The Biology of Balochistani Weed : Cyperus rotundus Linnaeus . A Review . Abdul

Cyperus rotundus L. is considered one of the world's top 10 noxious weeds of agricultural fields of different economically important crops. Its rapid growth tendency and extensive underground rhizome/tuber system makes it extremely difficult to control. Although this weed also produces seeds but it mostly spreads by tubers. In this review, morphology, reproductive biology, economic importance, and different preventive measures of this weed are described in detail.

underground modified stem which is commonly known as rhizome. Besides rhizomes, C. rotundus also produces tubers, basal bulbs and fibrous roots below ground. In early stages of growth the rhizomes are white and fleshy with crusty leaves and later on become fibrous, woody and dark brown with numerous long-creeping stolons [4]. Inflorescence is terminal (umbel) and flowers are numerous but these flowers produce only few seeds, therefore seeds are considered not the main source of propagation in C. rotundus [5]. The flowering period of C. rotundus is between April -October [6]. The underground modified parts e.g. rhizome, tubers and corms are the main sources of propagation of C. rotundus [5, 7]. The morphological resemblance of C. rotundus with yellow nutsedge (C. esculentus L.) often causes confusion in identification. C. rotundus has brownish flowers, and its stolens occur in chains while C. esculentus has yellowish-brown flowers, and its stolens occur at the end of rhizomes. rotundus is a C4 weed, which is characterized by high photosynthetic efficiency and makes it a troublesome weed compared with C3 weeds [7]. C. rotundus has been quickly spreading in different agricultural fields due to modified underground storage vegetative parts i.e., tubers, which move from one area to another in soil with the help of agricultural equipment. It is reported that under favorable conditions, a single plant which arises from a single tuber can produce 100 or more tubers in about 100 days [5]. Similarly, about 80-95 percent of these tubers are to be found within the 6 inches of top soil and under constant moisture conditions these tubers remain viable for two years [5]. These tubers are light sensitive and once they are brought to the soil surface due to soil tillage than they lose the viability within a week. The polymorphism in tuber sizes is correlated with different levels of dormancy which is the most important adaptive factor that enables C. rotundus to cope with unfavorable environmental conditions. Therefore, dormancy plays an important role in survival of C. rotundus against herbicide applications or hand weeding. The deleterious effects of C. rotundus on yields of different economically important vegetables and crops are reported by different researchers. Working on different vegetables, Keeley reported that the interspecific completion between C. rotundus and different vegetables showed negative impacts on yields of these plants. For example, there was an 89% reduction in yield of onion, 62% in okra, 39-50% in carrot, 43% in cucumber and 35%in cabbage when they grow in fields infested with C. rotundus [16]. Similarly, Santos et al. reported that there was a 70% yield loss in radish when grown in completion with C. rotundus [17]. where less antibacterial activity was found [37]. From these results it was concluded that the cell wall of gram-positive bacteria contain lipopolysaccharides which is sensitive to oily substances of C. rotundus [38].

Population Dynamics
The purple nutsadge produces only few viable seeds which are generally responsible for the introduction of C. rotundus to a new area, however, tubers and rhizomes are the main sources of a local infestation. There is paucity of relevant scientific literatures on seeds behavior and germination of purple nutsadge and most of the researchers emphasized on the structure and behavior of tubers and rhizomes. Therefore it is imperative that seed behavior should be considered for future research which will be helpful in understanding of population dynamics of C. rotundus. The morphological characteristics of C. rotundus make it relatively poor competitor, Iqbal et al. found C. rotundus to be more susceptible to interspecific competition than to intraspecific competition [15]. In early stages, growth of C. rotundus is slow but in later stages it is found fastest particularly 30 to 45 Days after seeding. During this period C. rotundus shows high competitiveness for different crops. Juraimi and Begum observed that the sowing timing of Tef (Eragrostis tef (Zucc.) Trotter) played an important role in competitiveness of this crop when grown in C. rotundus infested field and delayed sowing of crop very critical with respect to the C. rotundus interference [39]. It was suggested that the delay of 7 and 15 days of sowing reduced plant height between 6.97-11.53%, panicle length between 8.21-12.32% and grain yield up to 16%. The competitive ability of C. rotundus is due to its widespread tuber system. Research conducted by Iqbal et al., on the effect of number of tubers on morphological behavior of C. rotundus when different densities of tubers (5, 10, 15 and 20 tubers) were planted in pots revealed that shoot density was significantly increased (78-151%) by increasing tubers numbers per pot compared with lower number of tubers [15]. Similarly shoot length, shoot biomass, underground biomass; number of tubers per pot and tubers weight was considerably increased with increasing the number of tubers up to 15 tubers per pot. However, 20 tubers per pot drastically reduced the vegetative structure of this plant. It is mainly because of intraspecific competition among the individual C. rotundus plants. Therefore the competitiveness of C. rotundus is depending upon the number of tubers to a certain limit and eventually increased with increasing in numbers of tubers.

