April 25, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, April 25 2017, 8:00 – 9:00 AM
Guest speaker: George Sundin, Professor of Plant Pathology, Michigan State University
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

April 25th Call Stream: CLICK HERE

Regional update
Across southern Wisconsin and northern Illinois Zestar and Idared began bloom near April 20th.  Most cultivars in this area are currently at full pink.  Orchards further north, e.g. La Crosse, Twin Cities and Chippewa Falls, are at early pink on the earliest cultivars.  Above normal precipitation for April across the region has resulted in multiple wetting events since bud break, however at numerous locations these rains have resulted in only one scab-infection period since McIntosh green tip.  A long, favorable fall and mild winter have resulted in very robust bud appearance.  We may however be seeing some instances of winter injury in cultivars such as SnowSweet with lower chilling requirements.

Early season disease management with Dr. George Sundin, Professor of Plant Pathology, Michigan State University

How much of a concern is introducing a fungicide-resistant strain of apple powdery mildew when planting new trees?

  • Powdery mildew resistance is difficult to study since it cannot be grown in the lab. There is always a chance of introduction of new diseases on trees, yet there is less discussion on powdery mildew coming in on new trees compared to fire blight.
  • Too reduce resistance concerns when targeting powdery mildew it is recommended to not make more than two sequential applications of one mode of action before switching to a different mode or action. Sulfur is a broad-spectrum protectant and may be tank mixed with sterol inhibitors (DMIs) or strobilurins (QoIs) for added protection and resistance management for powdery mildew.

Incidence of cedar apple rust was high in some locations in 2016.  This is perhaps explained by the warm and wet weather during and after bloom that is favorable for rust infection.  Given the requirement for an alternate host to complete the disease life cycle of this pathogen, does last year’s prevalence predict anything about inoculum levels this year?

To date many orchard soils have remained at or near saturation since bud break.  At what point should we become concerned about “wet feet” given that some of the newer rootstocks have unknown tolerance for root-rot pathogens, e.g., Phytophthora cactorum?  How early can Aliette (aluminum tris) or one of the other Group 33 fungicides, e.g., Phostrol (phosphorous acid), ProPhyt (potassium phosphite), be usefully applied to foliage for this disease complex?

  • Michigan does not have many issues with Phytophthora, especially on good sites as the soils will dry out eventually. Sites with heavy soils and poor drainage are more of a concern.
  • When tree roots are submerged in water and go without oxygen, root rots can begin to die in as little as three weeks. If this happens several times per season, there could be a significant amount of root damage to trees.  Once this cycle of root decay begins, it invites a whole series of other pathogens which can injure the tree.  Improving the soil drainage needs to be the number one priority.

Fire blight management
Many growers have had in excess of three inches of rain since applying copper, yet we are only just approaching bloom.  Has the copper then had no significant impact on fire blight inoculum?

  • Three inches of rain is the benchmark for complete wash off of copper residue. Unfortunately this means the dormant/delayed dormant application is all gone and will have no effect on any fire blight bacteria coming out of cankers.  It’s a risk we take every year when making this application.

Host-plant defense inducers and bio-fungicides: We have yet to document streptomycin resistance in fire blight (Erwinia amylovora) in Wisconsin, however growers concerned about resistance development are alternating with materials such as Actigard (acibenzolar-s-methyl) or Mycoshield (calcium oxytetracycline).  Your recommendations?

  • Organic growers have three primary materials, Serenade Opti (Bacillus subtilis), Blossom Protect (Aureobasidium pullulans), Cueva (copper octanoate). Serenade Opti does not kill the bacteria, rather it inhibits growth and provides 50% less control then streptomycin.  Serenade has utility, and should be fairly effective, in a commercial orchard (conventional or organic) if pressure is low to moderate, i.e., Maryblyt model’s EIP (epiphytic infection potential) is between 30 and 60.  Blossom Protect is a yeast that is supposed to outcompete the pathogen on flower or block nectaries openings to prevent bacteria from entering.  Has had good success with Blossom Protect, yet there are two main issues that reduce its utility in our region: 1) can cause fruit russeting; 2) in conventional sense it is sensitive to most fungicides applied for scab.  Cueva effective for fire blight, yet rate on label is too high (results in russeting at high rate).  Cueva has greater utility in western US where they can spray in low humidity, in Midwest with higher humidity results in fruit finish issues.  Reducing the rate of Cueva to 1 QT per acre is a good start to still get decent control.
  • Streptomycin is still the best material for fire blight if you do not have resistance and if used judicially, i.e., two to three timer per year, resistance is not likely. Resistance to streptomycin stems from growers making multiple applications throughout the season.  If you are able to limit use, there is no need to alternate to another option, i.e., Kasumin (kasugamycin), Mycoshield (oxytetracycline).  During bloom if the Maryblyt model EIP reaches 70 use streptomycin.  Note: During extended bloom, and ideal conditions, all materials targeting fire blight need to be applied more frequently.  Under severe conditions for the pathogen two consecutive applications during bloom may be warranted to get best control.  No material can completely keep the fire blight pathogen in check.  For more information visit: A primer for Streptomycin, Kasumin, and Oxytetracycline use for fire blight management, May 6 2015, George Sundin, Michigan State University Extension, http://msue.anr.msu.edu/news/three_antibiotics_available_for_fire_blight_management_during_bloom
  • Actigard is a plant-resistance inducer and when applied will stimulate general resistance response in plant. Actigard is still in the testing phase, inconsistent results (some years with good results, some mixed), and has potential yet is not a replacement for streptomycin.  The effect is stronger when spraying leaves when the shoot tip is becoming infected and may have greatest utility in high-density orchards where growers do not want to spray Apogee.  Actigard is much more effective than the phosphorous acid materials, e.g., Phostrol, and Regalia (extract of Reynoutria sachalinensis) for fire blight control.

