A single breakthrough discovery for managing citrus greening in Florida in the future is unlikely, says a new report by the National Academies of Sciences, Engineering, and Medicine. The committee that wrote the report called for a systems approach to prioritize research on the disease and strategically distribute resources for research to effectively manage the disease, which is the most serious threat for citrus growers worldwide.
The disease Huanglongbing (HLB) or citrus greening — associated with bacteria that are spread by a sucking insect, the Asian citrus psyllid — was initially observed more than 100 years ago in Asia and was first detected in Florida in 2005. The infection results in blotchy mottling of leaves, stunting of shoots, gradual death of branches, and small, deformed fruits with bitter juice. Although infected trees do not die right away, they can remain in a steady state of decline for several years. Between 2010 and 2014, acreage of citrus trees in the state declined from roughly 750,000 to 476,000 acres, and production volume has declined by 58 percent since 2005. In Florida, citrus greening has caused a cumulative loss of $2.9 billion in grower revenues from 2007 to 2014, an average of $374 million a year.
The Citrus Research and Development Foundation (CRDF), a $124 million state citrus-industry initiative, has invested nearly 90 percent of its funds in HLB research. CRDF asked the Academies to review its research portfolio and determine if its efforts have followed recommendations outlined in the Academies' 2010 report, which originally called for the organization's creation. The committee found that CRDF was responsive to several recommendations from the previous report, and along with other funders, has advanced our knowledge about the disease. However, HLB remains a serious danger to Florida's citrus industry, having progressed from an acute to a chronic disease throughout the state.
The report notes that significant barriers to progress toward an HLB solution still exist, among them the inability to culture the bacteria in the laboratory, the lack of advanced diagnostics for early disease detection, and the absence of standardized research methodology that would improve the comparability of results across studies. Resolution of any one of these issues would constitute a significant step, according to the report.
The committee recommended continuing support for both basic and applied research for short- and long-term research efforts. In the long run, HLB solutions would likely utilize new technology, such as gene modification and gene editing, focusing on targets that mediate molecular interactions among plant, bacteria, and the vector, the committee said. As interest in using genetic modification in research grows, CRDF should also consider funding research to assess stakeholder acceptance of the technology and expand efforts to educate growers, processors, and consumers to facilitate the eventual deployment of genetically modified citrus lines.
In the meantime, growers in the state will need short-term solutions for the industry to remain viable. The report recommends finding the best suite of strategies to control the disease in different environmental and growing conditions, vector and pathogen pressures, tree varieties, and stages of tree health, which would help growers in Florida and other states where HLB also occurs.
The report also highlights the need to better understand the economic and sociological factors that impact decision-making and behaviors of growers, which influence the adoption of HLB management strategies. CRDF should create accessible databases to support sociological and economic modeling of citrus greening-related research outcomes and application projections.
The report recommends researchers communicate about the outcomes and evaluation of their efforts in a timely and systematic way. Additionally, current approaches to research prioritization and funding based within individual federal and state funding agencies have not led to development of a master plan for HLB research and subsequent management solutions. CRDF should work with other funding agencies to create an overarching advisory panel to develop a master plan for HLB research, communication, and management.
The study was sponsored by CRDF. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. The National Academies operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln. For more information, visit http://national-academies.org.
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Citrus Grower Workshop REMINDER (April 26)
Dr. Beth Grafton-Cardwell will present findings from her continuing survey of ACP populations across Ventura County, including data on the effects of pesticide treatments on ACP abundance. Other speakers will present updates on the statewide Citrus Pest and Disease Prevention Program, the status of Huanglongbing disease in California, grower participation in the local ACP suppression effort, and updates to the Fall 2018 ACP area-wide treatment schedule. The workshop will be from 9:30 to 11:30 a.m. on Thursday, April 26, at the Agriculture Museum, 929 Railroad Ave., Santa Paula. Attendance is free, but advance registration is required. Please register online at: https://vctaskforce-workshop.eventbrite.com.
The number of trees confirmed as being infected by HLB has reached 552 (321 in Orange County, 228 in Los Angeles County and 3 in Riverside County). All were in residential settings, not commercial groves. The HLB quarantine boundaries and the latest tally of HLB confirmations, updated weekly, is available online at https://citrusinsider.org/maps/. As confirmations increase and spread closer to commercial citrus, it is a good time to consider removing citrus trees not worth the resources required to protect them from ACP and HLB.
ACP Areawide Treatments
Thank you to those submitting timely ACP treatment pesticide use reports (PURs) and providing the grower liaisons with updates such as contact information and farm manager/applicator/PCA changes. This helps ensure ACP treatments are immediately recognized, and allows more effective communication with growers.
The Spring uncoordinated ACP treatment window begins now through July 15. Although these treatments are not coordinated, psyllid populations must be kept low to reduce the risk of HLB. Scout/monitor and treat if you see ACP, and use an ACP-effective material during spring/summer management. Click here for University of California recommendations for ACP monitoring.
