Citrus: UC IPM Pest Management Guidelines
|Publication Number: 3441
Copyright Date: Rev. 2017
Length: 234 pp.
Inventory Type: PDF File
|This is a free publication if you access it as a web page or downloadable PDF document.
These official UC-approved guidelines for pest monitoring techniques, pesticide use, and nonpesticide alternatives for agricultural crops are essential tools for anyone making pest management decisions in the field. This 124-page guideline covers citrus fruit.
Updated August 2015.
A hard copy version of these guidelines can be purchased as Publication 3441P.
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- Author: Joey Mayorquin, Mohamed Nouri, Florent Trouillas, Greg Douhan and Akif Eskalen
Recently, an outbreak of shoot and twig dieback disease of citrus has been occurring in the main citrus growing regions of the Central Valley of California (Fig 1). The causal agents of this disease were identified as species of Colletotrichum, which are well-known pathogens of citrus and other crops causing anthracnose diseases. At this time, it is unclear how wide-spread the disease is in California citrus orchards, but surveys are being conducted to evaluate the spread of this disease in orchards.
The disease was first noticed in 2012 by several growers and nurserymen in various orchards in the Central Valley. Symptoms included leaf chlorosis, crown thinning, gumming on twigs and shoot dieback, and in severe cases, branch dieback of trees (Fig.2). The most characteristic symptoms of this disease are the gum pockets which appear on young shoots either alone or in clusters and the dieback of twigs and shoots (Fig.3). These symptoms were primarily reported from clementine, mandarin, and navel orange varieties. In order to determine the main cause of this disease, field surveys were conducted in several orchards throughout the Central Valley. Isolations from symptomatic plant samples frequently yielded Colletotrichum species.
Field observations indicate that symptoms initially appear during the early summer months and continue to express until the early fall. Trees showing dieback and gumming symptoms characteristic of this disease are usually sporadic within an orchard and generally only a few twigs or shoots are affected within a tree. Morphological and molecular phylogenetic studies allowed the identification of two distinct species of Colletotrichum (Colletotrichum karstii and Colletotrichum gloeosporioides) associated with twig and shoot dieback. Interestingly, these Colletotrichum species were also isolated from cankers in larger branches. Although C. gloeosporioides is known to cause anthracnose on citrus, a post-harvest disease causing fruit decay, it has not been reported to cause shoot dieback of citrus. C. karstii however has not been reported previously from citrus in California and our laboratory is currently conducting field and green house studies to determine the pathogenicity of this species in citrus.
At present, it is unclear how widespread this disease is in California orchards or how many citrus varieties are susceptible to this disease. Pest control advisors are advised to remain alert and monitor citrus trees for the presence of the disease in the Central Valley (particularly clementine, mandarin, and navel varieties) during the early summer months. Continuing research lead by Dr. Akif Eskalen (UC Riverside) in collaboration with Dr. Florent Trouillas (Kearney Agricultural Research and Extension Center), Dr. Greg Douhan (UCCE Farm Advisor Tulare County), and Craig Kallsen (UCCE Farm Advisor in Kern County) is focused on further understanding the biology of the fungal pathogens as well as factors influencing disease expression in order to develop management strategies against this emerging disease.
Shoot dieback symptoms on Clementine
Branch dieback symptoms on Clementine
Gumming symptoms on Clementine
(photos: A. Eskalen)
- Author: Robert Kourik
A little something that a friend wrote for gardeners, but is applicable to farming. You can read more of Kourik's stuff at:http://www.robertkourik.com/tidbits.html
Some garden suppliers now offer beneficial microbial and fungal inoculants to “boost” the soil's fertility. Some products tout the benefits of mycorrhizae inoculants for plant roots.
I contacted soil scientist Dr. Phillip J. Craul, a soil scientist and Senior Lecturer at the Graduate School of Design at Harvard University with the question: “what do the new packaged microbial and fungal products offer gardeners?” His immediate response: “I'm going to be frank, most of the time the home gardener doesn't need to fuss with (inoculants). Such products are only helpful in special cases where you're working with sterile material; (however), most of the biological analyses show enough organisms are usually present under artificial conditions to repopulate the soil—even in urban areas.”
In some cases, here with California native plants, inoculation with mycorrhizae had less new shoot growth—measured on a dry basis—than native soil.
“New Research in the Use of Mycorrhizaefor Nursery Production” by Lea Corkidi Mike Evans and Jeff Bohn, Tree of Life Nursery September 2008.
Furthermore, the soil's vast complex of biota defends its own territory from “invading” microorganisms. Existing microbes and mycorrhizae can be very good at fending off inoculants. According to Martin Alexander, “Microorganisms inoculated into non-sterile soil lead to poor growth and often the seeded species is eliminated in a period of days or weeks...(due to) a rivalry for limiting nutrients, the release by one species of products toxic to its neighbor and direct feeding of one organism upon a second.”
In a study with established willow oak (Quercus phellos), red maple (Acer rubrum) and pin oak (Quercus palustris) trees it was found that “Our data indicated no apparent measurable growth benefit [to estblished sreet trees], under the terms and conditions of this research, to inoculation with a commercial mycorrhizal fungal product unless combined with fertilizer.” “Mycorrhizal fungal Inoculation of Established Street Trees” by Bonnie Appleton, Joel Koci, Susan French, Miklos Lestyan, and Roger Harris. Journal of Arboriculture 29(2): March 2003.
From The Packer:
South Florida university researchers are using dogs and drones to sniff out a disease that's killing the region's avocado trees.
The Florida International University researchers are sending dutch sheppards and belgian malinois into avocado groves to locate trees infected by the lethal laurel wilt disease, which is spread by the redbay ambrosia beetle.
Detection is a major problem and trees can start to wilt within two weeks.
By the time infected trees are detected, the fungus has likely spread to nearby trees via root grafting, said DeEtta Mills, a biological sciences professor.
She and Kenneth Furton, a university provost and forensic chemist, are leading research that trains and deploys five dogs into Miami-area groves.
Drones flying above the groves can detect symptomatic trees, which signal researchers to direct the dogs to infected areas.
The dogs run through the groves and with their powerful noses, have been 90% accurate in locating infected trees, Mills said.
Because of permitting paperwork delays by the Federal Aviation Administration, the researchers haven't been able to use the drones.
The researchers hope to receive approval for drones by August and are relying on growers to point them to infected trees.
The drones provide higher accuracy and can better cover larger areas because running the dogs too long can overheat them and wear them out, Mills said.
Their heavy panting can dull their sniffing senses so after about 20 minutes, the researchers return them to kennels in air conditioned vans, Mills said.
The dogs are trained with diseased wood and infected tree samples detected by the dogs are sent to researchers who examine DNA to verify contamination, she said.
“These dogs, they love to do this and it's amazing to watch them,” Mills said. “These ‘girls' come out of the kennels of the van and ask us where we would like to send them and what we would like them to do. They're extremely highly-driven dogs. If we can get permission to use the drones, it will help us identify areas we need to go in with the dogs and help us verify infection much faster so the dogs won't have to cover as much ground.”
Canine detection is another way of helping save the state's multi-million dollar avocado industry and ultimately, the North American industry.
Florida growers have lost about 4,000 of nearly 800,000 trees and the disease has spread throughout the Mid-Atlantic and into Mississippi.
If it travels farther west, the dogs and drones detection system could also help growers in California and Mexico protect their much larger production, she said.
The Miami university is also working with University of Florida researchers and growers.
N.B. These techniques could also be used to trace Polyphagous Shot Hole Borer infested trees, as well.