Streptomycin rate per acre versus concentration, e.g., 1.5 lb./acre vs. 8 oz/100 gal.  Typically for blossom blight, streptomycin is applied at 1 lb. per acre and tank mixed with 1 pint Regulaid.  Should we alter this?  Many, but not all, growers apply streptomycin during bloom with 100 gallons water per acre.  If a grower applies the same rate per acre but with less water, how quickly can efficacy drop?

  • Applying a higher rate per acre (1.5 lb./acre) insures that you are delivering enough material to the trees. Tank mixing Regulaid with the streptomycin application does help, but does not alter rate of streptomycin.  Where fire blight pressure is high, applying a higher rate of streptomycin will be more effective at knocking populations down.  You are not completely eliminating the fire blight, rather you are eliminating individuals (it’s a numbers game).  If the gallons of water applied per acre is lower, maintain streptomycin rate; if Regulaid is used the rate needs to be adjusted (Regulaid is treating water, streptomycin is treating trees).
  • If the EIP is outrageously high during bloom, e.g., >200, it is still reasonably fine to focus on most sensitive varieties, than treat less susceptible cultivars. Coming out of blossom blight, shoot blight can spread more easily into less susceptible varieties.

Plant growth regulators
Can you review best practices for reducing shoot blight with Apogee (prohexadione calcium), e.g. single vs. multiple applications?  Additionally the chart on page 259 of MSU’s Fruit Management Guide suggests a season total application of 17 oz per acre Apogee for small trees, considerably less than the 36 – 48 oz. recommended elsewhere.  Given the variability of tree vigor, crop load, and varietal sensitivity, please explicate as possible?

  • Three applications are recommended, with the first beginning at the king bloom petal fall stage (or full bloom). This application can be tank mixed with antibiotics or Serenade.  It takes 10 to 14 days for the Apogee to take effect (shoot growth and fire blight control), then make two more applications at two week intervals; a fourth spray might be necessary during a wet season.  If season is dry the risk of infection is low.  Shoot blight right after bloom needs to be controlled immediately, early shoot blight will continue to drive continued infection.
  • George is investigating how low you can go with rates to still get control, especially for use in young high density orchards. Growth over five-year period is 20-30% less, yet yields were not that much less.
  • Lower rates can be used for young dwarf trees. If you want to maximize Apogee effect on larger trees go with higher rate.  For more information visit, Apogee application time in apples, May 24 2016, Nikki Rothwell and Phil Schwallier, Michigan State University Extension, http://msue.anr.msu.edu/news/apogee_application_time_in_apples

Organic scab management
Bio fungicides and host-plant defense inducers – None of these “biological” products are listed in the Fruit Management Guide in the apple scab control section, conversely several are mentioned in the fire blight section.  Does this reflect differing efficacy results from your research trials?  I have suggested that organic growers with limited options begin using some of these products around tight cluster when sufficient leaf area exists to colonize or absorb.  How would you use any of these products in organic scab control?

  • George has not had success with the biologicals that he has tested since it is not possible to get biological to grow on tree like a blanket to protect tissue from infection. Need to have coverage from biological, long season with a lot of green tissue.

How would you best employ lime sulfur in scab management, i.e. post infection period or as protectant? Note: With the high number of robust flower buds on most cultivars, and moderate temperatures forecast for bloom, this seems to be a good year to make use of this phytotoxic fungicide.

  • George does not have much experience with lime sulfur in scab management. Sulfur is a good choice and copper (as much as you can stand).

Although Syllit (dodine)-resistant apple scab (Venturia inaequalis) is considered common here, it is not universal; its reduced cost per acre has made its use more attractive.  What is the rationale for MSU’s Fruit Management Guide recommendation that Syllit be used in the first two fungicide applications of the season?

  • The manufacture changed the label several years ago, and it can no longer be applied after pink. Syllit has utility if it has been a really wet season and missed an infection.  Other good options include the CaptaZeb strategy (captan tank mixed with mancozeb) or Vangard (cyprodinil) or Scala (pyrimethanil), tank mixed with a protectant.

What is the status of the SDHI fungicides in Michigan?  Is it known if apple scab resistance is likely to be qualitative or quantitative?  Why does the Fruit Management Guide recommend a half rate of a multi-site protectant when tank mixed with SDHI’s but a full rate if any other single-site fungicide is being used?

