Major Crop Weeds and their Control

Abstract

The research work conducted through financial assistance of Pakistan Science Foundation under Project entitled "Major crop weeds and their control" for two crop seasons vin; 1976-77 and 1977-78 is summarized as under:

1. Weed problem in men's heat crop in Sind: Weeds in Wheat crop from three districts of Sind (Dadu, Bukkur and Hyderabad) were identified and intensity of weed infestation was determined during Winter 1976-77. In all 230 samples were taken from irrigated and unirrigated (Bosi), Broad-can’t and row planted Wheat crop. It was observed that: Average weed infestation in Wheat crop in Sind was 461 weds/sqm. As high as 661 weeds/sq: were recorded in Broad-casted (irrigated) Wheat. Row planted (irrigated) crop had low infestation of 762 weeds/Sqm. Un-irrigated Broad casted Wheat had lowest infestation of 310 weeds/sq: m. Weed spites found to infest Wheat crop numbered to thirty, out of which 17 weeds were commonly found at all locations. The problem weeds found in abundance at all locations were Melilotus alba Desr., Chenopodium album L., Convolvulus arvensis L., Vicia hirsuts Fotch., Cyperus rotundus L., Cynodon dactylon pers., Asphodelus tenuifolius C: Rumex dentatus L., Polygonum plebejun Brodad, Anagallis arvensis L., Brassica campestris L and Sonchus spp; Medicago denticulata, Wild. and Alhagi raururum Desr; Chichorium intybus L. Phalarin minor; Lachyrun aphaca L, were common in Dadu and Sukkur diatricts, Avena Sativs L and Dodder also infested wheat crop near cities or near towns of Dadu and Sukkur districts. Apremone mexicano L. Heliotropium indicum, Carthamus oxyacantha Bieb were common in Hyderabad fields. Perennial weeds such as field Bind weed, Bermuda grass, Nut sedro and Deamostochya bipinnata atapf (Drubh) were common at all locations. Farmer's old methods of growing Wheat caused increased infestation of weeds viz; Use of impure Wheat seeds, contaminated with weed seeds, inadequate land preparation and levelling due to shortness on. Practicing broad-casting of Wheat, Partial or no weeding practices in Wheat. These are some of the main reasons of high weed infestation in farmers’ fields in Sind. As compared to some of the farmer's crop which had comparatively low weed population (less than 50 weeds/m²) at grain formation stage, weedy crop height was reduced by 10-15%. ear head length was reduced by 4 to 6 CMS and crop stand was poor. Thus, high weed infestation due to partial and untimely or no weed control practices caused on an average grain yield loss of 25% of potential production of Wheat in the province. Al-though instances of more than 50% reduction in yield were not un-common. This huge loss in Wheat production is tolerated every year without much realization.

2. Weed competition in Wheat crop.

Study of weed competition up to various growth stages of Wheat crop for the years (1976-77 and 1977-78) revealed that: Weed competition in wheat crop for more than 30 days after sowing becomes harmful for growth and grain yield of Wheat crop. Allowing PE-140 weeds per square meter of Wheat crop for 45, 60, 80 and 130 (Maturity) days after sowing caused average grain yield reduction of 650.00, 1423.00, 2267.00 and 2430.00 kgs/ha respectively. Thus, average reduction in grain yield was 14% when weeds competed with crop for first 45 days. Yield reduction increased as period of competition increased beyond 80 days after sowing. Weed competition for full season resulted in to reduction of 53% in grain yield as compared to minimum competition level. Grain yield decreased due to adverse effects of presence of weeds on almost all the yield components of Wheat crop. Highest grain yield of 51.2 mands per acre (4.604 t/ha) was obtained when weeds were controlled either from crown root formation state or early tillering stage, Grain yield thus increased by 113% (2.43 tons/ha). Removal of weed competition since 20 and 30 days after sowing provided net profit of Rs: 810.00 and Rs: 841.00/acre over control after deducting weeding cost of Rs: 200.00 and 180.00 per acre respectively. Appropriate time of weeding in Wheat crop was found to be tillering stare between 30 and 45 days after sowing. Weeding at this critical stage was found to be the most beneficial. For obtaining increased production of Wheat crop weeds must be kept under control from 30 days after sowing to crop flowering stage (up to 80 day) of as this was found to be most critical period of weed competition. Results of this study revealed that presence of weeds for full season or beyond flowering stage caused 2.43 tone reduction in grain yield/ha and then Wheat worth Re: 1014.40 van 1oot due to weed competition.

