**2. Sugar beet weeds**

### **2.1 Introduction**

The sugar beet is an important strategic crop in the irrigated perimeter of Tadla. During these 5 last years, an annual surface of 12000 ha is emblaved by this crop. The average yield obtained in the region is approximately 45 to 50 T/ha, which is very low compared to the potential yield which would be of 100 T/ha. Several constraints of technical order are at the origin of this low production, among which the weak control of sanitary problems particularly weed management. In order to achieve a good control of weeds, these last must be well identified. Tanji and Boulet (1986) drew up a general floristic and biological inventory of these weeds in Tadla area (All crops included). The objective of this work was to study thoroughly this inventory in sugar beet.

#### **2.2 Material and methods**

#### **2.2.1 Presentation of the study area**

The plain of Tadla is located at the foot of the Middle Atlas Mountain (Center of Morocco) (Figure 1). This plain has an area of about 360,000 hectares. The altitude varies between 250 m and 500 m and an average of 400 m. According to Emberger climagram , the plain of Tadla has an arid climate with mild winter for the area north of the Oued Oum Er Rabia; winter to charge for the south as well as some of Beni Amir.

In general, natural vegetation is limited to the most degraded soils, the shallower and less suitable for agriculture are sheltered pastures. The average rainfall varies between 556 mm in Beni Mellal as maximum and 327 mm in Dar Ould Zidouh and is averaging 346.6 mm.These datas are decreasing because of climate change. Average monthly temperatures range from 10.2 ° C in January to 28 ° C in August. Minimum monthly temperatures range from 3.23 ° C in January and 18.5 ° C in August and the average maximum temperatures range from 17.8° C in January and 37.5°Cin August.

Fig. 1. Localisation of the studied region in Morocco map (12).

#### **2.2.2 Prospecting and sampling**

382 Herbicides – Properties, Synthesis and Control of Weeds

The sugar beet is an important strategic crop in the irrigated perimeter of Tadla. During these 5 last years, an annual surface of 12000 ha is emblaved by this crop. The average yield obtained in the region is approximately 45 to 50 T/ha, which is very low compared to the potential yield which would be of 100 T/ha. Several constraints of technical order are at the origin of this low production, among which the weak control of sanitary problems particularly weed management. In order to achieve a good control of weeds, these last must be well identified. Tanji and Boulet (1986) drew up a general floristic and biological inventory of these weeds in Tadla area (All crops included). The objective of this work was

The plain of Tadla is located at the foot of the Middle Atlas Mountain (Center of Morocco) (Figure 1). This plain has an area of about 360,000 hectares. The altitude varies between 250 m and 500 m and an average of 400 m. According to Emberger climagram , the plain of Tadla has an arid climate with mild winter for the area north of the Oued Oum Er Rabia;

In general, natural vegetation is limited to the most degraded soils, the shallower and less suitable for agriculture are sheltered pastures. The average rainfall varies between 556 mm in Beni Mellal as maximum and 327 mm in Dar Ould Zidouh and is averaging 346.6 mm.These datas are decreasing because of climate change. Average monthly temperatures range from 10.2 ° C in January to 28 ° C in August. Minimum monthly temperatures range from 3.23 ° C in January and 18.5 ° C in August and the average maximum temperatures

**2. Sugar beet weeds** 

**2.2 Material and methods** 

**2.2.1 Presentation of the study area** 

to study thoroughly this inventory in sugar beet.

winter to charge for the south as well as some of Beni Amir.

range from 17.8° C in January and 37.5°Cin August.

Fig. 1. Localisation of the studied region in Morocco map (12).

**2.1 Introduction** 

A total of 126 sugar beet fields were explored. Only fields not chemically treated and weedy full kept by farmers were prospected. A stratified sampling according to Gounot (1969) was established taking account of some factors mainly type of soil, rainfall and temperatures. Meanwhile, farmers were questioned about cultural practices and soil samples were taken in order to characterize soil texture and total calcium content.

