Even though it's been a mild winter; other than fire, rain and some cool nights, we did have a few days of hot weather, which is just what sets off citrus dry root rot. It pops up after the first hot weather of the spring, and there it was driving down the road. There's nothing that can be done with this tree. Tree removal and replacement is the answer. Prevention is the solution. We know that Fusarium fungus is usually associated with the collapse, but wounding is the key. Mechanical injury from weed whips, discs, gophers, voles, rabbits. Wounding from salt damage might do it too.
Dry root rot, a disease caused by the soil fungus Fusarium solani, has a long history of hindering production of citrus in California. Fusarium solani is a weak pathogen that infects only when there is some kind of stress in citrus tree. However, presence in almost all citrus orchards everywhere in the world including California, enhance its quick exploitation of such stresses. Some of the factors that are possible stress include invasion by other pathogens, such as Phytophthora and Citrus Tristeza Virus (CTV). Other stresses are wounding by gophers/rodents or insects, girdling, asphyxiation especially drowning the tree with too much water, soil nutrient content and fertilization, irrigation, and other cultural practices in the orchard. The pathogen is an opportunist on citrus. With the stress, Fusarium solani begins infection by colonizing the cortical tissue of feeder roots, advances into the lower tap root and/or scaffold root, and move up through the bud union into the center of the trunk. Studies over the years have shown that many rootstocks are susceptible and old trees as well as young twigs are not spared of the disease.
Photo: collapsed tree near and older one on the right, but also near a younger one that probably was a replacement for one that had collapsed several years prior
This note from Cressida Silvers, either go to Temecula or maybe do a more local version of the training:
The upcoming CAPCA meeting (see below for details) in Temecula is a 2-day event (12 CEUs), including a workshop and field visit focused on detecting live ACP in citrus trees, and using monitoring strategies to evaluate ACP presence in orchards.
If there is enough interest locally (SLO, Santa Barbara, Ventura), we could put on a similar workshop/field training for ACP monitoring for anyone interested. Let me know if that would be helpful, and how far you would be willing to travel for that.
ACP/HLB Grower Liaison
Ventura, Santa Barbara and San Luis Obispo Counties
CAPCA Spring Summit Focuses on
Asian Citrus Psyllid:
April 24 – 25
The California Association of Pest Control Advisers (CAPCA) will host its 2018 Spring Summit on April 24 – 25 in Temecula. Summit attendees will tour UC Riverside's citrus grove and experiment station, and will learn about Asian citrus psyllid mitigation standards for bulk citrus movement, scouting techniques, identification and management strategies.
With more than 500 HLB-positive trees confirmed in Southern California, it is critical that pest control advisers involved with citrus stay up to date with ACP detection and management strategies. The Spring Summit will include the following topics and speakers:
- Strategies for management of Asian citrus psyllid in California – Dr. Beth Grafton-Cardwell, University of California Division of Agriculture and Natural Resources
- Mitigation standards for the new Asian citrus psyllid regional quarantine – Victoria Hornbaker, California Department of Food and Agriculture
- Scouting techniques and identification of Asian citrus psyllid in the field – Alan Washburn, Citrus Pest & Disease Prevention Program
- Update on Asian citrus psyllid and HLB management – Bob Atkins, Citrus Pest & Disease Prevention Program
The event is accredited for 12 hours (2.50 Laws and 9.50 Other) of continuing education units by the Department of Pesticide Regulation, as well as 11.50 California Crop Advisers hours. To view the full program schedule, click here.
To register for the CAPCA Spring Summit, click here.
This is the summary of a recent article by Allen Morris, a retired University of Florida Extension Economist
Even when a cure for HLB is implemented, unless something is done to stop the decline in orange juice consumption, the citrus-growing part of the industry will become too small to support the infrastructure of input suppliers, harvesters, grove caretakers, etc. necessary for it to function competitively. For example, assume that the lower prices from lower cost production get into the orange juice market evenly over the 2023–24 to 2031–32 nine-year period, reflecting the time required for fruit produced from new plantings of HLB-resistant trees to increasingly impact prices. Ten years after the first plantings, by 2031–32, only 58 million boxes of Florida oranges and no orange juice imports will be needed. In spite of an 11 percent increase in the orange juice market stimulated by the lower prices, the underlying rate of decline in orange juice consumption eliminated its benefit.
