**1. Introduction**

380 Herbicides – Properties, Synthesis and Control of Weeds

Richardson, B., Davenhill, N., Coker, G., Ray, J., Vanner, A. & Kimberley, M. (1996a).

Richardson, B., Vanner, A., Ray, J., Davenhill, N. & Coker, G. (1996b). Mechanisms of *Pinus* 

SAS Institute Inc. (2004). *SAS/STAT 9.1 user's guide, Vols. 1-7* (1st ed.). SAS Institute Inc. Cary,

Shibu, J., Ranasinghe, S. & Ramsey, C.L. (2010). Longleaf pine (*Pinus palustris* P. Mill.)

Thatcher, R. C., Searcy, J. L., Coster, J. E. & Hertel, G. D. (Eds.). (1980). *The Southern Pine* 

Service. U.S. Government Printing Office. Pineville, Louisiana.

size. *New Zealand Journal of Forestry Science* 26(1/2): 265-275.

*Journal of Forestry Science* 26(3): 421-437.

446). John Wiley and Sons. New York, NY.

North Carolina.

Optimising spot weed control: first approximation of the most cost-effective spot

*radiata* growth suppression by some common forest weed species. *New Zealand* 

restoration using herbicides: overstory and understory vegetation responses on a coastal plain flatwoods site in Florida, U.S.A. *Restoration Ecology* 18(2): 244-251. Stout, I. J. & Marion, W. R. (1993). Pine flatwoods and xeric pine forest of the southern

(lower) coastal plain. In W. H. Martin, S. G. Boyce & A. C. Echternacht (Eds.), *Biodiversity of the southeastern United States, lowland terrestrial communities* (pp. 373-

*Beetle*. (USDA Technical Bulletin 1631). Expanded Southern Pine Beetle Research and Application Program, Science and Education Administration, USDA Forest

Sugar beet occupies each year about 65.000 hectares in Morocco which allows a production that approaches or exceeds three million tons of roots, with an average yield of 46 tonnes per ha (54% of national needs sugar consumption). Since its introduction in Morocco in 1962-1963, sugar beet yield increased significantly in quantity and quality. In Morocco, the sugar beet is a very important crop because of its products and by-products, mainly:


In Morocco, sugar beet is planted from September through June - July. Yield obtained by farmers, averaging 46T/ha, is significantly below the request potential that would be 90 to 100 T/ha. Many factors contribute to low sugar beet production. Poor stand establishment, inadequate weed control, inadequate insect control and inadequate nitrogen fertilization are the main causes of low tonnage and poor quality sugar beet in Morocco.

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 representing 23% / of the national area. The average yield obtained in the region is approximately 45 to 50 T/ha, which is very low compared to the potential yield.

Sanitary problems particularly weed management is a great constraint to sugar beet production and weeds may cause high yield losses (Rzozi et al., 1990). This paper presents the main results of investigations and experiments conducted in Tadla region to improve the weed management program by identifying mains weed species encountered in sugar beet field, studying the effect of weeds on sugar beet growth and estimating yield losses and determining the critical period of weed control and evaluating herbicide treatments.

Sugar Beet Weeds in Tadla Region (Morocco):

in order to characterize soil texture and total calcium content.

2: averagely abundant species, low recovery, irregular distribution 3: abundant species, covering less than 50%, regular distribution 4: abundant species, recovery of 50 to 75%, regular distribution

5: very abundant species, recovery from 75 to 100%, regular distribution

+: Very rare species (1 to 5 feet), virtually no recovery. 1: scarce species, recovery very low, irregular distribution

(Boulet et al, 1984). The methodology was as follows:

**2.2.2 Prospecting and sampling** 

index is as follows:

Species Encountered, Interference and Chemical Control 383

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

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

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

ADI Covering Average covering

5 75 – 100 87,5 4 50 – 75 65,5 3 25 - 50 37, 5 2 5 – 25 17, 5 1 1 – 5 5 + < 1 1

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

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 only species with a frequency higher than 20% are taken in consideration.

and Santa (1962-63) and Negre (1961-62) on flora investigations.
