• Applying roundup to the base of lemon tree canopies: effects on leaves, flowers, fruitlets, and yield

      McCloskey, William B.; Wright, Glenn C.; Wright, Glenn; Kilby, Mike; Department of Plant Sciences, University of Arizona, Tucson, Arizona; Dept. Plant Sciences, U. of A., Yuma Mesa Agricultural Center, Yuma, Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1999-11)
      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.
    • Evaluation and management of a "salina" strawberry clover cover crop in citrus: first year preliminary results

      McCloskey, William B.; Wright, Glenn C.; Wright, Glenn; Kilby, Mike; Department of Plant Sciences, University of Arizona, Tucson, Arizona; Dept. Plant Sciences, U. of A., Yuma Mesa Agricultural Center, Yuma, Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1999-11)
      Two orchard floor management strategies were evaluated beginning in the fall of 1997 in a 'Valencia' orange (Citrus sinensis) grove at the University of Arizona Citrus Agricultural Center (CAC) in Waddell, Arizona. The clean culture or bare ground treatment produced more yield than the ‘Salina’ strawberry clover treatment when harvested on March 10, 1999 and the tree canopy volume of the clean culture treatment was also greater than that of the clover treatment. Yield efficiency (lbs of fruit per cubic meter of canopy) was similar in the two treatments. The clean culture treatment produced more large size fruit (size 88 and larger) and less small size fruit (size 113 and smaller) than the strawberry clover treatment. Although the yield efficiency parameter suggests that it may be possible to produce as much fruit in the clover treatment as the clean culture treatment, the total yield and fruit size distribution of the clover treatment compared to the clean culture treatment were characteristic of the negative effects of competition from vegetation on the orchard floor found in other studies. Based on previous studies, competition for water was the most likely cause of the negative competitive effect. Installation of additional tensiometers to measure soil moisture at greater depths and leaf water potential measurements to assess the degree of water stress in both treatments prior to irrigation will hopefully allow further improvement in irrigation scheduling to eliminate the negative affect of having vegetation on the orchard floor in the clover plots.
    • Results of scion and rootstock trials for citrus in Arizona - 1998

      Wright, Glenn C.; Tilt, Philip A.; Peña, Marco A.; Wright, Glenn; Kilby, Mike; Dept. Plant Sciences, U. of A., Yuma Mesa Agricultural Center, Yuma, Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1999-11)
      Five rootstocks, 'Carrizo' citrange, Citrus macrophylla, Rough lemon, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1998-99 results indicate that trees on C. macrophylla and C. volkameriana are superior to those on other rootstocks in both growth and yield. C. macrophylla is beginning to outperform C. volkameriana. 'Swingle’ and Carrizo' are performing poorly. In a similar trial, Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 1998-99 results indicate that the 'Limoneira 8A Lisbon' selection is superior, and that ‘Corona Foothills Lisbon’ may also be superior to the other selections in both growth and yield. Results from another lemon cultivar trial suggest that 'Cavers Lisbon', 'Limonero Fino 49' and 'Villafranca’ lemons may be good candidates for plantings as well. Results from two other lemon scion trials, a navel orange cultivar trial and a 'Valencia' orange trial are presented as well.