3. Evaluation of weedicides for weed control in Wheat crop. Weedicides evaluated for weed control in Wheat crop were Ioxynil, Bromoxynil and U-46 Cat 1.5 to 2.0 L/ha: each) and Benvel-M (0.3 to 0.60 L/ha). The weedicide treatments were compared with handweeding and untreated weedy check plots. Thus, ten treatments were replicated four times in Randomized complete Block design. The observation on effects of weed control levels on growth of weeds and Wheat crop revealed that: Infestation of 98.0 weeds/m² for full growing season in untreated Wheat crop was detrimental to growth and caused 50% reduction in grain yield. The was the reason that lowest rain yield of 2.25 tons/ha (25.0 mds/ac), was obtained from untreated weedy crop. Whereas, all the weed control treatments provided highly significant. increase of 62-104% in grain yield by controlling 72 to 95% of weeds present in Wheat crop. Highest grain yield of 4.6 tons/ha (50.60 mands/ acre) was obtained from the crop from which 95% of weeds were eliminated by doing two hand weedings in the season. Among weedicide treatments Banvel-M (0.3 and 0.6 L/ha) and U-6 (1.5 to 2.0 1/ha) proved to be equally effective for controlling weeds as 86 to 93% of weeds were destroyed with these weedicides and grain yield increased from 76-93%. The most effective herbicide treatments were Banvel-M (0.3 L/ha) and U-46 (2.0 L/ha), which provided statistically similar grain yield of 4.36 and 4.10 tons/ha (48.4 and 45.6 mds/ac) at 1.0% level of significance. Other weedicide treatments such as Benvel-M (0.6 l/ha), U-46(1.5 t/hs), Bromoxynil 2,0 L/hs. Bromoxynil 1.5 L/ha 1oxen11 2.0 and 1.5 L/ha provided grain yield of 4.0, 5.78, 5.95, 3.80, 3.7 and 3.6 toho/ha respectively. Thus 62-78% increase in grain yield over untreated control was also highly significant. The increase in yield was due to favorable effects of weed control levels on the growth of Wheat crop. Removal/control of weeds resulted into 10-12 cms increase in height, 23-55% increase in tillering and 34 to 60% increase in ear head formation of Wheat crop. The weedicides used in this study were found to be safe for the crop, normally Bevel-M + Bromoxynil equally effective as hand weeding provided highly significant increase in grain yield. over control and therefore are recommended for weed control in Wheat crop

4. Weed survey in Cotton crop.

Search for number and kinds weeds infesting. Cotton in central and eastern zone of Sind (Districts Dadu, Hyderabad, Sanghar and Tharparkar) revealed that 40 weed species infested Cotton crop. Grasses (14-species) were found to be major weed problem followed by broad leaves and sedges. Cyperus rotundus (Nut sedge) was only one kind of sedges present in Cotton but this was most common and obnoxious weed at all lecations. Among grasses Eleusine spp. Brachiaria reptans and Echinochloa colonum were the most. common. While among Broad leaf weeds Convolvulus arvensis (field bind weed) Fhalanthus niruri, Direra arvensis, el t Eclipta alba, Trianthema monogyma, Amaranthus spp, chorchorus spp and portulaca oleracene were present in comparatively greater numbers. On an average weed Infestation in Farmers crop ranged between 35 to 105 smed/². The fields, which were mechanically weeded by evade and ploughed in inter-row spaces had low weed population of 20-50 weeds/e. The fields which were inadequately weeded by doing only one ploughing in inter-row spaces had moderately bath weed population of 60-80 weeded/. The fields which were left un-weeded had highest infestation of weeds ranging between 81 to 150 weeds/n. Due to adverse effects of high weed infestation in farmer field, cotton crop stand (Plants per unit area). height and boll formation were very much reduced. It was estimated that weeds reduced need cotton yield in Sindh to the extent of 13 to 40% of potential production.

