- Posted By: Franz J.A. Niederholzer
- Written by: Franz Niederholzer
At least one on-line weather forecasting site is predicting rain for Aug 20-22. That is right about the time prune harvest may begin in the Sutter/Yuba area. The forecast could be mistaken, but it might be a good idea to make sure your sprayer is ready and you have the best program (fungicide, sprayer set up and calibration) ready if needed.
Sprays to protect prune fruit from brown rot must be applied before rain. Research by Dr. Jim Adaskaveg, University of California professor of plant pathology, has shown the following materials and application practices to provide the best possible protection:
Best Materials (++++) in the 2011 UC Fungicide Efficacy and Timing publication followed by fungicide class (in parenthesis) appear below. Dr. Adaskaveg advises growers not to use the same fungicide chemistry more than 2 times in a single growing season. Check the label, consult with your packer and PCA before applying a fungicide preharvest.
- Bumper/Tilt (3)
- Indar (3)
- Quash (3)
- Pristine (7/11)
- Quilt Xcel (3/11)
Complete information at: http://www.ipm.ucdavis.edu/PDF/PMG/fungicideefficacytiming.pdf
I strongly suggest growers talk with their PCA about tank mixing two chemistry groups if allowed by the label and a premixed material has not been selected. For fruit brown rot control, Group 9 materials are rated +++ (good and reliable) by Dr. Adaskeveg compared to ++ (moderate and variable) for Group 11 materials. Group 9 materials should provide better resistance management support of Group 3 materials for fruit brown rot control than Group 11 materials.
Best results with research by Dr. Adaskaveg on prune fruit brown rot control include the following practices:
- Adding 1-2 gallons of 415 weight summer oil for each 100 gallons of spray water in the tank. Use of 440 weight oil instead of 415 oil may provide similar results, although this has not been tested. 440 weight oils are labeled for summer use, but max rate is 1 gallon per 100 gallons. Check the label of the oil product before spraying. Make sure there is NO sulfur in your spray tank (or sprayer filters) before adding oil to the tank.
- Using high spray volume ( for example 160-200 gallons/acre)
The most difficult spray job of the season is preharvest, when the canopy is most dense and weighed down by the weight of the crop. Slow tractor speeds will deliver the best spray coverage under these conditions. Slow down and do the best job possible.
Aerial application will provide less control than careful ground application.
Finally, lower your expectations. Fruit brown rot control preharvest is difficult. This is especially true when conditions (warm and wet weather + clustered fruit) favor infection. Complete control may not be possible.
- Author: Franz J.A. Niederholzer
put the rain gauge back up in my backyard today. Showers – OK, 30-90% chance of showers -- are predicted for the next three days. Spring rains can help bring about prune rust infections on prune leaves. Infested leaves will drop and defoliated trees produce small fruit.
If you haven’t already started looking for rust symptoms in your prunes, you should look after this series of cold storms roll through. Thursday is supposed to be clear and 79.
Details on rust scouting in prunes can be found at: http://ipm.ucdavis.edu/PMG/r606100611.html.
Basically, every week beginning May 1, look at 40 prune trees per block. Look for any rust spots. Spray (sulfur or labeled, Group 3 or 11 fungicide) once you see the first spot (see photos). Keep checking after you spray. If the number of trees with rust spots goes up, spray again. See the new UC ANR Fungicide Efficiacy and Timing publication at: http://ipm.ucdavis.edu/PDF/PMG/fungicideefficacytiming.pdf
Don’t let rust sneak up on you. It is easy to scout for and control as long as you know what you are looking for. Keep a healthy and profitable orchard with a strong canopy that can produce high quality prunes -- monitor prune rust and control when needed.
Prune leaf with three rust spots viewed from top and bottom. Rust spots appear angular and yellow from the top and rusty brown when viewed from the bottom.
- Posted By: Franz J.A. Niederholzer
- Written by: Bill Krueger
We are just finishing the bloom period and prune growers are anxiously waiting until the crop load can be accurately assessed. We all know there is no money in small prunes.
