October 30, 2003
Vol. 2; Issue 1

Production Update:

Planting of head lettuce and cole crops continues at a constant pace, with romaine, mixed and specialty lettuce and baby spinach plantings starting to increase in acreage. Temperatures have been extremely warm this fall, where during the first 8 weeks of the produce growing season (Sept 1- Oct 30) average temperatures were consistently above 80 ºF. In fact, the average maximum daytime highs exceeded 100 ºF (Table 1) for several weeks in September and October. This has resulted in stand establishment problems in some locations throughout the region. However, temperatures are gradually declining, and the cooler evening temperatures (Table 1) are ideal for stand establishment. Overall, no serious production problems have been reported in the produce crops. Based on lettuce and broccoli planted at the Yuma Agricultural Center, early harvests may be 7-10 days ahead of schedule. Crops grown in eastern Yuma county (Dome Valley/Wellton/Roll/) have had slightly cooler temperatures and may not be as far ahead. Cantaloupes and honeydew harvest is well underway and progressing well. Good quality and high sugars have been reported, perhaps a result of the warmer fall weather. No reports of significant virus incidence have been reported and the incidence of Monosporascus cannonbolis or other related soil diseases has been minor in melons thus far.

Pest Management Update:

Area-wide Trapping Network: Our trapping efforts this year have been modified. Instead of placing sticky traps throughout the growing region, we have intensified our trapping effort in the Yuma Valley, adjacent to produce fields and the Colorado River from Bard to Gadsden (Figure 1). Our rationale for changing is an attempt to gain a better understanding of Aphid movement. In particular, we are trying to determine hotspots of Foxglove aphid infestations. Last season this species emerged as a key aphid and appeared to be focused primarily in the Yuma Valley near the river (http://cals.arizona.edu/pubs/crops/az1323/contents.html). Based on trapping to date, aphid flights are just beginning (Fig 1), but have been primarily non-lettuce infesting species (ie, cowpea aphid, alfalfa and grain aphids). Trap catches have been higher on traps placed near the river. No colonization has been observed or reported from the field. Movement of whiteflies, leafminers and thrips has been unusually high in October, probably a reflection of the unusually warm temperatures.

Worm Management: Beet armyworm and cabbage looper pressure has been extremely high this past fall, and continues to be heavy in some areas of the Yuma and Gila Valleys. Reports from PCAs from the Imperial Valley, Yuma and Central Arizona indicate that insecticide treatments have been frequent as a consequence of continual and overlapping oviposition, and rapid plant growth. Warm nighttime temperatures during late-September and October were ideal for moth activity (Table 1). We feel that the high temperatures were the primary factor for the extreme pressure this year. Figure 2 shows armyworm and looper populations in untreated lettuce plots in experimental trials planted at YAC in 2002 and 2003 (Sep 4 and 5 respectively) and sampled at comparable times during the fall growing seasons. The data indicates that during October worm numbers were 2 to 4 times greater this past fall than numbers measured in 2002. These large differences coincide with a wide difference in average ambient temperatures (Fig 2). Worm populations this season peaked in mid-October at > 10 larvae per plant, and in one trial at almost 16 larvae / plant. During this period, temperatures were about 15 degrees warmer than the previous year when numbers only reached about 4 larvae / plant. With the recent drop in temperatures, worm pressure has dropped to more “normal” levels.

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

Fig 1. Sticky Trap Data

Figure 2. Relationship between temperature and worm infestations in untreated lettuce, Yuma Agricultural Center, Fall 2003.

AZMET Weather Data
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