The effect of Roundup on lemon trees (Citrus limon) was evaluated by repeatedly spraying 0.5, 0.75, 1, 1.25, and 1.5 lb. a.i./acre (corresponding to 0.5, 0.75, 1, 1.25, 1.5 quarts of Roundup Ultra/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 after three Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in either the sprayed or unsprayed portions of the tree canopies as judged by the counts collected from branches in each canopy zone. Similarly, in 1997 after five Roundup applications, and in 1998 after nine Roundup applications, increasing rates of Roundup had no effect on flower or fruitlet production in the sprayed or unsprayed portions of the tree canopies. Spraying Roundup on the bottom of the tree canopies did not reduce total lemon yield per tree in 1996, 1997 or 1998 at any of the application rates. In all three years of the study, increasing Roundup rates had no effect on the yield of the first or second ring picks or the percentage of the total crop picked on the first harvest date. Increasing Roundup rates also did not affect fruit size at any harvest date in 1996, 1997 or 1998. Similarly, increasing Roundup application rates did not affect fruit quality at any harvest in 1996, 1997 or 1998. Thus, there was no relationship between the rate of Roundup sprayed on the trees and yield, fruit size or quality in all three years of this study. The three years of data collected in this study indicate that accidental drift or inadvertent application of Roundup onto lemon trees when spraying weeds on the orchard floor has no significant effect on lemon tree productivity.

This experiment was established in January 2000 in a block of 'Washington' navel orange trees at Verde Growers, Stanfield, AZ. Treatments included: normal grower practice, winter low biuret (LB) urea application, summer LB urea application, winter LB urea application plus winter and spring potassium phosphite, winter LB urea application plus summer potassium phosphite, and normal grower practice plus spring potassium phosphite. Each treatment was applied to approximately four acres of trees. For 2000-01, yields ranged from 40 to 45 lbs. per tree, and there was no effect of treatments upon total yield, and only slight effect upon fruit size, grade and quality. For 2001-02, there was a slight effect of treatment upon yield as LB urea led to improved yield, while potassium phosphite led to reduced yield. Normal grower practice was intermediate between these two extremes.

The application of N-fertilizers mixed with a surface irrigation stream (surface N-fertigation) is widely practiced in the Yume Mesa. Guidelines for the efficient management of surface N-fertigation systems are needed. The purpose of the work reported herein is to evaluate the relative effectiveness of existing surface N-fertigation management practices in the Yuma Mesa. This has been accomplished through the following steps: (1) a complete set of performance indices that can be used to assess the relative merit of alternative management scenarios are identified and defined and Equations as well as solutions for quantifying the performance indices are proposed; (2) surface fertigation field experiments (using Br- as a tracer) were performed in two irrigation basins at the Yuma Mesa research farm of the University of Arizona during the fall season of 2000; (3) the spatial distribution as well as the application efficiency and adequacy of Br- applied with irrigation water was determined using the performance functions proposed herein; and (4) the results were analyzed to assess the merits and limitations of existing practices.

Granular (Rugby 10G) and liquid (Rugby 100ME) formulations of Cadusafos were evaluated for the control of Tvlenchulus semipenetrans on mature lemon trees in a commercial citrus orchard at Yuma, Arizona. Three applications of cadusafos, with two months between applications, at the rate of 2 g a.i. /m2 reduced nematode populations to undetectable levels and increased the yield and rate of fruit maturity of 'Rosenberger' lemons. Yields were increased 12,587 kg per hectare with Rugby 100ME and 8,392 kg per hectare with Rugby 10G. Nematode populations were suppressed for at least 12 months after the last application.

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. Leaf injury symptoms, flower and fruit counts, and yield data were collected The Roundup applications caused significant leaf injury in the sprayed area of the canopies and there was significant defoliation of branches at the higher Roundup rates. In 1996, flower and fruitier counts were not affected by the Roundup applications. However, flower and fruitier 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 yield data indicated that the Roundup applications did not significantly affect lemon yield, however, the effect of Roundup on the 1997 flower and fruitier counts suggests that there may be a yield effect in 1997. The preliminary data suggest that accidental drift of Roundup on to lemon trees when spraying weeds on the orchard floor has no short-term effect on grove productivity but this conclusion must be substantiated by further data collection.

An experiment was initiated in 2000 to study the feasibility of growing organic lemons in the southwest desert of Arizona. An eight-acre field was selected on Superstition sandy soil at the Mesa Agricultural Research Center to conduct this investigation. Lemon trees were planted at 25 x 25 feet spacing in 1998. The initial soil test in top 6 inches was 5 ppm nitrate-nitrogen and 4.9 ppm NaHCO3-P. Soil pH was 8.7 in the top 6 inches. Four treatments were applied in randomized complete block design repeated four times. The treatments were beef cattle feedlot manure and perfecta, clover and guano from 2000 to 2002, cowpea and guano in 2003, and guano and perfecta, and standard practice treatment. Soil samples were collected from 0-6 and 6-12 inches the first week of March 2003 and analyzed for available nutrients. Results showed a difference for most nutrients in 0 to 6 and 6 to 12 inches between treatments. Nitrate- nitrogen increased significantly from 3.25 ppm in standard treatment to 19.10 ppm in the manure treatment. Similarly, soil organic matter increased from 0.1% in standard treatment to 0.2% in the manure perfecta treatment. Phosphorus level increased significantly from 7 ppm in guano perfecta to 56.5 ppm in manure perfecta treatment. Leaf tissue analysis indicated that nitrate level was influenced by treatment. Both commercial standard and organic treatments were equally effective in controlling citrus thrips, but repeated applications were required. Mite population has been detected at low level with no significant differences observed among treatments.

Much of the citrus produced in southwestern Arizona is grown on sandy soils. Because these soils have a low ion exchange capacity, are highly permeable to water, and are prone to nitrate leaching, achieving efficient N management presents a continuing challenge. A field study was conducted on a superstition sand to evaluate the response of lemons to combinations of soil and foliar applied N. Lemon yields significantly increased by soil applied N. Foliar N increased yields of lemons the first harvest at the lower soil N rates. However, there were no other significant responses to foliar N. Overall, there were few meaningful changes in fruit quality to N fertilization. The N content of the leaves increased linearly to soil N application