- Author: Michael Hsu
Detection of fungus causing red leaf blotch spurs call for grower vigilance
Symptoms of red leaf blotch (RLB), a plant disease caused by the fungus Polystigma amygdalinum, have been observed for the first time in California across the Northern San Joaquin Valley.
Molecular DNA testing by the laboratory of Florent Trouillas, University of California Cooperative Extension fruit and nut crop pathology specialist, has confirmed the detection of P. amygdalinum. Formal pest confirmation by the California Department of Food and Agriculture is pending.
The disease, named for the characteristic orange-to-dark red blotches that appear on infected leaves, is typically nonlethal for trees but has been a long-standing problem for almond-growing regions across the Mediterranean. Causing trees to lose their leaves prematurely, the fungal pathogen can significantly diminish crop yields in the current year and the next.
“It is one of the most severe diseases of almonds for Spain and the Middle East,” said Trouillas, who co-authored an explanatory article on the UCCE San Joaquin Valley Trees and Vines blog.
With symptomatic trees seen in multiple orchards across Madera, Merced, San Joaquin and Stanislaus counties, Trouillas said RLB is already “somewhat widespread.”
“From the first observations so far, it seems like it affects some of the most-planted cultivars, like Nonpareil and Monterey,” he added. “We've observed it in a diversity of cultivars already.”
UC Cooperative Extension specialist urges taking preventive measures
According to Trouillas, RLB caused by P. amygdalinum is “highly specific” to almond trees, and generally only affects their leaves. Infection typically happens at petal fall, when small leaflets are first emerging and most susceptible to disease. After the pathogen's latent period of about 35 to 40 days, the first symptoms appear – small, pale-yellow spots on both sides of the leaves.
Those blotches become yellow-orange and then reddish-brown in the advanced stages of the disease during June and July. Now, with RLB symptoms becoming more prominent, Trouillas and UC Cooperative Extension advisors across the Central Valley have seen an uptick in calls.
“PCAs [pest control advisers] have been confused because they've never seen anything like this,” said Trouillas, noting that the yellow-orange-red blotches are symptoms unique to RLB and cannot be confused with other known almond diseases.
Applying fungicides after RLB symptoms appear is ineffective, Trouillas said. The best thing growers can do at this point is to report symptomatic trees to researchers so they can track the prevalence and distribution of the disease.
Growers who see signs of this new disease in their orchard should contact their local UC Cooperative Extension farm advisor.
Preventive measures are the best way to manage RLB, Trouillas said. He urges concerned growers to think ahead to next winter/spring and plan for fungicide applications at petal fall and – if rains persist – also at two weeks and five weeks after petal fall. Fortunately, those are the same three key timings for managing other diseases, like shot hole and almond anthracnose.
“Because RLB is something that is introduced and potentially aggressive, it will be important for growers to keep that in mind next year and be on schedule for next year's spraying program,” Trouillas said.
Additional information on RLB can be found at https://www.sjvtandv.com/blog/first-detection-of-red-leaf-blotch-a-new-disease-of-almond-in-california.
/h3>/h3>- Author: Denise Godbout-Avant
What are Mushrooms?
Mushrooms, also known as toadstools, are the visible reproductive body of a fungus which produces spores. Mushrooms seem to magically appear and then quickly disappear. The fruiting body you see releases its spores to be spread by air currents, with the mushroom then drying up. When spores land in a satisfactory location they will germinate, sending out long filaments called hyphae.
The standard visible morphology of a mushroom is a stipe (stem) topped by a cap with gills on the underside, but mushrooms come in a variety of sizes, shapes, colors and uses. The common mushroom is the cultivated white button mushroom we see in stores. Other shapes include puffball, stinkhorn, morel, bolete, shelf, truffles, bird's nests, orange peel, and agarics. Colors vary from white, black, brown, yellow, and occasionally orange and reds. Sizes range from microscopic to 5 feet in diameter!
Many mushrooms also have an underground filament called mycelium (plural: mycelia). You can sometimes see mycelia when turning over a rotting log or by digging underneath a cluster of mushrooms. The mycelia will look like a stringy mat of white fibers in and around plant and tree roots.