The three major orange juice brands will probably continue mainly as juice storing, blending and packaging operations, using orange juice imported primarily from Brazil and Mexico, but also using juice from the small declining volumes of Florida fruit still available to process. However, because of the high costs of processing small volumes of fruit in the large processing plants owned by the brands and the companies processing oranges for the Coca-Cola Company's Minute Maid and Simply brands, it is likely that one of the bulk processors may have an opportunity to process fruit for all three of the brands. This would reduce costs by processing all of the industry's remaining volumes of oranges in one plant, and thus allow that processor to continue to operate. The bulk processors, other than the ones storing and blending juice for the Coca-Cola Company's Minute Maid and Simply brands and the one which processes the remaining volumes of oranges, will soon have no economic reason to exist in Florida. Private labels' orange juice needs will be supplied by imports, primarily from Brazil and Mexico.
Because of the declining U.S. orange juice market, the brands will probably increase their focus on the European orange juice market, which, as was pointed out, is being positioned to grow. There will also probably be a proliferation of exotic juice blends like blueberry mango, pomegranate limeade, strawberry banana, watermelon, berry greens, etc. being introduced by the brands as they begin to position themselves away from citrus.
This conclusion doesn't have to happen. But it is likely to happen if something isn't done to restore the U.S. orange juice market to growth. One way to fund that is to partner with Citrus BR the way AIJN and the European orange buyers/packagers are doing. The U.S. orange juice market is second only to Europe in importance to Brazil as an export market for its orange juice. If approached, the Brazilians would probably be interested in working with the Florida Citrus Commission the way they are working with AIJN to restore growth to the U.S. orange juice market.
For the complete article, go to:
- Author: Roger Baldwin, Ryan Meinerz, Gary Witmer and Scott Werner
Baldwin and Meinerz are UC Davis and Witmer and Werner are USDA/APHIA/Wildlife Services-National Wildlife Research Center
Voles are short, stocky rodents that often cause extensive girdling damage to a variety of tree and vine crops throughout California. Vole management is often quite challenging given how numerous they can be in a given area. In more recent years, effective management has often relied on some combination of vegetation removal, exclusion using trunk protectors, and rodenticide application. Vegetation removal is a great tool for reducing numbers in a field, but doesn't always eliminate all problems in an area. Plus, vole population size tends to ebb and flow from low to high densities; when densities are high, vegetation removal is often insufficient to reduce girdling damage.
Exclusion through the use of trunk protectors can be a good way to reduce girdling damage as well. However, trunk protectors should be buried at least 6 inches below ground to keep voles from tunneling underneath the protectors. This substantially increases the amount of labor required to protect trees and vines. Ultimately, this approach is only cost effective if high levels of damage are anticipated.
Rodenticide applications are also frequently used to knock down vole populations. However, rodenticide applications are generally not allowable within an orchard or vineyard during the growing season, thereby eliminating the use of one of the most effective vole management tools when it is most needed. Clearly there is room for a new tool to be added to the proverbial IPM toolbox when it comes to managing voles in orchard and vine crops.
Chemical repellents are one such tool that could be considered. Historically, repellents have not proven overly effective for field application against voles. However, recent laboratory testing of anthraquinone indicated that even low concentrations of this chemical were effective at reducing grain consumption by voles. Furthermore, anthraquinone has proven effective as a bird repellent. Anthraquinone is a post-ingestive product that causes animals that consume the product to become ill, thereby making it less likely that the animal will consume the product again during a subsequent feeding event. This kind of repellent is ideally suited for trunk application given that the repellent can easily be applied to the portion likely to be consumed by the vole. If effective, minimal girdling damage should be observed. A repellent application also has the added advantage in that it can easily be paired with vegetation management to hopefully further reduce girdling damage when compared to using either one of these approaches alone. Therefore, we set up a study to test the potential impact that a combination of vegetation management and anthraquinone applications would have on girdling damage by voles to young citrus trees. We also tested the longevity of anthraquinone to determine if long-term repellency following field application was likely. We tested this impact during both spring (characterized by a cool-wet weather pattern) and summer (characterized by a hot-dry weather pattern) seasons to determine if weather impacted potential girdling damage.
