Calag Archive

For three years (1993 to 1995), we monitored organically and conventionally managed cotton fields in Madera County, and measured pest and beneficial arthropod populations, plant growth and development parameters, nutrient status, plant density, yields and lint quality. Square (flower bud) retention was similar in the two systems, although western tarnished plant bugs (Lygus hesperus or lygus bugs) were significantly more abundant on several dates in the organic fields. On most dates, populations of the predatory insects Geocoris spp. were significantly higher in the organic than in the conventional fields. Lint yields were not significantly different for the two production systems in any of the three years, but were lower than county averages in all years. In 1994, lint quality in the two treatments differed in that color grades were more variable in the organic cotton bales. Late spring rains also affected planting success in each year and the shortened seasons in 1994 and 1995 generally kept yields in both treatments at or below two bales per acre.

To compare peach tree water use with soil and plant water status measurements, two trees in a large weighing lysimeter were deficit irrigated with insufficient amounts of water for 3 weeks. Transpiration decreased soon after the deficit irrigation began and evaporation from the soil became relatively more important. Due to shallow, sparse rooting, high-frequency drip irrigation and high evaporative demand, allowable depletion in the wetted soil zone of the lysimeter was only 15% to 20% of available soil water. This indicates the small margin for error in managing irrigation of trees in this situation.

The water status of a peach tree is traditionally monitored by measuring its predawn or midday leaf water potential or midday stem water potential. A study conducted on ‘O'Henry’ peach trees at the Kearney Agricultural Center showed that continuous monitoring of trunk diameter can also be an accurate technique of detecting water stress. The trees were evaluated during 21 days of underirrigation followed by 17 days of full irrigation. Trunk-based measurements were generally more sensitive than discrete measurements to both the onset of water stress and the magnitude of tree water deficits. Parameters based on trunk diameter monitoring correlated well with established physiological parameters of plant water status. These trunk diameter oscillations, which are only available from continuous monitoring, hold promise for improving the precision of irrigation decision making.

Blossom blight was documented in some strawberry production fields in Watsonville in 1996 and 1997. Xanthomonas fragariae and Cladosporium cladosporioides were identified as the causal organisms. This is the first documentation of the two organisms causing blossom blight of strawberry in California. This is also the first report identifying C. cladosporioides as a pathogen of strawberry.

Large (~101 grams), medium (~93 grams) and small (~81 grams) 'Hayward' kiwifruits were stored in either ethylene-free air or in a controlled atmosphere (CA) of 5% carbon dioxide (CO2) and 2% oxygen (O2) at 32°F for 16 weeks. Under both storage conditions, large fruit had a slower rate of softening than smaller fruit. Air-stored kiwi-fruit softened approximately 2.6 times faster than CA-stored fruit. Under air conditions, large, medium and small kiwifruit reached 5.0 lbf (the minimum pounds firmness required for packaging with minimal bruising) by 12, 10 and 8 weeks, respectively, while those stored under CA conditions softened to 5.0 lbf by 49, 30 and 20 weeks, Understanding the relationship between fruit size and the rate of softening under air and CA conditions will help cold storage managers safely monitor kiwifruit softening during bin storage

Average daily historical reference crop evapotranspiration was calculated using 13 to 15 years of daily evapotranspiration from 10 sites in California. Maximum average values, generally occurring in June, ranged between 0.25 and 0.32 inches per day at most of the sites. Absolute percent relative errors were minimum during July and August, ranging between 5% and 13% for all but one site. About 25% to 35% of the variation in the historical data reflected year-to-year variation; the remaining variation was due to seasonal trend and variability about the seasonal trend. To prevent overirrigation or underirrigation during deviation from the historical evapotranspiration value, growers should monitor soil moisture or check real-time evapotranspiration.

Central San Joaquin Valley farmers have been working with researchers and consultants to evaluate soil and crop management practices, enhance biologically integrated pest management and facilitate information exchange through the West Side Biologically Integrated Farming Systems (BIFS) Project. As part of this project, the amounts and composition of aboveground bio-mass in postharvest residues of typical rotational crops of the region were surveyed from 1996 to 1998. Crop residue biomass ranged from 9,560 pounds per acre for corn following grain harvest to 570 pounds per acre for onions. A very large range of organic matter recycling thus results from the various intensive cropping strategies that are currently used in this region.