Efficacy of Different Glyphosate rates of Application on Weed Infestation in Citrus Orchards

Citrus weeding trial was conducted during the 2019 growing season. The aimof this study is to investigate the effect of three glyphosate rates of application on weed infestation in citrus orchards. Dominant weed botanical families belong to: Asteraceae, Amaranthaceae, Caryophyllaceae,Solanaceae, Poaceae and Primulaceae.Results showed that glyphosate applied at 1080 g/hectareand 720 g/hectare provided good weed control. Glyphosate rates of application at 1080 g/hectare and 720 g/hectare recorded respectively 88.07% and 81% of weed density reduction compared to weed density in the control plots and 93 .36% and 77.41% of weed dry biomass reduction compared to weed dry biomass in the control plots.Glyphosate rates of application at 1080 g/hectarerecorded 95% of visual weed control notation compared to weed infestation in the control plots.Glyphosate applied at 360 g/hectare showed very low efficacy and is not recommended in chemical weed control program in citrus orchards. Keywords— Weed infestation, citrus, glyphosate, efficacy, density, biomass, Larache, Morocco.


INTRODUCTION
Citrus is one of the important fruit trees grown in Morocco (Walali&al., 2003). This crop plays a socioeconomic role with an area of 125,000 hectares and a production average of 2 million tons per year (ASPAM, 2019). It contributes substantially to the improvement of the income of farmers and generates significant effects on job creation. Exports of citrus, represent an important source of foreign currency. Several biotic constraints limit their productivity including pests, diseases (viral and Cryptogamic), nematodes and weeds (Mokrini&al., 2018). In fact, weeds compete for growth factors such water, nutrients and light and reduce crop yield and quality (Onyegbule &al., 2014;Tucker & Singh 1993). The most common weeds in Moroccan citrus orchards belong to the following botanical families: Poaceae, Asteraceae, Fabaceae, Brassicaceae and Boraginaceae (Wahbi & Taleb, 1995;Hilali, 1995;Taleb &al., 1996;Bensellam &al., 1997;Talibi, 1999). There are various weed management practices that can reduce weed infestation in citrus orchards such cultivating, Mowing, Chemical weed Control, Biological Control and use of allelopathic plants (Tucker & Singh 1993). However, weed management with chemical control through herbicides is a cheaper and most effective practice against weed infestation especially when combined with other control measures (Bensellam & Bouhache, 2007).
Glyphosate is a nonselective herbicide that kills mono and dicotyledonous plants of annual or perennial cycles. Glyphosate block the biosynthesis of aromatic amino acids produced through the shikimate pathway phenylalanine, tyrosine and tryptophan (Gravena and al., 2012; Index phytosanitaire Maroc, 2017). This herbicide is largely used worldwide due to its large spectrum efficacy against weed and cheaper cost. However, good chemical weed control by applying glyphosate is dependent on the nature of the dominant weed flora and the rates of application (Bensellam & Bouhache, 2007). Therefore,this study aims to evaluate theefficacy of three glyphosate rates of application to determine the rate of application that allows thebestweed control in citrus orchards in Larache Morocco region.

Effect on visual efficacy rating
Statistical analysis revealed a very highly significant difference between treatments (table 3). Plots treated with 1080 g/hectare of glyphosate showed the best efficacy recording 95% of visual weed control notation compared to weed infestation in the control plots. Glyphosate Rate of application at 720 g/hectare s howed also pretty good efficacy recording 83.67%. Glyphosate applied at 360 g/hectare showed moderate efficacy recording 63.33%.

Effecton weed density reduction
Statistical analysis revealed a very highly significant difference between treatments (table 4). Plots treated with 1080 g/hectare and 720 g/hectare of glyphosate showed the best efficacy recording respectively 88.07% and 81% of weed density reduction compared to weed density in the control plots. Glyphosate Rate of application at 360 g/hectare showed low weed density reduction recording 56.79%. 3. Effecton weed dry biomass reduction Statistical analysis revealed a very highly significant difference between treatments (table 5). Plots treated with 1080 g/hectare and 720 g/hectare of glyphosate showed the best efficacy recording respectively 93.36% and 77.41% of weed dry biomass reduction compared to weed dry biomass in the control plots. Glyphosate Rate of application at 360 g/hectare sowed very low weed dry biomass reduction recording only32.44%. In fact, some authors reported that glyphosate applied at 2160 g/hectare on citrus orchards in Gharb region in Morocco showed just 64.89% on weed dry biomass reduction compared to weed dry biomass in the control plots (Bensellam &Bouhache 2007). In our trial, half of this glyphosate rate of application has shown very good weed dry biomass reduction (93.36%). This can be explained by the nature of the weed species since weed infestation in Larache region is different fromthat of Gh arb region. Therefore, it is important to test rates of application in different region before any recommendation to avoid low weed control (underdose) or the waste of herbicides (overdose).

IV.
CONCLUSION This study has shown that glyphosate rates of application at 1080 g/hectare and 720 g/hectare showed good weed control in citrus orchards in terms of dry biomass reduction, weed density reduction and visual weed efficacy notation. Glyphosate applied at 360 g/hectare is not recommended in chemical weed control program in citrus orchards in Larache region of Morocco.