January 7, 2003
Vol. 1; Issue 6

Production Update: Harvest of leafy vegetables continues at a steady pace, with a head lettuce harvest continuing at a steady pace. There has been some indication that the cool winter weather has effected lettuce quality in some areas. In addition, blistering of romaine has been observed on pre-harvest stage lettuce being grown at the Yuma Agricultural Center. By and large though quality of head and leaf lettuce, cole crops and spinach remains good to excellent. Spring melon planting has begun in the Yuma Valley. A few fields have been planted under plastic (mid-bed trench) thus far.

Weather: As noted above, temperatures may have had an impact on some fields. During the end of December, temperatures were very cool (Table 1), and often resulted in significant lettuce ice and delays in harvest. However, temperatures differed across the growing region. During the week from Dec 18 to Dec 26, ambient temperatures dropped below freezing, but varied at the AZMET stations. Temperatures dropped below 32º C 1 time in the Yuma Valley, but dipped below freezing 4 and 5 times respectively at the North Gila and Roll weather stations. Similarly, the weather system that just moved through the area earlier this week dropped measurable rain, but again, varied with locations. Nearly 0.05" of rain was recorded in the Yuma Valley, which equals our total rainfall for all of 2002 (Figure 1). No rain was measure in the North Gila Valley, and 0.21" fell in the Roll area. Overall, 2002 was the driest it has been in Yuma in the past 10 years. With the prediction of El Nino for 2003, more rain could possibly fall this spring. Historically, Jan, Feb, and Mar are our wettest months (Figure 2). Although during the past 10 year Sep has received significant rainfall, this is primarily a result of an abnormal storm event in 1997 where 2.67 " of rain fell on Sep 21.

Pest Update: Early signs of powdery mildew have been observed on both head lettuce and romaine in the Yuma Valley. Also schlerotinia and big vein have been observed sporadically throughout the region. Beet armyworm have been found on lettuce and cole crops in light numbers in several areas in the Yuma Valley. Overall insect activity (as measured by sticky traps) was light during late December (Table 2). This coincided with very cool evening and daytime temperatures (Table 1). However, thrips and aphids remain active. Based on field observations, thrips activity has increased with the warmer weather experienced in early January. Similarly, we continue to find small colonies (non-economic at this point) of foxglove, green peach and potato aphids (Figure 3), and turnip aphids in cole crops throughout the area. We anticipate aphid populations to begin to significantly increase, particularly if temperature remain at or above normal.

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

Table 2. Insect activity measured from yellow sticky traps at at three Yuma growing locations.

WF=Silverleaf whitefly; LM= Leafminers; THP=Thrips; APH=Aphids

Figure 1. Ten year average annual rainfall for the Yuma Valley as compiled by AZMET located at the Yuma Ag Center.

Figure 2. Ten year cumulative rainfall for each month for the Yuma Valley as
compiled by AZMET located at the Yuma Ag Center.

Figure 3. Wingless potato aphid adult on romaine lettuce leaf, Yuma, Arizona,
Jan 3, 2003

AZMET Weather Data

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