Economic analyses compared the returns of weed control methods for drip and sprinkler irrigated celery (Apium graveolens L. `Sonora'). The nine treatments included an untreated control, cultivation as needed for weed control, a pre-emergent herbicide (trifluralin), and six post-emergent herbicides. The effect of each treatment on weed control, yield, crop value, cost of control, costs for additional hand-weeding, net return, and dollar investment (marginal rate of return) was determined. The treatments that reduced weed populations under drip and sprinkler irrigation also increased yield, net returns, and rate of returns. Effective weed control reduced the additional costs of hand-hoeing the weeds not killed by herbicides, resulting in greater net return. The net returns of weed control were even greater when celery was drip irrigated than when sprinklers were used. In 1998, the sprinkler irrigated field returned $1148 to $3921/ha, compared with -$5984 for the untreated control. Net returns for drip irrigation were much higher, ranging from $3904 to $9187/ha compared with -$8320 for the untreated control. Net returns were also higher in 1999, ranging from $2466 to $5389 when weeds were controlled compared with a net loss of $5710 for the untreated control in the sprinkler irrigated field. The returns on the drip-irrigated field were much higher, from $6481 to $8920 when weeds were controlled, compared with -$8046 for the untreated control. The associated returns for every dollar invested (marginal rate of return) in the non-dominated treatment (more return and lower cost) ranged from 52% to 156% for sprinkler irrigation, and 59% to 144% for drip irrigation in 1998. In 1999, the rate of return for each dollar invested ranged from 104% to 324% for sprinkler and 2.4% to 321% for drip irrigated fields.
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