May 19, AppleTalk Call Summary

AppleTalk Conference Call Summary
Tuesday, May 19, 2015, 8:00 – 9:00 AM
Guest speaker: George Sundin, Michigan State University, professor of plant pathology
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

May 19th Call download: Click Here

Agenda
– Regional crop phenology
– Plum curculio
– Codling moth
– Preserving beneficial insects
– Q&A with George Sundin, Michigan State University, professor of plant pathology

Regional pest phenology

Plum curculio
Plum curculio (PC) movement into the perimeter of orchards begins when temperatures are above 60°F. This is a gradual process, as PC are primarily nocturnal and the entire population does not migrate into the orchard at the same time.

Growers who already applied a petal fall insecticide for PC should expect about two weeks of efficacy from insecticides, pending no significant rain fall. The forecast does not show temperatures that will speed up migration or rainy weather that will degrade efficacy of insecticide.  Growers should begin scouting the orchard borders and interiors towards the end of the effective life of the insecticide.  A perimeter application may be applied seven to ten days following a petal fall insecticide, if injury is found or to prevent the further migration of PC into the orchard.  This year, because of low temperatures, PC management may need to be extended for a longer amount of time and may overlap with codling moth control.

We can use a degree day model from 95% McIntosh petal fall to predict the end of PC migration from overwintering sites. It is expected that after 308 degree days, base 50°F, PC will no longer be moving into orchards from overwintering sites.  If no additional injury is found at this time, insecticide applications should be ceased.

If you have not applied a petal fall application, using a perimeter application may be a useful tool even if you are planning to apply a cover a later time.

Organic orchards have the option of applying Surround (kaolin clay) to the orchard. Another strategy is to leave trap rows of early varieties, without surround, that would be targeted with an insecticide, e.g., PyGanic.  An insecticide can be applied during warm nights when PC are active.

Codling moth
Cool weather has slowed down codling moth (CM) emergence and based on degree day accumulations across the region we expect flights anytime. Some growers who had warm temperatures from May 15 to May 18, may have had a CM flight.  Traps should be checked every several days to determine an accurate biofix.  Biofix is our first sustained flight, where we capture moths multiple days in a row.  Begin keeping track of degree days accumulated from biofix.  Codling moth fly between 6-11 pm and will not fly when wind is in excess of 3 mph, temperatures are below 62 F or if it is raining.

Proteoteras is genus of moths belonging to the Tortricidae Codling moths are also in this family, hence some similarities in appearance, but belong to the genus Cydia.  Proteoteras has a similar wingspan, but is slightly narrower and lacks the bronze coloring on the wing tips of CM.

Spotted tentiform leafminer
Spotted tentiform leafminer (STLM) was at one time a significant pest of apples and occasionally is seen at economically damaging levels in orchards. Growers using advanced IPM tend to not have problems with this pest because of parasitic wasps which exist in the orchard.  These parasitoids have proven to be very effective biological-control agents, especially when pre-bloom insecticides are not applied.  Insecticide sprays applied to the perimeter or as an alternate-row spray for PC, are good examples of how we can conserve these beneficial organisms, while protecting the crop from more economically damaging pests.

Q & A with guest speaker George Sundin, Michigan State University

Class VII (SDHI) fungicides

Do you recommend tank-mixing with full, or partial rate/acre of EBDC or captan, i.e., do you anticipate that if they’re used with full rates of protectant Venturia will remain susceptible longer?

  • SDHI options for growers include Merivon (pyraclostrobin, fluxapyroxad), Luna Sensation (trifloxystrobin, fluopyram), Luna Tranquility (pyrimethanil, fluopyram) and Fontelis (penthiopyrad) and next year there will be two new SDHIs available.  These all are slightly different compounds with different spectrums of activity.  Resistance will be very complex, e.g., resistance may appear to one compound, but not always the others and could be specific to individual orchards.  In Michigan we have resistance to strobilurins, e.g., Flint (trifloxystrobin).
  •  Growers should continue to use a partial rate of EBDC or captan in the mix.  In Michigan there were resistance issues with half rates of EBDC and strobilurins, where the interval was extended too long between sprays.  Currently, there is no science to support more than a half rate of a protectant fungicide.
  •  However, tightening intervals and increasing rates of protectant will help ensure good coverage and kill the pathogen.  The best way to protect against resistance is to eliminate the pathogen in the orchard.
  •  Protectants redistribute in the rain and SDHIs will move into the growing leaf.  SDHI’s will penetrate into the leave and move within the leaf and if the back side of the leaf is covered, it will move to the front and throughout the plant tissue.  Think about the target, if the leaf is just emerging and is small, it will not catch the fungicide when applied.  When the leaf is half of its full size, you will get enough fungicide to cover the leaf as it expands.

