Integrated Weed Management on Growth, Yield and Economics in Okra (Abelmoschus esculentus (L.) Moench) Under Kharif

Okra (Abelmoschus esculentus) L. (Moench)

• Okra is a member of the Malvaceae family and is an economically important vegetable crop grown in tropical and sub-tropical parts of the world.
• It is grown commercially in India, Pakistan, Burma, Japan, Malaysia, Brazil, Ghana, Ethiopia, Cyprus, and the Southern United States.
• India ranks first in the world with 5.7 million tonnes of okra produced from over 0.50 million ha land, with a productivity of 11.9 tonnes per hectare (NHB, 2015-16).
• It is quite popular in India because of easy cultivation, dependable yield, and adaptability to varying moisture conditions.
• Okra is a tropical, direct-sown vegetable with a duration of 90-110 days.
• It is the best source of iodine and calcium.
• The nutritional composition of okra includes:
  • Calcium
  • Protein
  • Oil
  • Carbohydrates
  • Iron
  • Magnesium
  • Phosphorus

Weed Competition in Okra

• In most vegetable crops, weeds are silent robbers of:
  • Plant nutrients
  • Moisture
  • Sunlight
  • Space that would otherwise be available to the main crop
• Weed competition is especially dramatic in direct-seeded vegetables like:
  • Okra
  • Cluster bean
  • Cowpea
  • Yard long bean
  • Lab lab
  • Gourds
• The critical period of weed competition (i.e., the period during which weed control is necessary) is longer in direct-seeded crops than in transplanted crops.
  • Example: If transplanted pepper must be weeded from the second week until the third month after transplanting to prevent a 10% yield loss, then direct-seeded pepper must be weeded during the first four months after emergence to prevent the same yield loss.
• Some traditional techniques are thought to increase crop competitiveness, such as:
  • Transplanting
  • Earthing-up
• Weather conditions and weed density have a great influence on the length of critical periods.
• Weeds also:
  • Harbour pests and disease-causing organisms
  • Cause adverse allelopathic effects on okra
  • Reduce yield and quality of produce

Impact of Weed Competition on Okra

• Slow growth rate of okra during the initial stages allows weeds to take advantage of:
  • Moisture
  • Soil fertility
  • Environmental conditions
  • Suppress the growth of the crop
• Due to weed competition, the crop remains weak and unhealthy, leading to:
  • Reduction in yield
  • Poor quality of the crop
• Yield loss of about 54.1% to 90.6% was reported in okra due to weed competition.
• The most critical period of crop-weed competition in okra is up to 2-6 weeks after sowing (Singh et al., 1981).

Weed Management in Okra

• In okra, pendimethalin (either alone or in mixtures with broadleaf herbicides) and supplemented with other weed control methods (especially hand weeding) has given effective control of weeds (Dhanappal and Gowda, 1996).
• Smith et al. (2009) obtained effective weed control with pendimethalin-based weed management methods in okra.
• Okra suffers heavy yield losses in the rainy season (kharif) due to weed infestation, owing to:
  • Congenial environmental conditions for luxurious weed growth
  • Wider row spacing
  • Slow growth at early stages
• Yield losses due to weeds varied from 40% to 80%, depending on:
  • Type of weed flora
  • Intensity
  • Stages of competition (Patel et al., 2004).

Challenges in Weed Control

• Scarcity of manpower at the critical period of crop-weed competition.
• Costly herbicides and availability issues in desired quantities.
• Cumulative effects of weeds on crop production lead to:
  • Crop losses due to competition
  • Allelopathic effects
  • Weeds acting as alternative hosts to pests and pathogens
  • Adulteration of farm produce

Need for Integrated Weed Management

• Considering the challenges posed by weeds, it was necessary to undertake a study to evaluate the performance of integrated weed management on:
  • Growth
  • Yield
  • Economics
• The study was conducted in okra (Abelmoschus esculentus (L.) Moench) during kharif seasons.

The experiment was conducted during three consecutive Kharif seasons of 2014 to 2017 at College Orchard (11.0152° N latitude, 76.9326° E longitude and 426 m altitude), Department of Vegetable Crops, HC&RI, Tamil Nadu Agricultural University, Coimbatore.

• The experimental soil was well drained and sandy loam in texture, having pH of 6.92.

• The experiment was laid out in a randomized block design (RBD) with seven treatments with three replications.

• The experimental fields was ploughed three times and FYM 10 kg, neem cake 1 kg, super phosphate 100 g and furadon 10 g/sq.m were incorporated uniformly in the last ploughing and ridges and furrows were formed.

• The ridges and furrow was earmarked for 45 cm apart for assigning treatments and replications.

• The drip laterals were laid over the ridges and furrow for irrigation.

