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International Journal of Pest Management
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/ttpm20
Allelopathic potential of winter and summer cover
crops on the germination and seedling growth of
Solanum americanum
Leandro Galon , Emanuel Rodrigo de Oliveira Rossetto , Ana Carolyna
Enderle Zanella , Daiani Brandler , Emanuel Luis Favretto , Jaqueline Mara
Dill , Cesar Tiago Forte & Caroline Müller
To cite this article: Leandro Galon , Emanuel Rodrigo de Oliveira Rossetto , Ana Carolyna Enderle
Zanella , Daiani Brandler , Emanuel Luis Favretto , Jaqueline Mara Dill , Cesar Tiago Forte &
Caroline Müller (2021): Allelopathic potential of winter and summer cover crops on the germination
and seedling growth of Solanum�americanum , International Journal of Pest Management, DOI:
10.1080/09670874.2021.1875152
To link to this article: https://doi.org/10.1080/09670874.2021.1875152
Published online: 19 Jan 2021.
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Allelopathic potential of winter and summer cover crops on the
germination and seedling growth of Solanum americanum
Leandro Galon
a
, Emanuel Rodrigo de Oliveira Rossetto
a
, Ana Carolyna Enderle Zanella
a
,
Daiani Brandler
a
, Emanuel Luis Favretto
a
, Jaqueline Mara Dill
a
, Cesar Tiago Forte
b
and
Caroline M€
uller
a
a
Laboratory of Sustainable Management of Agricultural Systems, Federal University of Fronteira Sul (UFFS), Erechim, Brazil;
b
Department of Agronomy, Federal University of Santa Maria (UFSM), Santa Maria, Brazil
ABSTRACT
Sustainable weed management strategies are important for reducing chemical inputs and
development of weed resistance. This study aimed to evaluate the effect of extracts from
winter cover crops (cereal rye, black oat, forage turnip, and common vetch) and summer
cover crops (jack bean, velvet bean, and brown hemp) on seed germination and seedling
growth of glossy nightshade (Solanum americanum Mill), under controlled conditions. The
aqueous extracts were produced from the shoot biomass of cover crops at concentrations of
0%, 25%, 50%, 75%, and 100%. Fifty S. americanum seeds were placed on Germitest paper
moistened with 15 mL of each extract concentration. Cereal rye extract at the highest con-
centration reduced total germination to 43% and caused a 62% reduction in the germin-
ation rate index (GRI) of S. americanum. Velvet bean extract reduced germination, GRI, and
seedling growth of S. americanum from the lowest concentration applied, while concentra-
tions of 75% and 100% completely suppressed seedling development. Decomposing cereal
rye and velvet bean cover crops have potential to suppress germination and growth of S.
americanum. Efficient cover crops could reduce herbicide applications, and thus improve
herbicide resistance management.
ARTICLE HISTORY
Received 1 June 2020
Accepted 7 January 2021
KEYWORDS
Weed control; allelopathy;
germination rate index;
Secale cereale;Mucuna
cochinchinensis
1. Introduction
The occurrence of weeds is an important factor that
interferes in the productivity of crops and in the
quality of harvested grains. Yield losses due to weed
incidence can be 23–56% in crops of agricultural
interest such as soybean, rice, corn, wheat, and cot-
ton (Oerke 2006; Adeux et al. 2019). Currently, the
use of herbicides is the main method used to con-
trol weeds. However, excessive dependence on these
products, in addition to increasing management
costs (Price et al. 2011), has led to the selection of
resistant weeds (Heap 2020), and environmental
pollution (Herek et al. 2020; Silva et al. 2020).
Among the most common weeds found in
Brazilian crops, glossy nightshade (Solanum ameri-
canum Mill.), belonging to the Solanaceae family, is
a problematic weed. In the southern region of
Brazil, this weed can be found in wheat, barley, oat,
and canola in the winter months, while during the
summer, it is a weed of corn, beans, and soybeans.
