MSc

Cassava, one of the most important tropical tuber crops, is known to sustain even
under marginal soil conditions. Being a widely spaced crop with slow initial growth, a wide
spectrum of weeds has been reported in cassava fields which may cause yield losses up to 90
per cent. Weeding is the main labour consuming activity of cassava fields as it is usually
carried out by tillage practices and earthing up. Presently, chemical weed control is becoming
popular among farmers as it is an efficient way of weed control with minimum labour cost.
However, relying only on chemical weed control may not be feasible in the long term.
Developing a complete weed management package by integrating chemical, physical and
cultural methods may be the best option for cassava to achieve optimum yield.
The present study entitled “Weed management in cassava (Manihot esculenta
Crantz)” was carried out at the Agronomy farm attached to the Department of Agronomy,
College of Horticulture, Vellanikkara from May to October 2015 to compare different weed
management practices for cassava. The treatments included applications of three pre
emergence herbicides viz., oxyfluorfen 0.2 kg/ha, pendimethalin 1.5 kg/ha and imazethapyr
80g/ha, directed application of glyphosate 0.8 kg/ha at 30 Days After Planting (DAP), all this
four herbicides followed by one hoeing and earthing up at 60 DAP, hoeing and earthing up
twice at 30 and 60 DAP, concurrent growing of fodder cowpea and in situ green manuring
and earthing up at 60 DAP, and unweeded control plot.
Weed management treatments significantly affected the growth and yield
characters. Number of tubers per plant was high when cassava was intercropped with cowpea
and when hoeing and earthing up was done twice. These two treatments also recorded longer
cassava tubers.
Higher tuber yields were recorded for the treatments hoeing and earthing up (31.20
t/ha), pendimethalin followed by earthing up (30.60 t/ha) and glyphosate followed byearthing up (28.40 t/ha). These treatments also showed higher top yield and greater dry
matter production.
The treatments significantly influenced the weed population and weed dry weight at
all the four stages of plant growth. The herbicide oxyfluorfen could control 99 per cent of
weeds at 30 DAP. Pendimethalin followed by earthing up was more effective in suppressing
the weeds in later stages and it resulted in 94 per cent control of weeds during harvest. Weed
control efficiency of all the treatments increased with a follow up earthing up. Pre emergence
application of imazethapyr alone was less effective in controlling the weeds and it recorded a
lower weed control efficiency compared to other plots. Weed index was lower in the
treatments hoeing and earthing up, pendimethalin followed by earthing up and glyphosate
followed by earthing up. Lower nutrient uptake by weeds was recorded in the treatment
which received pre emergence application of oxyfluorfen during early stages of plant growth.
At the time of harvest, the treatments pendimethalin followed by earthing up and glyphosate
followed by earthing up recorded lower uptake of nutrients.
The soil pH, organic carbon and phosphorus contents of the soil were statistically
on par in all the plots after the experiment. However, the contents of available N and K
showed significant differences among the treatments. Green manure cowpea intercropped
plots recorded higher available nitrogen content after the experiment.
The highest B:C ratio of 2.41 was obtained for the treatment pre emergence
application of pendimethalin followed by earthing up. The treatment with application of pre
emergence oxyfluorfen had a higher B:C ratio of 2.27. Even though hoeing and earthing up
produced higher tuber yields, the B:C ratio was lower because of the additional labour
requirement. The results of the present investigation suggest the possibility of reducing the
number of earthings up in cassava by applying a pre emergence herbicide such as
pendimethalin.