- Author: Ben Faber
Nick Sakovich, Emeritus Farm Advisor
Dry Root Rot has menaced growers in Ventura County for many years. In the ‘50's and ‘60's it seemed most prevalent on older orange trees. A few years after the wet winter of 1968-69, dry root rot became an increasing problem among citrus trees of all ages. At that time, most of the damaged trees were on sweet rootstock (susceptible to Phytophthora), and growing in fine-textured soils or soils with poor drainage. A few years after another wet winter/spring (of 1983), dry root rot again reared its ugly head, but this time predominately on young lemons.
The disease is caused by the fungus, Fusarium solani. This fungus is most likely present in all citrus soils in California. It is a weak pathogen in that by itself it will not attack a healthy tree. However, experiments conducted in the early 1980's by Dr. Gary Bender, showed that when seedlings were girdled, root invasion occurred. In the field, the fungus can infect trees once gophers have girdled the roots or crown. A Phytophthora infection will also predispose trees to Fusarium, as will asphyxiation. Therefore, the mere presence of the fungus in the orchard soil will not lead to the disease.
Description
Fusarium is a soil borne fungus that invades the root system. Once infected, the entire root will turn reddish-purple to grayish-black. This is in contrast to a Phytophthora infection which, in many cases, will attack only the feeder roots, but when larger roots are infected, only the inner bark is decayed and it does not discolor the wood. In addition, when observing the cross section of a dry root rot infected trunk, a grayishbrown discoloration in the wood tissue can be observed.
Dry root rot is a root disease, but symptoms of the root decline are seen above ground. They are similar to any of the root and crown disorders such as Phytophthora root rot, oak root rot fungus (Armillaria) and gophers. The trees lack vigor, leaves begin to turn yellow and eventually drop (especially in hot weather) causing twig dieback. Finally, the foliage will become so sparse that one will be able to see through the canopy of the tree. A period of two to three years may pass from the time of invasion until noticeable wilt. Many times, the tree will collapse in the summer, after a period of prolonged heat. In the case of dry root rot, the collapse is so rapid that the tree dies with all the leaves still on the tree. When looking for symptoms of dry root rot, keep an eye out for symptoms of other maladies as well — Phytophthora, oak root rot fungus and gophers being the most prevalent.
As mentioned previously, in order for Fusarium to infect a tree, there must be a predisposing factor such as girdling from gopher feeding. However, since many trees collapse from dry root rot without any apparent predisposing factor, there are obviously other factors which we have yet to identify. Therefore, in 1998, a grower survey was developed, along with intensive soil and leaf sampling, to attempt to identify as many new predisposing factors as possible. They might be elements in the soil, either deficiencies or excesses, or specific cultural practices such as irrigation patterns or fertilizer practices. Twenty orchards were identified from which 20 soil and 20 leaf samples were taken in diseased areas and another 20 soil and 20 leaf samples were taken from adjacent healthy areas. The owners or managers of the properties were given a questionnaire to complete regarding a variety of cultural operations. The objective was to identify those factors that would correlate well to trees becoming infected with dry root rot.
Survey Results
Soil analysis - The following laboratory procedures were conducted to see if there was any correlation between the disease and either deficiencies or toxicities of these elements or
conditions: sodium, boron, salt level, pH and soil type (sand, loam, clay). For these elements or conditions, no correlation was found. It would appear that for our sampling sites, these conditions, whether favorable or not (toxic or deficient), did not play a major role in predisposing the tree to dry root rot.
Leaf analysis - The following elements were analyzed for their concentration within the leaf: nitrogen, potassium, phosphate, manganese, magnesium and zinc. Of these, three correlations were found. Zinc and manganese levels were substantially higher in diseased trees. The third correlation showed a potassium deficiency in diseased trees. However, we do not believe that dry root rot is caused by elevated levels of zinc or manganese, or by potassium deficiency, but rather are a result of the disease. Unfortunately, it seems that we have still not identified any elements in leaf analysis that truly correlates and points to a predisposing factor for disease development.
