Biology Reference
In-Depth Information
that the allelopathic potential of certain crop species of wheat-rice cropping system
could be used to manage
P. minor
. They found that the use of sunflower (
Helianthus
annuus
L.) and dhaincha (
Sesbania aculeate
L.) as green manures could decrease
the seed germination of
P. minor
. In wildland settings, a carbon source has been
added to soil to reduce growth and seed set of fast-growing weeds (see chapter
“USA: Applying Ecological Concepts to the Management of Widespread Grass
Invasions” by D'Antonio et al., this volume). Needed now are field studies to deter-
mine the impact of rice straw on the emergence and establishment of
P. minor
seedlings.
14.3 Management
Several herbicides are employed to combat
P. minor
in wheat fields (Table 14.1).
Isoproturon has been used widely to control
P. minor
in wheat fields for the last 35
years by farmers of Haryana and Punjab (Singh et al. 1999). Since the first observa-
tion by Malik and Singh (1995), reports of
P. minor
biotypes with isoproturon
resistance have been increasing across northwestern India, likely as the products of
continuous and excessive use of isoproturon (Singh et al. 1999; Kaushik et al.
2005). Isoproturon, when applied as a preemergence herbicide at 0.5-1.5 kg ha
−1
,
inhibited seedling emergence of Delhi biotypes but not a Haryana biotype of
P. minor
(Sharma and Pandey 1997). Doubling the recommended dose of isopro-
turon to 1.9kg ha
−1
did not control the resistant
P. minor
biotypes from Punjab
(Walia et al. 1997). Continued use of isoproturon kills susceptible
P. minor
individ-
uals year after year. Increased herbicide selection pressure causes resistant biotypes
to outcompete susceptible biotypes. This practice results in a soil seed bank of
resistant biotypes and slow elimination of susceptible individuals from the
population.
New herbicides with different modes of action have been introduced periodically
to manage resistant biotypes of
P. minor
(Table 14.1). Tralkoxydim (acetyl-
co
-A
carboxylase (ACCase) inhibitor, 0.25 and 0.35 kg/ha) and diclofop-methyl (ACCase
inhibitor, 0.75 and 1.0 kg/ha) were preferred over chlortoluron for their efficiency in
reducing the population and biomass allocation of
P. minor
and increasing wheat
production (Walia and Brar 1996). Similarly, the application of sulfosulfuron (ace-
tolactate synthase (ALS) inhibitor, 25 g ai/ha), fenoxaprop-
p
-ethyl (ACCase inhibitor,
100-120 g ai/ha), or clodinafop (ACCase inhibitor, 35 g ai/ha) successfully control-
led isoproturon-resistant biotypes of
P. minor
and enhanced wheat yield by 200%
compared to that of weedy plots (Chhokar and Malik 2002). Isoxaflutole (5-cyclo-
propyl-4-isoxazolyl)[2-(methylsulfonyl)-4-(trifluoro methyl)phenyl]methanone) is a
preemergent, systemic, soil applied and nontoxic herbicide (Mitra et al. 2001).
It undergoes rapid conversion to the toxic by-product diketonitrile, which inhibits
the enzyme 4-hydroxyphenylpyruvate dioxygenase of carotenoid biosynthesis.
Isoxaflutole is an effective herbicide against some broadleaf and grass weeds (e.g.,
redroot pigweed, velvetleaf, and barnyard grass) (Bhowmik et al. 1999). Kaur et al.
