May 5 AppleTalk Call

AppleTalk Conference Call Summary
Tuesday, May 5, 2020 8:00 – 9:00 AM
Guest Speaker: Dr. Kari Peter, Penn State
Presenter: John Aue, Threshold IPM, jgaue@mwt.net
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org or send to Josie Dillon, jdillon@ipminstitute.org.

May 5th Call Stream: CLICK HERE

Guest Speaker Schedule

  1. May 19: Dr. Dan Cooley, University of Massachusetts presenting on orchard floor sanitation and apple scab.
  2. June 2: Dr. Brent Short, Trecé presenting on Codling Moth Lures and Mating Disruption
  3. July 14: Dr. Sara Villani, North Carolina State University presenting on Summer Fruit Rots

Regional update

Location Degree Days

(Base 32°F)

 Degree Days

(Base 43°F)

 Degree Days

(Base 50°F)
Eau Claire, WI 534 152 42
Gays Mills, WI 598 196 69
Hastings, MN 614 211 76
Harvard, IL 586 169 54
La Crescent, MN 604 204 72
Mauston (Northwoods), WI 546 149 40
Mequon (Barthel), WI 471 96 30
Rochester (Ela), WI 549 129 37
Trempealeau (Ecker’s), WI 591 184 61
Verona, WI 587 172 50

Table 1. Degree-day accumulations as of May 5, 2020 using data reported by Cornell NEWA Network. 

As we look towards bloom, today’s discussion could be best summarized as follows: If it remains cool and wet, managing apple scab will be the highest priority.  If temperatures are in the mid-60s or higher and it is dry, fire blight will be of greater concern.

Locations to the north, e.g., Eau Claire, Hastings, and closer to Lake Michigan and Lake Superior are behind in degree-day accumulation, and bud development and are at ¼ inch green to tight cluster. With warm temperatures occurring in the past week, many orchards to the south, e.g., Madison, La Crosse, and northern Illinois are now at tight cluster to early pink.

This week will bring cooler temperatures with below freezing temperatures predicted. The forecast continues to change, but regardless, orchards at pink are at a greater risk of crop injury from these temperatures and orchards that are still at tight cluster should fare better.

John spoke with Dr. Amaya Atucha on Monday about this upcoming freeze and she indicated there will probably be an inversion freeze. In an inversion freeze, cooler air pools at the ground rather than mixing with the warmer air above it. The winds forecasted for Thursday and Friday will be light and there won’t be sufficient air mixing, therefore running frost fans may be necessary to prevent freeze damage to trees at pink or bloom. This recent article from Michigan State outlines strategies growers can employ: thttps://www.canr.msu.edu/news/what-can-fruit-growers-do-if-a-freeze-is-coming

Critical temperatures for fruit damage to trees at tight cluster are 27°F for a 10% bud kill and 21°F for a 90% bud kill. If bud growth has reached pink, 28°F will result in a 10% kill and 24°F will result in a 90% kill. If temperatures do drop down below freezing, there is the option to turn on frost fans. If it is windy, the wind will have the same effect. For more information on critical temperatures for bud and blossom development, visit:

Apple scab
During primary scab season, it is important to maintain fungicide cover and reapply on five to seven-day intervals. If a protectant fungicide, e.g., captan, mancozeb, sulfur, was applied over the weekend or on Monday, new tissue growth may be present after seven days. Even with our cool temperatures, trees should be evaluated for new growth at the end of the week. There is a continuous 40% chance of rain beginning over the weekend and continuing through most of next week. Most locations will have reached 40% to 50% ascospore maturity, and depending on how many spores have been released, the next rain may be a significant infection period. Watch the weather forecast and keep a window of two to three days open to reapply fungicides. Next week, we will discuss ascospore maturity and review the scab model in more depth.

Tarnished plant bug
Tarnished plant bug (TPB) feeding was observed on blossoms in southern Wisconsin, though evidence of this damage on flowers is typically hard to see. Feeding damage will cause the flowers to fall off or not develop normally. Early fruit feeding leaves depressions that deepen as the fruit grows and is most noticeable at harvest. Egg-laying damage can be found on the calyx end of the fruit and is typically deeper than fruit feeding damage. The region hasn’t had a serious TPB infestation in the past several years but can be more prevalent when blooming plants and broadleaf weeds are located in the alleyways. Natural enemies will help to limit TPB population numbers and typically are not a big issue for growers. Tarnished plant bug are hard to monitor, as they fly away when disturbed. They may be monitored with white sticky boards or a beating tray.  For more information on TPB, visit: https://ag.umass.edu/fruit/fact-sheets/apple-ipm-tarnished-plant-bug

Spring lepidopteran
Codling moth traps can be hung at any time. Redbanded leafroller (RBLR) traps should already be up, but it is not too late to hang these traps. Obliquebanded leafroller (OBLR) traps do not need to be hung until the first week in June.

