Chemical Control of Curled Dock ( Rumex crispus L . ) and Other Weeds in Noncropped Areas

Rumex crispus L. is an invasive species widespread in our country and in particular in the region of North Bulgaria. It is characterized by high biological and ecological plasticity. Owing to its great reproductive potential, the weed has been assigned to the list of economically most important weeds in the country. With the purpose of studying the possibility of chemical weed control in noncropped areas with heavy natural background infestation with R. crispus L. and other dicotyledonous weeds, two field trials were carried out. A ready-to-use herbicide mixture 2,4-D 140.2 g/l-1 + Triclopyr 144 g/l-1, trade product Genoxon 3X (X0050), was tested at two doses of active ingredient, 3552 and 2842 ml/ha-1. It was found that: (1) population density of Rumex crispus L. can be successfully reduced by treatment at the stage of early stem formation; herbicide efficacy with 3552 and 2882 ml/ha-1 doses on the 21st day after treatment was 100% and 90.5%, respectively, at the end of vegetation 94.4 and 85.7%, respectively; (2) herbicidal efficacy was lower when R. crispus L. was treated at the 5 6 leaf stage, being 100 – 94.1% and 80 – 76.5% respectively for the indicated doses and time of recording; (3) at the studied doses the herbicide controlled both annual dicotyledonous weeds (Amaranthus spp., Chenopodium album L., Portulaca oleracea L.) and perennial dicotyledonous ones (Cirsium arvense L., Sonchus arvensis L., Convolvulus arvensis L., Carduus acanthoides L.), but it was not toxic to monocotyledonous weeds.


INTRODUCTION
Rumex crispus L. is an invasive species, widespread in our country and in particular in the region of North Bulgaria.Tonev (2000) has listed it in a group of one hundred economically most important weeds char-acterized by high biological and ecological plasticity.In crop rotation of lucerne and winter grain cereal, 64% of the weed survive after every ploughing (Pino, 1995).The importance of successful control of this species has attracted the attention of many researchers (Humphreys et al., 1999;Benvenuti et al., 2001;Pestic. Phytomed. (Belgrade), 23 (2008) 123-126 UDC: 632.51:632.954 Pestic. fitomed. (Beograd), 23 (2008) 123-126 Preliminary Communication * Prethodno saopštenje Van Eekeren and Jansonius, 2005;Van Eekeren et al., 2006).The chemical method has an important role in its control.Treatment with Asulam at the dose of 2400 g/l -1 has been found to kill 88-100% of dock species in lucerne (Prodanov, 1980).More than two decades has passed since the registration of this product, which necessitates a search for new options.
The objective of this study was to test a ready-to-use herbicide mixture, 2,4-D 140.2 g/l -1 + Triclopyr 144 g/l -1 (trade product Genoxon 3X (X0050), as a means of chemical control of Rumex crispus L. and other weeds in noncropped areas.

MATERIAL AND METHODS
The study included two field trials carried out in a noncropped area with a heavy natural background infestation with Rumex crispus L. (trial 1) and other undesired dicotyledonous weeds (trial 2).The trials were laid out in a block design with four replications and plot size of 10 m 2 .The study was conducted with a ready-to-use herbicide mixture of 2,4-D 140.2 g/l -1 + Triclopyr 144 g/l -1 as the trade product Genoxon 3X (X0050) in doses of 3552 and 2842 ml/ha -1 active ingredient.Asulam 400 g/l -1 was used as a standard in trial 1. Efficacy was recorded in permanent 1 m 2 sampling plots by the quantitative method and according to a 9-score scale of EWRS (0-100% killed weeds = score 9-1).The herbicides were applied with 500 l -1 / ha -1 working solution.

RESULTS AND DISCUSSION
R. crispus L. density was 15 to 21 plants/m 2 in the trial area, which was a prerequisite for real assessment of efficacy (Table 1).Toxic action caused epinastic curvatures of petioles and stems, growth inhibition and subsequent plant death.A high initial effect was observed in the recording 21 days after treatment at both stages.Completely killed plants reached 100% at 3552 l -1 / ha -1 mixture dose and 400 g/l -1 of the standard Asulam.Herbicide efficacy was lower at 2842 ml/ha dose, the completely killed weeds being 90.5-94.1%.A characteristic biological feature of the weed is its high regenerative ability.At the end of vegetation the regenerated plants reached 5.6-14.3%for treatment at the weed stage of early stem formation and 5% for the standard.Regeneration was considerably higher, 20.0-23.5%, for treatment at the 5-6 leaf stage, and 9.5% for the standard.Therefore, control of R. crispus L. was more successful when the weed was treated at the stage of early stem formation with the higher dose of the product.
The results presented in Table 2 show that the studied herbicide possesses a wide spectrum of action with regard to dicotyledonous weeds.An ideal herbicide efficacy (score 1) against Amaranthus spp., Chenopodium album L., Portulaca oleracea L., Cirsium arvense L., Sonchus arvensis L. and Carduus acanthoides L. and good efficacy (score 3) against Convolvulus arvensis L. were achieved with the higher dose.The product was not toxic to monocotyledonous weeds.