Clomazone was evaluated preplant incorporated (PPI) or post-transplant (PT) for weed control in sweet potatoes. No crop injury by clomazone was detected. Clomazone controlled (≥90%). broadleaf signalgrass, large crabgrass, barnyardgrass, and prickly sida at all rates and methods of application (MOA). Common cocklebur was controlled (≥93%) by clomazone at 1.1 kg ai ha-1 applied PT or at 3.4 kg ai ha-1 PPI in 1988 and at all rates and MOA in 1989. Clomazone did not control carpetweed.

The control of puncturevine in southern peas with imazethapyr and imazaquin and the potential for carryover of these herbicides to spinach was evaluated in Arkansas. Imazethapyr (0.07 kg ai ha−1) and imazaquin (0.14 kg ha−1) applied to southern peas either PPI tank-mixed with trifluralin (0.84 kg ha−1) or PRE or POST following trifluralin controlled puncturevine at least 70%. Imazaquin and imazethapyr remaining in soil after use caused injury and yield reduction to spinach planted 3 to 4 mo after herbicide application in the fall after southern pea harvest. In spring spinach planted 8 to 9 mo after herbicide application, the only injury observed was from soil residues of imazethapyr applied POST in one of two years, with no yield reduction. In rate by timing experiments, imazethapyr at 0.07 kg ha−1 applied PPI, PRE, and 3 and 6 d after puncturevine emergence controlled puncturevine at least 95% at the 2-wk rating. At the 4-wk rating, imazethapyr at 0.07 kg ha−1 applied PRE provided this level of control. Imazaquin at 0.07 and 0.14 kg ha−1 controlled puncturevine greater than 93% when applied up to 12 d after emergence. Puncturevine control was less with both herbicides at lower rates and as application timing increased.

Studies were initiated at two different planting dates and conducted at two different locations in 2001 to determine the critical weed-free period for certain populations of weeds in organically produced ‘Beauregard’ sweetpotato. Naturally occurring weed populations were used, and they included sicklepod, redroot pigweed, and yellow nutsedge. Treatments included allowing weeds to grow for 2, 4, 6, or 8 wk after transplanting (WAT) sweetpotato before weed removal and maintaining the sweetpotato weed-free for 2, 4, 6, or 8 WAT. Weedy and weed-free checks were also included in the study. These treatments were used to determine the length of time weeds can compete with sweetpotato without reducing yield and the length of time sweetpotato must grow before yield is no longer affected by newly emerging weeds. Yield of number one grade sweetpotato roots best fit a quadratic plateau curve for the grow-back treatments and a logistic curve for the removal treatments. Yields in weed-free plots of sweetpotato were higher at the early planting date, whereas yields in plots of weedy sweetpotato were higher at the late planting date. Weed biomass was lower in the grow-back treatments at the late planting date. Data indicate that sweetpotato may gain a competitive advantage over weeds when planted at a later date. At both planting dates, a critical weed-free period of 2 to 6 WAT was observed.