History & Uses
The terms “mushroom” and “toadstool” go back centuries. Much of their mystery is due to their association with poisonings and accidental deaths. They were thought to be special and supernatural by many cultures including Egyptians and Romans who associated them with their rulers and gods. Chinese and Japanese cultures have utilized mushrooms for medicinal purposes for thousands of years. Hallucinogenic mushroom species have a history of use among Indigenous people of Mesoamerica for religious purposes and healing from pre-Columbian times. People today correlate hallucinogenic mushrooms with the hippie period in the 1960s. Edible mushroom species have been found in 13,000-year-old archaeological sites in Chile. Truffles have been collected as far back as 1600 BC.
Edible Mushrooms
Poisonous mushrooms can be very hard to identify in the wild, so unless you have been taught how to classify mushrooms by an expert, it is recommended you buy from a reliable grocery store. Mycologists identify mushrooms by observing their morphology, getting spore prints, microscopic study, and with mushroom keys, though applying DNA technology is becoming common.
You can also grow your own mushrooms at home – kits are available online and at some plant nurseries.
Mushrooms in Your Garden and Lawn
- Common mushrooms in gardens include inky caps, stinkhorns, puffballs, or bird's nests.
- A “fairy ring” of mushrooms is an arc of mushrooms around a circle of darker green lawn, often in shady areas. They get their name from an ancient belief that fairies danced in these circles around the mushrooms.
- Mushrooms in lawns often develop from buried scraps such as pieces of wood or dead tree roots.
- A cluster of honey-colored mushrooms may appear at the base of a tree in the fall. These don't usually appear unless the host tree is dying.
- New lawns require frequent irrigation until established, thus creating a perfect setting for mushrooms, which is why they often appear in freshly planted lawns.
Remember, the mushrooms you see are the fruiting bodies that produce spores. Thus, removing them will not kill the underground mycelia from which they are growing, unless you pick them prior to their release of spores. However, you can try to reduce the number of mushrooms you have by decreasing the amount and frequency of watering your lawn and let the grass dry in between. For more information in dealing with mushrooms in your lawn, visit the UC IPM website at http://ipm.ucanr.edu/PMG/PESTNOTES/pn74100.html
Whether you see mushrooms in the forest, in your lawn or neighborhood, I hope you can appreciate and enjoy these unique, complex, beautiful, valuable, diverse, and magical organisms!
-This article was originally published on December 6, 2021.
Denise Godbout-Avant has been a UCCE Stanislaus County Master Gardener since July 2020.
/h4>/h4>/h4>/h4>- Author: Emily C. Dooley, UC Davis
Pathogen native to U.S. but had not infected pines until recently
Fungal pathogens that cause die-back in grape, avocado, citrus, nut and other crops has found a new host and is infecting conifer trees causing pine ghost canker in urban forest areas of Southern California.
The canker can be deadly to trees.
Scientists from University of California, Davis, first spotted evidence that the pathogens had moved to pines during a routine examination of trees in Orange County. Over four years, they found that more than 30 mature pines had been infected in an area of nearly 100 acres, according to a report in the journal Plant Disease.
Akif Eskalen, a professor of Cooperative Extension in the Department of Plant Pathology at UC Davis, suspects drought and other stress conditions brought on by climate change weakened the tree species, making it more susceptible to new threats.
“We have been seeing this on pine trees for the last several years,” he said. “Our common crop pathogens are finding new hosts.”
Pine ghost canker – caused by the fungal pathogens Neofusicoccum mediterraneum and Neofusicoccum parvum – usually infects the lower part of a tree's canopy, killing branches before moving on to the trunks. This dieback in some cases can be deadly.
Points of entry
The pathogens infect a tree by entering through wounds caused by either insects such as red-haired pine bark beetles or pruning – meaning trees in managed or landscaped areas could be at risk. Another route is via tiny natural openings known as lenticels that fungi can make their way through, said Marcelo Bustamante, a Ph.D. candidate in Eskalen's lab who is first author on the paper.
Spores from the fungi can disperse and the higher the prevalence means an increased chance of transmission. Rain, irrigation water and humidity by fog can trigger the right circumstances for the spores to spread, he said.
