The oldest method is tillage. Although it leaves a weed-free environment for a short time, clean cultivation can be detrimental to tree health and growth. Soil-borne diseases can be spread throughout the orchard. Soil erosion is usually increased with clean cultivation. Cultivation can also create a hard pan below the disked area, restricting water and root penetration.
Cover crops are another option.
Annual ryegrass as a cover crop in a peach orchard aids soil water retention and suppresses weeds in test plots. The ryegrass is allowed to grow until it begins competing for water in June, and then killed in place to create a mulch. This seems to be an easy and inexpensive weed control method. In pecans, research has shown many positive aspects of legume groundcovers in orchards. Legumes fix nitrogen sufficient to meet most if not all the nitrogen needed by the trees, and the legumes attract beneficial insects which may reduce the need for some pesticide applications.