In addition to being present in all seasons and in
various cultures, it is a highly competitive weed for
environmental resources such as water, light, and
nutrients (Cardoso et al. 2017).
Weeds represent the most important biotic factor
that affect yield, so nowadays, integrated weed man-
agement is carried out in the context of sustainable
agriculture, including the exploitation of allelopathic
mechanisms (Scavo and Mauromicale 2020). The
term “Allelopathy”was coined by Hans Molisch in
1937 (Molisch 1938), differentiated from the term
“competition”reported by Rice (1985). Allelopathy
is defined, as actually used by the International
Allelopathy Society, as any process involving the
secondary metabolites produced by plants, fungi,
bacteria, algae, or viruses that influence the growth
and development of agricultural and biological sys-
tems (excluding animals), including positive and
negative effects (IAS 1996). As a biological manage-
ment, allelopathic species can act to control weeds
by releasing chemical substances into the environ-
ment through leaching, volatilization, root exud-
ation, or plant decomposition (Inderjit et al. 2005;
Jabran et al. 2015; Muzell Trezzi et al. 2016),
improving cultivation practices of several crops.
CONTACT Caroline M€
uller carolinemulleram@gmail.com Universidade Federal da Fronteira Sul, RS 135 –Km 72, no 200, P.O. Box 764, 99700-
000, Erechim, RS, Brazil
Supplemental data for this article can be accessed at https://doi.org/10.1080/09670874.2021.1875152.
ß2021 Informa UK Limited, trading as Taylor & Francis Group
INTERNATIONAL JOURNAL OF PEST MANAGEMENT
https://doi.org/10.1080/09670874.2021.1875152
Allelochemicals can alter several physiological reac-
tions, such as electron transport, antioxidant enzym-
atic activities, cell division and ultrastructure,
membrane permeability, among others, which may
cause inhibition of germination, root necrosis, and
reduced growth and reproductive capacity of other
plants (revised by Lemessa and Wakjira 2014;Li
et al. 2019).
A practical way of obtaining allelochemicals from
plants is to use them as cover crops. In addition to
the release of secondary compounds, cover crops
maintain soil moisture, improve the soil organic
matter and the C/N ratio, and reduce soil erosion.
The use of black oat, velvet bean, and brown hemp
still naturally control the occurrence of nematodes
(Germani and Plenchette 2005; Berry et al. 2011;
Santana-Gomes et al. 2019). The use of cover crops
has been suggested in the management of Solanum
species in the field, as it restricts temperature vari-
ation, which favors the germination of these species
(Forte et al. 2019; Dong et al. 2020), and also
increase the depth of seed bank acting as a physical
barrier (Alonso-Ayuso et al. 2018; Forte et al. 2019).
However, there are no studies on the evaluation of
potential allelochemicals in the control of this weed.
Many plant species exhibit or are presumed to
exhibit allelopathy or produce allelopathic com-
pounds (Kong 2010). The potential of some crop
species to inhibit weeds has already been demon-
strated. Residues of Mucuna cochinchinensis (Lour.)
are reported to affect the emergence and dry weight
of Asystasia intrusa (Forssk.) and Paspalum conjuga-
tum (P. J. Bergius) (Sahid et al. 1993). The cultiva-
tion of corn and soybeans with cover crops of hairy
vetch (Vicia villosa Roth) and cereal rye (Secale cere-
ale L.), respectively, can reduce the need for herbi-
cide application when these cover crops suppress
weed species (Teasdale et al. 2007). Lawley et al.
(2011) found that the use of forage turnip
(Raphanus sativus L.) suppressed annual winter
weeds in autumn and early spring, and did not
affect the density and yield of the subsequent corn
crop. The inhibition of seed germination can delay
the emergence of new weeds in cultivated areas, in
addition to reducing their competitiveness for water,
nutrients, and light (Souza Filho and Mour~
ao
Jr. 2010).