Spring lepidopterans emerge between green tip and bloom and should expect RBLR and OBLR larvae to become active soon, even with the cooler temperatures. Redbanded leafroller and green fruitworm overwinter as pupae and emerge as adult moths shortly after green tip. Generally, these moths do not fly very far and will begin egg-laying shortly after emergence. Obliquebanded leafroller overwinter as third-instar larvae and emerge around tight cluster where they feed on floral parts and developing fruit. Larvae of GFW, OBLR, RBLR, spring canker worm and variegated leafroller will feed on growing terminals and blossom clusters as temperatures increase. John visited an orchard on Sunday with 5% open blossoms on Zestar and full pink throughout the rest of the orchard. These trees should have the most advanced insect emergence and only a few instances of lepidopteran feeding were observed.

The insect growth regulators Esteem (pyriproxyfen) or Intrepid (methoxyfenozide) may be applied between green tip and up to bloom. However, Esteem cannot be applied during bloom due to potential pollinator toxicity. Agree, Deliver and Dipel (Bacillus thuringensis), Bt, products are safe to apply when bees are active in the orchard during bloom. If blossoms are still closed a Bt application will not reach larvae that have tunneled into closed blossoms. Bacillus thuringensis 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. Bt products should be applied when it is warm (~60°F) and sunny. If an application is warranted, manage these pests in the early larval stage, e.g., first or second instar, while they are actively feeding on leaf tissue and before trees reach petal fall. After petal fall, these species will be harder to manage since many of them may be nearing the end of their life stage as a larva.

 Resources:

Fire blight biology
Orchards will be at risk for fire blight infections as trees move into bloom. Temperatures above 65°F will lead to rapid bacterial growth. Trees are only susceptible to fire blight infections if blossoms are open and moisture is present. These basic parameters need to be met for an infection to occur: 1) Inoculum or signs of fire blight last year, 2) open blossoms, 3) moisture, and 4) warm temperatures of greater than 65°F. Extended bloom are often caused by cooler temperatures, which lower fire blight risk.

Streptomycin applied 24 hours before or after a fire blight infection will inhibit bacterial growth for up to 48 hours. The fire blight Epiphytic Infection Potential (EIP), which references bacterial growth, should be tracked starting when blossoms open and restarted after streptomycin is applied. Additionally, the EIP drops to zero when temperatures fall below 40°F. If blossoms are closed, there is no risk of infection and streptomycin does not need to be applied. Growers will typically apply streptomycin with 50-60 gallons of water per acre, however, more water will always improve performance of streptomycin. One hundred gallons of water per acre is recommended by manufacturers. Tank mixing with other fungicides is generally admissible apart from captan, which should not be applied with streptomycin.

For a comprehensive discussion on fire blight and cultivar and rootstock susceptibility read Scaffolds Fruit Journal, May 4th, 2020: http://www.scaffolds.entomology.cornell.edu/2020/SCAFFOLDS-5-4-20.pdf

Discussion with Dr. Kari Peter, Associate Research Professor, Tree Fruit Pathology, PennState
Apple scab

