A. M. Tawaha

Allelopathic effect of black mustard (Brassica nigra L.) on germination and growth of wild oat (Avena fatua L.)

Abstract Black mustard ( Brassica nigra L.) contains water-soluble substances that inhibited the germination and seedling growth of wild oat ( Avena fatua L.). Determining where allelochemicals may be found in B. nigra in the greatest concentration would aid in trying to isolate the compound or compounds responsible for autotoxicity. This study investigated the allelopathic effects of various B. nigra plant parts on A. fatua L. germination and seedling growth. Aqueous extracts of B. nigra leaf, stem, flower and root plant part were made to determine their effects on germination and dry weights of hypocotyl and radicle length of 8-d old A. fatua L. seedlings over a range of extract concentrations. Increasing the aqueous extract concentrations of separated B. nigra L., plant parts significantly inhibited A. fatua L. germination, seedling length and weight. Radicle length was more sensitive to extract source than seed germination or hypocotyl length. Based on 8-d-old A. fatua L. plant radicle length growth, averaged across all extract concentrations, the degree of toxicity of different B. nigra plant parts can be classified in order of decreasing inhibition as follows: leaf, mixture of all plant parts, flower, stem and root. Soil incorporation of fresh B. nigra roots only or both roots and shoots reduced A. fatua emergence, plant height, and dry weight per plant.

Weed control in cereals in Jordan

Weeds are a problem in the rainfed parts of Jordan. They compete with major crops for the limited resources of soil moisture and nutrients. Yield losses of major crops caused by weeds may range from 30% to 80% in Jordan. Wheat and barley are vigorous crops that rapidly cover the soil surface and often out-compete weeds. Small grains and other grasses are often planted as cover crops to suppress weeds. However, weeds can be a problem in wheat and barley especially where crop rotation is not practiced. An integrated approach to weed management in wheat and barley includes preventing the introduction or spread of weeds, crop rotation, cultural practices that result in a vigorous crop, and chemical treatment when necessary. Weed seeds can be spread from weeds growing along ditch banks and other areas, by tillage and harvesting equipments, and through contaminated crop seed. Crop rotation is an integral component of weed management since many weeds are easier to control in certain crops. Early planting dates generally result in plants that tiller more and are more competitive with weeds. Drill seeding produces a more uniform stand than broadcasting and helps in weed control. High seeding rates are also more competitive with weeds. r 2003 Elsevier Science Ltd. All rights reserved.

The response of wild oats ( Avena fatua L.) to sowing rate and herbicide application

A 2-year field study was conducted during the rainy seasons of 1999 and 2000 at Houfa in northern Jordan, to study the influence of various sowing rates (20kg ha-1, 40kg ha-1 and 60kg ha-1) and 2,4-D application at two growth stages (stage 13 (3-leaf) and stage 44 (Mid boot)) on yield components and productivity of wild oats. The highest biomass and grain yields were produced at 60kg ha-1 and the lowest at 20kg ha-1 in both seasons. On the other hand, the highest number of tillers per plant was produced at 20kg ha-1 and the lowest at 60kg ha-1 in both seasons. Differences in weed number and fresh weight were significant among various weed control treatments in both seasons. Hand-weeding proved to be the best weed control method. In both growing seasons, yield reductions occurred when 2,4-D esters were applied to oats at stage 13 (3-leaf). Hand-weeding was more effective than 2,4-D applications in suppressing weed growth.