5. Cotton Crop-Weed Competition Studies,

Effects of weed competition in Cotton crop were studied for two consiquitive years i.e., Summer 1977 and 1978. Weeds were allowed to compete with the crop up to periods of 15 (Minimum competition level), 25, 45, 65, 85 and 154 (First picking) days after sowing time. The corresponding crop stares up to which weeds competed with the crop were seedling (4 to 6 leaf) stage, establishment stage (10"-12" height), squaring stage, flowering stage, Boll formation stage and the crop maturity stage respectively. It was observed that weeds such as Cyprus rotundas (Nut sedge), Cynodont dactyl on (Bermuda rasa) Convolvulus arvensis (field bind weed) and Eleusine aegyptiacs emerged within a week of sowing of Cotton and competed with the crop since its early growth. Competition of weeds was minimum for nutrients and light up to 5 days of sowing time; when only 29 weeds/m were found to infest the crop. The presence of weed up to 25 days shared the crop mostly for moisture and space, however the adverse effects were recovered. When crop was kept weed free from this time to crop maturity the crop growth and finally need Cotton yield was not affected. Competition became serious when weeds were allowed to row with cotton for more than 45 days after sowing. The effects of weed competition were quite obvious. The crop appeared retarded in growth pale yellow in color, some of the lower leaves became purple in color or with scorched margins. Shedding or buds, flowers and bolls increased and finally seed Cotton yield was reduced from 25 to 42%. Highest and Cotton yield of 2.36 tons/ha (25.5 manda/acre) was obtained when weed competition WAS kept at minimum (i.e., up to 15 days) and thus 72% increase in yield was obtained crop control (full season weed competition level), in which lowest yield of only 1.37 tons/ha (14.85 naunda/acre) was obtained, Next best yield of 2.28 tons/ha (2.65 msunds/acre)was obtained from the crop which was kept weed free after 25 days and statistically similar yield was obtained as compared to minimum competition level. Two years average results showed that weed. competition beyond 25 days after sowing caused highly significant reduction of 13, 25.5, 37.5 and 42% in seed Cotton yield, when weeds were allowed to grow with the crop for 45, 65, 85 and 154 (maturity) days after sowing respectively. Two years average economics of different weed competition levels showed that highest average total income of Rs: 4080.00/acre was achieved by spending Rs: 213.25 on six weeding’s to control weeds from 15 days of sowing to initial boll maturity period. Thus, on an average in:1712.00 van increase in income an income weedy crop. henceinet profit after deducting 15 weeding cost wan Rat1509.00/mare, starting weeding program for 25 day was found to be as profitable a minimum weed competition treatment, as statistically similar income of Ro13936/sore and net profit of Rs:1371 was obtained, Removal of weeds from cotton crop at any stage of growth up to 85 days after knowing was found to be profitable. But the net profit significantly decreased as the period of competition increased beyond 25 or 40 days after sowing. The results of this study indicated that the critical stage of weed competition was between 25 to 65 days after sowing (up to initial boll formation). Weeding during this period of growth was more profitable as compared to full season weedy crop. Yield increased from 4.4 to 10.70 maunds/acre and thus profit of Rs:575-1500/hare was obtained, Presence of weeds in cotton prop for full season caused 42% reduction (10.70 maunds/acre) in seed Cotton yield and thus reduced income to the extent of Re: 1712.00/acre. Thus, it could be concluded that weeds in cotton crop must be controlled from 15 or 25 days after sowing till crop attains sufficient growth to cover and shed the inter-row spaces. i.e., up to 60-65 days after sowing. As weed growth after this period will not be enough to affect the crop and losses in yield could be saved.

6. Study of weedicides for weed Control in Cotton crop.

four weedicides at two doses each were evaluated for weed control in Cotton drop. Treflan (3.0 and 4.0 lbs. ai/so) Gesagard (3.0 and 4.0.1bm al/ac), Ansar-529 (5. & 8. pints/ac) Plus Karmex 1.0 1b ai/acre tank mixed and Gramoxone (1.5 and 2.0 pints (Product)/ac) were tested and compared to Hand weeding and untreated weedy check plots. Thus 10 treatments were replicated four times in Randomized complete block design. Excellent weed control in Cotton crop vas obtained with the treatment of hand weeding by which 90% of weeds wore eliminated and thus highest seed Cotton yield of 2.10 tons/ha (22.50 munds/eerd) was obtained. As compared to this untres ted weedy crop yielded only 1.30 tons of seed cotton/ha. Increase in yield due to hand weeding was 60%. The herbicide treatments, which provided satisfactory weed control to the extent of 76-86% increased deed Cotton yield by 25 to 50% as compared to weedy crop. The increase in yield was mainly due to increased number of full-size productive bolls/plants. Seed cotton yield vas found to be negatively correlated with weed infestation i.e., lower the number of weeds/unit area greater was seed cotton yield. Herbicide treatments of gramoxone (1.5 & 2.0 pints/ ac) and Ansar 529 Earmex (5.0 pints + 1.0 lb. si and 8 pints+ 1.0 lb. ai/acre) provided statistically similar (P.05) seed Cotton yield of 1.97, 1.96, 180 and 1.84 tons/ha respectively as compared to hand weeding. Thus, increase in seed cotton yield over weedy check was 50, 49, 37 and 40% respectively. On the basis of results of this study it could be said that in place of hand weeding which is laborious and costly operation, careful use of these herbicides may be profitable and easy method of weed control by which yield could be increased.