MSc

An experiment entitled ‘Integrated weed management in cowpea (Vigna unguiculata
L.) was conducted at Instructional farm II of College of Agriculture, Padannakkad located at
Karuvacheri, from December 2020 to March 2021 with the objectives of evaluating the efficacy
of different weed management practices and to find out the economics of weed management
in cowpea.
The experimental design was Randomized Block Design (RBD) with 11 treatments
replicated thrice. The short duration cowpea variety namely PGCP 6 was used for the study.
The treatments consisted of T1 (pre-emergence application of pendimethalin @ 0.75 kg ha-1
at
0-3 DAS), T2 (T1 + hand weeding at 20-25 DAS), T3 (T1 + mulching @ 7 t ha-1
), T4 (postemergence application of imazethapyr @ 75 g ha-1
at 20 DAS), T5 (T5 + hand weeding at 35
DAS), T6 (mulching @ 7 t ha-1 + T5), T7 (mulching @ 7t ha-1 + hand weeding at 20 DAS), T8
(hand weeding alone at 15 and 30 DAS), T9 (mulching alone @ 7 t ha-1
), T10 (weedy
check/control) and T11 (weed free).
Weed density, dry matter and weed control efficiency (WCE) was lowest in weed free
plots throughout the observation period and weedy check (control) recorded highest density
dry matter and WCE among all other treatments. At 15 DAS, pre-emergent herbicide treated
plots recorded lowest density of weeds in the order T3 >T1 >T2. At 30 DAS, T2 and T7 recorded
lowest density of weeds. At 45 DAS, T5, T3, T8 and T7 were recorded with lowest density of
weeds and which were on par to each other. At 60 DAS, T8, T3, T7 and T6 were recorded lowest
density of weeds and which were on par to each other.
In the case of weed dry weight at 15 DAS, T3 recorded the lowest value for dry weight
compared to all other treatments except for T11. At 30 DAS, significantly lower value for dry
weight was recorded in T2, which was on par with T7 and T3. At 45 DAS, significantly lower
value for weed dry weight was recorded in T8 among all the treatments which were on par with
T5 and T7. At 60 DAS, dry weight recorded by the treatment T2 was significantly lower among
all the weed control treatments except for T3, T5, T7 and T8 which were on par to each other.
Lowest WCE was observed in control plot or weedy check (T10). At 15 DAS, the treatments
T3, T2 and T1 recorded the highest WCE. At 30 DAS, T2 was recorded with significantly higher
WCE. At 45 DAS, WCE was significantly higher in T8 and was on par to T5, T7 T2 and T3. At
harvesting stage (60 DAS), the treatment T2 recorded significantly higher value for WCE which
was on par to T3. Significantly lower value for weed index (WI) was recorded in weed free
plots and T7.
Plant height, number of branches per plant (harvesting stage) and leaf area index was
highest in weed free plot compared to that of all other treatments. Number of nodules per plant
was recorded significantly superior in T7 at flowering stage and T2 at harvesting stage. Total
dry matter production was highest in T7 which was on par with T3 at flowering and harvesting
stages. Number of pods per plant, pod yield and seed yield were highest in weed free plots
compare to that of all other treatments. Treatment T7 recorded significantly superior results in
the case of number of seeds per pod, pod weight per plant and test weight and which was on
par with that of pre-emergent application of T3 and T11. Among the available soil nutrients,
depletion of available N was highest in T10 and treatment T8 recorded highest soil N content.
Gross returns and net returns were highest in weed free plots compare to all other treatments
which was followed by T3. Similar trend was shown in the case of net return also. The highest
B:C ratio of 2.45 was obtained for T7 and T3 which were on par with T11 (2.42).
The overall results indicated that weed infestation significantly affected yield in cowpea
and integrated weed management (IWM) especially during the critical period of crop weed
competition in cowpea is inevitable for getting an economic yield and could reduce yield loss
even upto 67 per cent. Even though the cost of cultivation was highest in the weed free plots,
the B:C was on par with that of the best IWM practices owing to the superior yield in these
plots. Pre-emergence application of pendimethalin along with mulching; and mulching along
with hand weeding could effectively keep the field weed free for the critical period of crop
weed competition and this treatment resulted in highest B:C ratio and highest on par yields.