PhD

Alternanthera bettzickiana (Regel) Voss., commonly known as Calico plant, is
an invasive upland weed belonging to the family Amaranthaceae. Originating in
tropical America, it is now widely found in the southern and north-eastern states of
India, especially in Kerala, Karnataka, Tamil Nadu and Assam. In Kerala, A.
bettzickiana is now appearing as a major weed in vegetable, fruit and tuber growing
areas, and also in unutilized lands.
Surveys were conducted in 2020 and 2021 in the uplands/garden lands of
central zone of Kerala, which includes eight Agro-Ecological Units (AEUs) covering
Malappuram, Palakkad, Thrissur and Ernakulam districts. Except in two AEUs, A.
bettzickiana was dominant in uncultivated areas in surveyed areas. Density and
growth of A. bettzickiana showed significant positive correlation with soil organic
carbon and nitrogen contents.
A. bettzickiana is an erect or prostrate, dicot, annual/perennial herb. The weed
has sessile oblanceolate pubescent leaves and exhibits opposite phyllotaxy. Stem is
cylindrical, green, solid and branched. A. bettzickiana has a well-developed tap root
system and also produces adventitious roots at the stem nodes. Its inflorescence is a
white, globose to ovoid spike. On an average, A. bettzickiana produces 438-720 seeds
per plant and one thousand seed weight ranges between 0.46 to 0.5 g.
In the field, in the rainy season it takes four to six days for the seeds to
germinate. Vegetative phase of the weed occurs during June-August, and has an
average duration of 40- 45 days. Flowering period of the weed lasts for about three
months from August to October. Complete maturation of the seeds takes about four
months from November to February.
Alternanthera bettzickiana possesses both sexual and vegetative propagation
mechanisms. Morphological features like shoot length and number of branches were
comparatively higher in vegetatively propagated plants, whereas length and width of
leaves were higher in plants propagated through seeds.
Strong stimulation to seed germination of the weed was observed in light
condition and under higher temperatures (30-34°C), whereas lower temperature of 22
and 26°C and darkness inhibited germination. Seed placement at soil surface showed
highest emergence of A. bettzickiana and complete inhibition was observed with seed
placement beyond five centimeters. Higher soil moisture levels favoured germination.
Seed longevity studies revealed that germination of A. bettzickiana seeds increased up
to five months age and thereafter exhibited a decline, with no germination beyond the
age of nine months. Seeds taken out from net bags buried at a depth of 4 cm recorded
highest germination while those placed on the soil surface showed the lowest.
Application of aqueous extract of A. bettzickiana at various concentrations did
not show any prominent effect on mean seed germination and seedling vigour of rice,
whereas a delay in germination and reduction in seedling vigour was observed in
cowpea seeds treated with 8% extract. Incorporation of A. bettzickiana in the soil and
mulching with various quantities of the weed did not produce any significant effect on
rice or cowpea. Seedling parameters of both rice and cowpea were not affected by
either the concentration or application time of aqueous extract.
Field trials were conducted in 2021 (August to November) and 2022 (July to
October) to assess the efficacy of various pre- and post-emergence herbicides to
manage A. bettzickiana in oriental pickling melon (variety Saubhagya). At 30 DAS,
significantly lower density of A. bettzickiana, total broad-leaved weeds, grasses, and
total weed density, dry matter production and nutrient uptake by weeds were recorded
with pre-emergence spray of oxyfluorfen alone @ 0.15 kg/ha and in combination with
post-emergence herbicides 2,4-D @ 1 kg/ha or metsulfuron methyl+ chlorimuron
ethyl @ 0.004 kg/ha, and with hand weeding at 20 and 40 DAS. At 60 DAS, all these
parameters were significantly lower with pre-emergence spray of oxyfluorfen @ 0.15
kg/ha followed by post-emergence application of either 2,4-D @ 1 kg/ha or
metsulfuron methyl+ chlorimuron ethyl @ 0.004 kg/ha and was at a par with hand
weeding at 20 and 40 DAS.
Mean fruit weight and fruit yield of oriental pickling melon were significantly
higher with hand weeding twice at 20 and 40 DAS followed by pre-emergence
application of oxyfluorfen @ 0.15 kg/ha followed by post- emergence application of
either 2,4-D @ 1 kg/ha or metsulfuron methyl+ chlorimuron ethyl @ 0.004 kg/ha in
both the years. At 30 DAS, the same treatments and pre-emergence oxyfluorfen alone
resulted in higher weed control efficiency, while at 60 DAS only the combined preand post- emergence herbicide application had higher weed control efficiency. The
combinations also recorded lower weed index and higher net returns and B: C ratios.
Vermicomposting of A. bettzickiana along with banana pseudostem at various
proportions was attempted. Higher total N and total P content and lower total organic
carbon content and C: N ratio were recorded with A. bettzickiana alone and A.
bettzickiana + banana pseudostem at 8:1 ratio. Highest total organic carbon content,
C: N ratio and total K was recorded with A. bettzickiana + banana pseudostem at 1:1
ratio. Bulk density of the vermicompost ranged from 0.75 to 0.93 g/cm3
.
Concentration of heavy metals like cadmium, nickel and lead in the compost were
found to be non-significant between treatments, and all the three elements were found
to be within safe limits. The composting process was completed in 71-79 days.