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The effects of several preemergence herbicides at various rates were tested on bearing Redblush' grapefruit trees and non-bearing Navel orange trees. Some of the preemergence herbicides caused foliar injury symptoms on the trees including Hyvar X Diuron, and Krovar I although they did not cause significant yield reductions in the short time period of this experiment. Several herbicides including Solicam, Surflan, and Prowl did not cause foliar injury or reduce yield and provided good weed control for various lengths of time. The Prowl treatments provided the longest period of weed control in the experiment on bearing grapefruit trees.

When applied early-postemergence, Milestone at 0.75 and 1.0 lbs-ai/A provided excellent control of summer annual grasses and broadleaf weed for as long as 4 months, equivalent to Karmex. Princep and Krovar also provided good weed control but appeared to offer slightly shorter residual against some broadleaf species. Solicam, although it provided good weed control, particularly of the grasses, was the weakest material evaluated in this trial. Although Karmex is notorious for causing crop injury on the sandy soils of the Yuma Mesa, we did not detect any injury from this herbicide or any others in this trial.

The effect of Roundup on lemon trees was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb. a.i./acre on the bottom 20 to 24 inches of the tree canopies over a three year period. The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was also significant defoliation of branches at the higher Roundup rates in all three years of the study. In 1996, flower and fruitlet counts were not affected by the Roundup applications and the 1998 data were inconclusive. However, flower and fruitlet counts in 1997 in the sprayed zone of the canopy were significantly reduced by Roundup and the effect increased with increasing Roundup rate. The 1996 and 1997 yield data indicated that Roundup applied to the bottom 20 to 24 inches of the tree canopies did not significantly affect lemon yield. The preliminary data suggest that accidental drift or misapplication of Roundup on to lemon trees when spraying weeds on the orchard floor has no short-term effect on grove productivity.

Two field studies were conducted to evaluate metolachlor (Dual®) for preemergence weed control in spinach to provide support to gain registration through the IR-4 program. Dual® at 1.0 to 1.5 lb a.i./A gave acceptable control of London rocket, black mustard, lambsquarters, and knotweed. Nettleleaf goosefoot, cheeseweed, and yellow sweetclover control was not acceptable. In one test, dimethenamid (Frontier® or SAN -582H, Sandoz) controlled London rocket, lambsquarters, knotweed, and goosefoot at 0.25 lb ai. /A and did not control cheeseweed or sweetclover. Spinach was not injured by Dual® or Frontier®.

DCPA (Dacthal®) herbicide was applied preemergence (PE) to the soil surface after onion planting and no crop injury was observed for rates of 5.3, 7.5, and 10.5 lb. a.i. /A at one of two locations. Dacthal® gave good control of London rocket and cheeseweed (90 -94 %) at one location and marginal control at the second location (79 -85 %). Dacthal® did not exhibit a rate response to control the two weeds common to both locations. The lower rate of Dacthal® did not differ in efficacy compared to higher rates to completely control lambsquarters and nettleleaf goosefoot. All rates of Dacthal® marginally controlled yellow sweetclover and other mustard weeds present. Dacthal® provided adequate weed control to allow onion stand establishment.

Oxyfluorfen (Goal®) herbicide at 0.125 to 0.25 lb. a.i./A applied postemergence (POST) to onions at the 3-leaf stage of growth effectively controlled London rocket, yellow sweetclover, and prostrate pigweed with marginal injury to onions. Earlier POST applications on 1- and 2-leaf onions caused injury and some stand reduction. Bromoxynil (Buctril®) herbicide at 0.25 lb. a.i./A applied early POST gave generally good weed control but did not adequately control sweetclover. Buctril® applied in clear weather did not injure 1-leaf onions but caused severe injury on 2- and 3-leaf onions when applied during cloudy weather conditions. Buctril® plus pendimethalin (Prowl®) tank-mix combination applied POST provided good control of London rocket, sweetclover, and prostrate pigweed; however, onion injury was severe due to applying Buctril® in cloudy weather. Buctril® and Goal® effectively controlled weeds present in the onions but timing of POST applications was critical with respect to onion size and weather conditions to minimize injury.

Oxyfluorfen (Goal®) herbicide at 0.25 lb. ai./A and bromoxynil (Buctril®) at 0.38 lb.a.i. /A applied early postemergence (POST) to onions at the 1- to 2-leaf stage of growth gave near complete control ( >98 %) of lambsquarters, knotweed, cheeseweed, London rocket, and good control ( -90 %) of shepherd's purse. Buctril® did not control annual bluegrass and Goal® only slightly reduced some of the heavy population. Both herbicides caused marginally unacceptable onion injury at 17-20 %. Buctril® plus pendimethalin (Prowl®) tank-mix combination applied POST also gave very good broadleaaved weed control but annual bluegrass was reduced only 50 %. Similar onion injury was observed for the combination treatment as Buctril® alone. Buctril® caused onion injury when it was applied during cloudy weather. Buctril® and Goal® were effective for broadspectrum broadleaved weed control but onions were sensitive when treated before reaching the full 2-leaf stage of growth. Cloudy weather during applications also intensified the onion injury by Buctril® treatments.

Second year field studies continued to evaluate and determine efficacy and safety of postemergence herbicides for broccoli weed control. Goal® 2XL. a newly introduced formulation of oxyfluorfen. severely injured broccoli after application. London rocket (Sisvmhrium irio) control was not acceptable at less than 80%. Pvridate (Lentagran®) and clopyralid (Stinger®) were relatively safe on broccoli but did not affect London rocket.

Preplant incorporated and/or preemergence herbicide treatments including metolachlor (Dual®), EPTC with safener (Eradicane®), cyanazine (Bladex®), pendimethalin (Prowl®), and tank-mix combinations provided good (88 %) to excellent ( >98 %) weed control of prostrate and tumble pigweeds and purslane in sweet corn.