- Author: Peggy Mauk
Red imported fire ant (RIFA), Solenopsis invicta, has been reported as a pest in Florida where the fire ants girdle young citrus trees (Diepenbrock) https://crec.ifas.ufl.edu/media/crecifasufledu/extension/extension-publications/2021/2021_jan_fireant.pdf Florida researchers found that RIFA girdled the trees and killed them. In the summer of 2022, we discovered newly planted avocado trees being girdled and killed in WHERE?. Upon closer examination we discovered the girdling was from the activities of a fire ant. Dr. Dong-Hwan Choe, Professor of Extension – Entomologist at UC Riverside, identified it as Solenopsis sp. Figure 1 show the initial damage to an otherwise healthy avocado tree which weeks later was completely girdled and dead. Fire ants were controlled using a bait. This took 2 applications. Fire ant mound is evident in Figure 1B but is not the typical mound that is associated with fire ants so growers need to be watching for ant activity and treat proactively. The fire ants were very aggressive to both the tree and the people working the trees.
Figure 1: (A) initial holes made by fire ants. (B) girdled tree and mounds at basin of tree and (C) dead trees.
- Author: Ben Faber
Dr. Fatemeh Khodadadi joined UCR as an Assistant Professor of Extension and Assistant Plant Pathologist in October 2022. She is a plant pathologist with broad experience in fungal and bacterial diseases of fruit and nut trees. Dr. Khodadadi received M.S. and Ph.D. from University of Kerman, Iran with Shahid Bahonar. Upon completion of her Ph.D she had two postdoctoral fellowships (Cornell University and Virginia Tech). Both focused on fungal and bacterial diseases of nut and fruit trees. Dr. Khodadadi's M.S. research, she worked on aflatoxin-producing fungi contaminating pistachio. The first part of my master's project was focused on isolation, morphological and molecular identification, and the genetic variability of the aflatoxin-producing fungal species in pistachio nut samples collected from storages. The second part used the High-Pressure Liquid Chromatography (HPLC) coupled with molecular detection using aflatoxin biosynthetic genes including aflR for differentiation of toxigenic and non-toxigenic isolates and detection of aflatoxin B1 and B2 released from Aspergillus flavus and A. parasiticus species. In her Ph.D. research, she worked on the interaction between walnut and bacterial blight disease caused by Xanthomonas arboricola pv. juglandis (Xaj). She used walnut as a model to clarify the roles of polyphenol oxidases (PPO) in defense responses to Xaj using different molecular techniques and evaluated the susceptibility of walnut cultivars to pathogen, gene expression and enzyme activity of PPO and pathogenesis related proteins in walnut-bacterium interaction. Given that the modification of PPO expression in transgenic plants provides an opportunity to study the contribution of PPO to plant disease resistance, she transferred the JrPPO1 gene from walnut into tobacco to determine the reaction of transgenic tobacco plants against Pseudomonas syringe pv. tabaci. Part of her Ph.D. was conducted at University of California, Davis. In her postdoc at Cornell University and Virginia Tech, she conducted wide-spectrum basic and applied research in bacteriology, mycology, genomics, plant pathology and plant disease management focusing on Colletotrichum species (bitter rot of apple), Erwinia amylovora (fire blight), and Diplocarpon coronaria (Apple Leaf and Fruit Blotch). They used viability digital PCR (v-dPCR) in several key projects aiming to improve accuracy of exiting fire blight disease prediction models, elucidate fire blight biology, epidemiology and management and identify key stress factors that could aid in management of E. amylovora. She identified, described, and characterized for the first time a new Colletotrichum species that causes apple bitter rot and belongs to C. gloeosporioides complex of species. We named it C. noveboracense and it was first found on apple as a host.
The purpose of her research program in UC-Riverside is improving knowledge and understanding of plant pathogen diagnostics and detection, plant-pathogen interaction, biology and population dynamic of pathogens that could facilitate development of new disease management strategies on subtropical trees especially citrus and avocado. The three areas of my research focus are: 1. Identification, characterization and developing molecular methods to detect fungal, bacterial and viral diseases affecting citrus and avocado including but not limited to avocado branch canker and dieback caused by Botryosphaeria species, Phytophthora Root Rot, Sweet Orange Scab caused by Elsinöe australis, avocado sunblotch viroid, and other problematic pathogens on citrus and avocado in California; 2. Studying the citrus, avocado defense responses and molecular interaction with above pathogens; 3. Fungicides and bactericide efficacy trials in vitro and in the field and developing new strategies, tools and programs for disease management. The purpose of her extension program is to provide growers and industry with disease diagnostics and disease management recommendations specific to each fruit crop in cooperation with other Cooperative Extension Specialists and Farm Advisors throughout California. She is looking forward to conducting trials, participating in grower meetings as well as making farm visits and tours. She is available via phone, cell phone and emails, workshops and my blog webpage: https://subtropicalplantpathology.com/category/blog-posts/.
