© Benaki Phytopathological Institute
Competitiveness of alfalfa cultivars against silverleaf nightshade
43
leaf nightshade on the forage yield of alfalfa
are shown in Table 3. The presence of
S. elae-
agnifolium
was responsible for significant
reductions, up to 26, 15 and 14% in the an-
nual yields of the cultivars Gea, Dimitra and
Hyliki, respectively. The higher yields of all
three alfalfa cultivars during the second year
of experimentation (2011) compared with
the first year (2010) were probably due to
the significantly higher precipitation (38%)
during 2011 (Table 1). It has also to be not-
ed that the maximum yield reductions were
observed in the second and third harvest.
This finding may be attributed to the vigor-
ous growth of silverleaf nightshade during
summer (mostly July and August) and is in
full accordance with previous studies (Trav-
los, 2012). Our results also proved that even
in the presence of silverleaf nightshade, the
annual forage yield of Hyliki was 23 to 28%
and 12 to 13% higher than the yield of Gea
and Dimitra, respectively.
Regarding the density of silverleaf night-
shade, the weed was present at densities
ranging between 2 and 7 plants/m
2
in the
plots of Gea during the first year, while for
Hyliki the maximum density was only about
3 plants/m
2
(Table 4). The mean density of
the weed plants in the case of Hyliki was 31-
34 and 51-57% lower than the correspond-
ing values for Dimitra and Gea, respective-
ly. The more rainfalls during 2011 resulted to
a higher weed density compared with the
first, drier year of experimentation.
Concerning the weed biomass, the
mean growth of individual silverleaf night-
shade plants in the plots with Hyliki was 43
and 60% lower than the corresponding val-
ues for Dimitra and Gea, respectively. Addi-
tionally, in the fourth harvest of alfalfa (210
DAS), the number of
S. elaeagnifolium
plants
in the case of Hyliki was 65% lower than that
of Gea, while the fresh weight per plant was
also significantly lower (82%), as shown in
Table 5.
This less vigorous and less dense pres-
ence of theweed in the plots of Hyliki is prob-
ably due to the recorded faster regrowth
rate of this cultivar of alfalfa, compared with
the other two cultivars. Indeed, according to
our observations the regrowth ability of Hy-
liki after each harvest was significantly high-
er (scored as 4) than the other two cultivars
(scored as 2). It is considered that differenc-
es among alfalfa cultivars in their ability to
develop canopy structures early in the sea-
son could affect weed emergence (Huarte
and Benech Arnold, 2003). Alfalfa has the
Table 1.
Mean monthly rainfall and temperature during the field experiment in 2010 and
2011.
Month
Rainfall
Temperature
2010
2011
2010
2011
mm
°C
January
-
-
-
-
February
-
-
-
-
March
11
25.6
14.4
12.2
April
0
40
17.9
15.5
May
7
40.8
22.2
20.3
June
12
30.4
25.9
25.5
July
0
0
29.3
29.7
August
0
0.6
28.4
28.8
September
22.6
3.4
24.9
26.6
October
81.8
38.4
19
17.5
November
15.6
2.2
18.4
12.3
December
25
100.8
13.7
12
Total
175
282.2
-
-
1...,35,36,37,38,39,40,41,42,43,44 46,47,48,49,50,51,52