  1. Do you have any experience using potassium bicarbonate (Kaligreen, MilStop, Carb-O-Nator) to manage primary apple scab infections in organic systems? We have several organic growers using this product with a good degree of satisfaction, but due to its high cost, errors in its use are both costly to crop quality and to the spray program. Can you make any recommendations on rates and how to best time the application of products like Milstop and Kaligreen? These products offer very little guidance on the label and generally have wide rate ranges.
    • Dr. Peter has two years of data working with Kaligreen from 2018 and 2019. She began working with this product in 2018 after growers in Europe and Canada had good experiences. In Europe growers apply potassium bicarbonate according to the RIMpro, www.rimpro.eu, model which outlines a narrow window for applying the product post-infection. However, this is very hard for growers to accomplish.  Dr. Peter does not follow this model and applies potassium bicarbonate as a protectant fungicide before it rains.
    • In 2018, primary apple scab was not bad in Pennsylvania. Dr. Peter used Kaligreen at 3lbs. per acre and applied before rainstorms. It is important to note that efficacy is limited to scab and powdery mildew. At 3lbs. per acre, Dr. Peter saw 50% scab control on leaves and fruit. This is compared to 80% infection on the control blocks.
    • In 2019, there was a scab explosion in Pennsylvania, however Dr. Peter still saw 40% control with applications of Kaligreen at 3lbs. per acre from tight cluster through first cover. This year, Dr. Peter is looking at applying Kaligreen at 5lbs. per acre using a spreader/sticker.
    • Dr. Peter would recommend applying Kaligreen at 3lbs. per acre up to five times between tight cluster to first cover. From late pink through petal fall, it is okay to spray in the rain if it is very light to keep leaves covered. Treat it like a typical broad-spectrum protectant.
    • If there is a heavy precipitation event that lasts 24 hours, presumably most spores are released within the first six hours of the event. The potassium bicarbonate would be active during this initial spore release before wash-off during a long rain. Additionally, ascospore development will likely be low during the rain after all existing spores have been released.
  2.  Is it possible for ascospore release to occur from leaves with scab lesions still on the tree from last year?
    • Those leaves could be a problem because the leaf tissue is still intact. Scab needs the leaf tissue and organic matter to survive. The primary sanitation method is to break down the leaves and remove them so the spores will die.

Plant viruses

  1. Can you discuss your work on latent tree viruses, e.g., apple stem pitting virus and apple stem grooving virus, regarding their possible role in Rapid Apple Decline (RAD) or Sudden Apple Decline (SAD) or other disorders? What are nurseries currently able to do to reduce viral load & transmission to new stock?
    • Dr. Peter believes that RAD/SAD is caused by a complex of problems which is not fully understood yet, but could include plant viruses, environmental conditions, and herbicide injury. These viruses are likely synergistic. Due to increased technology we have today, scientists are discovering previously unidentified viruses which is adding more complexity and unknowns to understanding how these disorders are occurring. In situations where a tree is weakened and a virus is benign, the virus can still take advantage of the weakened tree. To diagnose trees with disorders like RAD and SAD, scientists are often using the process of elimination.

