Roger Duncan0 commentsJanuary 24, 2015Diseases

Dormant Sprays Not Reducing Lower Limb Dieback

Lower limb dieback (LLDB) continues to be a problem in some area almond orchards, especially in the Padre and Butte varieties.  Beginning in late April or early May, leaves on affected lower limbs begin to yellow and then turn brown.  Eventually, entire limbs die and by late summer, significant death of lower canopy wood can occur. Early studies indicated that species of Botryosphaeria and Phomopsis fungi played a significant role in this problem, but later efforts indicated that LLDB may not be a disease at all.  Multiple spring fungicide applications did not reduce limb death.  The bottom line is that LLDB is still not well understood although a compromised root system, especially from overly wet soils in the spring, may contribute to the problem. 

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Roger Duncan7 CommentsJanuary 21, 2014Diseases

Bacterial Spot Management

Almond growers and pest control advisors who attended our July bacterial spot field day in Manteca saw how devastating this new disease can be.  A map passed around at that field day showed two hot spots for the disease in our area.  The most severely affected area was between Highway 120 and the Stanislaus River in the Manteca/Ripon/Escalon area.  The second area was south of Turlock in the Delhi / Ballico area. 

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Roger Duncan13 CommentsJune 26, 2013Diseases

Bacterial Spot – A New Disease of Almond in the San Joaquin Valley

Written by: Roger Duncan, Brent Holtz, David Doll and Themis Michailides Earlier this spring, we received reports from growers and pest control advisors that they had observed a few San Joaquin, Stanislaus and Merced County almond orchards with large amounts of amber-colored gum balls exuding from the hulls.  The damage has been predominantly on ‘Fritz,’ but there are reports of similar damage on ‘Monterey’ and ‘Padre.’  In some orchards, Fritz is severely affected while the Nonpareil and other pollinators are very clean. 

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Roger Duncan10 CommentsAugust 23, 2012Nutrient

Hull Analysis for Boron – Why?

Harvest is here. This is a good time to pull a a bag of almond hulls for a boron analysis. In making this recommendation, there are questions that are consistently asked. I already know my leaf tissue levels, so why do I need to perform a hull analysis for boron? Leaf sampling is not effective in determining the levels of boron as there are no obvious foliar symptoms of moderate boron deficiency. Furthermore, leaf levels may appear adequate while the actual levels within the tree are too low or high. Since the hull of the almond is a “sink” for boron, the analysis of mature almond hulls is a better indicator of boron status. When should I collect samples for a hull analysis? Boron will continue to accumulate in the hull until harvest. The best time to collect a hull sample is anytime after shaking the nuts. Varieties within the orchard may have differing boron levels due to different yields; it may be useful to pull a sample from the other varieties. How do I interpret the results? Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Boron applied earlier in the season as foliar spray is not a substitute for this timing because it is sequestered into the hull and is unavailable for the developing fruit bud. Hull boron of less than 80 ppm indicates the need for a ground application.  Fertilize with 2-4 pounds of actual boron per acre.  This is equivalent to 10-20 pounds of a 21% soluble boron product (i.e. Solubor). Boron can be applied through the irrigation system, broadcast or

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Roger Duncan2 CommentsNovember 30, 2010Horticulture

