الفهرس 
INTRODUCTION
Effect of early and late weed competition periods on yield and yield componentsOnly 14 pages are availabe for public view
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Abstract
Two field experiments were conducted for two consecutive cropping seasons 2012 and 2013 at Shandaweel Agricultural Research Station, A. R. C. The aims of this study were to:
1. Determination of critical period of sesame-weed competition.
2. Study the effect of some weed control treatments on yield, yield components and its associated weeds.
The treatments were distributed in a Randomized Complete Block Design with four replications. The plots area was 10.5 m2. The normal cultural practices for sesame in the experimental were followed.
Part I:
Determination of critical period of sesame-weed competition:-
The experiment included fourteen treatments which were:
Late competition:
1. Weed free up to 2 weeks after sesame emergence.
2. Weed free up to 4 weeks after sesame emergence.
3. Weed free up to 6 weeks after sesame emergence.
4. Weed free up to 8 weeks after sesame emergence.
5. Weed free up to 10 weeks after sesame emergence.
6. Weed free up to 12 weeks after sesame emergence.
7. Complete weed free for whole season.
Early competition:
8. Weedy up to 2 weeks after sesame emergence.
9. Weedy up to 4 weeks after sesame emergence.
10. Weedy up to 6 weeks after sesame emergence.
11. Weedy up to 8 weeks after sesame emergence.
12. Weedy up to 10 weeks after sesame emergence.
13. Weedy up to 12 weeks after sesame emergence.
14. Weedy check for whole season.
The resulted can be summarized as follows:
1. Results showed that there were significant differences among all studied treatments, on dry weight of grassy, broad-leaved and total weeds in 2012 and 2013 seasons. Full season sesame weed competition produced highest values of weed dry weight of grassy, broad-leaved and total weeds compared with weed free whole season (zero competition). Generally, in late competition treatments dry weight of total weeds decreased by increased periods of weed free while, in early competition treatments dry weight of total weeds increased by increasing periods of weed competition.
2. Plant height decreased significantly with the increase in weed crop competition period (WCCP). The tallest plant in both seasons were observed in zero competition (complete weed free whole season) compared with full season sesame weed competition. Early competition between sesame and weeds beyond 4 WAE suppressed crop growth which was manifested in the form of reduced plant height.
3. Results indicated that as we increased number of weeks for weed competition the fruiting zone length decreased, in contrast as we decreased number of weeks for weed competition the fruiting zone length significantly increased, complete weed free whole season produced highest fruiting zone length compared with full season weed sesame competition in both seasons.
4. Results revealed that significant differences in number of branches / plant among various weed competition periods. The highest values of number of branches were attained when crop was kept free from weeds throughout its growth, in both seasons, respectively, compared with full season weed sesame competition.
5. Significant differences in number of capsules / plant between the various early and late weed competition periods. The highest number of capsules / plant was produced in plots where crop was kept weed free throughout growing season (zero competition) in both seasons. A successive decreased in number of capsules / plant can be observed as weed crop competition period prolonged until it encompassed whole of the crop growing season in which minimum number of capsules / plant were noted.
6. Results indicated that significant difference in weight of capsules by different weed removal and weed competition treatments in 2012 and 2013 seasons. The highest weight of capsule was attained when crop was kept free from weeds throughout its growth, in both seasons, followed by treatments of weed free to 12, 10, 8, 6, 4 WAE, weedy up to 2 WAE, weed free to 2 WAE, weedy up to 4, 6, 8, 10, and 12 WAE, compared with full season weed sesame competition in both seasons, respectively.
7. Full season weed free conditions gave the maximum value of seed yield / plant (g) which followed by weed free to 12, 10, 8, 6, 4 WAE, weedy up to 2 WAE, weed free to 2 WAE, weedy up to 4, 6, 8, 10 and 12 WAE, however. The minimum seed yield / plant (g) was achieved when weedy conditions were kept throughout the growing season of crop, in both seasons, respectively.
8. Results revealed that periods of weed competition significantly influenced seed weight (g), the highest 1000-seed weight (g) were observed from treatments of weed free up to 10 WAE and complete weed free whole season compared with full season weed sesame competition in both seasons, respectively.
9. The highest seed yield observed from treatments weed free for whole season and weed free up to 10 WAE in 2012 and 2013 seasons, respectively. Uninterrupted weed growth in weed competition whole season resulted in 80.5 and 80.8 % reduction in yield as compared to complete weed free, whereas 77.3 and 78.5 % as compared to weedy up to 2 WAE (the beginning of critical period) and 78.4 and 79.8 % as compared to weed free up to 6 WAE (the end of critical period) in 2012 and 2013 seasons, respectively.
10. Results showed that relationship between dry weight of total weeds (g/m2) at end of growing of both seasons and weed free periods (weeks) were linear and significant negative with prediction equation (R2 values 77.5 and 65.3 %) in both seasons, respectively. While, relationship between dry weight of total weeds (g/m2) at removal weeds of both seasons and weed competition periods (weeks) were linear and significant positive with prediction equation (R2 value 98.9 and 99.4 %) in both seasons, respectively.
11. According to simple regression equation, there is a significant and negative relation between sesame seed yield (ardab/fed.) and total weeds (g/m2) on weed free and weed competition periods, and from R2 values it is observe that weed biomass parameter is more effective in exhibiting changes in seed yield (ardab/fed.) by (96.2 and 94.4 %) and (90.9 and 94 %) in 2012 and 2013 seasons, respectively.
12. Data indicated that there were relationship significant negative between early competition periods and seed yield at early competition periods by correlation coefficients(-0.945 &-0.958), and relationship significant positive between early competition periods and total dry weight (g/m2) at early competition periods by correlation coefficients (-0.880 &-0.808) in both seasons, respectively. On the other hand, there were relationship significant positive between late competition periods and seed yield at late competition periods by correlation coefficients (0.799 & 0.824), and relationship significant negative between early competition periods and total dry weight (g/m2) at early competition periods by correlation coefficients (0.994 & 0.997 ) in both seasons, respectively.
13. Determination of critical period of sesame weed competition:
A- Classical biological.
Resulted indicated that to prevent a greater than 10 % yield loss, the maximum time for which weeds could be allowed to grow after crop emergence was 2 WAE, and the crop must be free of weeds to prevent a predetermined level of yield loss and that period was 6 WAE.
B- Regression approach.
Application equation reported that to maintain 95 % of seed yield (ardab/fed.) should be not allowed weeds to exceed one week after emergence. The same situation with weed free periods should be not allowed weed to exceed 13-14 weeks after emergence.
Part II:
Study the effect of some weed control treatments on sesame yield, yield components and its associated weeds.
The experiment included fourteen treatments which were:
1. Stomp Extra 45.5 % CS at rates of (0.750, 1.25 and 1.75 L/fed.) Pre-emergence.
2. Gesagard 50% SC at rates of (0.75, 1.00 1.25and L/fed.) Pre-emergence.
3. Dual Gold 96% EC at rates of (0.75, 1.00 1.25and L/fed.) Pre-emergence.
4. Select Super 12.5 % EC at rates of (0.25, 0.500 and 0.750 L /fed.) Applied at 30 DAP.
5. Hand hoeing twice at 21 and 40 days after planting.
6. Untreated (control).