February 13, 2003
Vol. 1; Issue 8

Production Update:
Harvest of lettuce has slowed down considerably due to lettuce ice delaying harvests until mid morning over the past week or so. Based on accelerated plant growth during January, the lettuce and broccoli harvests should last through early March, and perhaps end a little early this year. Certainly the cooler weather experienced in early February could alter those projections a little (Table 1). Quality of head and leaf lettuce, cole crops and spinach remains good to excellent. Winter wheat planting continues; emerging stands look good-excellent. Cotton planting appears to have begun, but have not observed any stands being irrigated yet. Spring melon planting continues in the Yuma Valley. Melons planted under plastic (mid-bed trench) appear to behave produced good-excellent stands in most areas. Melon planting on Yuma beds has increased significantly in the Yuma Valley.

Pest Management Update:
Powdery mildew on both head lettuce and romaine in the Yuma Valley has increased over the past two weeks. Incidence of downy mildew is high on untreated cole crops on the Yuma Ag Center. A few false chinch bug adults have been observed in mature head lettuce during the past week or so. This may have significance for Brassica seed growers, where this pest causes crops losses during seed maturation. Keep an eye out for these as the spring progresses. An increase in beet armyworm larvae has been noted in lettuce and cabbage looper eggs have become more noticeable following the warm weather. Leafminer activity remains variable in all areas (Fig 1-3) and no reports of field infestations have been noted. Thrips populations in head lettuce and romaine fields have increased sharply. This can be seen to some extent by their flight activity in some areas (Fig 1-3). However, damage to leaves and midribs has become more severe, and several PCA's have reported that their spray intervals have become shorter in an attempt to prevent marketable damage. Furthermore, aphids continue to be a problem in some areas. We have seen an increase in all aphid species (green peach, potato, foxglove and lettuce aphid) on untreated plots at the Yuma Ag Center. Additionally, foxglove aphids have been found colonizing Admire-treated lettuce at or near harvest on at least 3 commercial fields in the Yuma Valley. This seems to be specific for foxglove aphids, as other species have not been found in Admire-treated lettuce in significant numbers. This phenomena has also been observed in experimental plots at YAC where head lettuce treated with Admire at-planting was found to be infested with foxglove aphid at harvest (Figure 4). Numbers of foxglove aphid are not significantly lower in the Admire plots, but % of infested heads are. We have several more tests with similar comparisons which we will report on at a later time.

Table 1. Temperature recorded from AZMET stations at three Yuma growing locations.

Figure 1. Insect activity as measured by yellow sticky traps in the Yuma Valley, 2002-2003 produce growing season

Figure 2. Insect activity as measured by yellow sticky traps in the Gila Valley, 2002-2003 produce growing season.

Figure 3. Insect activity as measured by yellow sticky traps in the DomeValley/Welton Area, 2002-2003 produce growing season.

Figure 4. Contamination of Heads with Foxglove Aphid in Admire-treated and untreated head lettuce, February 10, 2003, Yuma Agricultural Center.

AZMET Weather Data

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