No abstract

Simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), anda,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were evaluated for weed control in pecan(Carya illinoensis(Wang.) K. Koch) orchard establishment. Maximum weed control and tree growth occurred in plots treated with diuron and simazine applied at 3.0 and 4.0 lb/A, respectively. During the second year, phytotoxic symptoms were observed in plots which had received superimposed annual treatments of diuron at 3.0 lb/A, but none appeared in simazine or trifluralin plots.

Recent evidence associates the persistence of invasive plant species with disturbance and fluctuations in distinct forms of mineral N in soils. We conducted soil and hydroponic experiments to investigate the influence of N form and availability on germination and seedling development of 2 invasive annual grasses, cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae) and 6 perennial grasses, bluebunch wheatgrass (Pseudoroegneria spicata), crested wheatgrass (Agropyron cristatum x A. desertorum), Sand Hollow and Seaman's Gulch big squirreltail (Elymus multisetus), and Little Camas and Little Wood bottlebrush squirreltail (E. elymoides ssp. brevifolius and E. elymoides ssp. elymoides, respectively). Seeds were sown in soils with no soil additions, barley straw (1 mg kg 1), NH4+ =10 mg N kg 1, NH4+ + I (nitrification inhibitor) = 10 mg N kg 1 + 37 ml nitrapyrin, or N03' =10 mg N kg1 to evaluate cumulative germination percentage for 20 days in an incubator. For the hydroponic experiment, grass seedlings were exposed to distinct forms and uniform concentrations of mineral N to monitor root and shoot growth for 21 days. Treatments were no N added, NH4+ (1 mM), N03-(1 mM), and NH4NO3 (0.5 mM). Treatments did not alter germination in the soil experiment. Lack of soil N effect on seed germination is attributed to the absence of seed dormancy in the populations of grasses we evaluated. Initial root length and overall shoot growth of grasses were greater in the N03-than in the NH4+ treatment more frequently for perennial grasses. Root and shoot growth of medusahead and cheatgrass generally exceeded that of the other grasses except crested wheatgrass. However, relative decreases in root dry mass for the no N treatment were greater for the invasive annual grasses than the perennial grasses when compared to the N-addition treatments.

Trifluralina,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied at 1.12 kg/ha inhibited lateral root development on field-grown pecan(Carya illinoensis(Wang.) K. Koch) seedlings. In a greenhouse study, inhibition of lateral roots, club-shaped radicles, and restricted penetration of tap roots resulted when pecans were planted in soil treated with 1.0 ppm trifluralin. When pecans were planted above soil treated with trifluralin, normal root development occurred only in the soil which had not been treated. Lateral roots were inhibited in the trifluralin-treated soil. Pecan nuts from trifluralin plots were smaller than those collected from controls, but other factors of quality were statistically equal or superior to nuts harvested in plots which had been treated with 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). The smaller nut size was attributed to lateral root inhibition by trifluralin early during nut development.

Sixteen male strawberry harvesters were monitored during two 3-h harvesting periods for dermal exposure to abamectin, a miticide/insecticide. Upper body exposures were monitored by cotton undershirt dosimetry, hand rinses, and facial washes. Exposure was greatest to the hands (833 ng/h) followed by the torso (380 ng/h) with negligible residues detected on the face. With <1% dermal penetration, the average systemic exposure was calculated to be 1.36 ng/kg/day. The ratio of the no-observed-effect level (NOEL) of 50 µg/kg/day to the worker exposure of 1.36 ng/kg/day yielded a margin of exposure (MOE) of 36 800. Abamectin foliar residues ranged from 40.7 to 0.17 ng/cm 2 at 2 h and 7 days after the second application, respectively. Dislodgeable foliar residue (DFR) data at the harvest time of 3 days after the second application, 0.84 ng/cm 2 , combined with the Zweig transfer factor (5000 cm 2 /h) and a dermal penetration of 1% resulted in a predicted worker exposure of only 5.6 ng/kg/day and a corresponding MOE of 8930. These results suggest that DFR data may be used to conservatively predict worker exposure to abamectin.