TILLAGE AND SEED DEPTH EFFECTS ON VELVETLEAF (ABUTILON-THEOPHRASTI) EMERGENCE

Understanding patterns of weed seedling emergence within a growing sea son and over years is important to develop models to predict optimum t iming of weed management practices. A study was conducted in a field w ith no previous velvetleaf infestations to describe emergence patterns following seed burial at three depths in two tillage systems. Freshly harvested velvetleaf seeds were planted 0, 2, and 6 cm deep in moldbo ard plowed (MP) and no-tillage (NT) corn stubble in October 1990. Velv etleaf seedling emergence was monitored over the following 4 yr in con tinuous corn. Emergence was higher in NT than in MP plots throughout 4 yr of observation. The first growing season following seeding, emerge d seedlings represented 9.3 to 15.8% of the seeds sown in NT, compared with 0.1 to 0.8% of seeds sown in ME After four growing seasons, emer ged seedlings were 12.5 to 25% of seeds sown in NT but only 6 to 7.4% of seeds sown in MP. Emergence was consistently higher from the 0-cm d epth than from the 6-cm depth in NT, but seeding depth did not influen ce emergence in MP due to mixing of the soil during tillage. Velvetlea f emergence was related to growing degree days (base 7.5 C), with grea ter consistency in NT than in MP. Averaged over years and planting dep ths, 50% velvetleaf emergence occurred within 8 and 13 d of the predic ted date in NT and MP systems, respectively.