The method of the "tower field" has been adopted to identify the weed species present (Maillet, 1981), for which an Abundance-Dominance Index (ADI) (+, 1, 2, 3, 4, 5) according to the scale of Montegut (Not dated) modified by Boulet et al. (1989) has been assigned. This index is as follows:


The agronomic importance of each species is judged based on its relative frequency and covering. The estimation of the average abundance of species during the reading was conducted assuming equivalences between the ADI and its average covering in percentage (Boulet et al, 1984). The methodology was as follows:


These values allow calculating the average covering R of each species at reading time. The combination of this index, of the absolute frequency of species and their ethological type, allowed attribution of a "Partial Nuisibility Index" (PNI) to species (Bouhache et al, 1984).

PNI = (Sum of coverage/number of reading) x 100. The perennial species are underlined and only species with a frequency higher than 20% are taken in consideration.

Species encountered were identified by using some documents such as Flora Europea (Tutin et al., 1964- 1984), Catalogue des Plantes du Maroc (Jahandiez and Maire, 1931-34) and Mauvaises herbes des regions arides et semi arides du Maroc occidental (Tanji et al., 1988). The ethological type for each species was determined according to classification elaborated by Raunkiaer (1905). The biogeographical origin of weed species was derived from Quezel and Santa (1962-63) and Negre (1961-62) on flora investigations.

Sugar Beet Weeds in Tadla Region (Morocco):

Asteraceae Poaceae Fabaceae Brassicaceae Apiaceae

Araceae Cyperaceae Iridaceae Portulacaceaa Primulaceae Rhamnaceae Urticaceae Verbenaceae

Caryophyllaceae Amaranthaceae Chenopodiaceae Euphorbiaceae Liliaceae Papaveraceae Plantaginaceae Polygonaceae Rubiaceae Convolvulaceae Malvaceae Solanaceae Lamiaceae Boraginaceae Geraniaceae Ranunculaceae Scrophulariaceae

Famillies Number of

species

Table 1. Specific contribution of botanical families encountered.

Table 2. Ethological aspect of sugar beet weed flora in Tadla.

82.6 11.9 3.4 2.1

The number of weed species per Sugar beet field varied from 9 to 26 and averaged 17,5. It is relatively low compared to that reported at Doukkala region. The weed survey allowed

Biological type %

Therophytes (Annuals) Geophytes (Perennials)

**2.3.4 Agronomic aspect** 

Hemicryptophytes (Bisannuals)

Chamaephytes and nanophanerophytes

Species Encountered, Interference and Chemical Control 385

Contribution

Ranking

( %)

13,2 13,2 12,5 6,2 5,5 5,5 4,2 3,5 2,8 2,8 2,8 2,8 2,8 2,8 2,1 2,1 2,1 2,1 1,4 1,4 1,4 1,4 0,7 0,7 0,7 0,7 0,7 0,7 0,7 0,7

#### **2.3 Results and discussion**

#### **2.3.1 Systematic aspect**

A total of 144 weed species including volunteer wheat belonging to 30 botanical families (Table 1) were inventoried in the 162 sugar beet fields prospected. This number correspond respectively to 43,6% and 17,2% of the total weed flora of Tadla region (Tanji and Boulet, 1986) and of Central West Morocco (Boulet et al., 1989) and is relatively low compared to that observed in the Gharb region (Tanji et al., 1984), more important than that showed in Doukkala region (Bouhache and Ezzahiri, 1993) and similar to that found in Moulouya region (Taleb and Rzozi, 1993).

Dicotyledonous species are prevalent (118 species) and correspond to 81,9% of total encountered. Similar results are shown in other regions where sugar beet is grown. Six families dominated particularly the weed flora (Table 1): Asteraceae, poaceae fabaceae, brassicaceae apiaceae and caryophyllaceae. They provide 51.8% of the total. Representing 81 species , these six families are also dominant in sugar beet in Gharb region (Tanji et al.,1984), in cereals (Taleb and Maillet, 1994) and generally for the national flora (Bouhache and bouleT, 1984 and Ibn Tatou and Fennane, 1989). The most dominant family is the asteraceae, that is represented by 19 species, representing 13.2% of the weed flora found. The Asteraceae is also the richest family in species by about 20.000 species worldwide (Taleb, 1995)

