LAHORE - The 22nd International Asia-Pacific Weed Science Conference started at the Government College University (GCU) here on Tuesday. The experts from Indonesia, United States, Bangladesh, Australia, Sudan, Jordon, Iran and India are participating in the five-day conference being held on the theme of 'Judicious Weed Management- Road to Sustainability. Addressing the opening session of the conference, Professor of Weed Science Dr Khan Bahadar Marwat said the weeds lost in Pakistan amount to Rs 250 billion annually in the major field crops of maize, wheat and rice. Besides economic lost, invasive weeds were major threat to our biodiversity; many of the weeds cause allergies and also promote insect and disease proliferation. Dr Bahadar said Canada thistle, a weed of sugarcane, had developed resistance against specific herbicides and spread to other crops in Peshawar Valley. GCU Dean of Sciences Dr Ikramul Haq said weed scientists were confronted with incalculable challenges in eradication of weeds injurious to crops. He said the changing behaviour of weeds was also causing problems for vegetation managers, which was compelling the human attitude towards sustainable management of weeds. Addressing the students, GCU Professor Emeritus Dr Khalid Hameed Shiekh said all researches were useless unless implemented. The researches done in the filed of weeds and seeds should be forwarded to the framers, so that they can draw benefits out of them, he added.