The Citrus Pest and Disease Prevention Committee will meet May 9 in Ventura. Attendance is free. Here is a link to the CDFA site with agenda, venue, and webinar information: https://www.cdfa.ca.gov/citruscommittee/.
Feel free to contact your grower liaisons if you have questions, or need pest-control or tree-removal referrals.
It's that time of year to see some drama in avocado orchards. Once healthy-looking trees can suddenly turn brown in a weekend and all the surrounding trees still look fine. And it can be quite common in some years along the coast. The winter weather will have mild, cool even rainy days and then suddenly there's one of those 97 deg days and the tree goes down,
The entire tree or only one or several branches wilt suddenly when affected by Verticillium wilt. Leaves turn brown and die, but the dead leaves usually remain on the tree for several months. Brown to gray-brown streaks are visible in the xylem of the branches or roots when the bark is removed. Sometimes the streaking is visible in the branches, but often it is found at the base of the trunk.
Trees with Verticillium wilt often send out new, vigorous shoots within a few months after the initial wilting. If well cared for, affected trees often recover completely with no reoccurrence of the disease. However, not all trees survive an infection and disease symptoms sometimes reoccur after an apparent recovery.
The fungal pathogen Verticillium dahliae infects many hosts, including various berry and flower crops, cotton, eggplant, olive, pepper, stone fruit trees, strawberry, and tomato. Verticillium wilt is present throughout the state but is less common in avocado than root rot and canker diseases. Verticillium dahliae persists for years as microsclerotia in soil. Microsclerotia spread in infested organic matter and soil that is moved. The fungus infects through feeder roots, and then moves up in the water-conducting xylem system, restricting or preventing water movement to foliage from the roots.
No known methods are effective in curing infected trees. Trees often recover completely and display no further symptoms, even though they are still infected. After dieback ceases and new growth begins, prune off dead branches. Provide optimal irrigation and modest fertilization to promote new growth. If a tree dies from Verticillium, remove it. But give it a chance, there's a good chance it will recover.
In areas where V. dahliae is known to occur, plant Mexican rootstocks instead of the more Verticillium-susceptible Guatemalan rootstocks. Do not plant avocado on land where crops susceptible to Verticillium wilt have previously grown. Do not interplant avocado with other hosts of Verticillium, which are listed in publications such as Plants Resistant or Susceptible to Verticillium Wilt (PDF). Even if they have recovered, do not use trees infected with Verticillium wilt as a source of budwood or seed.
Home is where the habitat is: This Earth Day, consider installing insectary plants
—Stephanie Parreira, UC Statewide IPM Program
Help the environment this Earth Day, which falls on Sunday April 22 this year, by installing insectary plants! These plants attract natural enemies such as lady beetles, lacewings, and parasitic wasps. Natural enemies provide biological pest control and can reduce the need for insecticides. Visit the new UC IPM Insectary Plants webpage to learn how to use these plants to your advantage.
The buzz about insectary plants
Biological control, or the use of natural enemies to reduce pests, is an important component of integrated pest management. Fields and orchards may miss out on this control if they do not offer sufficient habitat for natural enemies to thrive. Insectary plants (or insectaries) can change that—they feed and shelter these important insects and make the environment more favorable to them. For instance, sweet alyssum planted near lettuce fields encourages syrphid flies to lay their eggs on crops. More syrphid eggs means more syrphid larvae eating aphids, and perhaps a reduced need for insecticides. Similarly, planting cover crops like buckwheat within vineyards can attract predatory insects, spiders, and parasitic wasps, ultimately keeping leafhoppers and thrips under control.
Flowering insectaries also provide food for bees and other pollinators. There are both greater numbers and more kinds of native bees in fields with an insectary consisting of a row of native shrubs planted along the field edge (called a hedgerow). Native bees also stay in fields with these shrubs longer than they do in fields without them. Therefore, not only do insectaries attract natural enemies, but they can also boost crop pollination and help keep bees healthy.
Insectary plants may attract more pests to your crops, but the benefit is greater than the risk
The possibility of creating more pest problems has been a concern when it comes to installing insectaries. Current research shows that mature hedgerows, in particular, bring more benefits than risks. Hedgerows attract far more natural enemies than insect pests. And despite the fact that birds, rabbits, and mice find refuge in hedgerows, the presence of hedgerows neither increases animal pest problems in the field, nor crop contamination by animal-vectored pathogens. Hedgerow insectaries both benefit wildlife and help to control pests.
How can I install insectary plants?
Visit the Insectary Plants webpage to learn how to establish and manage insectary plants, and determine which types of insectaries may suit your needs and situation. If you need financial assistance to establish insectaries on your farm, consider applying for Conservation Action Plan funds from the Environmental Quality Incentives Program (EQIP) offered by the Natural Resources Conservation Service.
- Flower flies (Syrphidae) and other biological control agents for aphids in vegetable crops. (PDF)
- Good news for hedgerows: no effects on food safety in the field.
- Hedgerow benefits align with food production and sustainability goals.