Rootstocks for California Almond Orchards

Roger Duncan, University of California Cooperative Extension in Stanislaus County Joe Connell, UC Cooperative Extension in Butte County John Edstrom, UC Cooperative Extension in Colusa County Nemaguard has been the main rootstock of the California almond industry for many decades.  It is well adapted to the well-drained, non-calcareous loam and sandy loam soils common throughout the San Joaquin Valley.  Nemaguard is vigorous, immune to rootknot nematode, compatible with all almond varieties, doesn’t sucker much, has decent anchorage, and is easy to grow at the nursery.  Never-the-less, there are many situations in which nemaguard struggles.  Nemaguard, as with most peach rootstocks, is prone to lime induced chlorosis (yellowing / iron deficiency) in high pH soils.   It is also susceptible to salt toxicity (sodium, chloride & boron), “wet feet”, Phytophthora root rot, oak root fungus, crown gall and “heart rot”.  Despite the name “nemaguard”, this rootstock is susceptible to ring and root lesion nematodes.  The susceptibility to ring nematode leads to the danger of bacterial canker in orchards replanted into sandy soil.  Since 1998, UC Cooperative Extension farm advisors in Kern, Stanislaus, San Joaquin, Colusa and Butte Counties have researched several alternative rootstocks for California almond growers.  These include most of the common, commercially available rootstocks in California along with many newly available rootstocks from other countries.  While there is no such thing as the perfect rootstock, there are better choices than nemaguard where many chemical or physical soil problems exist.  Below are some suggestions for specific challenging situations. Heavy soil / poor drainage.  Nemaguard is not adapted to poorly drained soils and can become yellow, stunted or even die from lack of oxygen.  Lovell, another peach seedling rootstock, is not much better.  As a group, plum rootstocks are pretty tolerant to heavy soil.  Marianna 2624 has traditionally been the rootstock of

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Roger Duncan2 CommentsAugust 2, 2010Nutrient

Hull Samples for Boron Analysis

What is the most common nutrient deficiency in Northern San Joaquin Valley almonds? If you said nitrogen or zinc you are wrong. While zinc and nitrogen are commonly applied to area orchards, boron is often neglected and therefore boron deficiency is far more common. If you haven’t applied boron TO THE GROUND recently and your orchard is east of the San Joaquin River, you are almost certainly deficient. Boron is essential for pollen tube growth. There are no obvious foliar symptoms of moderate boron deficiency, but less than optimum boron can reduce nut set. Analysis of mature almond hulls is a much better indicator of boron status than a leaf analysis. Wait until harvest to collect hulls because they will continue to accumulate boron while splitting. Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Hull boron of less than 80 ppm indicates the need for a ground application. Fertilize with the equivalent of 10 – 20 pounds of a 21% boron product per acre. Boron can be injected through micro-irrigation systems, broadcast or sprayed on the ground, or included in a herbicide spray. Herbicide sprays containing glyphosate may need to be buffered to prevent reduction of herbicidal activity. Hull levels over 200 ppm indicate excessive boron.

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Roger Duncan5 CommentsOctober 6, 2009Nutrient

Post-harvest Boron Applications Can Increase Almond Yields

Written by Roger Duncan, UC Farm Advisor, Stanislaus Boron deficiency is very common in orchards and vineyards planted on the eastern side of our county. This nutrient is essential in pollen tube growth and fertilization of the flowers. Moderate boron deficiency does not produce recognizable foliar symptoms but trees do not set their full potential of fruit. Boron tends to accumulate in almond hulls and thus hull samples provide a better indication of boron status than do leaf samples. Harvest is an easy time to sample hulls. If samples are collected much earlier than harvest, a false reading may be obtained because boron may continue to accumulate in the hulls as long as they remain green on the tree. The current boron guidelines for hulls are as follows: 80 ppm or lower = deficient 80-150 ppm = adequate Over 200 ppm = may be toxic Soil applications are the best way to correct a deficiency. Be very careful when applying boron—a little boron fertilizer goes a long way and will last for a few years. Soil applied boron fertilizers should be broadcast, not banded. Research has shown that even orchards with up to 120 ppm benefit from a post-harvest foliar application of boron. In University of California trials in Stanislaus and other counties, postharvest boron sprays often increased nut set and yield 20-30% the following year compared to non-treated trees. Timing: The goal of the foliar application is to get the boron into the flower buds (actually pollen tube mother cells) that are developing for the next year. Therefore, timing of application is very important. During the growing season (March through July), large quantities of boron go into the developing hulls. If foliar boron is applied at this time, most of the boron will go into the hulls and is

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