Grower survey - The grower survey included questions on planting site (location, wind, previous crop, fumigation etc.), trees (source, type, rootstock, etc.), and cultural practices (irrigation, fertilization, gophers, history of Phytophthora, water quality, etc). Through statistical analysis it was found that the healthy and diseased sites were significantly different with reference to three conditions or situations: 1.) The presence of Phytophthora in an orchard will increase the chance of those trees succumbing to dry root rot. 2.) Orchards that have been fumigated have a less likely chance of succumbing to dry root rot. 3.) Balled vs. Container Plants -- growers were asked if their trees were balled or container
grown nursery plants. Healthy sites were significantly more likely to have been planted with balled trees (73% vs 33%). The results of this analysis were not strong, but rather they
suggest that there is a relationship between the disease and the type of tree planted - balled or container grown - and suggesting in favor of a balled tree for a healthy orchard.
Control Measures – What Works and What Does Not
Early experiments conducted by Menge, Ohr and Sakovich showed that the following circumstances or operations do not influence the incidence of this disease: fungicidal treatments, wounding the tap root at time of planting, sandy versus clay textured soils, spring versus fall planting and soil mounding.
- In choosing your nursery tree, the choice of rootstock is not important in that, as far as we know, all rootstocks are susceptible to this disease. However, since Phytophthora is a major component in dry root rot development, choosing a rootstock like sweet orange would certainly put those trees in a high risk category. We recommend that growers use Phytophthora resistant rootstocks like C35 or Citrumelo.
- According to the survey, it would be advantageous to fumigate before planting. Methyl bromide, although expensive, is the best fumigant as it is a complete biocide. If one chooses not to fumigate, the alternative would be a number of fungicide/nematicide applications to the newly planted trees. Generally speaking, this may work well with trees planted on a rootstock like Citrumelo or C35.
Phytophthora. Publications written in the 1970's, and again noted by our survey, showed that Phytophthora is a major culprit in the dry root rot complex. To control dry root rot, it is essential that the Phytophthora, when present, be controlled. This can be accomplished by fungicidal treatments, and by the proper application and timing of irrigation water. Overwatering creates a favorable environment for the multiplication of the Phytophthora fungus.
Gophers. It is well known that gopher damage provides entry points for Fusarium. Controlling gophers is an important factor in reducing the potential of infection by Fusarium.
Control
We presently have no direct control for dry root rot. To control the disease, we must control the predisposing factors such as gophers, Phytophthora, poor drainage and over-watering. If the predisposing factor(s) cannot be identified for a given diseased orchard, it will indeed be difficult to control the disease. Two things are certain though: 1.) There are no chemicals to date which will control this disease; and 2.) Presently, there are no rootstocks resistant to the disease.
Hear the latest on DRR with Akif Eskalen – a Webinar, July 24
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30658
- Author: Ben Faber
Newly Improved Thrips Key
The online Lucid Key, Thrips of California (https://keys.lucidcentral.org/keys/v3/thrips_of_california/Thrips_of_California.html), that identifies native and pest thrips resident in California, along with potentially invasive species not yet present in California, has been updated.
The revised version, Thysanoptera Californica (https://keys.lucidcentral.org/keys/v3/thrips_of_california_2019/), has been produced to overcome technical problems arising from Java software and to incorporate new information and images, together with some additional potentially invasive thrips species. Information pages are provided to 300 thrips species in 108 genera, with the identification system discriminating 249 species. Of these species, 40 are as yet unrecorded in California but are potential invaders, whether interstate or from overseas.
Remember, if you have one or many of these insects, there is always an "s" at the end of their name. One thrips is a thrips, three thrips are thrips.
- Author: Ben Faber
UC Riverside is testing whether a sesame seed-sized wasp can control a pest that could seriously damage California crops including wine, walnuts, and avocados.