“The detection of these pathogens in urban forests raises concerns of potential spillover events to other forest and agricultural hosts in Southern California,” Bustamante and others wrote in the report.
Dead branches can indicate a canker. Detecting the fungi is not an emergency but “people should keep an eye on their plants when they see abnormalities,” Eskalen said.
Cankers are localized areas on stems, branches and tree trunks that are usually dead, discolored and sunken. On bark, the spores can look like strings of discolored dots.
The lab has posted a brochure bout how to best manage wood canker diseases.
Tips include:
* Keep your trees healthy: Proper irrigation and maintenance will keep trees strong.
* Prune dead branches to reduce sources of infestation.
* Avoid unnecessary pruning; perform structural pruning only.
Karina Elfar, Molly Arreguin, Carissa Chiang, Samuel Wells and Karen Alarcon from the Department of Plant Pathology contributed to the paper, as did experts from Disneyland Resort Horticulture Department, State University of New York's College of Environmental Science and Forestry, UC Irvine and UC Los Angeles.
/h3>/h3>- Author: Ben Faber
Image: Allen King
A Fillmore grower recently reported honeybees collecting rust spores on willow trees!!! Her baskets are loaded with rust spores. Rust-collecting honeybees are reported by others so it's not an unusual occurrence.
From: Randy Oliver, “Fried Eggs” Identified! https://scientificbeekeeping.com/fried-eggs-identified/ Oliver shows bee-collected rust pollen from poplar trees in Spain in hive frames.
Quote: "Above is a photo of a typical comb filled with beebread consisting of rust fungus spores. Note the lousy brood pattern and the dying brood. When the colony is feeding upon this beebread, it goes downhill quickly. However, if we feed the hive several pounds of high-quality pollen sub, it will turn around immediately and grow again.
Antonio Pajuelo (pers comm) also reports a correlation between the consumption of poplar rust spores and colony mortality, but doesn't know whether it is due to spore toxicity or lack of better nutrition. It may be that the collection of rust spores is due to the lack of more attractive and nutritious floral pollen, and as such would simply be a generic indicator of poor colony nutritional status.
On the other hand, Schmidt (1987) found that caged bees fed Uromyces spores as a sole protein source actually had their lifespan reduced compared to those fed sugar syrup only—strongly suggesting that the spores were toxic. The spore-fed bees lived about 20 days less than those fed the most nutritious pollens!"
John Menge, a retired UC Riverside plant pathologist and mycologist has this reasoning:
The bee rust problem is very interesting.
I would have liked to work on that problem when I was at Riverside.
Two thoughts:
First I thought poplar rust was a Melampsora not Uromyces.
All the old literature gave the Uromyces name to all Uredospore stages.
Second, as you know, rusts have five different spore stages.
It would help to know what spore stages are in the hives.
One spore stage is pycniospores.
It is the spermatia stage and is sweet as honey.
It attracts all types of insects including bees.
Its job is to promote fertilization of the fungus so the bees are pollinating the fungus.
In the process of gathering the spermatia sugar, the bees are inadvertently gathering urediniospores.
Or perhaps there is lingering pycnia sugar on the urediniospores.
Or perhaps there are other attractants on the spore so the bees will disperse them.
At any rate I can tell the researchers are entomologists because they are worried about the bee colonies.
Mycologists worry about the cottonwood trees and the success of the rust fungi.
Apparently the fungi have outsmarted the insects again.
- Author: Elaine Lander
Fungal spores spend the winter on twigs and buds before germinating in the spring. Preventative applications of a fungicide can be made after leaves have fallen and before bud swell, typically between late November and February depending on your location in California. Spraying a fungicide during the growing season when you observe symptoms of peach leaf curl is not effective.
Always be sure to follow pesticide label directions for the correct coverage, mixing rate, and disposal. Prepare for the treatment by having the right pesticide application equipment (measuring cups just for pesticides, spray gear, etc.) and protect yourself by wearing the proper personal protection equipment.
For more information, see our Pest Notes: Peach Leaf Curl and Pesticides: Safe and Effective Use in the Home and Landscape.
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