#### **2.3.2 Ethological aspect**

According to RAUNKIAER classification, the 144 species surveyed belong to five ethological types (Table 2). The ethological spectrum is dominated by annuals (therophytes) with 119 species or 82,6% of the total. This data is similar to that obtained by the main regional botanical and floristic studies of sugar beet weed flora (Tanji et al., 1984; Bouhache and Ezzahiri, 1993; Taleb and Rzozi, 1993. The Geophytes follow with 17 species (11.8%), bisannuals (hemicryptophytes) with 5 species (3.5%) and the chamaephytes and others with 2 species (2.1%). The geophytes encountered are mainly monocotyledonous species with rhizomes, bulbs and tubers. The most important geophytes species inventoried are Convolvulus arvensis L., Solanum elaeagnifolium Cav. And Cynodon dactylon (L.) Pers. They cause serious problems to the crop.

#### **2.3.3 Biogeographical distribution of species**

The Mediterranean weed species (broadly defined) dominate the flora inventoried with 56.2%. This high rate of Mediterranean species confirms those of other authors (Bouhache and Boulet, 1984; Loudyi, 1985; Tanji and Boulet, 1986; Careme, 1990; Taleb, 1995; Wahbi, 1994; Bensellam, 1994) or for the entire Moroccan flora (about 2 / 3 according to Braun-Blanquet and Maire, 1924). European and eurasiatic species represent 5,5 and 4,9 % of the total. Cosmopolitan and sub- cosmopolitan are well represented (8,3%). This seems to be high comparatively to that reported by Bouhache and al., 1993. Concerning endemic species to north west of Africa, they are represented only by *Diplotaxis tenuissiliqua* Del., also reported by Tanji and Boulet (1986).


A total of 144 weed species including volunteer wheat belonging to 30 botanical families (Table 1) were inventoried in the 162 sugar beet fields prospected. This number correspond respectively to 43,6% and 17,2% of the total weed flora of Tadla region (Tanji and Boulet, 1986) and of Central West Morocco (Boulet et al., 1989) and is relatively low compared to that observed in the Gharb region (Tanji et al., 1984), more important than that showed in Doukkala region (Bouhache and Ezzahiri, 1993) and similar to that found in Moulouya

Dicotyledonous species are prevalent (118 species) and correspond to 81,9% of total encountered. Similar results are shown in other regions where sugar beet is grown. Six families dominated particularly the weed flora (Table 1): Asteraceae, poaceae fabaceae, brassicaceae apiaceae and caryophyllaceae. They provide 51.8% of the total. Representing 81 species , these six families are also dominant in sugar beet in Gharb region (Tanji et al.,1984), in cereals (Taleb and Maillet, 1994) and generally for the national flora (Bouhache and bouleT, 1984 and Ibn Tatou and Fennane, 1989). The most dominant family is the asteraceae, that is represented by 19 species, representing 13.2% of the weed flora found. The Asteraceae is also the richest family in species by about 20.000 species worldwide

According to RAUNKIAER classification, the 144 species surveyed belong to five ethological types (Table 2). The ethological spectrum is dominated by annuals (therophytes) with 119 species or 82,6% of the total. This data is similar to that obtained by the main regional botanical and floristic studies of sugar beet weed flora (Tanji et al., 1984; Bouhache and Ezzahiri, 1993; Taleb and Rzozi, 1993. The Geophytes follow with 17 species (11.8%), bisannuals (hemicryptophytes) with 5 species (3.5%) and the chamaephytes and others with 2 species (2.1%). The geophytes encountered are mainly monocotyledonous species with rhizomes, bulbs and tubers. The most important geophytes species inventoried are Convolvulus arvensis L., Solanum elaeagnifolium Cav. And Cynodon dactylon (L.) Pers.

