- 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
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: 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.