Response to Herbicides
Inconsistency in dormancy of tubers is one of the reasons which make C. rotundus a noxious weed which reduce the effectiveness of different herbicides. Therefore it is important that herbicides applied should be absorbed through the shoot system and translocation of the chemical to the extensive tuber system. In early stages of growth it is relatively easy to control it; however, in later stages of growth it is rather difficult to eradicate the older plants because of extensive root and tubers system which developed after the damage of shoots. When tubers of C. rotundus treated with the combination of glyphosate and 2,4-D (2,4-Dichlorophenoxyacetic acid), there was a 91% destruction of tubers after 30 days of spray. However, after 45 days of spray there was an increase in germination of tubers [40]. From these results it was concluded that effectiveness of auxinic herbicides (glyphosate and 2,4-D) may be temporary and C. rotundus rapidly recovered from the damages caused by these herbicide due to dormant stocks of tubers which sprouted in later stages when the effectiveness of herbicides diluted in the soil. As a non-selective herbicide, the timing of application of glyphosate to eradicate C. rotundus is important. For maximum control of C. rotundus for instance, glyphosate should be applied at flowering stages because translocation throughout the plant is limited before emergence of flowers. When applied at early stages of growth glyphosate only eradicate the aerial parts of plant and underground tubers and root systems escape the deleterious effect of herbicide. Best results with glyphosate only achieve 2-3 months after the initial emergence of C. rotundus which make this herbicide not suitable for agricultural purpose; however it can be used in lawn and other recreation centre where it used to eradicate this weed locally. In general, 2,4-D (3 kg /ha can kill 80 to 90 % nutsedge) in combination of dicamba (1 kg) and glyphosate applied as a post emergence herbicides for the control of C. rotundus. Similarly repeated application of Glyphosate showed positive results against C. rotundus. A list of different selective and non-selective herbicides for the control of C. rotundus in different crops is listed on table 1.

Cultural control methods
Most effective and common method of eradicating C. rotundus is hand weeding. However, this method is laborious and time consuming as well as is useless against C. rotundus because it removes only foliage parts and leaving tubers in the ground from which new plants appear rapidly. Therefore, it important the tuber of sprouting plant must be removed to control this weed. Similarly the traditional ploughing techniques are also useless because new plants can still grow from the damaged tubers. Extensive dormancy of tubers also prevents the effectiveness of ploughing and leads to rapid regrowth because it helps tubers to break their dormancy once they reached to the top soil. showed no effectiveness in eradicating C. rotundus over two growing seasons. From these results it was concluded that for proper controlling of C. rotundus season-long management is essential.

Biological Control
The inadequate effectiveness of chemical herbicide against C. rotundus tubers and other modified underground parts opened the way for the search of alternative preventive measures. Similarly chemical herbicides also affect non target plant species as well as public concern regarding environmental problems associated with chemical pesticide usage. Unfortunately the application of biological control agents is a lengthy process and users cannot get the desirable results in a short period, therefore it did attract the farmers who are used to indulging in quick results. During the last decade of previous century there were several promising bio-herbicide were discovered which were claimed to be alternative sources of chemical herbicides for the control of different weeds. However, when these bio-herbicides applied in the agricultural fields they did not provide adequate results therefore these bioherbicides lost the public attention rapidly.