Suppressing weeds with allelopathic cover crops
depends on the production and release of allelo-
chemicals from cover crops and the susceptibility of
the target plant. Sowing cover crops with allelo-
pathic potential may reduce the use of herbicides
and promote greater sustainability of agroecosystems
(Lemessa and Wakjira 2014). The objective of this
research was to determine if winter and summer
cover crops can inhibit the germination and devel-
opment of S. americanum.
2. Material and methods
2.1. Cover crop extracts
Plant extracts were prepared using the aerial parts
of four winter cover crops species: S. cereale L. (cer-
eal rye), Avena strigosa L. (black oat), R. sativus L.
(forage turnip), and Vicia sativa L. (common vetch);
and three summer cover crops: Canavalia ensiformis
(L.) DC. (jack bean), M. cochinchinensis (Lour.) A.
Chev (velvet bean) and Crotalaria juncea L. (brown
hemp). The cover crops were grown in the field, in
the municipality of Erechim, Rio Grande do Sul,
Brazil (latitute 27.7239, longitude 52.2944).
The climate in the region is classified as humid sub-
tropical climate (Cfa), according to K€
oppen classifi-
cation, with rainfall well distributed throughout the
year (CemetRS 2012). The seeds were sown with a
seeder/fertilizer machine in the seasons and with
recommended spacing for each cover crop. Basic
and surface fertilization was applied based on previ-
ous soil analysis, according to technical recommen-
dations (ROLAS 2016). Weed control was carried
out by weeding or manual plucking whenever neces-
sary. No pesticides were applied due to the absence
of insects and diseases.
The aerial part of the cover crops (stems and
leaves) was collected at the vegetative stage, in the
morning, and immediately taken to the laboratory.
Fresh plant material was disinfected with sodium
hypochlorite (10%) for 1 min and then washed three
times with distilled water. After drying the leaves at
room temperature for 2 h, crude aqueous extracts
were prepared by grinding the plant material in an
industrial blender. Grinding was done with distilled
water at ambient temperature (1 kg of the fresh
matter : 1 L of distilled water), for 9 min, with 5 min
intervals every 3 min. Afterwards, the extracts were
stored in a dark place for 24 h and sequentially fil-
tered through sieves and gauze and stored in a
freezer (20 C) until use. The crude aqueous
extracts were then diluted to concentrations of 0%
(control), 25%, 50%, 75%, and 100%.
2.2. Experimental design and
germination bioassays
The experiment was conducted at the Laboratory of
Sustainable Management of Agricultural Systems
(MASSA), located at the Federal University of
Fronteira Sul (UFFS), Campus Erechim, Rio Grande
do Sul, Brazil.
The experiment was carried out in a completely
randomized design, consisting of five concentrations
2 L. GALON ET AL.
of winter and summer cover crop extracts, with four
replicates. Seeds of glossy nightshade (S. ameri-
canum Mill.) were collected in March and April
2017 in Ibiraiaras, Rio Grande do Sul, Brazil (28
24019.100 S and 5137029.500 W). Black ripe fruits
were collected that could be easily detached from
the mother plant. The seeds were separated manu-
ally and disinfected with sodium hypochlorite (10%)
for 10 s, followed by three washes with distilled
water. The seeds were dried in the shade for 5 d
and stored in a dry place at room temperature in
plastic packaging. Before the initiation of the experi-
ments, seed dormancy was broken by alternating
temperatures as described by Forte et al. (2019).
Fifty S. americanum seeds were placed on three
sheets of Germitest paper moistened with 15 mL of
each aqueous extract concentration and placed in
germination chamber with a temperature of 23 C
and a photoperiod of 12/12 h (light/dark) for 16 d,
according to the Rules of Seed Analysis (RAS)
(Brasil 2009).
2.3. Evaluations
Germination was evaluated daily for 16 d; seeds
were considered germinated when there was a 2 mm
root protrusion, according to Brasil (2009). At the
end of the experimental period, the total germin-
ation (TG) percentage was calculated.
