields show maximum germination during December while those of barani except A. arvensis and T. polycerate during November. 4. Durations of various phenological events in the life cycles of different weeds are highly variable and show a great deal of overlapping, i.e., flowering in some individual of a weed population may start while majority of its individuals are still in vegetative phase. Maximum overlapping was seen in flowering, fruit formation and seed dispersal phases. Span of vegetative growth is longest in the case of C. arvensis and shortest in A. arvensis and F. indica especially under barani conditions. 5. In majority of the weed’s dispersal of their seeds after fruit ripening may start late in March and is completed by the end of April. In certain cases, like A. tenuifolias, P. minor, L. aphasa and C. arvensis it may continue till early May. However, in F. indica seed dispersal is complete even in early March in barani and mid-March in irrigated Wheat fields. 6. Of all the weeds T. Polucerata has the shortest life cycle completing it only in three months while A. tenuifolius, C. arvensis, M. denticulate and M. parviflora have logest life cycle extending over 61/2 months. Other weeds fall in between these two extremes. However, seed dormancy period is longest in T. polycerate as compared to other weeds. Climatic data: 7. To correlate phenological events of life cycles of various weeds with prevailing environmental conditions, climatic data of irrigated (Lahore) and barani (Jhelum) areas of Punjab was compiled. While the general trends of the various climatic factors in both the areas are similar throughout the year; in barani area weekly mean minimum temperature is constantly lower throughout the year, winter days relatively shorter and summer days longer and total monthly rainfall from October to May much higher as compared to their corresponding irrigated counterparts. Response to thermoperiodicity: 8. Germination response to thermoperiodicity was studies at two sets of alternating temperatures i.e., 20/5OC and 25/10OC. High temperature were maintained during light and low during dark periods. In P. Minor, L. aphaca and A. tenuifolius germination in 25/10OC thermoperiodic treatment was not only faster but also relatively higher than their respective 20/5OC counterparts. Furthermore, in 20/5OC thermoperiodic treatment, proportion of incomplete germination (only radicle emergence) was also relatively higher. On the other hand, in the case of M. denticulate, M. Parviflora, and C. arvensis germination was favored by 20/5OC thermoperiodic treatment. In the case of M. denticulate and M. parviflora 25/10OC temperature combination caused great reduction in germination percentage whereas in C. arvensis this thermoperiodic treatment stimulated germination during earlier period. Response of dry-chilled seeds to thermoperiodicity: 9. Seeds chilled dry at 0oC for five weeks were tested for their germination response in the above mentioned thermoperiodic treatments. Pre-chilling of P. Minor seeds tremendously improved their percentage germination and unlike unchilled seeds 92% germination occurred in 20/5OC and 84% in 25/10OC thermoperiodic treatment. In L. aphaca chilling of seeds did not cause any change in germination response in both the treatments whereas in A. tenuifolias pre-chilling treatment caused some reduction in germination in both the treatments as compared with their unchilled counterparts. In both these words, germination percentage in 25/10oC thermoperiodic treatment was relatively higher as compared to that in 20/5oC treatment. In the other three weeds, 20/5oC thermoperiodic treatment flavored germination more than the 25/10oC. in the case M. deniculata and C. arvensis pre-chilling treatment of seeds stimulated and greatly improved their germination at 25/10oC thermoperiod as compared to unchilled counterparts. The response to dry chilling at 25/10oC thermoperiod was not so marked in M. Parviflora. Response to soil moisture: 10. Effect of different levels of soil moisture (20 to 120% WHC) on germination and early seedling growth was investigated only on six weeds viz., P. Minor, A. tenuifolius, L. aphaca, M. denticulate, M. Parviflora, and C. arvensis. Highest all moisture level of 120% are totally suppressed germination in all weeds, germination percentage in all the weeds (except L. aphaca) was rather poor and even negligible in (A. Tenuifolius) at lowest soil moisture level of 20%. It increased gradually with successive increase in soil moisture level and in general maximum germination in all weeds occur at 40% soil moisture level. Marked reduction in