Weeds compete with crops for nutrients, moisture, space, sunlight and can release allelopathic compounds that inhibit crop growth. Weeds remove significant amounts of nutrients from the soil each season. They also transpire at higher rates than crops and can form dense canopies that shade out crops. The critical period of weed-crop competition varies by crop but is typically early in the growth cycle. Factors like weed density and species, soil fertility, moisture levels, pH, and climate can influence the intensity of competition between weeds and crops. Timely weed management is important for optimal crop yields.

2. CROP WEED COMPETITION
SUBMITTED BY:
Mr. SHIVAJI RAVASAHEB SURYAVANSHI
M.Sc. (AGRONOMY),
RCSM COLLEGE OF AGRICULTURE, KOLHAPUR
MAHATMA PHULE KRISHI VIDYAPEETH, RAHURI.

3. Contribution of pests in crop
yield reduction
Weed
45%
Others
5%
Insect pets
30%
Disease
20%

4. Weed crop competition :
Weed competes with crop plants for :
i. Nutrients
ii. Moisture
iii. Space
iv. Sunlight
v. Exert the allelopathic effects
vi. Increases pest and diseases

5. 1. Competition for plant nutrients
Removal of plant nutrients by weeds
Season N
Kg/ha
P
Kg/ha
K
Kg/ha
Kharif 46.6 12.1 73.3
Rabi 24.2 3.6 26.3
Sugarcane 162 20 203

6. Concentration of plant nutrients in weeds :
eg. Amaranthus viridus 3.16% N
Achyranthus aspera 2.21% N
Cassia occidaentalis 3.08% N
Wild legume weeds 1.5 to 6% N
Echinochloa colonum 2.98% N
Xanthium strumarium 2.47%
where as,
Wheat 1.33% N
Rice 1.13% N
Sugarcane 0.33% N

7. 2. Competition for moisture
The values of transpiration coefficient
( transpiration ratio ) of weeds is 2 to 3 times more
than crop plant.
Eg. Tridax procumbens 1402
Cynodon dyctylon 813
Tephrosia purpurea 1108
Digiteria sanguinalis 696
Values of consumptive use of Chenopodium album is
550 mm and that of Wheat is 479 mm.

8. 3. Competition for Space
1. Rhizosphere
2.Atmosphere
4. Competition for Sunlight ( Solar energy)
Weed seeds germinate earlier, grow faster,
attain more height and canopy coverage within a
short periods than the crops. This causes shedding
effect on crops and affects photosynthetic activities
resulting in poor growth and yield of crops.

9. 5. Allelopathy / Teletoxy
Allelopathic compounds are derivatives
of benzoic acids , cinnamic acids, phenolic acids ,
cineoles etc.
Some of the weeds like Cyperus rotundus,
Sorghum helepence, Chenopodium album,
Amaranthus spp. etc lower the germination,
growth and yield of any crops. This is due to the
certain phytotoxins or allelopathic compounds
released by weeds in soil.

10. 6. Weed increases infestation of insect pest and
diseases :
Insect pest / Diseases Host weed
Rice stem borer Echinochloa sp.
Gram pod borer Chinopodium album and
Amaranthus sp.
Grass hopper Grasses and dicot weeds
Downey mildew of maize Saccharum sponteneum
Powdery mildew of Spinach Chinopodium album

11. Factors affecting weed –crop competition

12. Critical period of weed crop competition in different crops
Name of crops Critical period (DAS)
Rice (Transplanted) 20 to 40
Rice (up land) 20 to 45
Wheat 20 to 40
Sorghum 15 to 45
Maize 15 to 35
Finger millet 25 to 45
Soybean 15 to 45
Black gram 30 to 45
Groundnut 20 to 40
Cotton 25 to 40
Sugarcane 20 to 60 days after planting
Fruit crops First 2 years or till their proper
establishment

13. 2. Intensity of weed
Higher weed intensity higher the competition
3. Weed species –
Differs in their competing ability at similar density
Example
1. Xanthium strumarium
2. Wild mustard
3. Nutgrass
4. Hariyali

14. 4. Soil fertility
Band application of fertilizer is beneficial to increase
the crop growth and suppress weed in wide spaced crops like
sugarcane, cotton etc.
5. Soil moisture status
Xerophytic weeds can compete more successfully in dry
farming condition and water loving weeds under ill drained
condition.
6. Soil reaction (pH)
The weed crop competition is more on
high or low pH soils than on normal pH soils.

15. 7. Climatic influence:
Some of the weeds tolerate adverse weather
conditions such as drought, heavy rainfall, Abnormal
temperature etc and put the crop under stress.
Many Xerophytic weeds tolerate drought condition
and growth of weed is more than crops under continuous
rains.
Therefore under adverse climatic conditions weed
management is necessary for successful growth and yield of
crops.

16. 8. Effect of cropping practices :
a) Time and method of sowing:
b) Crop density and plant geometry :
c) Crop species and varieties :