  • Scab control has been really successful with SDHIs, e.g., Aprovia (benzovindiflupyr), Fontelis (penthiopyrad), Merivon (fluxapyroxad, pyraclostrobin), Luna Sensation (trifloxystrobin, fluopyram). Currently, George is more focused on the single-active ingredient SDHIs, i.e., Fontelis, Aprovia, Sercadis (fluxapyroxad), since the strobilurin component (in the premixes) is not effective in Michigan where they have resistance.  All SDHIs should be identical in performance, yet Aprovia is best in very high pressure test orchards.  George anticipates resistance will occur eventually and will likely begin with the first generation materials, e.g., Fontelis.  At the moment, everything is safe as long as they are tank-mixed with a protectant.
  • Recommend to tank mix all sing-site fungicides with a half rate of a protectant. Protectant is there to kill any fungus that has potentially developed resistance.  If a higher rate of protectant is used you will get a better spore kill under high pressure.

Efficacy of fluazinam: Wondering about Syngenta’s expanded label for Omega 500.  Have you trialed it against apple diseases?  If it is an effective scab protectant how is it best integrated to slow resistance development to SDHI’s, e.g. tank mixed with mancozeb or captan, or with another single-site fungicide?  Does this fungicide penetrate the cuticle and become translaminar and/or locally systemic?

There is some question about its propensity for resistance development – FRAC seems to say it has some multi-site behavior (even as only a Group 29).  My understanding is this is so because ox-phos rxns involve multiple trips (electron transport) across the mitochondrial membrane, utilizing a number of different carriers, and fluazinam is able to block multiple carriers.  Interested in your opinion and experience.

  • Omega 500F (fluazinam) is supposed to be broad spectrum but is not a good fruit scab material in a high pressure scenario. Because of this, it does not provide attributes that we are looking for in alternatives.

Rapid apple decline or sudden apple decline: Dr. Patty McManus will be discussing this complex on our May 9 conference call.  It would be helpful however to have your observations from Michigan.

  • Rapid apple decline (RAD) or sudden apple decline (SAD) has captured the news, but George has not observed it in MI. In Ontario saw some fire blight and rootstock blight.  George suspects that most RAD might be rootstock blight since it is difficult to culture pathogen out of rootstock.  Does not think that this is the next big thing that will kill a lot of trees.  Fire blight can enter the rootstock at infection through suckers or at wounds at rootstock, e.g., black stem borer.  Rootstock blight may not show symptoms at top of tree since infection entered at the bottom of the tree.
  • Sudden Apple Decline: Trunk-Related Problems in Apples, David Rosenberger, Professor Emeritus, Cornell University’s Hudson Valley Lab http://www.hort.cornell.edu/expo/proceedings/2017/TreeFruitPestMGMT.AppleTrunkDisorders.Rosenberger.2017.pdf

Insect update

Insect management
Historically, it was common to apply a pink spray of a synthetic pyrethroid for spring lepidoptera, spotted tentiform leafminer, tarnished plant bugs and aphids.  However, this application comes at a cost by negatively impacting important beneficial insects and being toxic to pollinators.  Growers practicing IPM have found that after eliminating a pink spray, it is rare to see economic damage from these pests.

Growers with high-density plantings and young trees have begun to express more concern about spring lepidoptera stunting terminal growth and causing some fruit injury, most notably green fruitworm.  We will begin to observe these spring lepidoptera as warm temperatures return during bloom.  Necessity to manage these populations need to be confirmed through scouting terminals and blossoms.  We are beginning to see evidence of light feeding activity in fruit clusters, yet have only found a few live larvae.  If populations are confirmed, applications of Bacillus thuringiensis (Bt) may be applied between tight cluster and bloom.  Bacillus thuringiensis is non-toxic to pollinators.  These products include Agree, Deliver, Dipel, and need to be applied when larvae are small (tight cluster through bloom).  By the time we reach petal fall, these insects have completed much of their feeding and an applications of Bt may not be effective.

It is essential to scout for larvae following the first application of Bt, as an additional application may be needed (early petal fall).  Note: Bt must be eaten by the insect to be effective, and warm temperatures are needed in the 72 hour period following an application for good mortality.  As with most insecticides, young larvae are generally more susceptible than older larvae.  Early detection of a pest is critical for good control.  The spray deposit may only last one to three days before it is washed off by rain or broken down by sunlight.  Sticker substances that promote adherence to leaf surfaces and UV light inhibitors that protect Bt from photo-degradation may enhance efficacy.  For more information on application timing and use of Bt products visit http://nysipm.cornell.edu/organic_guide/apples.pdf.

Intrepid (methoxyfenozide) is an insect-growth regulator that only works on lepidoptera and does not have effect on honeybee larvae.  It is not recommended to apply Esteem (pyriproxyfen) during bloom.

European red mite
Healthy European red mite (ERM) eggs and six-legged nymphs are being found on cluster leaves.  Oil would still be effective if applied before bloom.  Use caution when using oils at full pink.  Continue to monitor these populations.