We found that anthraquinone was in fact highly repellent following trunk application, with a >90% reduction in girdling damage observed following application regardless of the season when it was applied. Anthraquinone exhibited substantial longevity, with no increase in girdling damage observed for the entire summer (5 weeks) and spring (6 weeks) sampling periods. This clearly indicates substantial repellency for anthraquinone applications, with repellency to last for at least two months, and likely for much longer given that we observed no upward trend at all in girdling damage at the end of our study period.
When combined with anthraquinone treatments, the removal of vegetation completely eliminated all girdling damage during summer. However, we did not observe this same collective impact during spring. That said, the inclusion of vegetation management with anthraquinone applications is likely warranted given our understanding of the need for multiple management strategies to maintain the long-term effectiveness of rodent management programs.
These results clearly indicate effective repellency of voles following anthraquinone applications, but at this time, anthraquinone is not registered for use against any mammalian species. We are hoping to gauge the interest of growers for the registration of this repellent against voles in orchard and vine crops. This is where we need your help. We have developed a very short survey (will take less than 3 minutes to complete) to gauge this interest. Please take this very quick survey to assist in this effort:
ITHACA, N.Y. — New clues to how the bacteria associated with citrus greening infect the only insect that carries them could lead to a way to block the microbes' spread from tree to tree, according to a study in Infection and Immunity by Agricultural Research Service (ARS) and Boyce Thompson Institute (BTI) scientists.
Citrus greening, also known as “huanglongbing,” is a serious disease dramatically affecting citrus production across the world. Trees with this disease all die after only a few years. Citrus greening has been detected in every citrus-producing county in Florida, throughout the southern citrus growing states and in isolated spots in southern California. There is no effective prevention or cure.
The disease is associated with the bacterium Candidatus Liberibacter asiaticus, CLas for short, which is spread from tree to tree only by a tiny insect vector—the Asian citrus psyllid. If CLas cannot infect the psyllid, its ability to spread citrus greening is halted.
With the long-term goal of disrupting this CLas-Asian citrus psyllid interaction, research molecular biologist and BTI professor Michelle Heck, with the ARS Emerging Pests and Pathogens Research Laboratory, and BTI researcher Marina Mann focused on an important point: not all psyllids spread CLas equally well.
To be spread by the Asian citrus psyllid (ACP) effectively, the bacteria must pass through the cells lining the insect's gut and multiply. Scientists in Heck's lab had previously shown that the gut cells of adult ACP show severe stress responses when infected by CLas. The cell nuclei become fragmented, and some cells react to the point of dying, allowing the bacteria to move out of the psyllid and into the tree.
Now, the researchers have found that, unlike adult psyllids, young psyllid nymphs appear to be resistant to the effects of exposure to CLas, and their nuclei rarely reach the same level of disruption. This means CLas cannot enter psyllid gut cells to multiply.
The next step will be to identify the mechanism for this resistance in the nymphs so that it might be manipulated to also halt the spread of CLas by the adults. An important clue lies in how psyllid nymphs interact with symbiotic bacteria in their gut, especially Wolbachia pipientis.
Many insects are hosts for Wolbachia and often depend on these bacteria for important benefits—much like how human health depends on gut bacteria. In their study, Mann and Heck showed that in psyllid nymphs, Wolbachia and CLas are commonly found within the same cells.
The authors hypothesize that, in accommodating the beneficial bacteria, the nymphs also let in more CLas. This is supported by their finding that CLas levels in psyllid nymphs are strongly correlated with Wolbachia levels. Though this link remains to be tested directly, understanding its mechanism could yield an important target for disrupting CLas-psyllid interaction.
“CLas exploits the way nymph and adult psyllids differ in their guts to gain entry into its insect vector,” Heck said. “We may be able to use this new foothold in our understanding to develop ways to block transmission by insects in the citrus grove.”
If this works, “citrus growers will be in a much better situation in terms of disease control and saving the U.S. citrus industry,” said Dan Dreyer, Chairman of the California Citrus Research Board, which funds this and other research aimed at developing a management strategy for citrus greening.
“There are still many unanswered questions about CLas, how it is acquired and transmitted via the Asian citrus psyllid, and how it causes the disease,” continued Dreyer. “The more we learn about CLas and its vector, the closer we will get to moving citrus production past the threat of citrus greening.”
The Agricultural Research Service is the U.S. Department of Agriculture's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.