David Doll4 CommentsJuly 19, 2020Irrigation

Regulated Deficit Irrigation: Is it appropriate for your operation?

Regulated deficit irrigation is the practice of reducing irrigation to obtain some type of desired stress level. This practice is often used during the initiation of the hull-split period to reduce hull-rot strikes. It also has been utilized during periods of water shortages to save 5-15% of the seasonal water use of almond. Due to the limited effect on yield, as well as the benefits, it has been advocated for application within orchards by the University and industry (including myself!). This practice, however, can have negative impacts when applied incorrectly and should only be used if deemed appropriate. In theory, this practice is easy to apply. Water application rates should be cut to achieve -15 bars stem water potential for two weeks preceding the onset of hullsplit (e.g. Blank split). This stress should be maintained at this level for this period. At the end of the two weeks, regular irrigation resumes and the orchard prepares for harvest. The difficulty in application has everything to do with accurately monitoring plant stress. Every orchard and orchard practice creates a different approach in application. For example, assuming similar irrigation levels, stress levels achieved in a mature orchard planted on sandy soil will occur in a shorter time frame than an orchard on a heavier clay loam. Every orchard site requires careful monitoring to determine when to cut and resume full irrigation. I have observed numerous orchardists apply tree stress only to see a reduction in kernel yield. This is due to ongoing gains in nut weight that occur between the onset of hull-split and harvest. If the tree is significantly stressed during this period, the conversion of carbon to fats is reduced, impacting the final crack out percentage. One closely monitored orchard in which I worked, demonstrated a 10-15% reduction in kernel weights

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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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