germination occurred at 80% soil moisture level and at 100% WHC responses was almost negligible in all the weeds. Seedlings of all the weeds invariably showed the beast growth at 40% and 60% soil WHC levels. Response to soil salinity: 11. Seeds of these six weeds were also germinated over a range (EC 1 to 15 mmhos/cm) of soil salinity levels. EC 15 mmhos/cm totally suppressed germination in all weeds while EC 7 and 10 mmhos/cm greatly delayed and reduced it in all except L. aphaca. M. Denticulate and M. Parviflora were rather sensitive to any increase in soil salinity beyond EC 1 mmhos/cm. C. arvensis, A. tenuifolius and P. Minor showed maximum germination at EC 4 mmhos/cm while in L. aphaca there was no appreciable decrease in germination even at EC 10 mmhos/cm. Seedling’s growth was best in almost all the weeds at EC levels 1 and 2 mmhos/cm. There was a general decline in seedlings growth beyond EC 4 mmhos/cm and it was severely curtailed at EC 10mmhos/cm. Longevity of seeds: 12. Seeds of all these weeds were tested for their germinability after storage for different periods i.e., 0, 1/2, 1, 2, 3 and 4 years. Fresh seeds (0-year storage) of all the weeds (except H. Parviflora) either foiled in germinate or showed negligible germination. In case of P. Minor, M. Parviflora and C. arvensis, germination percentage increased with increase in storage from ½ to 1 year followed by reductions proportionate to the length of storage period. Maximum germination occurred in seeds stored for one year and minimum in 4-year-old seeds. On the other hand, storage of seed of L. aphaca and A. tenuifolius from 1 to 2 years caused a gradual increase in their germination percentage followed by successive reduction with further increase in storage period. In M. Denticulate germination was almost similar and maximum in seed stored for ½, 1 and 2 years but any further storage caused great reduction. Longer stronger period in general not only delayed but also slowed down the rate of germination. Of all the storage treatment, seedling of all the weeds from seeds store for 1 year showed most vigorous growth in terms of their length. Effect of sowing depths on germination: 13. Seed of all the above mentioned six weeds were tested for their germination at 0, 2.5, 5, 7.5, 10 cm soil depth under field condition. In the case of M. Denticulate germination of pods at above mentioned soil depths was also tasted. Maximum germination in all the weeds occurred in seeds buried at 2.5cm depth. Further, increases in burial depth caused successive reduction and no germination occurred in those buried at 15cm on depth in all wood except L. aphaca and P. Minor. In the case of M. Denticulate both seeds and pods failed to germinate even at a soil depth of 7.5cm while seeds of M. Parviflora failed to do so at 10cm depth. Germination in surface sown seeds was generally low to moderate. Increasing burial depths progressively delayed germination in all the weeds. Herbicidal control of weeds: 14. A field experiment on post- emergence response of various weeds to Dicuran MA and Arelon and their consequent effect on wheat growth and yield was carried out under natural conditions. Weeds were grown in competition with wheat individually and all mixed together at a weed-wheat density ratio of 4:1. 15. Arelon caused almost 100% mortality in P. Minor, M. parviflora and M. Denticulate in 90 % in mix weeds after three weeks of spraying. Dicuran MA was highly effective against P. Minor and C. Arvensis causing 90 % mortality it caused 70 to 75% mortality in M. Parviflora, M. Denticulate and mixed weeds. The survival of these weeds was further reduced by both herbicides especially Arelon at the time of harvests 1 and 11. 16. Wheat biomass losses at harvest I (13-week-old plants) caused by all weeds (except C. Arvensis in all weeds check were statistically significant as compared to hand weeded control and varied between 43 to 50%. Application of both the herbicides reduced the magnitude of wheat biomass losses. Losses of grain yield caused by various weeds were also greatly reduced by herbicide application. Arelon was relatively more effective in controlling almost all weeds and increasing wheat biomass and yield as compared to Dicuran MA. In the case of mixed weeds and M. Parviflora, application of Arelon caused 108% increase in grain yield over the weedy check in contrast to 56 and 70% increases in their Dicuran MA treated counterparts. In L. aphaca, increase in grain yield due to Arelon was three times higher than that of its Dicuran MA counterparts. Response in rest of the weeds (except C. Arvensis) was similar through of lesser magnitude.