David Doll3 CommentsJune 23, 2017Horticulture

What influences hull-split timing?

Hull-split often occurs around the end of June though the first week of July within the San Joaquin Valley. The start and duration of hull-split is influenced by the variety, weather, and tree stress. As many are aware, the variety has the strongest influence on hull split initiation and progression, but this article will focus on the influence of weather and tree stress. Most people believe the weather experienced in mid-June strongly influences the start of hull-split. Research has indicated, however, that this is not true. Work by Ted DeJong (UC Davis Plant Sciences), has found that the beginning of hull-split (which is indicated as 1% hull split) can be predicted by weather conditions experienced during the first 90 days after bloom. Cooler conditions experienced during this time will lead to a later hull-split, while warmer conditions result in an earlier split. Temperatures in the latter half of the spring and early summer have a minimal influence on nut progression, regardless of being warmer or cooler than normal. The model can be found at http://fruitsandnuts.ucdavis.edu/Weather_Services/almond_hullsplit_prediction/ and can be applied using localized CIMIS data. There is some evidence to support that tree stress and nutrient status influences the duration of hull-split. Stress in June decreases water content within the hulls, which means a faster drying time when they begin to split (think of hull-split progression like a bell-shape curve – stress in June shortens the x axis).  This is often related to high heat experienced in June, which leads to tree stress due to inability to properly manage the irrigation or the application of regulated deficit irrigation (RDI). Nitrogen status of the tree also influences the rate of split, in which trees having a higher nitrogen content have a longer duration of hull split. Often vigorous orchards are grown with minimal

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David Doll0 commentsJuly 14, 2011Insects

Timing of Hull-split sprays for Navel Orange Worm

Written by Walt Bentley, UC IPM Specialist, San Joaquin Valley. Hullsplit of Nonpareil almond, the most susceptible cultivar to navel orangeworm (NOW), is almost 2 weeks behind schedule in the central San Joaquin Valley.  Interestingly, the development of the second generation of NOW is not behind schedule with eggs being laid during the first week of July (see figure below).  This presents an interesting situation.  I believe many of these eggs will result in suicidal emerging larvae, not being able to infest the nut meat until hullsplit occurs.  This, however, doesn’t mean we are home free concerning NOW infestation.  It points to the importance of timing sprays to the development of the susceptible stage of the nut (initiation to 5% hullsplit).  Such timing will optimize the effects of any insecticide applied with the residual remaining through the complete second generation egg laying.  I believe a good portion of the early second generation eggs will hatch and be unable to infest the nut.  The remainder of the generation, that can reach the nut meat, will be shorter in time duration than normal.  If sprays are timed correctly, excellent chemical control should be achieved.  The same scenario that could optimize control of NOW in Nonpareils may result in making later splitting varieties such as Carmel, Sonora and Price more susceptible.  This is a scenario that we see from time to time.  Here the third generation eggs may be timed to Carmel hullspit resulting a greater potential for infestation.  Try to focus on early harvest of any late soft shell variety.  It may still be a good idea to monitor egg traps to see how NOW egg laying coincides with the hullsplit of these later soft shell varieties.  This can give you an idea if additional chemical control may be needed. 

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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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David Doll1 CommentJune 27, 2009Insects

Hull Split is Approaching…

Hull split is approaching the the central San Joaquin Valley. In Kern COunty, hullsplit of almonds has been observed on the edges of blocks and tops of the trees, and will progress rapidly from this point forward. Hullsplit is a traditional time of making an application of insecticide to reduce navel orange worm damage and late season mite pressures. Blanks, or unpollinated or aborted fruit, will split first before the rest of the crop. So, as a grower, what do we need to keep in mind during hull split? 1. Insect pest management, which includes Navel Orange Worm and Spider Mites. 2. Water Management to reduce the incidence of hull rot. We will cover point 1 today, and the disease hull rot later this week. 1. Insect Pest Management practices for Hull split. Spider Mites: A miticide will be necessary if a pyrethroid was used within the orchard. Pyrethroids target both spider mites and predator mite populations. Once the predator mites are reduced, the faster reproducing problematic spider mites can flare up, causing tree defoliation. It is essential to include a miticide tank mixed if spraying a pyrethroid. If not using a pyrethroid, scouting the trees can give you an idea if you need to include a miticide. Scouting for mites is simple, should be done in the morning when it is cool, and can give a good idea about the ratio of predator mites to spider mites in your orchard. Please refer to the University of California Integrated Pest Management page for information on how to scout for mites: UC IPM Scouting for Spider Mites. There are several miticides to choose from at hull split. The most commonly used include Acramite, Envidor, Fujimite, Kanemite, Oil, Omite and Zeal. Each of these products can be effective, depending upon populations of

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David Doll16 CommentsJune 22, 2009Horticulture

The Seasonal Patterns of Almond Production

When reviewing previous posts of this blog, I realized that not much information has been provided about the general biology of the almond tree. To cover this area, I decided to focus on the seasonal cycle of almond trees. In general, the season progresses in the following pattern: Dormant,Delayed Dormant, Bloom, Post-Bloom, Fruit Development, Harvest, and Post Harvest. Each period will be broken down and discussed. Dormant:As the temperatures from the late fall continue to drop, the tree enters a period of rest that lasts through December/Early January. At this time, the tree has dropped all of its leaves naturally or through an application of zinc, and is maintaining a low level of water use and starch consumption. This “low” flow of starch through the tree is needed as the catabolic breakdown of starch to sugar prevents the sap from freezing. This is, of course, only if the tree was able to develop enough starch reserves in the previous fall. In the rare occasion of low starch reserves, cold damage can occur leading to canopy and scaffold loss. Picture 1: A dormant spur. The cold temperatures that the tree is exposed to at this time helps with the development of the fruit buds. The tree requires a certain amount of moisture and chilling hours to come out of dormancy. Once the chilling hour requirement has been met, bud grown will begin with warmer temperatures. Chill hours are dependent upon the variety,but almonds generally need between 500 and 600 chill hours. In general, chill hours are the number of hours between the temperatures of 32-45 degrees Fahrenheit. Winter hours above 60 degrees are subtracted from the totals. Delayed Dormant:In late January/early February the tree begins to push a flush of fine feeder roots. These roots provide moisture and nutrients for the

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