Weed seed germination in crops would be significantly reduced by tilling at night or by covering the seeder with a dark plastic sheet to prevent light from reaching dormant weed seeds according to eminent weed ecologist Professor Claudio Ghersa (photo).

The Department of Agriculture, Western Australia recently sponsored a visit by Professor Ghersa from Argentina’s University of Buenos Aires to deliver seminars on weed seed dormancy, endophytes and herbicide interaction.

Department researcher Abul Hashem said Professor Ghersa’s position was based on the assumption that light reaching weed seeds would activate the phytochrome system that would stimulate seed germination.

During his three week visit, weed scientists and agronomists from the public and private sector and farmers had the opportunity to discuss his research and weed management work first hand.

Professor Ghersa said weed seed dormancy was regulated by complex interactions among environmental factors including temperature, light and soil water during seed production and ripening periods.

These factors were commonly affected by on-farm agronomic practices such as cultivation, sowing time and method, seeding rate, spraying and harvesting which alter crop canopy, weed seed dispersal timing and distribution in the soil profile, together with water and gaseous conditions.

The germination of many weed seeds, such as annual ryegrass, depended on the alternating temperature of the top soil layers where most weed seeds were present.

Some seeds buried in the soil for a long time need exposure to light for a fraction of a second to be able to germinate.

According to Professor Ghersa, soil tillage not only changed the position of the seed in the soil layer, but also temporarily exposed the weed seeds to light, leading to a release in seed dormancy and subsequent germination of weed plants.