The pest, a sap-sucking spotted lantern fly, is originally from China and was first detected five years ago in Pennsylvania. Since then, large populations have spread rapidly to grape vines, apple trees, and other plants in New York, Delaware, New Jersey, Maryland, and Virginia.
Experts believe the lantern fly is likely to make its way to California soon.
Mark Hoddle, director of the Center for Invasive Species Research at UC Riverside, explains why the lantern fly is so harmful.
“It secretes copious amounts of “honeydew,” a waste product that encourages black, sooty mold and damages a plant's ability to grow,” he said. The honeydew also attracts undesirable insects such as ants and hornets.
The impacts could extend well beyond California. According to industry reports, the state is the world's fourth-largest wine producer, selling an estimated $35 billion domestically and exporting $1.5 billion annually.
Around 44% of nonnative insects arriving in California were first established elsewhere in the U.S. Given the speed with which the spotted lantern fly has spread, Hoddle realized the state needed a proactive approach to this predictable problem.
“Normally, when a bug shows up, we try to contain and eradicate it,” Hoddle said. “But by the time the population is found, it tends to already be widespread and hard to handle.”
The state Department of Food and Agriculture recently granted Hoddle $544,000 to test whether a tiny parasitic wasp, also originally from China, could be the solution to the looming problem. Hoddle explained that the wasp has a needle-like appendage it uses to lay its own eggs inside the lantern fly's eggs. While developing, the wasp larvae eat and kill their hosts, and then emerge after chewing escape holes through the lantern fly eggs.
These wasps pose no threat to plants or people, but before they can be used to control the lantern fly, Hoddle must prove they won't cause unnecessary harm to other native insects. “We can't just release a Chinese parasite into the wild in California,” Hoddle said. “Chances are low it will harm the wrong targets, but we have to be sure.”
Safety testing will be conducted in a highly secure quarantine facility at UC Riverside. Native lantern flies, the subjects of safety testing, will be collected from natural areas in California and southern Arizona this summer.
Though the wasp is now being evaluated as a biological control on the East Coast, populations of lantern fly there have already grown large enough to cause significant concern for the grape industry, Hoddle said.
A spotted lantern fly's wingspan is about 1.5 inches, and at most they can fly a few hundred feet at a time if they're assisted by the wind. The lantern fly has spread so fast in part because the females lay eggs on nonbiological materials, such as train cars, motor homes, wooden pallets, and trucks that inadvertently move them into new territories.
“Anyone on the East Coast driving to California should be especially vigilant about checking their vehicle for egg masses before they make the journey,” Hoddle warned. “Failing to notice them could have serious consequences.”
Hoddle's testing will take roughly three years, and he estimates that this may be around the time when the wasps will be needed in California. “We hope to be ready to release these wasps immediately when the spotted lantern fly shows up, giving us a really strong head start on the invasion,” he said.
reposted from: https://news.ucr.edu/articles/2019/06/17/looming-insect-invasion-threatens-california-wine-and-avocados
Great video of Lantern Fly life stages from Penn State
https://www.youtube.com/watch?v=Wumtju2_0JM
Photo: Lantern fly egg mass
/article>- Author: Ben Faber
The California Master Beekeeper Program (CAMBP), directed by Extension apiculturist Elina Lastro Niño of the University of California-Davis Department of Entomology and Nematology, is hosting two short courses in early August: one on “Planning Ahead for Your First Hives” and the other, “Working Your Colonies.”
Each will take place from 9 a.m. to 4 p.m. in the Harry H. Laidlaw Jr. Honey Bee Research Facility on Bee Biology Road, west of the central campus. The deadline to register is Thursday, Aug. 1.
“These courses are foundational to beekeeping husband excellence,” said Wendy Mather, program manager. “They are great for folks who are thinking about getting bees next season, as well as those who currently have bees and want to ensure they're doing whatever they can to ensure the success of their hives.”