The Mediterranean weed species (broadly defined) dominate the flora inventoried with 56.2%. This high rate of Mediterranean species confirms those of other authors (Bouhache and Boulet, 1984; Loudyi, 1985; Tanji and Boulet, 1986; Careme, 1990; Taleb, 1995; Wahbi, 1994; Bensellam, 1994) or for the entire Moroccan flora (about 2 / 3 according to Braun-Blanquet and Maire, 1924). European and eurasiatic species represent 5,5 and 4,9 % of the total. Cosmopolitan and sub- cosmopolitan are well represented (8,3%). This seems to be high comparatively to that reported by Bouhache and al., 1993. Concerning endemic species to north west of Africa, they are represented only by *Diplotaxis tenuissiliqua* Del., also

**2.3 Results and discussion 2.3.1 Systematic aspect** 

region (Taleb and Rzozi, 1993).

(Taleb, 1995)

**2.3.2 Ethological aspect** 

They cause serious problems to the crop.

reported by Tanji and Boulet (1986).

**2.3.3 Biogeographical distribution of species** 


Table 1. Specific contribution of botanical families encountered.


Table 2. Ethological aspect of sugar beet weed flora in Tadla.

#### **2.3.4 Agronomic aspect**

The number of weed species per Sugar beet field varied from 9 to 26 and averaged 17,5. It is relatively low compared to that reported at Doukkala region. The weed survey allowed

Sugar Beet Weeds in Tadla Region (Morocco):

into four groups on the basis of their PNI.

weed and a very troublesome species in all Tadla region.

**3. Weed interference and critical period** 

(Schweizer, 1983; Cooke and Scott, 1993).

multiplication.

*Vaccaria hispanica* Med.

**2.4 Conclusion** 

the crop.

**3.1 Introduction** 

Species Encountered, Interference and Chemical Control 387

identifying 39 major weed species including volunteer wheat that are relatively frequent and cause serious problems and yield loss for the crop (table 3). These species were divided

Weeds belonging to group 1 are mainly monocotyledonous species such as *Lolium rigidum*  Gaudin., *Phalaris brachystachys* Link., *Avena sterilis* L. And volunteer wheat (*Triticum aestivum* L. And *Triticum durum* L.). This later generally precede sugar beet in the plot. These species competes highly with sugar beet because of their relatively high covering and early emergence in the season. The perennial rhizomatous weed *Convolvulus arvensis* L. is also a dangerous species and it is very difficult to control because of its important vegetative

Group 2 contain many species with PNI between 500 and 1000 that also could be noxious for the crop regarding their covering. These weeds are mainly dicotyledonous species such as *Anagallis foemina* Miller, *Papaver rhoeas* L., *Medicago polymorpha* L., *Chenopodium album* L., *Sinapis arvensis* L., *Galium tricornitum* Dandy. *Solanum elaeagnifolium* Cav. is deep rooted

Other species with relatively low covering (Groupe 3 and 4) are often encountered in sugar beet field but they are less competitive compared to those belonging to group 1 and 2: *Rumex pulcher* L., *Chrysanthemum coronarium* L., *Bromus rigidus* L., *Calendula Arvensis* L., *Vicia sativa* L., *Chrysanthemum segetum* L., *Reseda alba* L., *Plantago afra* L., *Scorpiurus vermiculatus* L.,

The sugar beet weed flora in Tadla region is much diversified. Effectively, 144 species belonging to 30 botanical families were encountered in the 126 field prospected. The most represented families are asteraceae, poaceae, fabaceae, bracassicaceae, apiaceae and caryophyllaceae. Therophytes (annuals) and dicotyledonous species dominate with 82,6% and 81,9 respectively. The floristic diversity vary from 9 to 26 species per field and it average 17, 5. The weed survey allowed identifying 39 major weed species including volunteer wheat that are relatively frequent and cause serious problems and significant yield losses for

Weeds compete with crop plants for water, light nutrients and space and cause considerable yield losses. Integrate weed management (IWM) involves a combination of cultural, mechanical, biological, genetic and chemical methods for effective and economical weed control (Swanton and Weise, 1991). The principles of IWM should provide the foundation for developing optimum weed control systems and efficient use of herbicides. The critical period for weed control (CPWC) is a key component of an IWM program. Weeds are limiting factors in sugar beet production (Cooke and Scott, 1993). Integrated weed control management is necessary for minimizing weeds interference and maximizing the crop yield


Table 3. Partial Nuisibility Index (PNI) of the most frequent weed species in sugar beet.

identifying 39 major weed species including volunteer wheat that are relatively frequent and cause serious problems and yield loss for the crop (table 3). These species were divided into four groups on the basis of their PNI.

