Posts Tagged: disease
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citrus
Wet Weather Tree Diseases
After years of drought, we welcome rain in California. But we also recognize that rain can help...
Praise the Rain, Pass the Fungicide
Although, it's probably too late for the fungicide to correct Citrus Brown Rot
and Septoria on coastal lemons.
In normal rainfall years, a skirt spray of copper is done to prevent rain splash bringing spores of various Phytophthora species in contact with fruit. The spray is done the fall especially if high rainfall is expected that year, and can be reapplied in January/February if indeed rain has arrived. The spray is usually only up about 4 feet from the ground, rarely needed above that. But this year, there has been lots of wind and brown rot has appeared throughout tree. There has been lots of wind to spread the spores and create disease in fruit quite above ground level. Fruit on these trees is going to need to be selectively picked to avoid the infected fruit, adding to harvest costs.
https://ipm.ucanr.edu/agriculture/citrus/brown-rot/
Septoria is less common than brown rot along the coast where a skirt spray is or used to be normal practice. This was before the drought and low lemon prices made the practice less common. In the case of septoria, a whole tree copper spray is recommended in the fall. The disease, although not unseen, is not common, so most growers would apply only a copper skirt spray for brown rot. With this 2023/2024 rain year, the disease has showed up in many orchards, and of course, it is above the brown rot spray line in the canopy.
https://ipm.ucanr.edu/agriculture/citrus/septoria-spot/
Both of these diseases are going to cause problems for growers, because once in the fruit, it's not treatable or salable.
UCCE Tulare County Assists UC Davis Pathologists in Survey for Decay Fungus in Prunes
Recently, extensive wood decay-related limb breakages have been reported in commercial prune...
Figure 1: Symptoms of advanced Phellinus pomaceus infection, showing white rot internal decay of heartwood. Scale bars 10 cm.
Figure 2. Fruiting body of Phellinus pomaceus. Characteristic association with pruning wounds shown in A, B, D, E. Scale bars 10 cm
Almond growers should prepare for possibility of unusual disease outbreak
Wet winter, El Niño create favorable conditions for aerial Phytophthora pathogen
With heavy rains in the forecast amid strengthening El Niño conditions, almond growers should be on the lookout for a rare disease that can cause severe damage to their orchards, according to Florent Trouillas, a University of California Cooperative Extension specialist in fruit and nut pathology.
Phytophthora, soilborne microorganisms dubbed “water molds” because of their dependence on water, typically cause root and crown rot at the base of trees. But a few aerial Phytophthora can travel upwards and infect the higher parts of the tree. One species – Phytophthora syringae – is drawing special attention due to an unprecedented outbreak last winter, fueled by the atmospheric rivers that lashed California.
“It was found statewide – meaning in every almond-producing county – and disease incidence in orchards ranged from 10% of the trees infected to 75%,” said Trouillas, a UC Davis plant pathologist whose lab is based at UC Agriculture and Natural Resources' Kearney Agricultural Research and Extension Center in Parlier.
Trouillas and his colleagues, UC Davis graduate student Alejandro Hernandez and UC Riverside plant pathology professor Jim Adaskaveg, recently published a detailed online article describing the pathogen, which can infect a range of crops but mainly impacts almonds in California.
Although it doesn't kill the tree, the disease causes branch dieback that requires significant additional work and expense for almond growers. In 2022, almonds were the state's fourth-highest valued commodity, at $3.52 billion.
During last year's aerial Phytophthora outbreak, researchers also observed a new and troubling phenomenon: P. syringae, historically known to attack the cuts caused by pruning, was directly infecting the young shoots on almond trees – without any wounds.
“This was really the first time we had seen widespread evidence of infection on the twigs,” Trouillas said.
Although generally rare, outbreaks of P. syringae have been traditionally associated with wet El Niño years, according to Trouillas – and recent and persistent rain across the state should have growers on high alert.
Prune in dry weather, monitor, mitigate if necessary
While almond growers tend to prune during the downtime of winter, they should keep an eye on the forecast and aim for a 10- to 14-day window of dry weather to perform those tasks, whether training young trees or maintaining the established ones.
“If growers were to prune around a rain event – before, during or shortly after – this increases the likelihood of infection because this pathogen moves around with water,” Trouillas explained.
Researchers speculate that P. syringae, normally found in the soil, gets carried into the upper parts of a tree through strong winds and heavy rain. Alternatively, harvest processes like shaking and sweeping also produce air movements that may blow the microorganism into the canopy, where it waits for a favorable wet environment. The pathogen then attacks the wounds or young shoots, producing characteristic cankers and gumming.
The patterns and colors of the gum balls are keys to diagnosing an infection of this particular aerial Phytophthora. Starting around bloom time (mid-February), growers should monitor pruning wounds and young shoots on their trees, especially in the canopy, for signs of the disease.
The unique coloration of the gum balls – ranging from gold and amber to dark burgundy to bright red (see photos) – generally indicates P. syringae infection. But growers are urged to contact their local Cooperative Extension advisor for confirmation.
“It is super critical for growers that, whenever they see gumming, not to assume that it is this aerial phytophthora, because there are many other diseases that can cause gumming on the tree,” Trouillas said.
If the diagnosis is confirmed, growers may apply a compound that can mitigate the infection. The plant pathologists' recent writeup describes several curative treatment options, as well as a preventive measure that reduces the amount of pathogen in the soil and thus the likelihood of infection.
For more information on the pathogen's history and biology, as well as various options for disease management, visit the article on Sacramento Valley Orchard Source: https://www.sacvalleyorchards.com/almonds/trunk-soil-diseases/aerial-phytophthora-outbreaks-in-wet-years.
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