- Author: Ben Faber
California Avocado Growers Seminars Series 2023
Scheduled Topics
You missed this in-person meeting, but see it here
From: February 15 (10 AM - 12 PM)
In-Person and Zoom
Get Down - Fertilizers
How to apply them and how to choose them.
Dr. Danny Klittich - Director of Agronomy at Mission Produce
How to choose and what to look out for with different fertilizer application methods
(venturi, water-powered, batch tank, electric powered, etc.)
and the chemical properties of different fertilizers.
And
How to Read and understand Soil and Water reports.
Ben Faber - UC Cooperative Extension
in-person meeting was at:
United Water Conservation District offices (1701 N. Lombard ST., Oxnard)
and zoomed for those who would prefer that option.
click here: https://californiaavocadosociety.org/seminars.html
- Author: Ben Faber
California Avocado Growers Seminars Series 2023
Scheduled Topics
You missed this in-person meeting, but see it here
From: February 15 (10 AM - 12 PM)
In-Person and Zoom
Get Down - Fertilizers
And
How to Read and understand Soil and Water reports.
in-person meeting was at:
United Water Conservation District offices (1701 N. Lombard ST., Oxnard)
and zoomed for those who would prefer that option.
click here: https://californiaavocadosociety.org/seminars.html
NITROGEN DEFICIENT AVOCADO LEAF
/h2>/h3>/h3>/h3>- Author: Ben Faber
One, one hundred, one thousand
This little mnemonic, or memory aid, in the title is helpful in remembering the critical levels of toxic constituents in irrigation water. The “one” stands for 1 part per million (ppm) of boron (B), the” one hundred” flags 100 ppm of sodium (Na) and chloride (Cl) and the “one thousand” represents the level of total soluble solids (TDS or salts) in water. Levels exceeding the critical values for any of these constituents can present problems for tree growers. The problems typically show themselves as tip-burn and defoliation. The B, Na and Cl are toxic elements at relatively low concentrations, but symptoms appear similar to the damage caused by high salinity.
Water that exceeds the critical levels mentioned in the mnemonic has a greater tendency to cause damage if sufficient leaching is not applied. It doesn't mean the water is impossible to use, only that greater attention needs to be made to ensure that these salts are adequately leached. High levels of these salts accumulate in the soil with each irrigation; the salts are absorbed by the tree and end up in the leaves where they do their damage.
Irrigation is a necessary evil. Every time we apply irrigation water we apply salts, and unless some technique is used to minimize salt accumulation, damage will result. This damage can be more than just leaf drop, but also the stress that induces conditions for root rot. In most years we rely on winter rainfall to correct the salt imbalance resulting from irrigation water.
The last two years have had winters largely without rain. Irrigation water was applied throughout the winter, spring, summer and fall and many trees looked stressed this spring. Even well irrigated orchards in the spring of 2022 had leaf burn due to the gradual accumulation of salts from irrigation. Avocados, which are generally more sensitive to salts than citrus, dropped their salt-burned leaves this spring when flowering began.
We usually think that it is not necessary to irrigate in the winter, but these last two winters should change that opinion. To add to the lack of rain problem, it may be necessary to irrigate even if there is rain in the future. The wetted pattern that is created by a drip or microsprinkler emitter also creates a ring of salt in the outer band of the wetted patter. If there is less than an inch of rainfall to push this salt down, this salt tends to diffuse towards the tree where it can accumulate back in the root system. Orchards with even good water quality would find it advisable to run the irrigation system with the first rains. Those with poor water quality definitely should run the microsprinkler system with an equivalent of one-half inch applied water (13,500 gallons per acre) during or soon after the first events of less than one-half inch rainfall. Growers with water quality exceeding one, hundred, or thousand should be especially alert to the need to manage water in low rainfall winters.