• Crisphead Lettuce Variety Trials 1995/96

      Wilcox, Mark; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
    • Management of Downy and Powdery Mildew on Lettuce: Efficacy of Fungicides in 1996 Field Trial

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Downy and powdery mildew are caused by the plant pathogenic fungi Bremia lactucae and Erysiphe cichoracearum, respectively. Cool and moist environmental conditions favor development ofdowny mildew, while warmer and dry weather is conducive for development of powdery mildew. Potential new fungicides were evaluated for management of these diseases in 1996. Both downy and powdery mildew developed in the test plots. All tested materials significantly reduced the severity of downy mildew compared to plants not treated with a fungicide. Compared to nontreated control plants as well as some tested materials and rates, significant reduction of powdery mildew was achieved with Azoxystrobin 80WDG + Latron B-1956, BAS 490 02F, Ciba G /MZ + Mancozeb 75DF, Dithane 75DF + Latron CS-7, Propamocarb 6EC (high rate), R11-7281 2F + Larron CS-7, and Microthiol 80WDG.
    • Management of Sclerotinia Leaf Drop on Lettuce: Efficacy of Fungicides in 1996 Field Trial

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Leaf drop of lettuce is caused by the plant pathogenic fungi Sclerotinia minor and S. sclerotiorum. Cool and moist environmental conditions favor disease development. Potential new fungicides were evaluated in a field trial for management of this disease in 1996. For plots containing Sclerotinia minor, all compounds and rates tested significantly reduced the number of diseased heads compared to plots not treated with a fungicide. All treatments except Ronilan at the 0.5 lb. a. i./A rate yielded a significantly higher number of marketable heads compared to nontreated plots infested with S. minor. For plots containing S. sclerotiorum, all materials except the Ciba compound at the low and high rates decreased the number of diseased heads and increased the number of marketable heads compared to nontreated plots.
    • Mixed Lettuce and Romaine Variety Trials 1995/96

      Wilcox, Mark; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
    • Optimal Soil Placement and Application Method of Admire® for Sweetpotato Whitefly Control in Head Lettuce

      Palumbo, John; Kerns, David; Sanchez, Charles; Wilcox, Mark; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      The effects of Admire formulation and soil placement on colonization by sweetpotato whitefly, Bemisia tabaci (Gennadius), at three plant growth stages of lettuce, Lactuca sativa L., were evaluated in experimental and commercial lettuce plots in 1993-1994. We also evaluated the effects of Admire treatments on yield response and incidence of chlorosis associated with whitefly control. Admire placement had a significant affect on whitefly colonization in lettuce throughout the experimental period. Whitefly densities on lettuce varied at each plant stage relative to depth of placement within the lettuce seed bed. Applications made to the soil surface and at 1.5 inch sub-seed furrow followed by irrigation, provided the most consistent control of whitefly nymphs in both small plot and on -farm lettuce plots. These Admire soil treatments also prevented reductions in head size and incidence of leaf chlorosis associated with whitefly colonization in lettuce. Our data suggest that incorporation of Admire into the upper 1.5 - 2 inches of soil below the seed furrow is optimal for absorption and translocation by lettuce roots. Admire soil treatments may provide a more environmentally suitable and effective alternative to control of whiteflies in lettuce than is currently possible with foliar insecticide reatments.
    • Residual Activity of New Insecticide Chemistries Against Beet Armyworm in Lettuce

      Kerns, David L.; Palumbo, John C.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Three new insecticide chemistries (Alert, Success and Confirm) were evaluated and compared with standard chemistries for residual activity to beet armyworm in lettuce. Lettuce was treated in the field with the insecticides and left for 0, 3, 5 and 7 days. Leaves from treated plants were then brought into the laboratory where second instar beet armvworms were reared on them. Mortality was estimated 5 days after the worms were placed on the leaves. Bioassay were conducted at the thinning, heading, and harvest stages of lettuce. Under high temperature and light intensity, only Alert and Confirm provided the best residual control of beet armyworm, exhibiting good activity for about 3 days after application. Success had better residual activity than Lannate, and both were better than Xentari. Under cool temperatures and low light intensity conditions, Alert, Confirm and Larvin exhibited good activity for at least 5 days following an application, (7 days or greater for Alert and Confirm). Lannate and Xentari both had greater residual activity late in the season, but were not as effective as Alert, Confirm or Larvin. Late season activity of Success did not appear to differ much from early season observations, and did not appear to provide more than 3 days residual activity.
    • Temporal Activity of New Insecticde Chemistries Against Beet Armyworm in Lettuce

      Palumbo, John C.; Kerns, David L.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Three new insecticide chemistries (Alert, Spinosad and Confirm) were evaluated and compared with standard chemistries for temporal mortality of beet armyworm in lettuce. Field assessment and lab bioassay were conducted at the thinning, heading, and harvest stage of lettuce. Results from both the field and laboratory indicated similar trends for the temporal activity of the products. Alert appears to be have the most rapid "knockdown activity" with 100% mortality consistently occurring by 2 DAT. Spiniest, a naturalyte insecticide, has activity similar to Larvin. Both require 2-3 days to achieve complete larval mortality. Confirm, a new IGR selective for lepidoptera, requires significantly more time to achieve complete mortality (4-5 DAT). It can be compared with Bt (Xentari) activity in that it has initially slow activity. However, unlike Bt, it can effectively cause complete beet armyworm mortality. The results of this study are consistent with similar studies we conducted in 1994 and 1995 and provide basic guidelines concerning the activity and assessment of the performance of these materials in the field. However, PCAs and growers will ultimately be able to develop specific use patterns for these materials within their individual lettuce pest management programs.
    • Thermodormancy in Lettuce

      Hurlburt, M. W. II; Ray, D. T.; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Most lettuce (Lactuca sativa L) seed fails to germinate at high temperatures. This phenomenon thermodormancy, is common in desert regions where 87% of all lettuce is grown in the U.S.A. A study was conducted using a non-thermodormant plant introduction, PI 251245, and two highly thermodormant Dutch butterhead cultivars, 'Dabora' and 'Severa'. Reciprocal crosses were made and germination trials conducted to observe how maternal and paternal influence and seed color contribute to thermodormancy. At 25 °C, germination was 100% for the three parents and the reciprocal F1 hybrids. Germination differences occurred at both 30° and 35 °C among the parents, with P1251245 with 100% germination and Dabora and Severa with less than 10% germination at both temperatures. Segregating F3 and F4 populations from Dabora x PI 251245 were investigated further. Genetic variation found between families suggests that breeding lettuce for improved thermotolerance may be possible. Seed color did not influence thermodormancy.
    • Timing and Frequency of Provado® Applications for Management of Aphid Populations in Head Lettuce

      Palumbo, John; Mullis, Clayton Jr.; Reyes, Francisco; Amaya, Andreas; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1996-08)
      Provado insecticide (imidacloprid) was compared to Admire and other standard insecticides for management of aphids in head lettuce in Yuma 1995 and 1996. Foliar applications of Provado appear to provide an alternative method of controlling aphids on lettuce comparable to prophylactic applications of Admire. The prevention of aphid colonization in lettuce heads with Provado may depend greatly on the timing and frequency of applications before harvest occurs. These studies and other studies on spinach suggest that more than one application of Provado will be necessary to adequately suppress aphid contamination in heads. The label suggests that applications be timed 5-7 apart. Our data tends to support this recommendation. Furthermore, timing applications should be based on days to harvest, level of aphid colonization and duration of aphid migration.