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Prune Reference Size Table Reference Harvest Size (dry) (count/lb) Size Green Orchard Sizing Potential (count/lb) Average Good Excellent 50 32 31 30 55 36 34 32 60 39 37 35 65 42 40 38 70 46 43 41 75 49 45 43 80 53 48 46 85 56 51 48 90 60 54 51 95 63 57 54 100 67 60 56 105 70 63 59 110 74 66 61 115 77 68 63 120 81 71 66 125 84 74 68 130 88 77 70 135 92 79 73 140 95 82 75 Table 1. Prune reference date and average harvest dry size table. Use the reference size fresh count per pound and read across for orchards with average, good or excellent sizing potential. |
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Figure 1. Extracting endosperm at reference date. |
Matching the crop load with the tree’s ability to size the fruit and achieve desired size is the goal. Fruit size at reference date, when the endosperm is visible in 80 to 90% of the fruit (Figure 1), can be used to estimate fruit dry fruit size at harvest (Table 1.). Reference date in the Sacramento Valley usually occurs in early May about one week after the pit tip begins to harden but may be later this year because bloom was delayed. At reference date, a random sample of sound (non-yellow) fruit should be collected and the number of fruit per pound determined. Sample 20 fruit from 20 trees. Use orchard history to determine the sizing potential of the block being considered. Unfortunately, with large crops this procedure may overestimate fruit size. Having a good estimate of the number of fruit per tree will help avoid this. Estimate the number of fruit per tree by removing as much of the fruit as possible with a shaker (prune or walnut) from a representative tree or two. Place a tarp under the entire tree before shaking. The remaining fruit should be removed by hand or estimated. Weigh all the fallen fruit. A subsample of at least 100 sound fruit is taken from the removed fruit. The number of sound fruit per pound is determined. Multiply the weight of the total fruit removed from the tree by the subsample count per pound to determine the number of fruit per tree. Adjust this number to allow for fruit drop from reference date until harvest to estimate the fruit per tree at harvest. Work done in the Sutter-Yuba area in the 1970's suggested that approximately 40% of the fruit would drop between reference date and harvest. More recent work in Glenn and Tehama Counties has suggested that fruit drop may be closer to 20%.
By dividing the estimated fruit number at harvest by the estimated or desired dry count per pound and then multiplying by the number of trees per acre, you can estimate the dry pounds per acre. This number will allow you to judge if your estimated fruit size at harvest (from Table 1) is realistic, based on comparisons with crop history – size and yield – from that orchard. You can then determine how many fruit of the desired dry size are necessary to give the expected dry yield and adjust the number upward by 20% to allow for drop. Now compare the two sets of numbers. If the number of fruit per tree measured in your orchard matches the number of fruit per tree at harvest needed to produce a certain size and tonnage of fruit (plus added 20% to account for drop), then you don’t need to thin. If the number of fruit measured in your orchard far exceeds the needed number of fruit at harvest (+20% for drop) then you should thin. For example, if your orchard trees should carry 5000 fruit to produce a solid crop in your orchard (for example, 3 dry tons of 60 count fruit) and your trees have 10,000 fruit/tree at reference date – regardless of what Table 1 predicts -- you should thin.
Mechanical thinning with the same machinery as is used for harvest can be used to remove the desired amount of fruit. Shake a tree and, and using the same methodology described above, calculate how much fruit was removed. Adjust the shaker and repeat the procedure until the desired amount of fruit is removed. Set the shaker and thin the block. The earlier thinning can be done, the greater effect it will have on fruit size at harvest.
- Posted By: Franz J.A. Niederholzer
- Written by: Franz Niederholzer
According to work by Dr. Ted DeJong in the Plant Sciences Department at UC Davis, the first 30 days after bloom can tell a grower quite a bit about 1) the sizing potential for a stone fruit crop and 2) the time to harvest. See back ground info and predictive model at: http://fruitsandnuts.ucdavis.edu/Weather_Services/Harvest_Prediction__About_Growing_Degree_Hours/.
