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Healthy Fruit 2009 Vol. 17:8

May 26, 2009

Current (through May 25) degree day (DD) Accumulations

Location: UMass Cold Spring Orchard (CSO), Belchertown, MA

  • Base 43: 718
  • Base 50: 407
  • Plum curculio model: 167 (Base 50 from petal-fall, 05-11-09; 308 is the 'end')

Significant upcoming orchard events based on degree days (Base 43):

  • codling moth first flight peak: 593–1017
  • obliquebanded leafroller pupae present: 601–821
  • lesser appleworm 1st flight peak: 347–739
  • spotted tentiform leafminer 1st flight subsides: 666–944

The way I see it

Apple fruits are generally approaching 15 mm in Belchertown. Hopefully most of you got your thinning sprays on last week. The current weather is not particularly good for thinning, although warmer weather is predicted for the weekend and that may be a good time for a last chemical thinning shot if necessary. Peaches are entering shuck-split and become susceptible to insect injury (plant bug) at this time. The first sweet cherries are just three weeks away from harvest. In fact, they are starting to turn red already! That's the way I see it, although there is more below.

J. Clements

Cabrio and Endura supplemental labels for stone fruits

According to Gar Thomas of BASF Technical Services, Cabrio and Endura have received supplemental labels for 2009 ONLY on stone fruit to control primarily (cherry) leaf spot and brown rot. The active ingredients -- pyraclostrobin in Cabrio, boscalid in Endura -- are the same as in Pristine, which is in very short supply. Thus, the two can be substitured for Pristine, which is a good stone fruit brown rot rotational fungicide. According to an e-mail from Thomas, "Please be crystal clear with growers that they should tank-mix use of both these products. Doing the tank-mix will optimize disease control and Mode-of-Action stewardship practices that are realized with the Pristine premix. Each label has a single use rate and when used as a mix will deliver the same amount of boscalid and pylaclostrobin found in 14.5 oz/A of Pristine."

J. Clements

Apple scab season almost over

The degree-day model predicts all ascospores have been released for most Massachusetts orchards. Unless you are 100% comfortable with your apple scab control program to date, you will want to maintain some fungicide coverage through this current cool, rainy period. The we'll be done June 1. (Big surprise, pretty average.) It seems to have been a pretty easy scab control year, but no doubt some will show through where coverage may have been inadequate and you will want to keep an eye on that. Hands-down, Captan is the logical fungicide choice now until we are completely out-of-the-woods.

J. Clements

Plum curculio season half-over

In Belchertown, we are about half-way through the degree-day accumulation model (see current DD accumulations above) that predicts the end of plum curculio season. (As long as insecticide coverage is maintained through that date.) I expect there was some activity last weekend. The current cool weather will slow things down, but the next warm-up with rain and/or humidity will "bring them on." Be prepared with good insecticide coverage when that happens. (Consult the 2009 New England Tree Fruit Management Guide for specific insecticide recommendations.) Border-row sprays might be enough, but I am not sure I would take the chance.

J. Clements

Sprayer 'testing' program to begin

I have finally assembled all the parts and the ability to transport some specialized equipment that will allow us to 'inspect' the performance of airblast sprayers. This, thanks to a Region I EPA grant. The sprayer 'test bench' includes a nozzle flow tester, and 'patternator' that visualizes the spray pattern produced by the sprayer. I can begin to come around and run your sprayer through the test bench at your convenience, the objective being to make sure the sprayer is performing the way you think it is, and to provide some guidance to optimize it's performance and reduce the potential for off-site drift. The whole procedure should only take a morning (or afternoon) of your time. If you are interested, please let me know and we will set up a date.

J. Clements

Fire blight -- has it made an appearance?

It has been a bloom season of very close calls with fireblight depending on your location and stage of bloom. You can see a chart of the relative fireblight risk at Belchertown here. I would not be surprised to see some fireblight given the increased prevalence of this disease here in Massachusetts. If you start to see any fireblight in spurs or shoots now, don't panic, but do take it very seriously. I thought this advice from David Rosenberger of Cornell's Hudson Valley Lab to be particularly useful if you are now seeing any fireblight in apples. I have reprinted it here from Mike Fargione's daily grower e-mail of 05/27/09:

J. Clements

  • Prune out infected limbs as soon as symptoms are seen. Failure to do so increases the likelihood that blight will continue to spread. Trees must be examined at least two or three times weekly. It may be more cost-effective to immediately remove entire trees (especially on susceptible cultivars like Gala) if trees are severely affected.
  • Cuts should be made at least 12 inches below symptoms. Sterilizing pruning shears between cuts may be impractical. Instead, make all cuts into at least 2-year-old wood and leave "ugly stubs" by cutting branches between nodes and at least several inches away from the central leader. Small cankers that form on these stubs can then be removed during winter pruning.
  • If rain is predicted during the period of pruning, one must weigh the risks of spreading blight by pruning in wet weather versus the risks of giving the epidemic a full week, or even a two- or three-day head start. With highly susceptible cultivars like Gala, it is probably best to remove blight as quickly as possible, even if that means that some removal would be done in less than ideal weather.

    In orchards with fire blight, growers should implement management practices that promote early cessation of tree growth. Withholding irrigation and delaying orchard mowing (so that the ground cover competes with trees for water) can help to shut down tree growth. No additional nitrogen fertilizers should be applied in orchards with active fire blight. Allowing trees to carry a heavier-than-normal crop can also help slow growth and reduce the spread of fire blight.
  • Streptomycin sprays should NOT be applied during summer because summer applications will result in rapid development of streptomycin-resistant strains of the blight pathogen. The only exception is growers should apply streptomycin (2 lb/A along with Regulaid or another good spreader) ASAP after hail damage in blocks where blight was present and in adjacent upwind blocks. Effectiveness of strep is greatly diminished after 24 hr from the hail event (there probably is no point in applying strep beyond 48 hours after trauma events like hail). The 2 lb/A rate is higher than the standard rate recommended during bloom, but trees have much more foliage to cover at this time of year than they do at bloom, and getting the streptomycin to penetrate injured leaves and fruit is essential for maximum effectiveness. The preharvest interval for streptomycin on apples is 50 days. The risk of hail-induced trauma blight is relatively low if apple shoots are not actively growing, so mature orchards with a full crop should not need a strep spray if hail occurs after terminal buds are set.
  • Apogee applications are not effective for blight control if the first spray is applied only after the first blight symptoms appear. Copper applications during summer have not proven effective and may cause unacceptable fruit russetting.
  • Hand thinning or bud pinching while blight is active in the orchard should be avoided until after terminal bud set.
  • There is data suggesting potato leaf hoppers (PLH) might spread fire blight after bloom, although details remain to be worked out. The proven approach for controlling PLH will involve traditional insecticides such as Provado. However, the possibility that sulfur applied to control powdery mildew might also assist in suppressing fire blight is a hypothesis worth testing in research trials. Pruning out fire blight strikes as they appear is still recommended whenever removal by pruning is feasible.