**3.4 Conclusion**

392 Herbicides – Properties, Synthesis and Control of Weeds

Weed interference caused a sharp decline in sugar beet root yield in both years (Figure 6 and 7). Based on 10 % permissible decrease in root yield, weeding should start from 4 WAE and 7 WAE in 2003 and 2004, respectively (Figure 6 and 7). For the given 10% root yield reduction, weed control should be continued until 15 WAE and 12 WAE in 2003 and 2004, respectively (Figure 5 and 6). Weed interference caused a sharp decline in sugar yield (data not shown). Based on 10 % permissible decrease in root yield, weeding should start from 3.5 WAE and 7 WAE and must be continued until 15 WAE and 11 WAE in 2003 and 2004

The results show that the critical period begins earlier in 2003 and its duration is longer comparatively to that observed in 2004 which is shorter and begins relatively later. This may be due to date of sowing. Effectively, in 2003, sugar beet was sown October 15 and this allows to many weed species, particularly gramineous including volunteer wheat, to germinate and emerge in great number and vigorously at the same time of the crop germination and emergence. In 2004, sugar beet was sown 25 November. At this time, a great number of weed species (mainly gramineous) has germinated and emerged from soil

Emergence time of weeds influences the critical period of weed control (Zimdahl, 1987; Weaver *et al*., 1992; Mesbah *et al*., 1994; Ghadiri, 1996). In Shahrekord, sugar beet is planted in May and June; this delay in seedbed preparation and planting may lead to earlier germination of weeds over the sugar beet crop. Therefore, critical period of weed control starts earlier and its duration is longer. At early growth stages, sugar beet has a low competitive ability against weeds; as a result critical period would start sooner. In 2003, presence of weeds for the entire growing season reduced root yield by 97.6% relative to weed free control. In 2004, the reduction was 68.6 %. A similar 71% root yield reduction was

Fig. 5. Effect of weeds on sugar beet leaf dry matter.

and destructed during the seedbed preparation.

**3.3.4 Critical period of weed control** 

respectively.

A field experiment was conducted during two growing seasons 2003/2004 and 2004/2005 to assess the effect of weeds on sugar beet growth parameters and sugar beet yield and to determine the critical period of weed control (CPWC). Weed free treatments and weed infested treatments included the removal (or not) of weeds at 4, 7, 9, 11, 13, 17 and 21 weeks after emergence of sugar beet. Dry matter of weed, sugar beet leaves/plant, sugar beet leaf area and sugar beet dry weight was measured during all growing season. Weed free periods resulted in lower weed dry matter and weedy periods resulted in high weed dry matter. Maximum total weed dry weight generally decreased as weed-free duration was increased. The presence of weeds during the entire growing season decreased root yield by 97.6 % and 68.9 % in 2003 and 2004, respectively. All crop growth parameters were significantly reduced by weed infestation.

The critical period of weed control began at 4 and 7 weeks after sugar beet emergence (WAE) and continued until 15 and 12 WAE in 2003/2004 and 2004/2005 respectively depending on sowing period. It was concluded that the CPWC is longer in 2003/2004 than in 2004/2005.

Fig. 6. Critical period of weed control (2003/2004).

Sugar Beet Weeds in Tadla Region (Morocco):

Abundance – Dominance-Index (ADI).

**4.2.4 Evaluation of herbicide efficacy** 

**4.2.5 Observations on the crop** 

regional sugar factory.

Table 4. herbicides tested.

growing season.

**4.3 Results and discussion 4.3.1 Importance of weed flora** 

0.05).

calculated comparing its dry matter to that of the check.

**4.2.6 Experimental design and statistical analysis** 

**Commercial product Active ingredient**

Goltix 70 % metamitron

Venzar 80 % lenacil

Safari 70 % triflusulfuron methyl

Fusilad Super 125 g/l Fluazifop p-butyl

Tramat Combi 30 % ethofumesat + 12 % lenacil

**4.2.3 Observations on weeds** 

Species Encountered, Interference and Chemical Control 395

The importance of weeds encountered in field experiments was estimated according to the

Weed dry weight were measured during at 60 days after treatments (DAT) for all individual plots. Four 0.5 m x 0.5m quadrates per plot were placed randomly over the plot. Weeds within the sampling area were removed by hand, taken to laboratory and dried at 60° C for 48 h to determine total weed dry weight. The efficacy in percentage (%) for each treatment is

The sugar beet yield was estimated on the two central rows at harvest. Sucrose percentage and the concentration of impurities (sodium, potassium, amino-N) were measured at the

The experiment was a randomized complete block design with four replicates. Individual plots were 4m x 8m size. Data on efficacy (%) were first transformed to Arc Sin% if necessary. Sugar beet yield and efficacy data were subjected to an analysis of variance using statistical STATITCF software. The means were compared using Fisher's protected LSD (α =

Betanal Progress 16 g/l desmedipham + 62 g/l phenmedipham + 128 g/l ethofumesat

In Fqih Ben Salah location, weed flora is dominated by gramineous mainly volunteer wheat. Some dicotyledonous species such as *Malva parviflora, Medicago polymorpha, Emex spinosa* and *fumaria parviflora* are important (Table 6). In Deroua location, infestation by gramineous was low and *cichorium endivia*, *Sinapis arvensis* and *convolvulus arvensis* were dominant in 2003/2004 and *Rumex pulcher*, *Papaver rhoas* and *Ridolfia segetum* dominated the weed flora in 2004/2005. Concerning Afourer, C*ichorium endivia*, *Sinapis arvensis, Polygonum aviculare, Lamium amplexicaule and Ridolfia segetum* were the most important species in both two

Fig. 7. Critical period of weed control (2004/2005).
