David Doll4 CommentsJuly 19, 2020Irrigation

Regulated Deficit Irrigation: Is it appropriate for your operation?

Regulated deficit irrigation is the practice of reducing irrigation to obtain some type of desired stress level. This practice is often used during the initiation of the hull-split period to reduce hull-rot strikes. It also has been utilized during periods of water shortages to save 5-15% of the seasonal water use of almond. Due to the limited effect on yield, as well as the benefits, it has been advocated for application within orchards by the University and industry (including myself!). This practice, however, can have negative impacts when applied incorrectly and should only be used if deemed appropriate. In theory, this practice is easy to apply. Water application rates should be cut to achieve -15 bars stem water potential for two weeks preceding the onset of hullsplit (e.g. Blank split). This stress should be maintained at this level for this period. At the end of the two weeks, regular irrigation resumes and the orchard prepares for harvest. The difficulty in application has everything to do with accurately monitoring plant stress. Every orchard and orchard practice creates a different approach in application. For example, assuming similar irrigation levels, stress levels achieved in a mature orchard planted on sandy soil will occur in a shorter time frame than an orchard on a heavier clay loam. Every orchard site requires careful monitoring to determine when to cut and resume full irrigation. I have observed numerous orchardists apply tree stress only to see a reduction in kernel yield. This is due to ongoing gains in nut weight that occur between the onset of hull-split and harvest. If the tree is significantly stressed during this period, the conversion of carbon to fats is reduced, impacting the final crack out percentage. One closely monitored orchard in which I worked, demonstrated a 10-15% reduction in kernel weights

Read More
David Doll3 CommentsMay 30, 2017General, Technology

Small Drones and Monitoring Orchards: Project Update and Field Day

Aerial imaging can provide real-time information to growers regarding water usage and crop health. Within agriculture, these tools provide a valuable service for identifying problematic areas within fields, thereby increasing efficiencies for both small and large scale producers. Currently, most aerial imaging is conducted by flights with mid-elevation aircraft or satellites. These flights and corresponding images are usually conducted by a service company and provided on a weekly or monthly basis. Autonomous or Unmanned Aerial Vehicles (UAVs) may provide a format in which more regular flight data can be obtained. Most discussions within agricultural settings have been focused around large fixed wing drones. However, smaller, less sophisticated and less autonomous UAVs could provide a useful platform for California farmers. These smaller UAVs would be less expensive to construct, may require less regulatory permitting, and provide a mobile platform that can be quickly deployed within a field setting. In these settings, small UAVs would have the ability to quickly monitor crops for water stress, nutrient management, and pest and disease epidemics. A major barrier for small UAVs is camera/imager selection and processing. Currently, most work within crop stress management has focused on the use of thermal cameras that operate in the far-infrared spectrum (Maes and Steppe, 2012). These cameras are expensive, which inhibits the adoption of UAV technology. More commonly used spectral wavelengths, such as visible and near-infrared wavelengths can be used for other vegetation indices need to be researched to determine if they provide comparable results as thermal imaging. These imagers and indices are attractive to the end-user due to the lower cost to implement. With these challenges in mind, a research project sponsored by the University of California Agricultural and Natural Resource Competitive Grants Program was awarded to determine the feasibility of using small UAVs for perennial crop water

Read More
David Doll7 CommentsAugust 3, 2009Insects, Irrigation

Shothole borer damage on Almond – Varietal Differences in Response to Water Stress

The water crisis on the West side of the valley has presented opportunities to see problems not typically observed in almond production. Many of these issues tend to be directly related to tree stress caused by lack of water, failure of salt leaching due to decreased winter rains, and chronic water stress from prolonged drought. Typical observations of drought stressed trees range include yellowing leaves and leaf drop in mild cases, wilted new growth during moderate stress periods, and poor crop set, thinned canopy, and scaffold die back in chronic cases. A visit was made to an Aldrich-Monterrey-Nonpareil orchard located near Los Banos, CA. All varieties were on Nemaguard rootstock. This orchard has been under moderate drought stress for the past two years as determined by the use of a pressure bomb. This year, the grower was again short on water and had to water at about 80% evapotranspiration rate for the season. The grower was concerned about clear gumming coming from multiple wounds on his trees. Orchard observations included those listed above for orchards suffering from chronic drought stress: poor vigor, thinned canopies, and reduced crop load. On the affected trees, gumming was seen extending form the graft union up to the scaffolds. The issue was predominantly found on Aldrich trees, with some strikes on the Nonpareil, and very few, if any, strikes on the Monterrey. Upon seeing the damage (Picture 1), it was very clear that it was shothole borer, Scolytus rugulosus, an insect that invades and lays eggs in the branches/trunks of stressed trees. Borer insects are able to push their eggs through the bark and into the tree. A tree that is healthy enough to elicit a response then gums profusely in order to flush the egg out of the tree’s tissue (Picture 2). This gum

Read More