Franz Niederholzer6 CommentsJanuary 22, 2013Horticulture

What is Dormant?

I see what seems like a lot of leaves still left in some orchards around the Sacramento Valley, even after a wet and windy end to 2012.  Aldrich trees look to have the most leaves remaining.  This observation got me thinking about questions I’ve heard regarding leaves, dormancy, chilling and bloom timing/duration.  These questions include: Are trees with leaves remaining in January less dormant or somehow different than trees that are defoliated or naturally bare by January? Doesn’t spraying trees with zinc in the fall make them dormant faster? They don’t have leaves… Do trees with some leaves left in the canopy in January accumulate less chilling than trees with no leaves in December?

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David Doll5 CommentsJanuary 4, 2013Horticulture

Winter Chill Reduction from Climate Change

I came across these papers discussing the reduction of winter chill due to climate change within the central valley of California: 1. Luedeling E, Zhang M, Girvetz EH (2009) Climatic Changes Lead to Declining Winter Chill for Fruit and Nut Trees in California during 1950–2099. PLoS ONE 4(7): e6166.  2. Baldocchi and Wong (2008). Accumulated winter chill is decreasing in the fruit growing regions of California.  Climatic Change. March 2008, Volume 87, Issue 1 Supplement, pp 153-166.

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Franz Niederholzer3 CommentsDecember 21, 2012Horticulture, Insects, Weeds

What did I learn at the Almond Board’s annual conference?

The Almond Board of California’s annual conference is a chance to connect with others in the almond industry, listen to world class researchers talk about their work, and check out a huge almond-focused trade show all at one event. The 2012 meeting was last week (Dec 11-13).  Here is a quick review of some of the things I picked up from researchers and informed industry members at that meeting…

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David Doll0 commentsSeptember 14, 2012Diseases, Horticulture

Reducing Winter Kill in Walnut

Straying from the usual almond entries, I thought I would address the issue of winter kill on walnut. There have been a lot of new walnut blocks planted through Merced and surrounding counties. Winter kill damages trees that are growing very vigorously in late fall. Damage can occur on both young and old walnut blocks, but young trees are more frequently damaged. Prevention of winter kill requires two steps – hardening off the tree by stopping the new growth by late September, then re-applying water to ensure adequate soil moisture before the first frost. Specific recommendations are below:

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David Doll3 CommentsJuly 28, 2012Horticulture, Nutrient

Nitrogen and Potassium Leaf Content: Is There Such Thing as Too Much?

I have received a few questions regarding results of mid-July leaf tissue analysis. In many cases, when reviewing the leaf samples, I have noticed that levels of nitrogen and potassium are often much higher than the recommended mid-July levels. Having leaf nutrient contents well above adequate levels does not necessarily increase yield, but can increase fertilizer costs and hull rot incidence. Rationale for “pumping” up the trees above the adequate value is to address the “silent hunger” that may be taking place within the field. In other words, by overfeeding some trees, we are assuring that we are maintaining trees that may be borderline above the level of sufficiency. Performing this action may increase yields as some trees that are deficient will perform better; however, too much fertilizer will lead to waste. Assuming that the leaf samples were collected properly, the UC-established mid-July leaf values should be used for comparison.With nitrogen, leaves with 2.2-2.5% leaf nitrogen content indicate that the sampled trees are receiving enough nitrogen. Being a few tenths of a percent over this value (3.0%) is a good indication of over-fertilization, increasing the risk for hull rot. Regarding potassium, the sample is considered sufficient if it is above 1.4%. Most growers attempt to maintain their potassium leaf levels around 1.8-1.9% within their samples, buffering for the tree use and compensating for the spatial variability of potassium within the tree. I have seen several leaf analysis with potassium levels greater than 2% and have heard from growers that trees need to be above 2% to maintain production. This is not true. Research by Roger Duncan (Farm Advisor, Stanislaus County) found that orchards with potassium leaf levels greater than 2% did not have greater yields than orchards with leaf levels above 1.4%. If leaf samples are well above the sufficient levels, plan to reduce,

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David Doll29 CommentsJune 30, 2012Horticulture