The germination rate index (GRI) was deter-
mined as described by Maguire (1962), as being:
GRI ¼X
n
i¼1
ni
i
where ni ¼number of seeds germinated on day i; i
¼number of days.
Germination was also evaluated over time by
adjusting Gompertz curves, based on the function
described by Richards (1969):
Y¼ae be kt
where Y represents germination at time t;ais the
inflexion point of the curve; bbecomes a unit when
time is measured from the inflection point, in this
case when Y ¼a/e;krepresents the “constant rate”
that determines the extend of the curve along the
time axis.
The shoot length (cm) of the plants was meas-
ured 16 d after the beginning of the experiments,
using 10 seedlings per experimental unit.
2.4. Statistical analysis
Data of TG, GRI, and shoot length were subjected
to analysis of normality (Shapiro–Wilk test). As the
data were not normally distributed, even after trans-
formations, they were subjected to non-parametric
analysis, and the means were compared using the
Kruskal–Wallis’test (p<0.05). The daily germin-
ation curve was adjusted to the Gompertz model.
Statistical analyses were performed using Statistica
software version 8.0 (StatSoft Inc., Tulsa, OK).
3. Results and discussion
3.1. Total germination
The aqueous extracts of winter and summer cover
crops caused differential responses in the germin-
ation and seedling growth of S. americanum.
Among the extracts, cereal rye showed the highest
percentage inhibition of S. americanum germination
(43%), followed by oat extracts (19%) and forage
turnip (10%) at the highest concentration evaluated
(Table 1).
Aqueous cereal rye extracts have also been
reported to inhibit completely the germination of
willowherb (Epilobium ciliatum Raf.) and horseweed
[Conyza canadensis (L.) Cronquist], and reduce the
germination of barnyard grass [Echinochloa crus-
galli (L.) Beauv.]; all these weeds are resistant to
triazine herbicides (Przepiorkowski and Gorski
Table 1. Total germination (%) of Solanum americanum seeds exposed to different concentrations of aqueous extracts from
winter (cereal rye, black oat, forage turnip, and common vetch) and summer (jack bean, velvet bean, and brown hemp)
cover crops, for 16 d.
Extract concentration (%)
0 25 50 75 100 Kruskal-Wallis PValue
Winter crop
Cereal rye 98.7 ± 0.47Aa 91.5 ± 2.2ABa 98.0 ± 0.8Aa 94.7 ± 1.7ABab 56.7 ± 1.3Bbc H
4,20
¼15.66 0.0035
Black oat 98.7 ± 0.47Aa 98.0 ± 1.2ABa 97.5 ± 1.5ABa 94.5.0 ± 0.9Abab 80.0 ± 2.2Babc H
4,20
¼13.02 0.0112
Forage turnip 98.7 ± 0.47Aa 96.0 ± 0.0ABa 97.5 ± 1.5ABa 96.5 ± 2.9ABab 88.5 ± 2.4Babc H
4,20
¼10.11 0.0386
Common vetch 98.7 ± 0.47Aa 96.0 ± 1.6Aa 95.3 ± 0.5Aa 99.0 ± 0.6Aa 99.0 ± 1.0Aa H
4,20
¼9.50 0.0497
Summer crop
Jack bean 98.7 ± 0.47Aa 98.5 ± 0.9Aa 96.5 ± 1.0Aa 98.7 ± 0.5Aa 96.5 ± 0.9Aab H
4,20
¼7.27 0.1224
Velvet bean 98.7 ± 0.47Aa 59.5 ± 20.5ABa 33.3 ± 14.3ABa 3.00 ± 1.7Bb 1.00 ± 0.6Bc H
4,20
¼14.93 0.0049
Brown hemp 98.7± 0.47Aa 96.0 ± 1.6Aa 98.0 ± 0.8Aa 93.0 ± 3.9Aab 95.0 ± 2.4Aab H
4,20
¼3.45 0.4861
Kruskal-Wallis H
6,28
¼0.000 H
6,28
¼14.45 H
6,28
¼14.00 H
6,28
¼16.93 H
6,28
¼24.63
p-value 1.000 0.0250 0.0296 0.0096 0.0004
Mean ± SEM (n¼5). Means followed by the same letter, uppercase in the rows and lowercase in the columns, do not differ by Kruskal–Wallis’
test (p0.05).