• The treatments consists of:

  • T1: Weedy check

  • T2: Weed free check

  • T3: Pre-emergence application of pendimethalin @ 1.0 kg/ha

  • T4: Pre-emergence application of pendimethalin @ 1.0 kg/ha + one hand weeding

  • T5: Pre-emergence application of pendimethalin @ 1.0 kg/ha + Quizaflop ethyl 0.5 kg/ha at 20 DAS

  • T6: Post emergence application of Metribuzin @ 0.5 kg/ha at 20 DAS

  • T7: Post emergence application of Glyposate @ 1.0 kg/ha + 10 g urea as protected spray at 25 DAS

• The field was fertilized with recommended doses of NPK at the rate of 100:100:100 kg/ha, respectively, and the fertilizers were given as WSF through drip fertigation system uniformly for all the treatments throughout the cropping period.

• The seeds of okra cv. COBhH 1 were sown on ridges at 60x30 cm spacing.

Morphological Parameters

• The plant height was measured from the base of the plant to the terminal growing point of the main stem at last harvest.

• The average plant height was worked out and expressed in centimeters.

• The total numbers of fruits from 10 tagged plants were counted in all the pickings and the average total numbers of fruits per plant for each treatment was worked out.

• Ten numbers of fruits from each treatment was weighed and they were worked out for single fruit weight and expressed in grams.

• The fresh fruit yield from the net plot area was taken to calculate the fruit yield per hectare.

• The total number of weeds present in 0.5 sq. mt area in a permanently marked sampling area was counted at 30 and 60 DAS in each treatment.

• The observation on plant height (cm) at final harvest stage, number of fruits/plant, fruit yield per plant, fruit length, fruit girth, fruit yield q/ha and weed density 60 days after sowing were recorded.

The benefit-cost ratio was arrived by using the formula given below:

• Data were subjected to statistical analysis by analysis of variance method (Panse and Sukhatme, 1985).

• The critical difference was worked out for 5 per cent probability.

• The results of the experiment were tabulated and presented below.

• The results of the investigation on integrated weed management on growth, yield, and economics in okra (Abelmoschus esculentus (L.) Moench) cv. CO Bh H 1 under kharif over the three years was pooled and the mean values were presented (Table 1 & 2) and discussed hereunder.

Growth Characters

• Weed management practices significantly influenced the crop growth characters like plant height (cm) and the data is presented in Table 1.

• The plant height varied significantly due to different treatments.

• Pre-emergence application of pendimethalin @ 1.0 kg/ha + one hand weeding (T4) showed superior performance in plant height than all other treatments tested except weed-free check (T2), with a plant height of (146.43 cm).

• This indicates that pre-emergence application of pendimethalin + hand weeding practice had a positive effect on the growth and development of okra followed by weed-free check T3 (143.80 cm).

• The lowest plant height (73.73 cm) was recorded in weedy check.

• The herbicides when used in combination with one or two hand weedings improve their efficiency.

• The pre-emergent herbicides are beneficial to keep the crop weed-free in the early stages.

• During later stages, hand weeding helps to reduce the cost of weeding and keep the weed population below the economic threshold level throughout the crop growth period. (Shivalingappa et al., 2014) (Adejonwo et al., 1989).

• This has been attributed to the fact that okra varieties are sensitive to environmental changes (Ijoyah et al., 2009) and also it might be due to the reason that the crop faced minimum crop-weed competition because of herbicidal action and hand weeding practice and it resulted in maximum height of the plant.

Table. 1. Effect of different weed management practices on growth and yield attributes in okra

Table. 2. Effect of different weed management practices on yield, weed density and economics in okra

Weed density was recorded in the treatment weed free check (T₂) 12.03 at 60 DAS (Table 2 & Fig 2), followed by (T₄) pre-emergence application of pendimethalin @ 1.0 kg/ha + one hand weeding (15.73 at 60 DAS). The variability in weed density in different treatments can be attributed to the fact that some herbicides are more effective for weed control than others (Khan et al., 2008).

The lowest weed density was observed in the weed-free check treatment, which may be ascribed to the fewer number of weeds, rapid depletion of carbohydrate reserves of weeds through rapid respiration (Dakshinadas, 1962), and reduced photosynthetic activity (Hilli and Santkemann, 1969).

The maximum benefit: cost ratio (3.57) was obtained under pendimethalin (extra) (0.64 kg/ha) pre-transplanting + one hand weeding at 40 DAT + pendimethalin (extra) (0.64 kg/ha) at 45 DAT compared to weed-free check (T₂).

Pre-emergence application of pendimethalin @ 1.0 kg/ha + one hand weeding has a more significant effect, resulting in maximum plant height, highest yield-attributing characters, high weed control efficiency (WCE %), and better economics than all other treatments tested except the weed-free check.

It is therefore recommended that pre-emergence application of pendimethalin @ 1.0 kg/ha + one hand weeding will be optimal for okra production in the kharif season.