Ecology and management of an exotic weed Phalaris minor - Invasive Plants: Ecological and Agricultural Aspects - page 159

and yield of wheat, particularly in the wheat-rice ( Oryza sativa L.) cropping
system in India and Pakistan [1, 3, 4].
Wheat yield reductions are positively correlated with P. minor densities [5].
A density of 50 and 250 Phalaris minor plants m -2 reduced wheat yield by 8%
and 44%, respectively [6]. Continuous and excessive use of isoproturon ( N , N -
dimethyl- N '-[4-(1-methylethyl)phenyl]urea) has selected for resistant biotypes
of P. minor in Haryana and Punjab [1]. Isoproturon-resistant P . minor has
caused yield reductions of 30-80% and thus massive income losses. New her-
bicides, such as clodinafop (( R )-2-[4-[(5-chloro-3-fluoro-2-pyridinyl)oxy]phe-
noxy]propanoic acid), fenoxaprop ((±)-2-[4-[(6-chloro-2-benzoxazolyl)oxyl]
phenoxy]propanoic acid), sulfosulfuron (1-(2-ethylsulfonylimidazol[1,2-
a ]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyridimidin-2-yl)urea) and tralkoxy-
dim (2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethyl phenyl)cyclo-
hex-2-enone), resulted in four-fold increases in herbicide cost from INR 450
per ha (approximately US$ 10 per ha) to INR 1,500-1,800 per ha (approx.
US$ 33-40 per ha) [7].
Poor farmers, due to inadequate finances, continue to use isoproturon, which
further magnifies the problem of P. minor resistance to isoproturon. Inadequate
management of P. minor results in low wheat yield; consequently low income
and lack of capital in the subsequent year, which is a self-perpetuating mecha-
nism [8].
Most research on P. minor has focused on its management; questions
regarding its ecology largely remain neglected. These include: 1) why is P.
minor the predominant weed in wheat fields, particularly in a wheat-rice crop-
ping system; 2) why is it largely restricted to cultivated fields and not escap-
ing its field boundaries; and 3) what makes a favorable habitat for P. minor
establishment and growth? Answers to these questions may help in designing
an effective management strategy to control P. minor .
The aim of this article is to discuss: 1) P. minor as an invasive weed; 2)
favorable habitats for P. minor ; 3) agricultural practices that affect herbicide
efficacy on P. minor ; iv) correlation between P. minor biotypes, herbicide
resistance, and substratum ecology; and v) an integrated management
approach for P. minor.
Is Phalaris minor an invasive weed?
There are diverse views concerning invasive weed terminology [9-12].
Colautti [13] reviewed invasion terminology and argued in support of stage-
based terminology for invasive plants. Pyˇek et al. [14] suggested definitions
for native, exotic, naturalized, and invasive plants (Tab. 1). However, these
authors cautioned that their definitions might not fit universally because vari-
ous stages of invasion represent a continuum. P. minor is not native to India,
and therefore is an exotic plant. Two questions arise: 1) whether P. minor can
be identified as a naturalized plant and 2) is it an invasive plant?