Eclipta is a seed-borne summer annual that is problematic in the production of container-grown landscape plants. Halosulfuron at 70 g/ha is registered as a directed application to landscape areas but not to container-grown landscape plants. Halosulfuron was applied preemergence (PRE) to seeded eclipta and postemergence (POST) to progressively older eclipta seedlings at rates ranging from 0.18 to 100 g/ha. For halosulfuron PRE treatments, eclipta control was determined from the foliage weight of surviving seedlings. For halosulfuron POST treatments, control was determined from the weight of foliage regrowth following the removal of the treated foliage 2 wk after treatment. Nonlinear regression and log-logistic analysis indicated that the rate required for 90% control (I90) for halosulfuron PRE was 45 g/ha. For halosulfuron POST, the I90 was 60 g/ha for plants having five or fewer true leaves and 98 g/ha for plants that had lateral branching from the basal crown. Analysis estimated the I90 for flowering-sized eclipta exceeded 300 g/ha. Selective placement studies revealed that the phytotoxicity resulting from POST treatments occurs by foliar and root uptake, with foliar exposure having greater activity. For POST treatments that were limited to foliage-only contact, a split application increased control up to 25% compared with a single application of the same total dosage. However, control remained inadequate because the rate required for 75% control (I75) was 157 and 121 g/ha for single and split applications, respectively. Halosulfuron sorption by a pine bark–based rooting substrate, as used in container production, was 96% of the amount applied. The propensity for surface-applied halosulfuron to be leached in this substrate was evaluated by eclipta bioassay. After 2 wk, with 23 cm of cumulative irrigation and rainfall, halosulfuron was detected 12 cm below the substrate surface. The propensity for substrate-adsorbed halosulfuron to return to the water phase may also contribute to PRE activity for eclipta control.

It has been previously reported that POST-applied isoxaben can effectively control established hairy bittercress. Experiments were conducted to determine the relative importance of root vs. foliar entry of POST-applied isoxaben. At a common isoxaben rate of 0.56 kg/ha, foliar-only and foliar plus soil applications provided 10.5 and 23.3% control, respectively, as determined by fresh weight reduction. In contrast, soil-only application provided 47.0% control. Hairy bittercress foliar absorption of 14C–isoxaben did not exceed 15% of the amount applied after 72 h. Therefore, the comparatively less effectiveness of foliar-only applications may be attributed primarily to limited absorption. Minimal isoxaben concentration required to inhibit root growth of hydroponically grown hairy bittercress was 0.0025 mg/L. Higher concentrations were required to produce a response in the foliage. Sorption of isoxaben by pine bark rooting substrate, typical of what is used in container nursery production, exceeded 99% of amount applied after 36 h. Even with 99% sorption, the probable concentration within the aqueous phase remains sufficient to inhibit hairy bittercress root growth. Additional studies with 14C–isoxaben established that approximately 35% of the root-absorbed isoxaben was translocated into the foliage. Translocation from the roots into the foliage was reduced to 16% when the experiment was repeated during environmental conditions less favorable for vegetative growth (i.e., longer day length and higher temperature). Results indicate that the control of hairy bittercress with POST-applied isoxaben is likely the result of root absorption and root-growth inhibition. Expression of phytotoxicity within the foliage is also a component, but is dependent upon the root-absorbed isoxaben being translocated into the foliage. Extent of this translocation is dependent upon plant maturity and prevalent environmental conditions.