How do you recommend their use, once, twice or more during primary release?

  • Two applications is the recommended use.  Strobilurins have a life time, e.g., 20 applications and you have resistance.  We are concerned we don’t know the exact number of applications, before resistance will develop to the SDHIs, so two applications per year for ten years is better than having it only last five years or less.
  • Many growers have likely made 20 applications of some type of a strobilurin. 

Do we need to differentiate between Flint and Sovran (kresoxim-methyl)?  

  • In this case the strobilurins will act the same and resistance can be masked.  The first year strobilurin resistance was documented in Michigan, it showed up only in McIntosh.  Therefore, resistance can be hidden in low scab years and then explode during a year of high-scab pressure.

Can we select out strobilurin resistant scab through rotation? 

  • It would be possible if we are getting really good control and killing everything in the orchard, but not likely to happen.  The strobilurin-resistant strains seem to be very stable and not likely to be replaced by susceptible pathogens.
  •  Growers need to apply fungicides before the infection period, so spores are killed before they even germinate.

Do you recommend SDHIs not be used beyond petal fall for management of powdery mildew and summer diseases – but instead use the strobilurins or DMIs against these pathogens?

  • Strobilurins are still very effective against powdery mildew.  Flint should still offer good control and the combination products, e.g., Merivon and Luna Sensation manage powdery mildew better than Fontelis and is likely the strobilurin in the pre-mix that is working on powdery mildew.
  •  Flint, Sovran, Topguard (flutriafol), Rally (myclobutanil), are all great options for powdery mildew.  Let’s not apply fungicides with good scab susceptibility, past primary-scab season for powdery mildew.  

Do we know the likely type of resistance Venturia inaequalis will develop against this class (qualitative or quantitative)?

  • Fontelis is a first generation SDHI and is similar to the boscalid in Pristine (boscalid, pyraclostrobin).  We would expect resistance to happen first to this first-generation SDHI.  Luna Sensation and Merivon are second generation.  If we develop resistance to Fontelis, we would expect the Luna Sensation and Merivon to continue controlling scab.  Taking resistance management seriously is going to be important because we are not expecting many new chemistries to emerge, in the next few years.  

Considering the question from above, is there a biological reason to use the highest labeled rate of a material such as Fontelis, rather than the 16 oz./A we’ve been recommending in a tank-mix?

  • The MSU test orchard have McIntosh, a highly scab susceptible variety and have very high disease pressure.  We do this to separate the best, mediocre and worst products and can differentiate on rate.  We have seen differences in performance based on rates.  This difference is not great, but is statistically significant, i.e., we may see a 3% vs. 6% difference in scab control.  A concern is the lower rate can subtract years off the life span of the product.  When cherry leaf spot resistance developed in Michigan to Pristine, we think the lower rate of Pristine being applied by growers drove the development of resistance in just seven years, an amount of time that is too short to lose a fungicide.
  • Growers need to commit to the higher rates to prolong the life of a fungicide.  The scab in your orchard is yours, the spores don’t move that far and are not likely to move scab between orchards.  Unless you are in a region with back to back orchards, we are controlling the populations in our own orchards and you protect your fungus from becoming resistant by using the higher rate.  In a bad scab year we expect to see better control, but hope to not see the difference if inoculum levels are kept low. 

Do you think the evidence for honeybee mortality from pyraclostrobin is strong enough to suggest not using Merivon or Pristine during bloom or Cabrio on stone fruits?

  • Currently we are conducting honey bee experiments with Bravo and Indar.  The study from several years ago in Belgium used field rates and examined pollen collection from bees within the orchards.  The rates seemed realistic and the researchers had a long list of fungicides contained in the pollen.  Most had no effect, some had a positive effect to reduce the pathogen that exists in the gut of the bees and some had a negative effect.
  •  George recommends to not use Merivon during bloom on stone fruits.  It is great for powdery mildew, brown rot and could be used at first cover/shuck split on stone fruits and again for brown rot.  Indar should also still work on Brown rot or European brown rot, but seeing some decreased sensitivity.

Fire blight

When the Maryblyt EIP is >110, after rain, during bloom or after a trauma event, post-bloom, is streptomycin the only antibiotic (of the three registered) that is effective if applied within 24 hrs. post-infection?

