CONTENTS

Research Notes
J.Res. ANGRAU 41(2) 115-117, 2013
EVALUATION OF DEFOLIANTS ON MUNGBEAN Vigna radiata L.
AS HARVESTING TOOLS
B. PADMAJA, M. MALLA REDDY, S. MALATHI and D. VISHNU VARDHAN REDDY
AICRP on Pigeon pea, Regional Agricultural Research Station,
Acharya N.G.Ranga Agricultural University, Warangal – 506 007
Date of Receipt : 06.12.2012 Date of Acceptance : 10.05.2013
India is the largest producer and consumer of
mungbean and it alone accounts for about 65% of
the world acreage and 54% of the world production
(Singh and Singh, 2011). It is cultivated across the
country throughout the year. Manual harvesting of
mungbean is labour-intensive and hence mechanical
harvesting is an option to overcome labour shortage
and reduce production costs. Mungbean foliage does
not dry or abscise when pods are mature. This is the
major limiting factor in mechanical harvesting. Hence,
plants must be defoliated to facilitate mechanical
harvesting. Moreover, it aids in the addition of organic
matter to the soil through leaf fall before harvesting.
Defoliation is shedding of leaves that usually
occur when the leaves become physiologically
mature. Leaf shedding (abscission) results from
activity of special cells in the abscission layer at the
base of the leaf petiole where it joins the stem.
Several factors like frost, disease, drought and
mineral deficiency cause defoliation. It also can be
artificially induced by the use of certain chemicals
called “defoliants”. Desiccation is drying of plant
tissues due to disruption of cell membranes and rapid
loss of moisture, often resulting in “stuck leaves”.
Defoliants or desiccators are widely used in cotton
production. There are many categories of defoliants.
Hormonal defoliants enhance ethylene production and
/ or inhibit auxin transport in the plant (Gwathmey
and Craig, 2007). The balance of these hormones
affects leaf abscission. Cells in the abscission layer
in the petiole separate due to cell wall degrading
enzymes that respond to decreasing auxin-toethylene
ratio. Herbicidal defoliants injure the plant
causing it to produce ethylene in response. Ethylene
promotes leaf abscission by increasing the activity
of enzymes such as pectinase and cellulase, which
degrade cell walls and middle lamellae in the
abscission zone of the petiole. Defoliation response
of hormonal defoliants is generally more sensitive to
temperature and crop conditions than that of
herbicidal defoliants.
The indeterminate flowering habit of mungbean
coupled with accumulation of more dry matter during
rainy season, can pose many harvesting problems.
Further, in mechanical harvesting, weeds in the field
may also pose problems to the performance of
harvesting machines. Hence herbicides like
Glyphosate (4.0 lit/ha) and Paraquat (2.5 lit/ha) can
be used to remove weeds and to achieve defoliation
(Copur et al., 2010). Bi et al. (2005) reported that
other chemicals like CuEDTA and ZnSO 4
also
promote defoliation of leaves in plants. The ideal
stage of harvesting is when majority of pods are
physiologically mature, and 90% of the pods have
turned either yellow or black. At this stage the crop
attains maximum maturity and will be at optimum
yield and quality. At this stage the crop should be
considered ready for either desiccant or defoliant
application. Available literature indicates that
information on defoliants in mungbean is scanty.
Therefore, an experiment was conducted to assess
the effect of certain chemicals on the defoliation of
mungbean.
The experiment was carried out at Regional
Agricultural Research Station, Warangal during rainy
season of 2009. The soil was sandy loam with a P H
of 7.9 and EC of 0.2 d Sm -1 , low in organic carbon
(0.3%) and available N (263 kg/ha), medium in
available P 2
O 5
(28 kg/ha) and available K 2
O (295 kg/
ha). Mungbean crop variety, WGG-37 was sown on
June 30 th 2009. All the cultivation practices were
followed as per the recommendations to the region.
The experiment was laid out in a Randomized Block
Design comprising seven treatments with three
replications each in plot size of 6.0 x 6.0 m. Spraying
of test chemicals was done at physiological maturity
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