Weed Study Important Point
Subject:- Weed Science
Weed Study Important Table
1.Critical Period or Crop-Weed Competition
| Crops | Critical Period (Days) | Reduction in Grain Yield (per cent) |
| Cereals | ||
| Paddy-Direct sown | 20-45 | 15-90 |
| Paddy Transplanting | 30-45 | 15-40 |
| Paddy Upland condition | Entire period | 40-90 |
| Wheat | 30-45 | 20-40 |
| Maize | 15-45 | 40-60 |
| Sorghum | 15-45 | 15-40 |
| Pearlmillet | 30-45 | 15-60 |
| Pulses | ||
| Pigeonpea | 15-60 | 20-40 |
| Greengram | 15-30 | 25-50 |
| Blackgram | 15-30 | 30-50 |
| Cow pea | 15-30 | 15-30 |
| Chickpea | 30-60 | 15-25 |
| Peas | 30-45 | 20-30 |
| Lentil | 30-60 | 20-30 |
| Oilseed | ||
| Soybean | 20-45 | 40-60 |
| Groundnut | 40-60 | 40-50 |
| Sunflower | 30-45 | 30-60 |
| Castor | 30-50 | 30-35 |
| Safflower | 15-45 | 15-40 |
| Sesamum | 15-45 | 15-40 |
| Rapeseed mustard | 15-40 | 15-30 |
| Linseed | 20-45 | 30-40 |
| Commercial crops | ||
| Sugarcane | 30-120 | 20-30 |
| Potato | 20-40 | 30-60 |
| Cotton | 15-60 | 40-50 |
| Jute | 30-45 | 50-80 |
| Vegetable crops | ||
| Cauliflower | 30-45 | 50-60 |
| Cabbage | 30-45 | 50-60 |
| Okra | 15-30 | 40-50 |
| Tomato | 30-45 | 40-70 |
| Onion | 30-75 | 60-70 |
2.Importance of Weeds with Example
| Importance | Example |
| Maintain soil fertility | Typha spp. (add 1-35 per cent nitrogen) |
| Control soil erosion | Cynodon dactylon, Convoloulus arvensis |
| Used as fodder | Cichorium intybus, Cynodon spp. |
| Have medicinal value | Leucas aspera is used in snake bite.
Striga spp. is used in diabetes. Phyllanthus niruri is used in Jaundice. Argemone maxicana is used in skin disease |
| Have economical value | Roots of Cichorium intybus is used in adding flavour to coffee.
Cyperus rotundus is used in making agarbatti. Saccharum spontaneum is used in roof making. |
| Maintain pH | Argemone maxicana is used for making alkaline soil to acidic.
Rumex acetocella is used for making acidic soil to alkaline |
| Used as ornamental plants | Lantana camara, Eichhornia crassipes |
| Used in cleaning water | Eichhornia crassipes |
| Adds organic matter to soil | Amaranthus viridis, Convolvulus arvensis |
| Used as vegetables | Chenopodium album, Amaranthus viridis |
| Religious purpose | Cynodon spp. |
| Useful for cottage industries | Saccharum spontaneum, Typha spp |
| Donating genes to crop plants (crop breeding) | Saccharum spontaneum (used in sugarcane) |
| Used as nematicides | Crotolaria, Parthenium |
| Used as pollution indicator | Brassica kaber (Wild mustard) to indicate NO2, pollution.
Stellaria redia (Chick weeds) to indicate SO2 pollution |
3.Biological Control of Weeds
| Weeds | Bio-agent | Remark |
| Lantana camara | Crosidosema lantani | A moth |
| Opuntia spp.(Cactus) | Cactoblastic cactorum | An Insect |
| Cyperus rotundus | Bactra varutana | Shoot boring moth |
| Eichornia crassipes | Rhizoctonia solani | A fungus |
| Orabanchi spp. | Sclerotia spp. | A fungus |
| Xanthium stramarium | Chinese grass carp (T. idella) | A beetle |
| Aquatic weeds | Cassia cerassia / tora | Grass carp fish |
| Parthenium hysteroforus | Zygrogramma bicolarata | Competitive plant, Mexican beetle |
| Water hycinth | Neochetina spp. | weevil |
4.Herbicides and their Respective Mode of Action
| Herbicides | Mode of Action |
| IPC (Chlorpropham) | Causes of epindal to boundry layer. |
| 2,4-D ethyl ester | Highly volatile – Abnormal cell division. |
| 2,4-D sodium salt | Highly soluble – Abnormal cell division. |
| Glyphosate | Non selective, translocated and zero persistence and general metabolic inhibitors. |
| Diquate | Disturb of cell permeability. |
| Triazines group | Photosynthesis inhibitor. |
|
Atrazine
|
Selective (Conjugation). |
| Pendimethaline | Microtubule assembly inhibition. |
| Paraquate | Contact herbicide; inhibition of DNA synthesis. |
| Dinitroaniline herbicides | Inhibition of respiration. |
| Oxadiazone | Inhibition of CO2. |
| Trifluralin | Inhibition of RNA synthesis. |
|
Butachlor and Alachlor
|
Inhibition of protein synthesis and GA production during germination. |
| Dalapan | Inhibition of vitamin synthesis. |
| Thio-carbamate | Inhibition of lipid synthesis. |
| Carbamate groups | Inhibition of cell division. |
| Auxin type herbicides | Abnormal tissue development. |
| Propanil | Degradation or metabolism. |
| 2,4-DB | Reverse metabolism. |
| Paraquate, Diquate & Glyphosate | Knock down effect. |
5.Methods of Herbicides Application
| A) Soil Application | |
| Soil surface application | Most of the Triazines, ureas and amide group |
| Soil application | Anilines group ie. Fluchloralines |
| Sub-surface application | Only for deep rooted and perennial weeds |
| Band application | Weeds in maize (spraying of Atrazine) |
| B) Folier Application | |
| Blanket application | Application of herbicides over the entire leaf area (only selective herbicides) |
| Direct application | Application of herbicides in between the crop rows directly towards weeds. |
| Spot application | Herbicide solution is poured on weeds in cropped and non cropped fields infested with abnoxious weeds in isolated patches. |
| Basal application | Brush wood and unwanted trees are treated with herbicides. Generally, the bark of the trees at the base of the stem up to 30 cm height is removed and a drenching spray of herbicides is given to the base. |
Weed Study Important Point
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