Residual effect of 2,4-D on whole-stalk- and billet-planted sugarcane

Field studies conducted for two growing seasons evaluated the effect of 2,4-D applied at 1.6 kg ai/ha to 'LCP 85-384' sugarcane 7, 5, 3, and 1 wk before planting (WBP). Sugarcane was planted in mid September using both whole stalks and billet (45 cm) stem sections. When 2,4-D was applied 5 wk or closer to planting, sugarcane shoot emergence and population averaged across planting methods and years were reduced up to 28 wk after planting (WAP) relative to the nontreated control. By 52 WAP, sugarcane had compensated and stalk population was equivalent among treatments. Sugarcane height in response to 2,4-D varied between years, and only in 2001 at 52 WAP was a height reduction observed when 2,4-D was applied 1, 3, or 5 WBP. Crop injury in 2001 was further reflected in reduced sugarcane yield (at least 11%) and sugar yield (at least 12%) more than 1 yr after 2,4-D had been applied 5 wk or closer to harvest of sugarcane for seed. Sugarcane and sugar yields were equivalent for the nontreated control and the 7 WBP 2,4-D treatment in 2001, but 2,4-D application in 2002 did not negatively affect yield. Even though sugarcane shoot populations across the growing seasons were consistently higher for the billet planting system, yields averaged across 2,4-D application timings were greater for billets (18%) compared with whole stalks only for the first year. Because 2,4-D can have a residual effect on sugarcane yield more than 1 yr after the initial foliar application, a 7-wk period should be allowed between herbicide application and harvest of LCP 85-384 for billet or whole-stalk planting.