INTERNATIONAL JOURNAL OF PEST MANAGEMENT 3
1994). The major groups of allelochemicals in plants
are alkaloids, benzoxazinoids, coumarins, flavonoids,
glucosinolates, phenolic compounds, quinones, and
terpenes (see reviews by Jabran 2017; Mac
ıas et al.
2019). Cereal rye mainly contains (3H)-benzoxazoli-
none (BOA) and 2,4-dihydroxy-1,4-
(2H)benzoxazine-3-one (DIBOA), benzoxazinoids,
in addition to phenolic acids (Carlsen et al. 2009;
Cimmino et al. 2015). However, DIBOA was
reported to be more phytotoxic than BOA in inhib-
iting weeds (Burgos and Talbert 2000; Mac
ıas et al.
2005). Burgos and Talbert (2000) also reported that
Figure 1. Accumulated germination (%) of Solanum americanum seeds exposed to different concentrations of aqueous
extracts from winter (cereal rye, black oat, forage turnip, and common vetch) and summer (jack bean, velvet bean, and brown
hemp) cover crops, for 16 d. Symbols represent means (n¼5). Curves fitted to the Gompertz model (equations shown as
Supplementary Material, Table S1).
4 L. GALON ET AL.
small-seeded weeds such as E. crus-galli,Eleusine
indica (L.) Gaertn, Digitaria sanguinalis (L.) Scop.
and Amaranthus palmeri S. Watson were more sen-
sitive to cereal rye extract compared with medium-
to large-seeded weeds [Ipomoea hederacea Jacq.,
Senna obtusifolia (L.) Irwin & Barneby and I. lacu-
nosa L.]. In field experiments, cereal rye planted
four weeks before alfafa (Medicago sativa L.)
reduced weed density by 77% (Adhikari et al. 2018).
The production of allelochemicals, however, can be
altered depending on the harvest time and genotypic
characteristics (Carraro-Lemes et al. 2019; Scavo
et al. 2019). Scavo et al. (2019) reported that the
harvest time accounted for 53% of the variance in
the total sesquiterpene lactones (STLs) of Cynara
cardunulus L. According to the authors, plant
material that was collected at the developmental
stage of 50% of the maximum leaf mass (i.e.
8.5 months after planting) showed higher dry leaf
extract yield for all genotypes, and reached values
2.4 times higher than previous collection times (i.e.
2.5 and 5.5 months after planting). However, the
production of allelopathic compounds showed great
variation between collection times. In addition, the
use of solvents such as ethanol or methanol for the
metabolites extraction can alter the composition of
polyphenols and potentiate phytotoxic effects (Scavo
et al. 2020).
Considering the extracts of summer crops, jack
beans and brown hemp did not affect the germin-
ation of S. americanum seeds (Table 1). However,
velvet bean inhibited germination of S. americanum
seeds, by 97% and 99% when exposed to extract
concentrations of 75% and 100%, respectively, com-
pared with control treatment (Table 1). Previous
studies have shown that aqueous extracts of velvet
bean reduced TG of the weeds A. intrusa and P.
conjugatum by, on average, 25% (Sahid et al. 1993),
and of E. indica by 94% (Ibrahim et al. 2018). The
main allelopathic compound in velvet bean is L-3,4-
dihydroxyphenylalanine (L-DOPA), a non-protein
amino acid precursor of alkaloids and phenylpropa-
noids (Soares et al. 2014).
3.2. Germination rate index
Associated with the total percentage of germination,
it was possible to observe phytotoxic effects on the
GRI of S. americanum seeds (Figure 1 and Table 2).
