Posts Tagged: citrus
What Are the UC Ag Experts Talking About?
Join the online crowd
February 19, 2020
Dr. Elizabeth Grafton-Cardwell will talk about how insects develop resistance (including examples of resistance in citrus thrips, California red scale, and citricola scale), pesticide use tactics to avoid resistance, the potential for resistance in Asian citrus psyllid, and best practices for citrus pest management. One hour of DPR continuing education unit is approved.
webinar registration at Pesticide Webinar
This presentation is part of the series of 1-hour webinars, designed for growers and Pest Control Advisers, highlighting various pest management and horticultural topics for citrus and avocados. During each session, a UC Expert on the subject will make a presentation and entertain write-in questions via chat during and/or after the presentation. As we develop this program, we may expand to other crops.
- Gibbing in Avocados (Ben Faber, March 2020)
- Citricola scale by Elizabeth Grafton-Cardwell (April 2020)
- Invasive shot hole borers in avocado by Akif Eskalen (May 2020)
- Vertebrate pests by Roger Baldwin (June 2020)
- Ants in citrus by Mark Hoddle (July 2020)
- Use of plant growth regulators on citrus by Ashraf El-kereamy (August 2020)
Citrus greening disease, or Huanglongbing (HLB), is deadly, incurable, and the most significant threat to the citrus industry. Most HLB research focuses on the tree canopy, but scientists in California studied the impact of HLB on root systems. They recently published the first study to report on the response of two different varieties of citrus to the causal bacterium, 'Candidatus Liberibacter asiaticus' using metabolomics and microbiome technologies.
"Metabolomics is a cutting-edge field of study that provides snapshot information about the metabolism of living things," explains author Emily M. T. Padhi, "while microbiome studies provide valuable information about the microbial communities living in a particular ecological niche - some microbes are beneficial to the host, while others can be harmful."
Padhi and colleagues wanted to see how the root system of two varieties of citrus responded to HLB. They collected roots from healthy and infected Lisbon lemon and Washington Navel orange trees grown in greenhouses at the same time and under the same conditions.
They found that both varieties experienced a reduction in root sugars and amino acids when exposed to HLB. However, they also found differences. While the concentration of malic acid and quinic acid (two metabolites involved in plant defense) increased in the navel roots, they decreased in the lemon roots. They also found that the beneficial bacteria Burkholderia increased substantially in navel plants but not in lemons, which contradicts previous studies.
"Overall, this is the first study to compare two varieties of citrus using a combined metabolomics and microbiome approach and demonstrates that scion influences root microbial community composition and, to a lesser extent, the root metabolome."
There is evidence to suggest that the causal bacterium moves to the root system soon after a plant becomes infected. A key strategy for preserving the health of an infected tree is root system management and research on different responses to HLB may help devise new variety-specific preventative and treatment measures.
Images of the bulk root mass and sample leaves from healthy and 'Candidatus Liberibacter asiaticus' lemon and navel plants.
Credit: Emily M. T. Padhi, Nilesh Maharaj, Shin-Yi Lin, Darya O. Mishchuk, Elizabeth Chin, Kris Godfrey, Elizabeth Foster, Marylou Polek, Johan H. J. Leveau, and Carolyn M. Slupsky/h4>
HLB infected roots
Several calls have come in from growers lately about yellow avocado and citrus trees. the yellowing is most common on the late summer flush leaves or can affect the whole canopy on young trees. In severe cases leaves fall. This happens going into winter after a warm fall when growing conditions are good. During the winter, the root systems become depleted of stored starch and die.
During winter, trees go into what is called a “quiescent” state, a version of dormancy found in subtropical tree crops. This is a resting mode that protects them to a certain degree from frost damage. There is not much that can be done in a field setting until temperatures warm up and the trees begin growing again in late winter/early spring. As the temperatures increase, the trees gradually recover and the foliage re-greens.
Winter Yellows can be exacerbated in years when we do not have leaching rains to remove salts from the root zone. And it can also be more severe when we have those years when winter rains just never seem to stop and rootzones become waterlogged. We may never see that time again.
Photo by Greg Moulds
citrus winter yellows
It has been a struggle to get through the summer this year. Weird. Hot. Then fog in August. Hot. Then fog in October. It's supposed to be clear,, blue skies in October. perfect weather for avocado persea mite and citrus leaf miner. Hot times then cooler. How to irrigate? A lot of folks just decided not to irrigate. Why do it when it's so crazy? Forecast was for no rain, but it's cool. And then it rained, and suddenly that beautiful citrus that has just broken color and is an orange globe, splits. It's most common in navels, but all citrus that ripen in the fall – tight-skinned satsuma mandarins, early clementines, tangelos and blood oranges. With the hot summer, it seems that a lot of citrus fruit have accelerated their maturity and are ready, ripe and sweet right now, and maybe ready to split.
