David Doll4 CommentsJune 22, 2018Diseases

Alkaline treatments have been shown to reduce hull rot

Recent research has found that alkalizing treatments applied at hull split are able to reduce the severity of hull rot caused by Rhizopus stolonifer. Over the past two years, work by Dr. Jim Adaskaveg and colleagues out of UC Riverside has repeatedly shown that several products reduce hull rot incidence. These products included dipotassium phosphate (applied as the product diKaP) applied at 48 ozs/acre, calcium hydroxide applied at 320 ozs/acre, and Cinetis applied at 24 fl. ozs/acre. A single application of each of these products made at 5% hullsplit was shown to be as effective as several fungicide combinations and reduced hull rot strikes by over 75% in comparison to the untreated control. Multiple applications, with one made at early suture split (traditional first navel orangeworm (NOW) timings), did not seem to reduce strikes further. The cause of the reduction in strikes is unknown. It doesnt appear to have a fungicidal effect on the fungus as often the fungus is present within the hulls. The current thought is that these products neutralize the fumaric acid that is produced by this fungus (this is the acid responsible for limb death).  It could also be due to an increase in tolerance to the toxin from the foliar product. Work is ongoing. With these products, timing is key. Apply around 5-10% hull-split. Since these products may be tank mixed with NOW products as well as other fungicides, confirm compatibility by running a jar test. If struggling in managing hull rot, consider trying these products on a selected blocks to see if they provide any reduction in observed damage. Just remember to leave an area untreated in order to determine treatment effectiveness.  Finally, keep in mind that the use of these type of products for hull-rot enters the “grey world” of registration.  Follow appropriate

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Brent Holtz0 commentsNovember 5, 2017Diseases

Aspergillus niger induced hull rot on almond

Written By Brent Holtz, Ph.D., UCCE Farm Advisor San Joaquin County   In September I visited an almond orchard in San Joaquin County with the Supareil variety showing symptoms that looked very similar to hull rot typically observed on Nonpareil.  Symptoms showed dieback of vigorous young shoots and lower limbs (photo 1-blighted shoots).    Leaves were stuck on many shoots and typically blighted while hulls were unusually shriveled (photo 2-shriveled hulls), with fungal sporulation observed on the inner hull next to the shell (photo 3-fungal sporulation).  The fungal sporulation, however, didn’t look similar to the sporulation typically observed on hulls infected with Rhizopus stolonifer or Monilina fructicola, the typical pathogens associated with hull rot of almond.  Many of the larger blighted shoots seemed to still be alive even though they had defoliated, while other blighted shoots were starting to push new leaves in September—not typical of blighted shoots infected with Rhizopus or Monilinia. Samples of infected hulls were sent to Dr. Themis Michailides, a plant pathologist with UC Davis / Kearney Research and Extension Center, where he isolated Aspergillus niger from 88% of the samples collected.  The other 12% of the diseased nuts collected were found to be infected with Rhizopus stolonifer, the typical bread mold pathogen commonly associated with hull rot.  Aspergillus niger has not commonly been associated with hull rot in the San Joaquin Valley, but Dr. Mohammad Yaghmour, Farm Advisor in Kern County, has also observed similar hull rot. Hull rot can reduce yields of vigorous young almond orchards in the central and southern San Joaquin Valley.  Symptoms often observed are dieback in lower limbs that often exhibit less bloom in the spring.  I’m wondering how the Supareil return bloom will be in this particular orchard next spring?  I believe severe hull rot can enhance the shading out

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David Doll0 commentsAugust 22, 2015Diseases, Irrigation

Irrigation Rates and Hull Rot

Written by Andrew Ray, Staff Research Associate for Univ of CA Cooperative Extension, Merced County Our water production function (WPF) project within almond has given us an opportunity to look at how irrigation rates can impact the amount of hull rot that develops.  The goal of the WPF is to be able to calculate the impact that water applied has on yield.  This plot is replicated in three different places across the Central Valley. In the Merced WPF plot, there are five different treatments of water applied at the rates of 110%, 100%, 90%, 80% and 70% of the evapotranspiration rate (ETc).  There are 3 blocks of these treatments within an 80 acre orchard.  Irrigation rates stayed constant with their established relationship to ET through hull split, and reduced deficit irrigation was not applied. During mid August hull rot occurrence was estimated in the Merced WPF plot on two trees in each treatment within each block.  Twenty five branches were counted on each quarter of the tree, totaling 100 branches per tree, and the number of incidents of hull rot was recorded. There were two ratings performed by two different people and the estimated percentages were averaged. Table 1 shows the averages by treatment of all the trees rated.  Included in the table is the average stem water potential (SWP) for each tree and leaf nitrogen percentage.  The SWP measurements were taken with a pressure chamber on three separate occasions during hull split in early July.  Baseline SWP during that time was -9 bars.  Leaf tissue samples were taken in mid July and the average percentage of nitrogen for each treatment. Table 1: Average hull rot percentage observed in each irrigation treatment, along with average SWP during hull split, and leaf tissue nitrogen percentage. %ET % Hull Rot SWP (bars) %N

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David Doll0 commentsAugust 1, 2015General

