The participant shall: Keep turf properly mowed; Control weeds in such a manner as not to allow distribution and spread of either weeds or their seed, or both; Control injurious insects or diseases; Produce the best quality turf possible under existing climatic and environmental conditions; and Maintain each field continuously in accordance with accepted turf grass management principles. In a pure stand, the participant shall rogue other plant species before the Department makes its final pre-harvesting inspection. In mixtures, the participant shall rogue or spray with an effective herbicide all weeds and other objectionable plants before the Department makes its final pre-harvesting inspection. The participant shall treat a field with a history of annual grassy weeds with an effective pre-emergent herbicide at the proper time of year. The Department may not certify turf grass unless it is uniform in density, color, and texture, and free of excessive amounts of thatch, insects, diseases, nematodes, and any other abnormal condition.