- Habitat restoration promotes pollinator persistence and colonization in intensively managed agriculture. (PDF)
- Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops.
Use of ProgGibb LV Plus® Plant Growth Regulator Increases Total Yield/ Fruit Size of Hass Avocados
As of March 27, 2018, foliar application of GA3 (ProGibb LV Plus®, Valent BioSciences, Corp.) to ‘Hass' avocado trees in commercial orchards has been approved. Dr. Carol J. Lovatt, emerita professor of plant physiology at the University of California – Riverside, recently completed research concerning the effectiveness of ProGibb LV Plus® on avocado fruit size and yield. A summary of her research — including best practices — follows.
Application Best Practices
ProGibb LV Plus® should be applied as a foliar spray when 50 percent of the trees in a block are at the cauliflower stage of inflorescence. If a grower cannot make an application at this time, it is best to apply the spray later, rather than earlier in order to ensure effectiveness.
The spray should be applied like a pesticide spray — full canopy coverage with a focus on the inflorescences. Those applying the spray should avoid spraying to run-off.
The ideal dilution for ground application is 12.5 fluid ounces of ProGibb LV Plus® (25 grams active ingredient [gai]) per 100 gallons of water/acre. For aerial application, use 12.5 fluid ounces (25 gai) in 75 gallons of water/acre. According to the research, the ideal application rate is 25g GA3 per acre; higher and lower doses were less effective. The pH of the water used should be adjusted such that the final pH of the spray solution is between pH 5.5 – 6.0.
Dr. Lovatt utilized organosilicone surfactant Silwett L-77® or Widespread Max® at a concentration of 0.05 percent as a wetting agent. Similar pure organosilicone type surfactants would be acceptable as wetting agents. It is important to note that until additional research can be conducted, other materials should not be included in the ProGibb LV Plus® spray solution.
Effect of ProGibb LV Plus® (GA3)
Dr. Lovatt's research team tested the effect of ProGibb LV Plus® on fruit size and yield for both ground and aerial applications. Overall, the research team noted that GA3 had no negative effects on ‘Hass' avocado fruit quality.
Ground applications were tested in March at groves located in Corona, Irvine and Somis, California. The tests were run on Duke 7 clonal rootstock trees at the cauliflower stage of inflorescence development. Each of the groves reported net increases in total yield and large/commercially valuable size fruit. The results were as follows:
Table 1. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size (pounds/tree) of ‘Hass' avocado trees in Corona, CA.
|Treatment||Total Fruit||Net Increase (%)||Large fruit (213-354 g/fruit)||Net increase (%)|
|GA3||74.7 az||84||34.3 a||128|
|Control||40.6 b||15.0 b|
z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Salazar-García and Lovatt, 2000).
Table 2. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size as pounds and number of fruit per tree in an alternate bearing ‘Hass' avocado orchard in Irvine, CA.
|Year 1 Yield|
|Treatment||Total Fruit||Net Increase (%)||Valuable Size Fruit (178-325 g/fruit)||Net increase (%)|
|GA3||92.2 az||70||67.9 a||65|
|Control||54.2 b||41.2 b|
|GA3||215 a||76||141 a||70|
|Control||122 b||83 b|
z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Lovatt and Salazar-García, 2007; Zheng et al., 2011)
Table 3. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development at on yield and fruit size of ‘Hass' avocado trees in Somis, CA. Percent net increase reflects the benefit of GA3 at 25 g ai/acre relative to the untreated control trees.
|Treatment||Total Fruit||Net Increase (%)||Valuable size fruit (178-325 g/fruit)||Net increase (%)||Large fruit (213-354 g/fruit)||Net increase (%)|
|GA3||408.1 az||10||379.4 a||13||294.1 a||16|
|Control||372.6 b||335.3 b||253.3 b|
z Values in a vertical column followed by different letters are significantly different by Fisher's Protected LSD test at the P-values indicated.
Overall, ground application of GA3 resulted in a net increase of 3,905 lb/acre, with a net increase of 4,851 lb/acre of commercially valuable size fruit (packing carton sizes 60+48+40; 178-325 g/fruit) and a net increase in large fruit (packing carton sizes 48+40+36; 213-354 g/fruit) of 4,488 lb/acre.
Aerial applications were tested on groves located in Pauma Valley and Carpinteria, California. Together, the aerial applications demonstrated that GA3 increased fruit set (fruit retention) by 55 percent into the last week of August and fruit size by 6 percent through mid-August.
Ultimately, Dr. Lovatt's research indicates that use of GA3 could result in substantial increases in net dollar return per acre to the grower due to increase in yield and commercially valuable size fruit. In addition, growers whose avocado groves are not suited to ground applications (groves located on slopes or in high-density formations) can benefit from the efficacy of utilizing aerial applications. In summary, ProGibb LV Plus® is “vital to the California avocado industry to increase grower income per acre to help sustain the California avocado industry.”
N.B. Remember, only well managed trees are going to respond. This will not turn around a poor producing orchard. only potentially increase production on an already good producing orchard. Ben