2015 Harvest Time Updates

Over the past week, a few interesting observations have been made. These include: 1. Hull rot in Nonpareil appears worse in many ‘Nonpareil’ orchards. This is most likely due to the higher-than-normal humidity levels experienced during the initiation of hull-split. Most of the hull rot appears to be from the black bread mold Rhizopus. The dieback being observed is from the translocation of the toxin back into the limb. This often causes gumming which can reduce the ability to remove nuts during shaking. Applying a fungicide now will not cure the infections or prevent the movement of the toxin. 2. There have been several reports of Fuller Rose Beetles clogging micro-sprinklers. These insects lay a mass of eggs in the opening of the sprinklers, reducing water flow. Surprisingly, reports are even coming from growers who have switched to pop-up micro-sprinklers, which are considered more resistant to clogging. This nocturnal beetle has one generation per year with most of the adult activity occurring in August – October. The beetle needs to feed on leaves for a few weeks prior to laying eggs. Although chemigation of the soil is not effective for controlling the insect or eggs, there is some thought that treating the trunks with a registered broad spectrum insecticide may kill the beetle as it migrates from the soil to the trunk. If attempting this strategy, be wary of the PHI of the product you are planning to use. More information can be found in this presentation and at the UC IPM website (You may need to look under a different crop). Keep in mind that the best long-term management of this pest has been through the use of clog resistant, pop-up type microsprinklers. 3. Reports of gummy kernels from boron deficiency and stuck nuts from boron toxicity. Gummy kernels that occur may

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David Doll0 commentsAugust 20, 2011Diseases

Reports of Hull Rot

I have been getting a few calls regarding hull rot. I have covered this topic before (link to previous article), but some of the particular questions regarding the disease are answered below. What is Hull Rot?Hull rot is infection of the almond hull by two fungi, Rhizopus stolonifer (common bread mold), or Monilinia fructicola. These pathogens are common throughout the environment, and are, in this case, serving as opportunistic pathogens. Upon infection, they release toxins that are translocated into the fruiting wood, which kills the wood, causing crop loss. What do you mean by opportunistic pathogen?Once the hull splits, the perfect micro-climate for fungi is created. The hull is full of nutrients and water – the two things that fungi want from a host. Since the spores of these fungi are found throughout the air, they invade the newly split tissue, infecting, and completing their life cycle. By reducing the “home” for the fungi, we can reduce the number of hull rot strikes. These strategies include reducing the water and nutrient content of the hull. How can I prevent Hull Rot?Asking “How to prevent” is a good start. Prevention is the key to reducing hull rot strikes. Hull rot often affects high vigor orchards. Nitrogen should not be applied after kernel development is completed. This is typically the end of May, but this year it extended into mid-June. A slight to moderate water stress at the onset of hull-split should be applied. Applying both of these practices to the orchard has been shown in multiple research trials to reduce hull rot by 80-90%. Often times, this is all growers need to do to prevent severe hull rot issues. I tried those things, I still have hull rot!Severe outbreaks of hull rot have been observed. Last year, hull rot infections occurred in many orchards. I

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David Doll2 CommentsJuly 12, 2010Insects

2010 Hull Split time…

I feel that the majority of topics regarding hull split have been discussed in prior entries, so I thought I would briefly make a few points of considerations for 2010: 1). Navel Orange Worm (NOW)/ Peach Twig Borer (PTB): Both insects cause damage to almonds, often NOW damage hiding PTB damage. Both insects are susceptible to the same insecticides. The 2010 treatment window for the 2nd flight of PTB will be overlapping with hullsplit. This is good because we can make one spray for NOW and PTB. This is bad because in years were the 2nd PTB flight occurred during hullsplit, worm damage was higher.  If no PTB treatments have been made and no NOW/PTB treatments are scheduled, I would plan to make one within the coming week. Reduced risk products or pyrethroids will provide control for both worms. Related topics previously covered: Peach Twig Borer, Navel orange worm, and hull split insect management. 2). Apply pesticides slowly – do not exceed 2 MPH with spray rigs. 3). Hull rot: Hopefully nitrogen applications have ended. Plan to reduce water to 80% ET for the coming two weeks. By the last week of July, first week of august, resume full ET. This will help reduce hull rot. Please see the previous article on hull rot. 4). Mites: Haven’t been much of a problem this year, but keep in mind that the use of a pyrethroid at hullsplit will most likely cause a mite flare up by harvest. A miticide should also be applied at hullsplit if a pyrethroid is used. There are a few products available that can knock down high populations of spider mites should a flair up occur. It is critical that these products are applied before webbing appears. 5). Harvest: Hullsplit appears to be a week later this year, suggesting that harvest will be

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Brent Holtz10 CommentsJune 30, 2009Diseases

Hull Split Part 2: Hull Rot of Almond

As almond trees approach harvest, at about mid hull split, clusters of dry leaves begin to appear scattered through the tree canopy. Individual spurs, small shoots or entire small branches may collapse due to hull rot infections (Photo 1). The loss of fruiting wood, especially in the lower parts of the tree, can negatively affect yield for years to come. Nonpareil is usually the most severely affected cultivar though Sonora and Kapareil can also sustain extensive damage. Hull rot is caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Monilinia fructicola is best known as one of the brown rot fungi and R. stolonifer is often called the bread mold fungus, and will turn bread left out black and moldy. Photograph 1: Hullrot of almond caused by Rhizopus stolonifer. In the southern San Joaquin Valley I believe that Rhizopus is the primary pathogen responsible for hull rot while Monilinia may be more important in the Sacramento Valley. These two organisms are very different but can cause similar disease symptoms on almond. As the name implies, a lesion or dryish rotted area develops on the hull, and dense masses of Rhizopus spores produce a powdery dark gray to black growth between the hull and the shell (Photo 2). Monilinia spores are buff-colored and can be seen on inner and outer hull surfaces. The nut meat is not damaged, but a toxin produced in the infected hull moves from the hull into the neighboring leaves and shoots causing death of these tissues. Neither Monilinia nor Rhizopus are able to invade the healthy outer hull surface. Only after hull split begins can spores gain access to the inside of the hull and initiate infections. Once hull split starts, trees are at risk of becoming infected. One or both pathogens may be

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