MSc

Isachne miliacea Roth. is one of the predominant weed in the low land rice fields of Kerala. The weed belongs to the family poaceae. Locally it is known as ‘Chovverippullu, Naringa, Njammal, Changalipullu.’ Previous studies conducted in Kerala Agricultural University showed that I. miliacea alone can contribute to 61 per cent reduction in the production of rice in Onattukara region. Presently, the weed is reported to be spreading to other rice growing regions of Kerala. It is found both during the Rabi and Kharif seasons. Eradication of the weed is very difficult, as it is propagated through seeds and stem cuttings. Hence a study was proposed to understand the growth and propagation of I. mliacea in different rice growing soils and also to understand the response of the weed to common herbicides popular in the state.
The effect of different soil types on growth and phenology of I. miliacea was studied in pot culture with soil collected from five different rice growing regions viz. Onattukara, Kole, Kuttanad, Pokkali and Palakkad. Ten kg soil each was filled in plastic boxes of size 50 x 25 cm and five replications was maintained for each soil type. Ten seeds were sown in each box and the germination was noted. At two leaf stage when the seedlings were identifiable, a single seedling was retained in each box and the excess seedlings were removed, irrigated regularly and the different phenophases and the morphological attributes were observed at 15 days interval.
The study showed that soil type had a profound influence on the phenology and growth pattern of the weed. Due to high acidity (pH -3.6) and salinity (EC – 4.46 dS/m) seeds sown in Pokkali soils did not germinate. Plants grown in Kuttanad soil showed earlier germination, tillering, flowering, seed formation and seed maturation, while those from Palakkad soil required more number of days to reach these phenophases. The variation in morphological attributes such as total shoot length, leaf number, internodal length, number of panicles and seeds produced per plant were significant. Plants grown in Palakkad soil had higher total shoot length
and internodal length as compared to Kuttanad soil, but the leaf number, number of panicles per plant and number of seeds produced per panicle were higher in Kuttanad soil, where the potassium, phosphorus and organic content was higher compared to other soils. As the nutrient status of Onattukara and Kole land soils were similar (potassium, phosphorus, magnesium, zinc, manganese and sulphur), the performance of the weed in those two soil types were also on par for many of the morphological characters.
Propagation of I. miliacea was affected by ambient temperature, shade, depth of burial and moisture level of soil. The seeds germinated when the temperature range was between 15 - 400C, the highest germination was obtained at 250C. Growth of the weed was highest in open condition compared to shaded condition. Under 50 per cent shade, seed germination declined by 70 per cent. Higher germination per cent of weed was obtained under moist condition, while stem cuttings performed well in both moist and submerged condition. The germination per cent of the weed, reduced with depth of burial.
Sensitivity of the weed to pre emergence herbicides was tested using seed bioassay technique. In the first set, herbicide soaked filter paper was placed at the bottom of petri plates and seeds were placed on it (TP method). In the second set, the herbicide soaked filter paper was placed on top of the seeds and another water soaked filter paper was placed at the bottom (BP method I). In the third set, seeds were placed in between two filter paper soaked with herbicides (BP method II). BP method II gave the best result for all the pre emergence herbicides. However, oxyfluorfen and butachlor showed higher weed suppression in all the methods tried.
Sensitivity of the weed to post emergence herbicides was tested using whole plant bioassay technique. Here, the weed was grown in mud pots and the herbicides were sprayed when the weed was in the vegetative phase. Among post emergence herbicides tested, best control was obtained for azimsulfuron followed by cyhalofop butyl and fenoxaprop p- ethyl. The weed was susceptible to these chemicals. In the case of bispyribac sodium and penoxsulam though initial control was observed,
regrowth was seen after two weeks and so the chemical was classified as moderately resistant to the weed. The weed was resistant to pyrazosulfuron, where no drying symptoms were observed. All the four non-traditional rice herbicides tested viz., glyphosate, diuron, paraquat and glufosinate ammonium gave excellent control of I. miliacea and no regrowth was observed after two weeks