Raghad Soufan
General Commission for Scientific Agricultural Research-
Admin. of Plant Protection Research
Damascus University, Faculty of Agriculture
 2009

Abstract

Maize (Zea mays L.) is one of the important agronomic summer crops. Many annual weeds can infest and compete this crop like: Amaranthus retroflexus L., Chenopodium album L., Portulaca oleracea L., Xanthium strumarium L. and Datura stramonium L. in addition to some  perennial weeds like: Cyperus rotundus L.,  Convolvulus arvensis L. and Sorghum halepense L.. These species differ in their competeition ability the maize and in their effects on plant height at flowering stage, and seed yield. The results revealed that maize production was affected by S. halepense, and this effect was proportional to weed’s density. Also, C. rotundus has negatively affected maize.
The results determined the economic threshold level of S. halepense in maize crop was (22-6) plant/m², and 20 plant/ m² for C. rotundus for two growing seasons (2006 and 2007).
Yield losses does not explain by the traditional competition between maize and weeds, but it certainly occurred by the inhibitory effects of allelochemicals.
Weeds aqueous extract of C. rotundus, C. arvensis and S. halepense at the concentration of 20% and 80% exhibited inhibition of germination percentage (%), plant height and fresh and dry weight of maize.
The variable effects have related to the plant parts, extract concentration and different isolation methods.
The results showed that weeds affect on the maize growth by producing  inhibitors and activators chemical substances which is called (allelochemicals), and not only by  competing the crops for place, soil, moisture, light and nutrients.