  • 2015 has been a very risky year for fire blight because of heat and rain, though parts of MN and WI have not had the heat.  In Michigan we detected bacteria at bloom, even though we did not find any cankers oozing.  The fire blight pathogen, Erwinia amylovora, can divide about ten times or more on an 80 °F day.  A bacteria count of 1 million is enough, especially with bees moving bacteria around, to have a serious infection, when it rains.  
  •  Even if you had dry weather, temperatures in the 70s or 80s may require a streptomycin spray to knock the population back.  This could be advantageous, in the event you encounter conditions when you can’t spray, prior to a wetting event.  While you may not have an infection to the flower because you did not receive rain, fire blight can survive and cause shoot blight.  This is what we suspected happened in the Northeast least year.  Note: Growers with bloom temperatures in the 50s, have nothing to worry about because the populations of fire blight bacteria take too long to multiply and do not build up.
  •  Where growers do not have resistance, streptomycin is better than Kasumin and efficacy between the two materials is about the same.  The difference is streptomycin is systemic.  Streptomycin will control bacteria already on the flower and can work post infection.  If we don’t have streptomycin resistance, there is no reason to use Kasumin.  If streptomycin is used, limit to three applications or less per season, e.g., summer sprays and five applications, increase the risk of resistance.  If we limit these streptomycin sprays, the chance of resistance is very low.  It is not necessary to alternate with Kasumin for resistance management, unless you require more than three applications of streptomycin.  We will also always have the risk of resistance from nursery trees and could bring in resistant fire blight in nursery stock.  If the EIP is above 75 or more, growers can apply streptomycin or Kasumin.  If it is below 75, this is where we can use oxytetracyclene.  At the end of bloom, we can spray streptomycin because of its reach back.  Don’t apply Kasumin post bloom because it is not systemic.  Save streptomycin for a hail storms.  

There are lots of non-antibiotic products labeled for control of Erwinia amylovora during bloom – some Extension recommendations suggest alternating these with an antibiotic. What are your thoughts on the biological rationale for this approach?

  • We are still working with non-antibiotic products, e.g., serenade, to optimize their use.  Serenade will only work on moderate to low pressure fire blight and will never work under high pressure.  In high pressure-scenarios they have only documented 30% control.  The issue with serenade and oxytetracycline is they do not kill the pathogen.  These may control blossom blight, because the flower is only infectable for six days after it opens and sometimes the flower can escape infection.

In an earlier conference call, Dave Rosenberger reported a number of New York growers had employed very low rates of copper hydroxide throughout the season in 2014 to manage shoot-blight in a historically bad year – without significant fruit russeting or phytotoxicity. Similarly, the combined or alternating use of Cueva and Double-Nickel has been suggested for the same purpose.  What are your thoughts on this strategy in both fruited and non-bearing trees.  David Rosenberger had discussed growers with shoot blight during 2014, used low rates of Kocide or about 4 oz. of actual copper ion and found very little russeting in NY.  This supplies about the same amount of copper as Cueva.  Is this something to pursue? 

  • If you’re going to try copper, it needs to be applied under very fast drying conditions.  Russeting is caused by prolonged drying.  The fire blight bacteria is very susceptible to copper and low rates could be helpful.  In the absence of storms, we can have ooze in the orchard and flies and other insects will move bacterial ooze around.  Perhaps the shoot blight could be controlled with a low rate of copper, when a storm comes through the low rates will not work as well and growers are better to apply apogee to increase plant cell wall thickness and develop some host plant resistance. 
  • Regarding the tank mix of Cueva and Double Nickel that was widely used in the Northeast in, we lack data to suggest and recommended its wide spread use.  There is data which suggests it could be a good control, but only have one year of data and really need at least three years of data.  For growers with non-bearing trees, it is worth a shot!

 Using Apogee for shoot-blight control. In 2014 an orchard applied Apogee quite late, after severe symptoms of blossom blight were wide-spread.  Affected trees were mature and on M7 and M26 rootstocks and typically grow significant amounts of wood each year.  After the Apogee application, very minimal shoot-blight developed and expected the trees to be virtually brown by August.  Is this just luck or cause and effect? How likely is this phenomenon to be replicated?

  • Considering the warm weather at bloom and the high fire blight EIP, growers should apply apogee on at petal fall and king bloom.  Apply apogee now to get maximum effect, the best growth effect will be observed when shoots are at one to three inches in length.  Apogee can be spaced out over several week intervals.  If you get shoot blight on young trees, the bacteria can kill the whole tree.  However, often growers do not want to spray Apogee because we want them to grow and establish.  We can reduce rates on the non-bearing trees and the Apogee will wear off and trees will grow again.  Prune out shoot strikes as they occur and throw in row middle and let them dry out before chopping up and removing.  Shoot blights will ooze and we find that it holds lots of bacteria and enough in one ooze drop to infect all the shoots in an orchard.

 Additional resources

May 18, 2015 Scaffolds Fruit Journal
Applying Apogee to apples in 2015, Michigan State University
A primer for Streptomycin, Kasumin, and Oxytetracycline use for fire blight management, Michigan State University