Seeds exposed to the control treatment germinated
from the fifth day of incubation (Figure 1). The cer-
eal rye extract delayed germination of S. ameri-
canum seeds by 7 and 9 days, at concentrations of
25% and 100%, respectively (Figure 1), resulting in
a decrease in GRI (Table 2).
The extracts of black oats and forage turnip
reduced the S. americanum GRI at concentrations
above 50% and 100%, respectively (Table 2). Black
oat root exudates were also reported to interfere on
the time and medium speed of soybean seeds ger-
mination (Bortolini and Fortes 2005). Oat exudates
contain scopoletin (6-methoxy-7-hydroxy coumarin)
(Fay and Duke 1977), tryptophan, precursor of
some alkaloids (Kato-Noguchi et al. 1994), phenolic
compounds and flavonoids (Iannucci et al. 2012; Liu
et al. 2016) and forage turnip has mainly the flavon-
oid quercetin (Souza et al. 2019). Souza et al. (2019)
also found that a cereal rye and forage turnip con-
sortium were effective alternative for weed control
in agroecological systems.
By delaying the germination of weeds, the com-
petitive capacity of the crop is favored (Lemessa and
Wakjira 2014). The competitive ability of weeds is
compromised with a decrease in population density
or when weeds germinate after the cash crop is
established (Agostinetto et al. 2013; Frandoloso
et al. 2020). In addition, some pasture species grown
in integrated systems were also efficient in reducing
dry biomass (>80%) and seeds production (>95%)
Table 2. Germination rate index (GRI) of Solanum americanum seeds exposed to different concentrations of aqueous extracts
from winter (cereal rye, black oat, forage turnip, and common vetch) and summer (jack bean, velvet bean, and brown hemp)
cover crops, for 16 d.
Extract concentration (%)
0 25 50 75 100 Kruskal–Wallis pValue
Winter crop
Cereal rye 6.84 ± 0.14Aa 4.34 ± 0.24ABb 5.25 ± 0.09ABab 4.65 ± 0.32ABbc 2.62 ± 0.30Bb H
4,20
¼16.87 0.0020
Black oat 6.84 ± 0.14Aa 6.69 ± 0.06Aa 6.27 ± 0.17ABab 5.69 ± 0.23ABabc 4.04 ± 0.40Bab H
4,20
¼15.33 0.0041
Forage turnip 6.84 ± 0.14Aa 5.98 ± 0.28ABab 5.87 ± 0.27ABab 5.80 ± 0.35ABabc 4.34 ± 0.11Bab H
4,20
¼14.80 0.0051
Common vetch 6.84± 0.14Aa 5.10 ± 0.21Bab 5.45 ± 0.40ABab 6.85 ± 0.03Aab 6.55 ± 0.19ABa H
4,20
¼12.66 0.0131
Summer crop
Jack bean 6.84 ± 0.14Aa 6.12 ± 0.17Bab 7.24 ± 0.14Aa 7.33 ± 0.15Aa 6.92 ± 0.19Aba H
4,20
¼12.36 0.0149
Velvet bean 6.84 ± 0.14Aa 3.13 ± 1.19ABb 2.56 ± 1.18ABb 0.11 ± 0.06Bc 0.03 ± 0.02Bb H
4,20
¼14.46 0.0060
Brown hemp 6.84 ± 0.14Aa 5.48 ± 0.23Bab 6.27 ± 0.32ABab 5.86 ± 0.5ABabc 5.84 ± 0.15ABab H
4,20
¼10.10 0.0388
Kruskal-Wallis H
6,28
¼0.000 H
6,28
¼21.90 H
6,28
¼19.94 H
6,28
¼22.46 H
6,28
¼25.44
p-value 1.000 0.0013 0.0028 0.0010 0.0003
Mean ± SEM (n¼5). Means followed by the same letter, uppercase in the rows and lowercase in the columns, do not differ by Kruskal–Wallis’
test (p0.05).
