- Author: Brad Hanson, UC ANR Weed Specialist
Here is an updated guide for herbicides that are registered for citrus, avocado and a few other tree crops.
- Author: Ben Faber
GAINESVILLE, Fla. — Researchers from the Institute of Food and Agricultural Sciences at the University of Florida are closer to finding a possible cure for citrus canker after identifying a gene that makes citrus trees susceptible to the bacterial pathogen.
Citrus canker, which causes pustules on fruit, leaves and twigs, is a highly contagious plant disease and spreads rapidly over short distances. Wind-driven rain, overhead irrigation, flooding and human movement can spread citrus canker. Human transport of infected plants or fruit spreads the canker pathogen over longer distances.
In Florida, the last extensive canker outbreak occurred beginning in 1995, which led to an ultimately unsuccessful eradication program that ended in 2006. That effort cost an estimated $1 billion and stimulated renewed efforts for more effective and economical controls. Farmers destroyed more than 16.5 million citrus trees between 1995 and 2012.
Yang Hu, a former doctoral student working with Jeff Jones, a professor in plant pathology, found the critical trait in the bacterium that is necessary for disease development. Hongge Jia, a researcher at UF's Citrus Research and Education Center in Lake Alfred, and Nian Wang, an associate professor in microbiology and cell science also based at the Citrus REC, along with six researchers from three universities worked on the project, as well.
Citrus canker continues to be a problem and exists in most citrus-growing areas in Florida. While scientists like Hu are devoted to eradicating the disease, many other researchers are now also battling citrus greening, which threatens to wipe out the $9 billion industry.
Citrus canker is caused by the bacteria Xanthomonas citri. While studying the bacterial pathogen's role in infected citrus, researchers were able to identify a gene in citrus critical to the development of citrus canker, known as the susceptibility, or “S” gene.
By finding the susceptibility gene, researchers say they are closer to a cure for the disease.
“The S gene represents an excellent candidate for control measures for the citrus bacterial canker,” Hu said.
Hu and Jones said they hope to secure funding to support further research, and have already identified several genes they believe could be engineered to obtain broad-spectrum plant resistance to most kinds of citrus canker.
“Once you know what the susceptibility gene is, it's possible to design multiple strategies for disease control,” Jones said.
The research paper was published online this month by Proceedings of the National Academy of Sciences: http://www.pnas.org/content/early/2014/01/08/1313271111.abstract.
- Author: Ben Faber
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
- Author: Ben Faber
I am amazed how such a simple procedure can go so wrong. For avocado and citrus growers, it’s time to think about planting in the spring. And every spring and summer I get called out to diagnose trees that are failing. It often turns out that the trees have been planted too deeply. There are various ways of killing a tree, such as digging a hole too deeply and then backfilling. When the ground settles, it settles around the root collar and the tree suffocates. Or installing a dry root ball and then not irrigating soon enough. Or adding fertilizer to the planting hole which burns the roots. One of the major problems of lack education and supervision of the planting crew. Don’t assume that everyone knows how to plant a tree.
Deep planting can result in death of woody plants either because they rot in moisture saturated soils or they dry out. In either case, the symptoms are similar: wilting, sunscald or burnt leaves, lack of growth, leaf drop and eventual death of leaves, shoots and branches. Root balls planted below grade cause several problems at establishment. Since native soil surrounds the ball, there is an immediate problem with and interface between the two soil textures. Most container media are lighter than bulk soil, which is done to make sure there is adequate drainage in the nurse. When these soil-free media are planted in soil which is of a heavier texture, the interface does not allow the water to enter the root ball.
When trees are planted too deeply, they are much more subject to fungal cankers and other pathogens that can girdle the stem, killing it and all above ground parts. Planting slightly higher than grade will prevent this. Just look for the color, textural change between the roots and stem and dig the hole no deeper than the root ball to prevent settling. Newly planted trees can’t draw water from bulk soil, not until the roots move out into the soil will they be able to absorb water. Also planting cannot be rushed, because that’s when errors in planting occur.
- Author: Ben Faber
USDA Creates Multi-Agency Emergency Response Framework to Combat Devastating Citrus Disease | |||||
USDA Providing $1 million to Jump Start Citrus Response Framework | |||||
WASHINGTON, December 12, 2013 - The U.S. Department of Agriculture today announced the creation of a new, unified emergency response framework to address Huanglongbing (HLB), a serious disease of citrus that affects several U.S. states and territories. This new framework will allow USDA and its many partners to better coordinate HLB resources, share information and develop operational strategies to maximize effectiveness. "USDA listened to the citrus industry's request for more urgency and greater coordination on the response to HLB and is implementing an emergency response structure," said Secretary Tom Vilsack. "To jump start this initiative and affirm our commitment to industry, USDA is also providing $1 million to be used in support of research projects that can bring practical and short-term solutions to the growers in their efforts to combat this disease. Through the Specialty Crop Research Initiative of the Farm Bill, USDA has provided $9 million in research to blocking the ability of insects to spread HLB to healthy trees. We need Congress to quickly pass a new Farm, Food, and Jobs Bill that continues to support this kind of research to protect a crop worth more than $3 billion in the last harvest." The new framework will bring together USDA's Animal and Plant Health Inspection Service (APHIS), Agricultural Research Service (ARS) and National Institute of Food and Agriculture (NIFA), along with state departments of agriculture and the citrus industry into a Multi-Agency Coordination (MAC) Group for HLB. It will provide industry with a single contact for all the federal and state entities that work on citrus issues and better enable the collective to collaborate on policy decisions, establish priorities, allocate critical resources, and collect, analyze, and disseminate information. The HLB MAC Group will also help coordinate Federal research with industry's efforts to complement and fill research gaps, reduce unnecessary duplication, speed progress and more quickly provide practical tools for citrus growers to use. HLB, also known as citrus greening, is named for the green, misshapen, and bitter-tasting fruit it causes. While this bacterial disease poses no danger to humans or animals, it has devastated millions of acres of citrus crops throughout the United States and abroad. In the United States, the entire States of Florida and Georgia are under quarantine for HLB, and portions of California, Louisiana, South Carolina and Texas are also under quarantine for the disease. The U.S. Territories of Puerto Rico and the U.S. Virgin Islands are under HLB quarantines as well. You can find more information about HLB and the HLB MAC Group on USDA's Multi-Agency Response to Devastating Citrus Disease website. See the USDA Animal and Health Inspection Service's website for additional Q&A Contact: # Note to Reporters: USDA news releases, program announcements and media advisories are available on the Internet and through Really Simple Syndication (RSS) feeds. Go to the APHIS news release page at www.aphis.usda.gov/newsroom and click on the RSS feed link. USDA is an equal opportunity provider and employer. To file a complaint of discrimination, write: USDA, Office of the Assistant Secretary for Civil Rights, Office of Adjudication, 1400 Independence Ave., SW, Washington, DC 20250-9410 or call (866) 632-9992 (Toll-free Customer Service), (800) 877-8339 (Local or Federal relay), (866) 377-8642 (Relay voice users). |
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