- Author: Franz J.A. Niederholzer
As I write this, early bloom is just beginning to show in some prune blocks in the Yuba City area. Even though it has been a relatively dry winter, there is rain predicted starting this weekend (Mar 10-11) or early next week, so growers should prepare to protect their crop from disease at bloom -- especially brown rot.
When crop stage and weather indicate there is a need to protect a crop, make sure to rotate between different pesticide classes to reduce the risk of fungicide resistance developing in a disease population in your orchard. Using different FRAC (Fungicide Resistance Action Committee) group pesticides -- pesticides that use different modes of actio on disease organisims -- is the best way to manage fungicide resistance in your orchard. See the tables below for details on timing, relative resistance risk, and efficacy of many pesticides registered for prunes. The FRAC group or groups in a particular fungicide product are listed on the first page of the label.
In wet bloom weather, UC recommends a two spray program for blossom brown rot control -- once at green bud and once at full bloom. The full bloom spray is the most important, although the green bud spray should be included as well. At full bloom, include a captan or chlorothanil (Bravo, etc.) material for russet scab control. As stated above, alternate between FRAC classes with each application. For example, for blossom brown rot control, you could use Vangard (FRAC Group 9) at green bud and Tilt/Bumper (FRAC Group 3) at full bloom. In a wet year at full bloom, combining two fungicides in the tank -- one for brown rot and one for scab management (for example, Tilt + captan) -- is the best approach. Captan and chorothanil are effective for scab control, but only mediocre brown rot materials.
In a dry bloom season, research by Dr. Jim Adaskaveg, UC Professor of Plant Pathology at UC Riverside, has shown that effective brown rot control can be acheived with a single bloom spray at 50-70% bloom. This year is not shaping up to be a dry bloom. Hopefully that will help with fruit set!
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Table 1. Examples of general effective timing, resistance risk, relative efficacy, and target diseases of different FRAC group fungicides (alone or as mixtures) available to prune growers in California at the beginning of bloom, 2012. Low, medium, and high resistance risk groups are listed under “Low RR”, “Med RR”, and “High RR”, respectively. Stars after each mixture indicate relative efficacy of the product(s) – limited and erratic (*),moderate and variable (**), good and reliable (***), and excellent and consistent (****). See Table 2 for product names to match with FRAC numbers listed here. Consult with your PCA for specific fungicide application rates and timing(s) for disease control in your orchard. The information in this table is drawn from Efficacy and Timing of Fungicides, Bactericides and Biologicals for Deciduous Tree Fruit, Nut, Strawberry and Vine Crops, 2011.
|
Disease |
Green bud |
White bud |
Full bloom |
May |
June |
July |
|
Brown rot |
Low RR 2(+oil)**** Med RR 3/9**** High RR 3**** |
Low RR 2(+oil)**** Med RR 3/9**** High RR 3**** |
Low RR 2(+oil)**** Med RR 3/9**** High RR 3**** |
|
Med RR 3/11**** High RR 3****
|
Med RR 3/11**** High RR 3****
|
|
Lacy scab |
|
|
M4*** |
|
|
|
|
Rust |
|
|
|
Low RR M2** Med RR 3/9*** 3*** |
Low RR M2** Med RR 3/9*** 3*** |
Low RR M2** Med RR 3/9*** 3*** |
Table 2. Examples of FRAC groups (2, 2, 9, etc.) and FRAC group combinations (3/9, 3/11, etc.) available to prune growers in California at bloom, 2012. Always read the label before applying pesticides. Consult with your PCA regarding spray timing, rates, etc. Not all generic products available in the market are listed in this table.
|
2 |
3 |
3/9 |
3/11 |
7/11 |
9 |
11 |
17 |
M2 |
M4 |
M5 |
|
Rovral |
Tilt/Bumper |
Inspire Super |
Adament |
Pristine |
Scala |
Gem |
Elevate |
Sulfur |
captan |
chlorothanil |
|
|
Elite/Tebuzol |
|
Quadris Top |
|
Vangard |
Abound |
|
|
|
|
|
|
Indar |
|
Quilt Xcel |
|
|
|
|
|
|
|
|
|
Quash |
|
|
|
|
|
|
|
|
|
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The best single source for information on disease management tool efficacy and timing in California deciduous tree and vine crops is Efficacy and Timing of Fungicides, Bactericides and Biologicals for Deciduous Tree Fruit, Nut, Strawberry and Vine Crops, 2011 written by UC researchers/advisors J. Adaskaveg, D. Gubler, T. Michailides, and B. Holtz. Please follow the hyperlink in the title above to view this excellent, free document.
BloomFungcides.2012
- Posted By: Franz J.A. Niederholzer
- Written by: Franz Niederholzer
San Jose scale is a small, slow moving insect that can cause significant, long term economic damage to prune orchards. The orchard in the picture below was removed shortly after the picture was taken due to extensive scaffold damage and loss of bearing wood caused by a buildup of San Jose scale.
Scale populations build slowly over time, so an annual scale “checkup”– and treatment when necessary -- can avoid this kind of damage. Especially if you have been following an “aphid only” dormant spray program of a pyrethroid (Asana®, Warior®, etc.) only or pyrethroid plus less than 2 gallon of oil/acre, a program that will not control scale, check your orchard for scale this winter.
Dormant spur sampling – done by the grower or PCA – is the annual scale checkup. The timing for this key part of an overall prune orchard management program is now through January.
Details on how to take a dormant spur sample and how much scale is enough to recommend a spray treatment are found by calling your local University of California Cooperative Extension office or on the internet at: http://ipm.ucdavis.edu/PMG/r606900511.html.
If San Jose scale shows up in the dormant spur sample, the best time for a control spray is before bloom. A high oil rate (4-6 gallons/acre) applied in the dormant (good) or delayed dormant (best) timing is enough to control low to moderate San Jose scale populations. The oil smothers the pest. The higher the oil rate, the better the control. If the San Jose scale population is high in an orchard (more than 20% of spurs checked show live scale) then oil plus a pesticide labeled for San Jose scale (Seize WP, Centaur, diazinon, etc.) will be needed. Consult with a PCA when deciding what pesticide(s) to use.
A dormant spray with a high rate of oil has the added benefit of advancing prune bloom several days. How many days? That depends on the year and is impossible to predict.
Finally, the higher the spray volume per acre, the better the scale control. If you have a real problem and want to get the best control, use 400 gallons per acre (gpa) of spray volume and spray in the delayed dormant period. Spraying in the dormant period with 100 gpa gives good control, but not great control.
Don’t let scale sneak up on you. Schedule your scale checkup now.
- 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.
- 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.