Weeds belonging to group 1 are mainly monocotyledonous species such as *Lolium rigidum*  Gaudin., *Phalaris brachystachys* Link., *Avena sterilis* L. And volunteer wheat (*Triticum aestivum* L. And *Triticum durum* L.). This later generally precede sugar beet in the plot. These species competes highly with sugar beet because of their relatively high covering and early emergence in the season. The perennial rhizomatous weed *Convolvulus arvensis* L. is also a dangerous species and it is very difficult to control because of its important vegetative multiplication.

Group 2 contain many species with PNI between 500 and 1000 that also could be noxious for the crop regarding their covering. These weeds are mainly dicotyledonous species such as *Anagallis foemina* Miller, *Papaver rhoeas* L., *Medicago polymorpha* L., *Chenopodium album* L., *Sinapis arvensis* L., *Galium tricornitum* Dandy. *Solanum elaeagnifolium* Cav. is deep rooted weed and a very troublesome species in all Tadla region.

Other species with relatively low covering (Groupe 3 and 4) are often encountered in sugar beet field but they are less competitive compared to those belonging to group 1 and 2: *Rumex pulcher* L., *Chrysanthemum coronarium* L., *Bromus rigidus* L., *Calendula Arvensis* L., *Vicia sativa* L., *Chrysanthemum segetum* L., *Reseda alba* L., *Plantago afra* L., *Scorpiurus vermiculatus* L., *Vaccaria hispanica* Med.

#### **2.4 Conclusion**

386 Herbicides – Properties, Synthesis and Control of Weeds

Table 3. Partial Nuisibility Index (PNI) of the most frequent weed species in sugar beet.

Species **PNI**

**Group 1: species with IPN>1000**

**Group 2: species with 500<IPN<1000**

*Lolium rigidum* Gaudin. *Phalaris brachystachys* Link. *Triticum aestivum* L. *Triticum durum* L. *Avena sterilis* L. *Convolvulus arvensis* L.

*Lolium multiflorum* Lam. *Cichorium endivia L. Anagallis foemina* Miller *Papaver rhoeas* L. *Ridolfia segetum* L. *Medicago polymorpha* L. *Melilotus sulcata* Desf. *Phalaris minor* Retz. *Galium tricornitum* Dandy *Chenopodium murale* L. *Chenopodium album* L. *Sonchus oleraceus* L. *Lamium ampexicaule* L. *Sinapis arvensis* L.

*Solanum elaeagnifolium* Cav.

*Emex spinosa* (L.) Campd.

*Chrysanthemum coronarium* L.

*Chrysanthemum segetum* L.

*Scorpiurus vermiculatus* L. *Vaccaria hispanica* Med. *Lathyrus ochrus* (L.) DG. *Cynodon dactylon* (L.) Pers.

*Polygonum aviculare* L. *Phalaris paradoxa* L. *Antirrhinum orontium* L.

*Reseda alba* L. *Plantago afra* L.

**Group 4: species with IPN<250**

**Group 3: species with 250<IPN<500**

*Malva parviflora* L. *Fumaria parviflora* Lam.

*Rumex pulcher* L.

*Bromus rigidus* L. *Calendula Arvensis* L. *Vicia sativa* L.

The sugar beet weed flora in Tadla region is much diversified. Effectively, 144 species belonging to 30 botanical families were encountered in the 126 field prospected. The most represented families are asteraceae, poaceae, fabaceae, bracassicaceae, apiaceae and caryophyllaceae. Therophytes (annuals) and dicotyledonous species dominate with 82,6% and 81,9 respectively. The floristic diversity vary from 9 to 26 species per field and it average 17, 5. The weed survey allowed identifying 39 major weed species including volunteer wheat that are relatively frequent and cause serious problems and significant yield losses for the crop.
