California Agriculture

Methyl bromide, a popular and effective crop fumigant, is being phased out in the United States and globally because of impacts on the ozone layer. Demand for a replacement chemical, 1,3-D (Telone), is expected to increase by up to 500% when methyl bromide is no longer available. However, not all California growers will be allowed to use 1,3-0, as its use has been restricted within townships to address air quality concerns. We estimated the impact of 1,3-0 use restrictions after methyl bromide is phased out in 2005 and found them to be binding in several major production areas of California. Impacts will be greatest in regions where strawberries and perennial crops are grown.

The results of a mealybug study in Central Valley vineyards, designed to develop sampling guidelines, reveal that mealybug distribution on vines varies greatly through the season and that mealybugs usually prefer concealed locations, such as under bark. This combination makes sampling difficult. A number of sampling techniques were compared. Three- or 5-minute timed counts were most efficient because samplers could follow the mealybugs' movement over the season. Midseason counts were much better predictors of damage at harvest than early season counts. This research confirms past control guidelines and opens new control options. Grape bunches touching vine trunks or spurs will have higher damage. Removing these bunches or using barriers between bunches and mealybug oviposition sites can also reduce damage.

Abnormal pistachio nuts, known as “early-split nuts,” have both the hull and shell split while still on the tree, exposing the kernel to invasion by insects and molds. Deficit irrigation of pistachio trees in April and May resulted in substantial increases in the formation of early-split nuts in late summer, while extreme deficit irrigation in July and August resulted in decreased formation. However, deficit irrigation during the period of shell hardening, mainly in June, did not affect early-split formation.

Using tree water status measurements in orchard irrigation management is predicated on the fact that these values are closely linked to important physiological processes, such as growth. In our study, stem water potential (SWP) was highly correlated with vegetative growth in almond trees. However, the SWP technique requires that leaves be covered by small, foil-covered plastic bags for a certain time prior to the pressure chamber measurement and that the atmospheric vapor pressure deficit (VPD) in the orchard be considered in interpreting the data. This can be time consuming and labor intensive for growers. Growers need alternative approaches for taking pressure chamber measurements that are rapid, simple and easy to interpret. We found that measurements of shaded leaf water potential (LWP), taken when the leaf was covered by a damp cloth for the short time between leaf excision and placement in the pressure chamber, correlated well with SWP. Moreover, air temperature at the time of measurement was as useful as VPD for interpreting shaded LWP as an indicator in irrigation management. In addition to weather, this work identified operator differences as a major source of variation in water potential measurements. Plant-based measurements can be useful tools if precautions are taken concerning variability. Shaded LWP has logistical advantages over SWP and this study suggests that it can be used without sacrificing accuracy.

A 1997 random survey of 2,000 participants in the U.S. Department of Agriculture's WIC Farmers' Market Nutrition Program found that the program helped motivate low-income, pregnant and breast-feeding mothers to buy (and eat) fresh fruits and vegetables from farmers' markets. In California, the program provides $20 in coupons to participants in the Special Supplemental Nutrition Program for Women, Infants and Children (WIC). We found a small but statistically significant increase in fruit and vegetable consumption among survey respondents. The total intake was 4.50 servings per day in the group that used coupons compared with 3.56 in the group that did not, an increase of almost 1 serving. Participants were also enthusiastic about returning to farmers' markets. Sixty-two percent of those who were given coupons used them. Most participants wanted to see the program expanded although many responded with suggestions to improve it.

The loss of nutrients from fertilizers can impair surface and ground waters. Environmentally sensitive crop management requires applying only enough fertilizer to ensure economic crop yields. We found that sugarbeets grown in soils rich in organic matter in the Upper Klamath Basin can be fertilized at very low rates and used to remove more nutrients in harvested roots than are applied as fertilizer. This in turn reduces the risk of leaching excess nutrients and may help protect surface waters in the region from additional enrichment.