The classes are not required to become a California Master Beekeeper, but are highly recommended, as “they will help folks prepare to become a science-based beekeeping ambassador,” Mather said. Instructors are Elina Niño and CAMPB educational supervisor Bernardo Niño, a staff research assistant in the Niño lab.
Planning Ahead for Your First Hives
“Planning Ahead for Your First Hives” will take place Saturday, Aug. 3 and will include both lectures and hands-on activities. Participants will learn what's necessary to get the colony started and keep it healthy and thriving. They will learn about bee biology, beekeeping equipment, how to install honey bee packages, how to monitor their colonies (that includes inspecting and monitoring for varroa mites) and other challenges with maintaining a healthy colony.
The course is limited to 25 participants. The $105 registration fee covers the cost of course materials (including a hive tool), lunch and refreshments. Participants can bring their bee suit or veil if they have one, or protective gear can be provided. For more information or to register, see https://registration.ucdavis.edu/Item/Details/572.
Working Your Colonies
“Working Your Colonies” will take place Sunday, Aug. 4 and will include both lectures and hands-on activities. Participants will learn what is necessary to maintain a healthy colony. Lectures will cover advanced honey bee biology, honey bee integrated pest management, and products of the hive. Participants also will learn about queen wrangling, honey extraction, splitting/combined colonies, and monitoring for varroa mites.
The course is limited to 25 participants per session. The $175 registration fee covers the cost of course materials, lunch and refreshments. For more information or to register, see https://registration.ucdavis.edu/Item/Details/559.
Participants can bring their bee suit or veil if they have one, or protective gear can be provided. All participants are to wear closed-toed and closed-heel shoes, long pants and a long-sleeved shirt.
The California Master Beekeeping Program uses science-based information to educate stewards and ambassadors for honey bees and beekeeping. For more information, contact Mather at wmather@ucdavis.edu.
- Author: Ben Faber
According to the latest USDA Foreign Agricultural Service GAIN Report (Global Agricultural Information Network), the European Union is still a major citrus producing area. EU citrus production is concentrated in the Mediterranean region. Spain and Italy represent the leading EU citrus producers, followed by Greece, Portugal, and Cyprus. For MY (October/September) 2018/19, Post expects overall citrus production to grow mainly in Spain due to favorable weather conditions. The quality of the fruit is forecast to be excellent and EU domestic consumption of citrus may stay flat in 2018/19.
EU lemon production is forecast to grow 10 percent and is stable compared with previous estimates. The overall growth is due to the strong production rise expected in Spain, the largest lemon EU producer. According to the latest data from the Spanish Ministry of Agriculture, Fisheries, and Food (MAPA), Spain's 2018/19 lemon production is forecast at 1.1 million MT, an increase of 19 percent compared to the previous year. Favorable weather conditions resulted in good flowering and fruit setting. In addition, in recent years Spain has increased its total planted area for lemons. Fruit quality is forecast to be excellent. ‘Fino' lemon is expected to increase by 14 percent due to the entry of new plantations over the last years. ‘Verna' lemon is expected to rebound; increasing by 90 percent as production of ‘Verna' lemon in the previous season was shorter than normal levels. Spain will continue to consolidate its leading commercial position in Europe with quality and phytosanitary guarantees. Following Argentina, Spain is the second largest lemon producer in the world but the first global exporter of lemons for fresh consumption. Spanish lemon production is concentrated in the regions of Murcia and Valencia, and the Provinces of Malaga and Almeria in Andalusia. ‘Fino' and ‘Verna' are the leading lemon varieties grown in Spain, accounting for 70 and 30 percent of the total production, respectively. The ‘Fino' variety is predominantly used for processing.
So far, Asian Citrus Psyllid and HLB are not a problem in the lemon producing areas of Spain and Italy. Read more about the citrus industry in the European Union – oranges, grapefruit, mandarins, fresh, processed, policy, export issues, MRLs and tariffs. Fascinating stuff and the potential impacts it has on California growers and production.
And what about what's going on in the Moroccan citrus world, right next door to Spain?