DIVERSITY OF WEEDS AND HERBICIDES IN SHALLOW RICE GRWING IN DALOA

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Methodology:-
An inventory of rice adventitious in the town of Daloa was carried out during a cropping cycle using the site survey method associated with the plot method on 60 plots. In each plot, three (3) squares (approximately 4 meters) delimited by bunds and representing plots were chosen at random. In these plots, all the weeds encountered were systematically counted, sampled and identified.
The absolute, relative frequencies and the specific contribution of each adventitious species were calculated from the expressions below in order to classify them according to their importance in the environment and their level of aggressiveness. The relative frequency is calculated as follows: Fr = Fa * 100 / NR with Fr: the relative frequency, Fa: the absolute frequency which corresponds to the number of times that a given species has been encountered during the plot surveys and NR: the total number of readings carried out The specific contribution (Cs) due to the frequency is obtained according to the ratio: Cs = (Fa / Σn1Fa) * 100 It reflects the importance of the species and can be interpreted in the following ways according to Daget et al (1982): If Cs is less than 1%: the weeds are not very aggressive; 1 ≤ Cs ≤ 4: the weeds are aggressive and if Cs is greater at 4 then the adventitious are said to be very aggressive. The specific diversity index (Ids) was taken into account to understand the mode of distribution of adventitious in the field calculated according to the expression: Ids = NE / NGo where NE is the number of species and NG the number of genera identified.
As for the herbicides used in chemical control, a survey was carried out among rice growers in order to identify the herbicides, their active ingredients, their formulations and their doses.

Diversity of rice adventitious:
The investigations permit to identify 34 species of weeds belonging to 30 genera and 15 families and two classes which are the Monocotyledons with a representativeness rate of 50% and the Dicotyledons also representing 50% of the weeds. The most represented families are the Poaceae with 26.37%, the Cyperaceae with 14.70%, the Asteraceae with 14.70%, the Euphorbiaceae with 8.82% and the Amaranthaceae with 5.71% (Table I).
The specific diversity index, which is 1.13, is relatively low and shows good homogeneity in the distribution of adventitous in the field. The values of the Specific Contribution of each species allow the adventitious of rice to be grouped into three (3) classes as shown in Table I. The class of major weeds, represented by a procession of 12 species of weeds is led by Alternantherasessilis accompanied by Echinochleacolona, Leptochloachinensis and Sacciolepis Africana which are very remarkable in the field. The class of minor adventitious is made up with 13 species led by Bidenspilosa and Cyperusesculentus which are species with strong reproductive power. The class of occasional adventitious is represented by border species in general as we have observed in the field.

Diversity of inventoried herbicides:
Investigations revealed fourteen (14) herbicide products with different trade names and are mostly in liquid form with different dosages. The characteristics of each product are given in Table II. We observe a great use of certain products like Herbextra, Gramextra, Ladaba, Herbo super, Bibana, Titan and Tout burned whose frequencies of use are higher or equal to 10%.

Discussion:-
The flora of the weeds identified is made up of 34 species, 30 genera and 15 families against 148 species, 102 distributed genera and 40 families counted by Sylla (2017) in his work carried out in the peri-urban areas of Daloa. The difference can be explained by the fact that our site is smaller than Sylla's. However, the most important families that this author had indicated are the same ones that our work indexes: the Poaceae, the Asteraceae, the Cyperaceae and the Euphorbiaceae. The comparison of the two floristic lists allows us to identify Alternanterasessilis and vernoniagalamensis for the first time in the present study. Their appearance could be explained by a selection of adventitious due to the spreading of herbicide products during farming cycles with always the same previous crop: rice. The five families most represented on the study site are among the ten families whose species are the most dangerous in the world with the dominant family the Poaceae (Kouamé, 2014;Kouassi, 2018).
For the management of this adventitious flora of shallow rice growing in Daloa, we note the use of 14 different herbicide products which really represent seven active ingredients including glyphosate and the 2,4-D amine salt are the most used. The glyphosate-based herbicides are total and are generally used pre-emergence or for the removal of plant biomass during plot preparation, while those based on 2,4-D amine salt are selective and used post-emergence. However, it should be noted that, for the rice grower, the choice of herbicide does not depend on the active ingredient. In fact, it has been observed that the herbicides Herbextra and Herbigro, which contain the same active ingredient at the same concentration, do not have the same frequencies of use. This is also the case for Ladaba and Glyphoder which have glyphosate in common as an active ingredient at 360g / l. Contrasting with this observation the level of study of most rice growers, we can understand that the choice of herbicide is based on personal experience or on other rice growers in relation to the effectiveness of a given herbicide as Kouassi noted. (2019) in Zuénoula.
It is important and it is now a necessity vis-à-vis environmental protection that farmers are trained on the composition and use of herbicides. This support, which is also a form of supervision of the rice-growing world, must be taken into account both by the authorities responsible for the rice sector and by the phytosanitary firms. Efficacy tests of the herbicides met must be carried out in the field on adventitious to affirm the effectiveness of these products in order to better guide the choice of the rice grower.

Conclusion:-
The study of floristic diversity reveals 34 inventoried species distributed equally between monocots and dicots. However, the poaceae remain the most abundant. The determination of the contribution due to the absolute frequency of the adventitious flora shows 12 species as being the most aggressive. In the context of chemical control, 14 herbicide products are used. The 2,4-D amine salts and glyphosate are the most common active ingredients for their efficacy on a wide range of adventitious. The high frequency of use of some herbicide products compared to others and the level of education of rice growers show that rice growers need to be trained on the nature, the use and the effectiveness of the herbicide met.