It has been just over a month since full bloom. So, what can we learn from the first 30 days of the 2011 prune crop?
Given a 50% bloom date of March 28, 7000-7600 growing degree hours (GDH) accumulated in much of the Sacramento Valley (Colusa, Nicolaus, Durham) in the 30 days that followed. So, the model (available free on line at: http://harvest.ucanr.org/) predicts harvest between Aug 29 and Sept 1 in 2011. Since the model is always long when applied to dried plums, I’m predicting a harvest date of Aug 18-21 for Sutter/Yuba region. That is when I predict prunes in an orchard with a good crop – say 3 dry ton per acre -- will reach 3-4 pounds pressure. DON”T take that to the bank, but I suspect it will be pretty close. What do you think? Send me a comment (see below), please.
Now for the bad new-- fruit sizing potential for an orchard with a "normal" cropload could be less this year compared to the same sized crop in the same orchard in the last few years. Why? The heat unit accumulation in the first 30 days after bloom also helps give growers an indication of the relative sizing potential of a given crop. A relatively high GDH 30 (accumulated GDH in 30 days after 50% bloom) means a smaller sizing potential. A smallish GDH 30 means a better sizing potential. In the past decade, GDH 30 has ranged from 5000-9000. In 2004 it was almost 9000. In 2006, a great year for sizing, it was around 5000. This year, at 7000-7600 GDH 30, we fall in the warmer side of the range. This suggests that the sizing potential of the crop will be less this year compared to the last few years. What does this mean to a grower? Count fruit/tree in a block as soon as reference date arrives – maybe as early as pit hardening. If you have to thin, thin hard and early.
A post on cropload evaluation post by Bill Krueger follows this one.
- Author: Franz J.A. Niederholzer
Prunes are just past petal fall, but I've been shown several examples of bacterial canker and/or blast in the last week (see pictures below).
These symptoms are caused by infections of Pseudomonas syringae pv. syringe, a common bacteria found throughout orchards. Particularly in years with cold wet winters/springs, the bacteria enter prune trees -- and other stone fruit and almonds -- damaging scaffolds (bacterial canker) and buds (bacterial blast). The bacterial blast generally is not a major economic issue for growers. However, canker can spread rapidly and kill trees from the top down. Strangely enough, the rootstock is not affected by the bacteria, and damaged trees often show vigorous sucker growth.
Once the symptoms appear, there is little to be done. Don't remove damaged trees when symptoms first show. The trees may recover.
Bacterial canker is associated with:
- Soil related stress such as acid soils, shallow soils over hardpan, or coarse texture (sandy) soils with nematode (specifically ring nematode) pressure. The bacteria don’t enter the plant through the soil – at least they don’t harm the rootstock, but soil stresses predispose the tree to above ground infection.
- Low soil nitrogen availability
- Pruning during wet, cool weather.
- Rootstock selection. M2624 is most sensitive to bacterial canker, although M29C is susceptible as well. M40 is reported to be the rootstock that is least susceptible to bacterial canker.
What can be done to avoid bacterial canker?
- Avoid soil stresses listed above, wherever possible.
- Spot fumigate to control nematodes in coarse texture (sandy) soils
- Maintain adequate soil nitrogen levels
- Prune in late summer/early fall or late spring
- Plant on M40 rootstock
Also, Jack Dibble, retired UCCE entomology specialist, told me that, in his experience, trees with bacterial canker pressure showed dormant oil burn more readily than trees not under pressure from bacterial canker. If your block is at risk from bacterial canker (sandy soils, low N levels, nematodes, etc.), consider avoiding high dormant oil rates.
Prune trees showing bacterial canker symptoms (scaffold collapse, gumming). Sutter Co. April 8, 2011
Prune buds damaged by bacterial blast.
