A transformed image of an almond orchard using the normalized difference vegetation index.

From The Almond Doctor

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.

Almond BloomAs forecasted, the weather for bloom 2017 looks wet. This will impact the number of fungicide applications, how we apply the material, orchard access, and bee concerns. This article is a follow up to what was written last week

Periods of leaf wetness favor fungal pathogen development. Although there are no specific models for blossom pathogens, I general suggest applying a fungicide prior to a rain event in which leaf wetness exceeds 24 hours. This suggests that short, passing storms may not need a fungicide spray, but multi-day storms or multiple passing showers would. With the impending week of wet weather, fungicide applications to reduce the occurrence of disease is strongly encouraged. More on fungicide selection can be found here at the UC IPM website.

Aggregation of leaffooted by on walnut in early October of 2016. The aggregation is comprised mostly of fifth instar.

For a few seasons now, I have been interested in understanding more and ultimately finding better monitoring tools for Leaffooted bug, Leptoglossus spp.  Most growers and PCAs have a  good working knowledge of this bug and likely have attended one or more of my talks covering the subject.  We know that leaffooted bug overwinters in aggregations consisting of just a few to several hundred individuals.  The aggregations tend to occur on citrus, palm frowns, Cyprus trees, pomegranate, walnut (Fig. 1), olive, and on/in non-plant substrates like pump houses, farm equipment, and wood piles.  The list is extensive.  The reason why aggregations can occur on such a diversity of substrates is that they are not necessary interested in feeding but more so in seeking a protected area to survive winter.  An  interesting behavior that I have made is that aggregations typically occur where the group can best collect heat from the sun during peak solar radiation periods. 

2014 12 09 12.57.032Field fumigation should be considered when replanting almond orchards.

It is the time of the year when many operations begin the process of replanting almond orchards. Orchard removal and eventual replacement is one of the more critical times of farm operations. The decision to remove a block varies by farmer. Some remove blocks based on a cycle of redevelopment, meaning that blocks are removed on a schedule based on age to assist with cash-flow. Some are removed due to expensive or inadequate resources (e.g. water). Many are removed when production drops below a certain profitability level.

Removing a block on profitability can be tricky. Blocks tend to alternate bear. An off year may trigger removal, but it could be coming into an on year. Prices also fluctuate. Therefore, this may not be the best way to decide on removing a block. Another consideration should be determining the the stand of trees remaining in the orchard and the rate of tree loss over the past few years. Commonly, in old orchards, trees are lost to heart rot decay fungi and corresponding wind throw. These losses tend to increase as the orchard ages. If this rate is increasing and the orchard stand is below 75%, removal and replanting should be considered. This is a conservative estimate, and should be evaluated with production records and tree stand for your own operations (This estimate is based on an 80% canopy coverage at maturity with minimal tree losses).

2015 09 14 10.34.28 150x150Trees with kinked or girdled roots do not usually show symptoms until 1-2 years later.

It is the time of the year when many operations plant potted almond trees. Although potted trees are convenient with the year round availability and planting time (almost any month if properly irrigated),  there are a few considerations at planting that must be considered in order to prevent root girdling and future orchard loss.

Root girdling of trees occurs when roots grow in odd directions. These roots wrap over or around other roots or the trunk, eventually preventing the flow of water and nutrients while limiting structural integrity. The problem is usually not noticeable at first, but 6-8 months after planting, the trees begin to show reduced growth. Later, these trees often become victim of wet feet or Phytophthora due to over-irrigation of the tree. Over-irrigation occurs from to the inability to pull water at the same rate due to the constricted xylem and reduced canopy size in comparison to healthy trees. In cases in which the trees survive and are kept through the third leaf, they may snap off at ground level from the shaking process. The issue seems to be more severe with more vigorous rootstocks.

2015 07 30 12.27.471Hull rot can increase the number of stick-tights.

     There have been a lot of reports of poor removal of ‘Nonpareil’ almonds. This issue may be caused by a few different issues, all which require a different management plan. The potential causes as well as some thoughts on management are provided below:

     1. Uneven ripening. Uneven ripening can be caused by several different things. A long, protracted bloom can create a delay in ripening due to the length of time between the first and last fruit that was pollinated and fertilized. Also, vigorous growing conditions can delay the ripening process. These include more than adequate water and nitrogen through the entire growing season. Often, this is observed in younger orchards as they are being “pushed” along with increased water and nutrients. Not much can be done about the long bloom period, but properly timed irrigation and nitrogen applications in the spring (especially early spring) can help reduce excessive vigor.

     2. Hull rot. Once a hull is infected by Rhizopus or Monilinia, a toxin is secreted which leads to the death of fruit wood. As this toxin kills tissues, it can cause them to gum – especially at the peduncle, effectively gluing the nuts to the spur. These nuts are very difficult to remove and hull rot management practices should be utilized to help reduce the occurrence of this disease. In years were humidity is high at the onset of hull split, cultural management practices appear to be less effective.