INTERNATIONAL JOURNAL OF PEST MANAGEMENT 5
of the difficult-to-control Parthenium hysterophorus
L. (Shabbir et al. 2018,2019).
3.3. Shoot length
Some extracts caused an increase in the shoot length
of S. americanum (Table 3). This increase occurred
because the seeds were moistened with distilled
water on the tenth day, which caused the dilution of
the extract and favored the growth of the germi-
nated seeds. Even so, the velvet bean extract caused
a 62% reduction in shoot length of S. americanum
with the lowest concentration and complete inhib-
ition with 75% concentration (Table 3). The M.
cochinchinensis had higher dry matter production
compared to other varieties of Mucuna spp. (Avav
et al. 2008) and greater suppression of weeds when
introduced in intercropping with corn 6 weeks after
sowing (Shave et al. 2012). Similar studies have
found that M. pruriens suppressed the growth of
Sphenostylis stenocarpa (Hochst ex A. Rich) Harms
and inhibited the growth of other weeds (Eucharia
and Edward 2010). The authors noted that Mucuna
species could potentially be used to control weeds in
crop rotation systems or when left as waste or
mulch, especially in conservation cropping systems,
such as no-till or minimal soil cultivation systems.
It can reduce rates application of synthetic herbi-
cides, in addition to providing nutrients for the suc-
cessor crop.
Among the evaluated crops, cereal rye can pro-
vide a uniform and dense coverage of the soil
(Mirsky et al. 2013; Korres et al. 2019), and the
large biomass of residues provided by velvet bean
allows greater accumulation of organic matter in the
soil and carbon sequestration (Barth
es et al. 2004),
which can provide long-term soil management.
Therefore, for the integrated management of weeds
in summer crops, cereal rye can be sown in winter
and cut during the flowering period, without the
need for desiccation, to promote the control of S.
americanum in successor crops, such as soybeans or
beans. Velvet bean species has already been used in
the Brazilian Cerrado as a summer cover crop
because it is extremely rustic and withstands periods
of drought –a common factor in the region –,in
addition to increasing N availability (Weiler et al.
2019) and biologically controlling nematodes in the
system (Calegari et al. 2020). This demonstrates that
cereal rye and velvet bean could be adopted by
farmers to improve soil fertility and suppress weeds
in traditional agricultural systems.
In addition to S. americanum, other summer
common weeds in the Southern region of Brazil
already show resistance to several herbicides, to
which the next studies will be direct, such as some
Conyza species [C. bonariensis (L.) Cronquist, C.
sumatrensis (Retzius) Walker, and C. canadenses (L.)
Cronquist] resistant to 5-enolpyruvylshikimate-3-
phosphate synthase (EPSPs; glyphosate), acetolactate
synthase (ALS; metsulfuron methyl), photosystem I
(PSI; paraquat), photosystem II (PSII; diuron), and
protox (saflufenacil) inhibitors (Heap 2020);
Digitaria insularis (L.) Fedde, resistant to EPSPs;
Amaranthus hybridus L., resistant to ALS and
EPSPs; and also Ambrosia elatior L., Elephantopus
mollis Kunth., Ipomea spp., and Euphorbia hetero-
phylla L. Regarding winter weeds, Lolium multiflo-
rum L. is resistant to ALS, EPSPs and ACCAse
inhibitors, and Raphanus spp., Echium plantagineum
L. and Sonchus oleraceus L. are resistant to ALS
inhibitors, which can also be managed with cover
crops such as velvet bean, brown hemp and
jack bean.
4. Conclusions
Cereal rye and velvet bean cover crops have promis-
ing potential for the control of S. americanum in
winter and summer crops, respectively. The allelo-
pathic properties of velvet bean caused total sup-
pression of S. americanum, and the use of cereal rye
Table 3. The shoot length (cm) of Solanum americanum seeds exposed to different concentrations of aqueous extracts from
winter (cereal rye, black oat, forage turnip, and common vetch) and summer (jack bean, velvet bean, and brown hemp)
cover crops, for 16 d.
