- (Focus Area) Pest Management
- 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: Whitney Brim-DeForest
- Author: Luis Espino
- Author: Roberta Firoved
- Editor: Taiyu Guan
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At our last meeting, we had some questions about the approved uses of pendimethalin in California rice. There are several products labeled for use on rice with pendimethalin as the active ingredient. As of June 2024, pendimethalin registered products (on rice) include Prowl H2O, Prowl 3.3, Harbinger, Satellite Hydrocap, Stealth, Helena Pendimethalin, Pavilion H2O, Pavilion 3.3, and a few others. Please make sure to always check the product label, as not all pendimethalin products allow use for the below-listed timings. Furthermore, labels are updated regularly, so it should not be assumed that the same use pattern applies from season to season. For the most currently-registered products, refer to the California Department of Pesticide Regulation website, product label databases, as well as manufacturers' websites for reference. Please remember the container label is the deciding point for pesticide use enforcement.
The mode of action of pendimethalin is disruption of mitosis (WSSA Resistance Group 3). In California rice, there is no other herbicide registered with this mode of action. The herbicide binds to clay soils, with residual activity of between 1 to 4 months, depending on environmental conditions. Pendimethalin can be readily absorbed by young roots, and thus, weeds are controlled as they germinate. Damage can also occur to rice or other crops as they germinate. Weeds are not controlled by this product once emerged and established.
Labeled controlled weeds are: junglerice, barnyardgrass, and sprangletop. Barnyardgrass and sprangletop are the two most abundant grass weeds in dry- or drill-seeded California rice, also causing the most yield loss. Rotating with pendimethalin can help to manage herbicide-resistance biotypes, as well as preventing the selection of herbicide resistance in these species.
Pendimethalin Rice Timings (product-dependent):
Preflood, preemergence: In drill- or dry-seeded rice, pendimethalin can be applied to the soil surface AFTER rice has been dry-seeded and lightly incorporated or drill-seeded. The product should be tank-mixed with a safener adjuvant. Water should be flushed across the field AFTER herbicide application (within 7 days).
Delayed preemergence: NOT a currently labeled use for any pendimethalin product registered in California.
Early postemergence: Only for dry-seeded rice and into fields with no standing water. Pendimethalin is usually applied with a tank-mix partner. Timing should be based on the leaf stage of the rice or weeds as appropriate for the tank-mix partner. Field should be flooded or flushed within 7 days after application.
Postemergence: For water-seeded rice (California ONLY) between the 4-6 leaf stage. Field must be completely drained with no standing water at time of the pendimethalin application and should be reflooded within 7 days after application.
- Author: JD Trebec
When I first bought my home in central Woodland six years ago, there wasn't much in the yard to interest dragons: a mature orange tree that produced amazingly delicious navel oranges in the winter, a human-planted valley oak on the street out front, and squirrel-planted valley oak too close to my neighbor's fence line that looks ready to wallop my workshop. The rest of my small yard was Bermuda grass that burped up a fluffy clouds of invasive oxalis in the early spring and then reverted back to tired looking grass when the summer heat arrived. Nothing of interest, really, for a dragon. They aren't that interested in acorns or sorrel salad, and thankfully, they don't care for amazingly delicious oranges either because, of course, dragons are carnivores.
I quickly (well maybe not so quickly, it took a couple years) dug up and lasagna'ed the lawn and set up some garden beds and patches of native plants. It was only a few years after that that I started to spot the dragons: a flame skimmer resting on a corn stalk, a blue-eyed darner lurking among the peach leaves. This left me somewhat confused because I did not believe that dragons would be interested in my land-locked urban lot.
I'm talking about dragonflies of course and there are no bodies of water anywhere near me. Everyone knows that dragonflies are aquatic insects, right? How did they end up here? I wondered if they had blown in from Cache Creek somehow or maybe hitched a ride over from the Yolo Bypass. They didn't seem to stay long. It wasn't until recently when I saw about a half dozen of what appeared to be four-spot pennants darting and swooping about ten feet overhead in the early evening that I began to put it all together.