Fire blight

  1. Most growers in our region are only making between one and three applications of streptomycin per year and avoid post-bloom applications, except for where there has been severe weather that damaged trees. As a generalization, orchards in Iowa, northern Illinois, Minnesota and Wisconsin have not shown symptoms of streptomycin resistant fire blight. Under these circumstances, is rotating use of Kasumin important to mitigating risk of streptomycin resistance?
    • Kasumin is the latest antibiotic that came out a few years ago. Researchers in Michigan and New York have observed good results where Kasumin performed equally to streptomycin. Dr. Peter hasn’t had the same results, and Kasumin did not perform as well as streptomycin. Kasumin is very expensive and has a different mode of action than streptomycin. Kasumin is bacteria static, meaning it arrests the growth and stops the bacteria from proliferating. Comparatively, streptomycin is a true bactericide that kills fire blight bacteria. Kasumin typically works best with Regulaid as a tank mix.
    • Dr. Peter recommends using streptomycin, where fire blight is still susceptible to streptomycin. There is also no advantage to tank mixing streptomycin with Kasumin, as it will decrease the efficacy of both products. To reduce dependency on streptomycin, Serenade (Bacillus subtilis) may be applied at early bloom, which is a bacteria-based product that produces antibiotics through its fermentation. When Serenade is strategically applied during the lowest risk of infection, there has been great results and it is not an inducer of host-plant resistance. Subsequently, when fire blight risk is high, e.g., full bloom, it is not recommended.
    • The environment plays a significant role in efficacy of a product. For example, when Dr. Peter applied Kasumin the same way as Cornell researchers, she got different results. Presumably, it would work for Midwest growers as our environment is more on par with Michigan and New York conditions.
    • If only using streptomycin two to three times per year, the chance of overuse and resistance is very low. Dr. Peter believes spending the extra money on Kasumin is likely not worth it.
  1. There are a variety of new biological products to manage fire blight. Products like LifeGard (Bacillus mycoides) and Actigard 50WG (acibenzolar-S-methyl) are inducers of host-plant resistance which mimic systemic-activated resistance that is supposed to occur naturally in plants. These are recommended to be applied around pink and boost the trees natural immune response to fire blight. Other products like Bloomtime (Pantoea agllomerans strain E325) and Blossom Protect (Aureobasidium pullulans) are to be applied on open blossoms just before an infection period. What have your experiences been with these products used in combination with streptomycin and with no streptomycin? Organic growers would be particularly interested in these products where no strep is used in the spray program.
    • Actigard 50WG is a synthetic product that activates the immune system within the tree. It is relatively expensive at $32 per ounce, but Dr. Peter believes it is worth the investment. The recommended rate is 1-2oz per acre and when applied correctly, it has great results. It takes 48 hours for activation and Dr. Peter recommends applying at late pink mixed with a fungicide spray. At early bloom, Actigard 50WG can be tank mixed with Serenade or streptomycin. It is very effective on younger trees as well. In greenhouse trials, there has been some increased immune system activity even after 10 days from the application.
    • LifeGard a plant-based inducer of host-plant resistance has not had the same effect as Actigard 50WG. Dr. Peter worked with LifeGard for two seasons and is not yet confident with recommending LifeGard. Researchers at Cornell trialed the product for two years and had much better results. This means that the severity of fire blight pressure may have an impact and under lower pressure, it could work. Similar to Actigard, it needs to be applied at least 48 hours before blossoms open.
    • Regalia (extract of Reynoutria sachalinensis) has a lot of utility, though Dr. Peter cautions applications during bloom, that could result in blossom burn. Regalia also turns on the plants immune system and may be of better use on non-bearing trees.
    • Bloomtime is another biological and Dr. Peter believes it doesn’t offer much efficacy.
    • Blossom Protect is a natural yeast and is effective, with as high as 40% fire blight prevention in recent trials. It coats the blossom and prevents the bacteria from entering the nectaries and must be applied when blossoms are open. There can be some russeting on fruit due to the yeast activation. At petal fall this yeast needs to be killed off to reduce russeting risk and can be done by applying OxiDate (hydrogen peroxide, peroxyacetic acid), Cueva (copper octanoate) or lime sulfur. Dr. Peter is testing these products this year.
  1. We know that fire blight can be brought into orchards from nurseries, this article, https://apsjournals.apsnet.org/doi/full/10.1094/PDIS-06-16-0892-RE, suggests that many young trees are asymptomatic. Fire blight was detected in asymptomatic trees up to 20 meters from trees showing fire blight symptoms. What other precautions can growers take to ensure they are receiving clean trees? Might there be other clues to identify fire blight in otherwise asymptomatic trees?
    • Growers will need to rely on nurseries to provide clean trees. Dr. Peter recommends aggressive treatment in the first year after planting using SAR products. There is no way of knowing if trees are infected and asymptomatic and removing blooms is important.
    • Copper applications will eventually wash off, whereas Regalia and Actigard 50WG will be absorbed. Therefore, apply a combination of copper and Actigard. Apply Actigard 50WG using the low rate of 1oz per acre. Copper should be used to keep bacteria load down and lime sulfur can be used to drop blossoms.
  1. Can you review best practices for removing fire blight infected limbs/trees, e.g., timing and how far below the infection they should be cut, sanitation?
    • Never prune in wet weather and cut at 8 to 12 inches below the site of infection, especially in dwarf trees. Dr. Peter will be looking at the best pruning practices this year and still needs to determine if disinfecting pruners is effective.
    • After an infection occurs, the bacteria will spread through the tree beyond the point of symptomatic infection. The more pruning that occurs, the more that growth will be encouraged, so limiting cuts is also important as this new growth is susceptible to fire blight infections.
    • Scout often for fire blight strikes, starting two weeks after bloom. The stub where pruning occurred will likely develop a canker which can be pruned out in the winter. Dr. Peter is not recommend snapping off shoots based on previous research.
  1. Badge SC and KOCIDE 3000 label offers a low-rate extended schedule where fruit finish is not a concern, however the label indicates these applications must end at first cover. The label for C-O-C-S does not offer an extended spray schedule. Besides Cueva, can any of these copper products be applied through mid-summer when fire blight risk declines on non-bearing trees? We’ve had lot of growers using both products into early July on non-bearing without apparent problems. If we can’t use these copper products, how do we best use copper soaps for mid-season fire blight management, this could include the Double Nickel + Cueva tank mix that was talk much about a few years ago.
    • Cueva is a fixed copper, where the copper ion is slowly released, while Magna-Bon is soluble and has all copper ions available and will kill what is there when applied. Both of these products are OMRI approved.
    • Using Cueva through July will help keep young shoots protected. The more copper that is applied, the more control, though it can be washed off and cause some phytotoxicity later on.