Extract concentration (%)
0 25 50 75 100 Kruskal–Wallis pValue
Winter crop
Cereal rye 1.39 ± 0.07Ba 2.05 ± 0.25ABab 2.63 ± 0.17Aa 1.74 ± 0.14ABab 1.37 ± 0.13Bab H
4,20
¼14.10 0.0070
Black oat 1.39 ± 0.07Ba 2.37± 0.18Aa 2.21 ± 0.04ABab 2.13 ± 0.09ABab 1.50 ± 0.15Bab H
4,20
¼14.46 0.0060
Forage turnip 1.39 ± 0.07Ba 2.13 ± 0.09ABab 2.46 ± 0.26Aa 2.69 ± 0.07Aa 1.81 ± 0.11ABa H
4,20
¼14.29 0.0064
Common vetch 1.39 ± 0.07Ba 1.70 ± 0.09ABab 2.27 ± 0.09ABab 2.28 ± 0.02ABa 2.43 ± 0.21Aa H
4,20
¼14.45 0.0060
Summer crop
Jack bean 1.39± 0.07ABa 0.62 ± 0.15Bb 1.33 ± 0.05ABab 0.71 ± 0.13ABb 1.45 ± 0.09Aab H
4,20
¼14.08 0.0070
Velvet bean 1.39 ± 0.07Aa 0.53 ± 0.10ABb 0.49 ± 0.22ABb 0.00± 0.00Bb 0.00 ± 0.00Bb H
4,20
¼17.70 0.0014
Brown hemp 1.39± 0.07Aa 0.44 ± 0.04Ab 1.44 ± 0.06Aab 1.44 ± 0.19Aab 1.46 ± 0.04Aab H
4,20
¼9.89 0.0423
Kruskal-Wallis H
6,28
¼0.000 H
6,28
¼22.95 H
6,28
¼22.54 H
6,28
¼25.67 H
6,28
¼20.57
pValue 1.000 0.0008 0.0010 0.0003 0.0022
Mean ± SEM (n¼5). Means followed by the same letter, uppercase in the rows and lowercase in the columns, do not differ by Kruskal–Wallis’
test (p0.05).
6 L. GALON ET AL.
cover may allow a reduction in the application of
herbicides to control the species. The future identifi-
cation of the allelopathic profile involved in the
phytotoxicity of the cover crops will decisively assist
in the management of weeds in conservation sys-
tems that use soil cover, as in the no-till system;
besides contributing to the synthesis of new bioher-
bicides. Efficient cover crops also reduce the appli-
cation of herbicides, costs and environmental, and
improve herbicide resistance management.
Acknowledgments
L. Galon and T.C. Forte are grateful to the CNPq, and C.
M€
uller is grateful to the Coordination for the
Improvement of Higher Education Personnel (CAPES/
PNPD, no. 88887.352933/2019-00) for fellowships.
Disclosure statement
No potential conflict of interest was reported by
the authors.
Funding
The authors thank the National Council for Scientific and
Technological Development (CNPq) and Federal
University of Fronteira Sul (UFFS) for financial support.
M€
uller is grateful to the Coordination for the
Improvement of Higher Education Personnel (CAPES)
for fellowships.
ORCID
Leandro Galon http://orcid.org/0000-0002-1819-462X
Emanuel Rodrigo de Oliveira Rossetto http://orcid.org/
0000-0002-5159-8175
Daiani Brandler http://orcid.org/0000-0002-3347-0522
Emanuel Luis Favretto http://orcid.org/0000-0003-
0060-4093
Jaqueline Mara Dill http://orcid.org/0000-0002-
3940-3152
Cesar Tiago Forte http://orcid.org/0000-0001-
7211-3096
Caroline M€
uller http://orcid.org/0000-0003-0507-9355
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INTERNATIONAL JOURNAL OF PEST MANAGEMENT 9
