Posts Tagged: fungus
Almond crop yields threatened by disease new to California
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 detected P. amygdalinum. Pest identification was confirmed by the California Department of Food and Agriculture and U.S. Department of Agriculture.
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, an associate professor in the UC Davis Department of Plant Pathology. He recently 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>Magical Mushrooms
With the cooler, damp weather due to the recent atmospheric storm and fog, you may have observed...
Fungus in the Field
Field Finds: Fungus Among Us
Siomara Zendejas, Ventura County UCCE SRA
I stumbled upon this delightful find while doing some field work in an avocado orchard. The light coming in through the canopy made it very easy to spot the branch among the leaf litter. It seemed to be a sort of shelf fungus that either settled in after the branch fell, or was itself the cause for the branch falling. I thought the decorated portion of branch would be harder to break off, but it was surprisingly easy because the wood inside was all soft and spongy, probably due to white rot. Even with all the rain we had this spring, it was still a surprise to find this treasure! Especially considering it was already dry by the time I found it.
Our own Dr. Jim Downer mentioned it could possibly be a member of the Trametes genus, which has a widespread distribution and contains roughly 50 species.The mushroom could potentially be Trametes hirsuta (hairy bracket), or Trametes versicolor (the famous turkey tail fungus). Both fungi can cause white rot and appear green due to tiny algae growing on their top surface. There are also two other look-alike fungi: Stereum ostrea (the false turkey-tail) and Trametes betulina (multicolor gill polypore). However, Stereum ostrea has no pores underneath and Trametes betulina has gills; my mushroom has many pores in its underside!
Fig 1. The top of the mushroom cap with green algae coloring it
Fig 2. Pores on bottom side of fungus
Fig 3. Underside of fungus distributed along dead branch
White rot, for those fortunate enough to have never found it in their trees, is a fungal disease that eats away at both the lignin and the cellulose of a tree. Both of these are very important compounds that give trees their strength and structure. The rot leaves the inner wood feeling spongy and soft, and appears pale or white. The danger of this rot, besides the potential death of the tree, is that infected branches or whole trees can fall despite looking healthy on the outside. The UCANR website has wonderful resources on how to identify and manage different kinds of rots that I'll include here: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74109.html A common result of poor pruning practice, or due to branch damage, is a residual stub that can easily be infected by these fungi. Prompt attention to this damaged wood can prevent infection along with good proper pruning, as indicated in the diagram below.
Remove a branch by making the pruning cut just outside the branch bark ridge and branch collar, as indicated by number 3. When removing a limb larger than about 2 inches in diameter, make three cuts in the order indicated. Make the first cut from below, about one-fourth of the way through the limb and 1 or 2 feet from the trunk. Make the second cut about 2 inches beyond the first cut, cutting from above until the limb drops. Make the final cut at number 3.
It may be worth it to keep a look out for any mushroom laden branches or suspicious stubs, because the can signal a deeper problem underneath the surface. We had a wet spring this year and many a mushroom flourished during that time! For now, this mushroom will be sitting on my desk as both a lovely decoration and a reminder to keep my eyes peeled for the next field find.
Lawn Toadstools and Fungi
If mushrooms or toadstools have suddenly appeared up in your yard, you are probably wondering why,...
Fungi that causes pine ghost canker detected in Southern California trees
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.
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