And that's the problem. Drought stress. Salt stress due to drought. Water stress due to miserly watering. A heat wave in July. And a weird fall with maybe rain and maybe no rain and is ¼ inch considered rain or just a dedusting? Irregular watering is the key to splitting this time of year. The sugar builds, the pressure to suck in water builds and the fruit has been held back by a constrained water pattern and suddenly some water comes and it goes straight to the fruit and Boom, it splits.
Years of drought, and a stressed tree are a perfect set up for a citrus splitting in fall varieties like navel and satsuma. The days have turned cooler and there's less sense on the part of the irrigator to give the tree water and suddenly out of nowhere, there is rain. That wonderful stuff comes down and all seems right with the world, but then you notice that the mandarin fruit are splitting. Rats? Nope, a dehydrated fruit that has taken on more water than its skin can take in and the fruit splits. This is called an abiotic disorder or disease. However, it's not really a disease, but a problem brought on by environmental conditions. Or poor watering practices.
Fruit that is not yet ripe, like ‘Valencias' and later maturing mandarins are fine because they haven't developed the sugar content and have a firmer skin. They then develop during the rainy season when soil moisture is more regular. Or used to be more regular. With dry, warm winters this may become more or a problem in these later varieties, as well.
Several factors contribute to fruit splitting. Studies indicate that changes in weather, including temperature, relative humidity and wind may exaggerate splitting. The amount of water in the tree changes due to the weather condition, which causes the fruit to shrink. Then with rewetting, the fruit swells and bursts. In the navel orange, it usually occurs at the weakest spot, which is the navel. In other fruit, like blood orange, it can occur as a side split, as seen in the photo below.
Proper irrigation and other cultural practices can help reduce fruit spitting. Maintaining adequate but not excessive soil moisture is very important. A large area of soil around a tree should be watered since roots normally grow somewhat beyond the edge of the canopy. Wet the soil to a depth of at least 2 feet, then allow it to become somewhat dry in the top few inches before irrigating again. Applying a layer of coarse organic mulch under the canopy beginning at least a foot from the trunk can help moderate soil moisture and soil temperature variation.
Once split, the fruit is not going to recover. It's best to get it off the tree so that it doesn't rot and encourage rodents.
(Photo by Ottillia “Toots” Bier, UCR)
ACP Management for Commercial Growers - UC Ag Expert Webinar, Dec 4 @3 p.m.
Take advantage of this opportunity for an interactive web-based presentation on ACP field management from UC researcher and ACP expert Dr. Beth Grafton-Cardwell. You don't have to travel for this one, it's free, and you can earn CEUs, too! Sign up here: https://ucanr.zoom.us/webinar/register/WN_fEKM2ScPTk6WF5ilga6V7Q
In San Bernardino County a single residential tree tested positive for the bacterium that causes HLB. As a result, the HLB quarantine has been expanded in the Montclair area. Also of note is an adult ACP that recently tested positive for the bacterium that causes HLB near Corona, outside of the HLB quarantine. See the latest HLB map for details: maps.cdfa.ca.gov/WeeklyACPMaps/HLBWeb/HLB_Treatments.pdf. As before, all HLB detections to date have been on residential properties, the infected trees have been or are being removed, and ACP treatments are applied on a recurring basis to remaining citrus in those areas. No HLB has been found in commercial groves via PCR testing.
Regulatory responses required by the state in response to an HLB detection are described in CDFA's Action Plan for ACP and HLB.
How Close Is HLB To Your Citrus? There's a New UC App For That!
Visit ucanr.edu/hlbgrowerapp , zoom to or type in your location and it shows your proximity to HLB+ detections, recommends best practices to protect your citrus from HLB based on your current proximity to know detections, and provides a link to the Voluntary Grower Response Plan for more information. As HLB detections via PCR increase and spread, it's important to be aware of possible actions you could take to further protect your citrus should an HLB detection occur in your area.
CITRUS REMOVAL PROGRAM: Citrus trees that are neglected or abandoned may harbor ACP and HLB, increasing risk to other citrus in the area. Abandoned and neglected trees may be reported to me or the county Ag Commissioner's office. The Citrus Matters ACT NOW program may be able to assist in citrus removal. For more information contact Joel Reyes at firstname.lastname@example.org or (559) 592-3790.
Additional Useful Links:
Summaries of the latest scientific research on combating HLB: ucanr.edu/sites/scienceforcitrushealth/
Science-based analyses to guide policy decisions, logistics, and operations: www.datoc.us
General updates and information on the state ACP/HLB program and regional activities: citrusinsider.org
CA Citrus Pest and Disease Prevention Program
ACP/HLB Grower Liaison
Ventura, Santa Barbara and San Luis Obispo Counties
805 284-3310 (phone or text)
ACP adult and nymph