Dhileepan (2003a, b) studied the effectiveness of leaf-feeding beetle Zygogramma bicolorata (Fig. 3), stem-galling moth Epiblema strenuana and stem-boring weevil Listronotus setosipennis introduced against P. hysterophorus in Australia. The moth Carmenta ithacae and leaf-rust Puccinia melampodi were released to eliminate this weed, but little success has been attained in this regard as the weed has great regenerative potential and moreover the insect consumes only the foliage of the weed which stimulates further leafy proliferation (Dhileepan and Strathie 2009). The flowers and seeds, which are the main source of its dissemination, remain unaffected.
Eucalyptus, a native of Australia, is a known allelopathic tree that exerts its toxicity through leachates and volatile terpenes on adjoining vegetation/agricultural crops. The volatile terpenes present in leaves of eucalyptus emanate in the form of vapours into the surroundings. The vapours get adsorbed to soil, curbing the seed germination and reducing the chlorophyll content as well as cellular respiration. The oil vapours increase water loss leading to wilting. Eucalyptus oils may be used as natural herbicides for the biocontrol of P. hysterophorus owing to its allelochemicals (Kohli et al. 1998). Cassia sericea has the ability to overgrow P. hysterophorus in North-East India. Also marigold (Tagetes erecta) is reported to suppress P. hysterophorus growth in field trials (Lakshmi and Srinivas 2007).The control agents for the weed P. hysterophorus
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