USE OF MULCHES FOR WEED CONTROL IN ORCHARDS

摘要

Comparisons have been made over several years of various mulches for weed control in apple orchards in Hawkes Bay, New Zealand. The mulches tested included the organic mulches straw, sawdust, bark, compost, wooldust and low growing ground cover species creeping red fescue (Festuca rubra), white clover (Trifolium repens), dichondra (Dichondra micrantha) and hydrocotyle (Hydrocotyle heteromeria).They were compared with conventional residual and non-residual herbicide treatments for weed suppression, effect on tree growth, yield and soil bioactivities. Creeping fescue and white clover were established from seed while dichondra and hydrocotyle were planted as established plants in soil plugs, all with and without herbicide assistance. Seedlings were difficult to establish in the mature orchard. Periodic mowing was necessary with all species to prevent weeds over-growing the young ground covers. Creeping red fescue and white clover persisted without herbicide assistance while dichondra persisted only with winter herbicide treatment. Hydrocotyle failed to persist under dry summer conditions. Of the organic mulches, straw gave the best weed control and compost generally encouraged weed growth. All the other mulches allowed some weed ingress and the few weeds that established became very large and required spot treatment. Established dichondra- provided good weed suppression, but only with herbicide treatment. Creeping red fescue also gave good weed suppression, with or without herbicide assistance, but needed mowing to restrict its growth. Soil temperatures in the mulch plots were slightly lower and fluctuated less than in the herbicide treated plots. Compost treatment had the highest soil respiration, soil microbial activity and earthworm numbers. There was a strong relationship between trunk growth and the total fruit yield. In the newly planted orchard the ground cover species reduced tree growth and fruit yield in the first season compared to herbicide and bark mulch.