Independence Almond – Some Observations

Many farmers are preparing their tree orders for next year’s planting. In that regard, I have received a few questions on Independence, a self compatible variety. What does it mean to be self compatible? Traditionally, almonds require cross pollination in order to ensure profitable harvests. In other words, pollen from one variety needs to move to the flower of another variety in order for the flower to be fertilized and set a nut. This is why we have multiple varieties of differing pollen groups planted within almond orchards. The newly released variety ‘Independence,’ however, is a self pollinating variety, meaning that pollen from an Independence tree can pollinate and fertilize a flower from another Independence tree. A single variety orchard has advantages over traditional 2-3 variety plantings. The obvious benefits come from the single bloom, hullsplit, and harvest timing. This provides savings in time as it may reduce the passes through the block, and even more so for growers relying on custom spraying, harvesting. These reasons where why Butte/Padre plantings were so popular. How does the tree look? At this point, although possibly premature, with observations of the oldest block that I know – 9th leaf – and a few younger plantings, it looks good. Yields have been up and down in the oldest block, but this has been due to frost events that have occurred in the late spring. In the younger blocks, the tree seems to bear well, and appears to have a good yielding potential based upon field observations.  The trees appear to be a little smaller than Nonpareil and a little more upright. Bloom time seems to overlap well with Nonpareil, if not a day or so earlier. Any obvious disease problems? The past few years I have walked the a few blocks looking for symptoms of various

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David Doll0 commentsApril 21, 2012Horticulture

Hail Damage from Last Week’s Storm

Photo 1: Hail damage to a mature orchard.Almonds and leaves litter the floor. I have had a few questions about what to expect from the hail damage experienced during last week’s thunderstorm. I have included a lot of photos as this is, thankfully, a rare event. Crop and leaf loss on mature trees was experienced (Photo 1), and delayed drop of damage nuts should be expected. Nuts that are damaged but do not fall may have kernel darkening at the spot of impact (Photo 2). This may become relevant at harvest grading. If crop loss has occurred on your farm, please contact the local ag commissioner’s office and inform them of the damage for their reports. Photo 2. Hail damage on a developing almond. The sunken spot indicates the point of impact.  Significant damage has been experienced in young trees as well (Photo 3). Trees that have experienced broken branches and tattered leaves should push out new growth. If the growth point of the branch was broken, the bud below the injury should push creating a fork (Photo 4,5). These may, although unlikely, present problems when selecting scaffolds at the end of the first growing year. Consider removing the branches in-season if a bad angle is being developed by a newly pushed scaffold. Photo 3. Damage to a young almond tree.Photo Courtesy of Stephen Boone. Photo 4. Damaged shoot top from hail on first leafalmond. Branch should push new growthfrom below the damaged area.Photo Courtesy of Stephen Boone. Photo 5. Damaged shoot on a first year almond tree. A new branch will push that may create problems at pruning.Photo Courtesy of Stephen Boone.

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David Doll0 commentsMarch 6, 2012Horticulture

Frost Prevention in Almonds

Windy and cold conditions are forecasted for the next few nights. The temperature is expected to drop just below freezing, indicating the possibility of an advection frost. If temperatures stay above 28F, damage should be minimal. Never-the-less, windy conditions will remove heat from the orchard, reducing the effectiveness of frost prevention measures. Here is further information regarding frost damage and control:General Information on Frost Damage PreventionRates of Irrigation to Prevent Damage Basically, application of water via irrigation will increase the heat within the orchard, reducing frost damage. Temperatures will dip to their lowest just before dawn, but irrigation should occur before this time in order to increase heat within the orchard canopy.

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David Doll0 commentsMarch 2, 2012Horticulture

Varietal Bloom Issues

Weak bloom experienced in an orchard:Nonpareil and Monterrey shown. I have received more calls about weak bloom on almond pollinators. These trees have low counts of fruit bud, and the vegetative buds have pushed giving the tree a green instead of white appearance. The reports have been coming in from orchards of “juvenile orchards” (7-10 years of age), which typically have yielded quite heavy for their age. Nonpareil is affected, but the later harvested varieties, which include Monterrey and Fritz, are affected more severely.   In being in these orchards, it is clear that the period of fruit bud development was affected sometime last year. Fruit bud development/floral initiation varies among varieties. Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds). Very fruit bud are found on the trees,the majority of the buds are vegetative (leaf). In regards to the weak bloom, working with the farmers, we were able to identify some of the possible stressors that may have occurred during the period of fruit bud differentiation. Although we are unsure of the exact problem(s), the ones we are considering include:1. Holding back of irrigation in order to “force” hull-split or harvest,2. Excessive foliar disease, including rust or scab, that caused defoliation,3. Improper nutrient management – usually very low potassium and boron, and 4. heavy yields that reduced the vigor of the tree, impacting growth and the number of fruiting spurs available for future crops. In many cases, more than one of these issues could have affected the orchard. In orchards that experienced defoliation to foliar disease, many

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