Dragonfly larvae are aquatic, but the adults certainly aren't, and with a cruising speed of about 16 kilometers per hour (10 mph), why wouldn't they stretch their wings and see the world? Just like birds or, closer to the mark, butterflies, many species of dragonflies migrate. While the migratory routes of butterflies like the Monarchs are well known, dragonfly movements are still something of a mystery. However, one of note, the appropriately named globe skimmer dragonfly, has been tracked from India to East Africa and over to Middle Asia, a total distance of 14,000 km (8,700 miles). https://india.mongabay.com/2021/11/high-flying-dragons-how-the-globe-skimmer-migrates-across-the-indian-ocean/
Like the Monarch butterfly, dragonfly migrations may take several generations as the insect swarms (I find the collective name ‘flight' more appropriate for dragonflies) follow a shifting path of ancestral pools. Some dragonfly flights follow the same flyways as hawks, and groups like the Golden Gate Raptor Observatory have added the occasional bug count to their seasonal observations of birds of prey. https://www.parksconservancy.org/park-e-ventures-article/smaller-winged-creatures-flying-through-headlands
I can't say for sure that the changes to my yard have inadvertently resulted in a bit of dragon habitat, but likely there are some additional tasty bug snacks now that merit a dragon flyby. I am happy to host them so long as they stick to eating mosquitoes, gnats, and any pests that are eyeballing my garden, and leave the oranges to me.
A Dragon(fly)! Blue-eyed darner (photos by JD Trebec)
and a Damsel(fly)! Arroyo bluet
Note: Accuracy of amateur insect identification may be questionable beyond the Genus level!
- Author: Kathy Keatley Garvey
It's the Fourth of July and what better time to post images of the aptly name "soldier beetles" than today.
These insects (family Cantharidae) resemble the uniforms of the British soldiers of the American Revolution, which is apparently how their name originated. They're also called "leatherwings" in reference to their soft, leatherylike wing covers.
Like lady beetles, aka ladybugs, these soldier beetles make short work of aphids and other soft-bodied insects. We've seen them devour so many aphids on our plants that they should be awarded the Aphid Belt, similar to Joey Chestnut's famed Mustard Belt.
Indeed, soldier beetles are eating machines, just like Joey.
Wikipedia describes Joey Chestnut (who, by the way, grew up in Vallejo, Solano County), as an "American competitive eater" ranked No. 1 in the world by Major League Eating. In addition to hot dog-eating contests, Chestnut has won contests devouring pizza, wontons, chicken wings, and corned beef sandwiches. And even poutine (french fries and cheese curds, topped with brown gravy).
No aphids, yet, though. Not even sprinkled on pizza slices.
- Author: Kathy Keatley Garvey
247 years!
The seven faculty members honored at the UC Davis Department of Entomology and Nematology's recent retirement luncheon amassed an amazing 247 years of service:
- UC Davis distinguished professor James Carey, 44 years, faculty member since 1980. He retired in June.
- UC Davis distinguished professor Richard Karban, 42 years, faculty member since 1982. He retired in June.
- UC Davis distinguished professor emerita Lynn Kimsey, 35 years, faculty member since 1989. She retired Feb. 1, 2024.
- Robert Kimsey, adjunct professor, 35 years, faculty member since 1989. He retired in June
- UC Davis distinguished professor Jay Rosenheim, 34 years, faculty member since 1990. He retired in June.
- UC Davis distinguished professor Diane Ullman, 29 years, faculty member since 1995. She retired in June.
- Sharon Lawler, professor emerita, 28 years, faculty member since 1995. She retired in January 2023.
Read about them on our UC Davis Entomology and Nematology website, with links to individual stories. You may have interacted with one or more of them through their research, teaching or public service.
As molecular geneticist and physiologist Joanna Chiu, professor and chair of the department, said prior to the retirement luncheon: “Our retiring faculty will leave behind some very big shoes to fill. “They have set the bar very high for all of us with their passion to lifelong scientific exploration, perseverance to achieve intellectual and mentoring excellence, and dedication to the department, UC Davis, and external stakeholders. We are so proud to call them colleagues and mentors and they will no doubt continue to inspire us to carry on their legacy. It is with our most sincere appreciation that we wish all of them the best in their new endeavors and adventures in this next chapter of their lives."
247 years of service!