April 28, 2020 AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, April 28, 2020 8:00 – 9:00 AM
Guest Speaker: Dr. Amaya Atucha, UW Madison
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.

April 28th Call Stream: CLICK HERE

Guest Speaker Schedule Update

  1. May 5: Dr. Kari Peter, Penn State presenting on Fire Blight Management and Streptomycin Alternatives
  2. May 19: Dr. Dan Cooley, University of Massachusetts presenting on Orchard Floor Sanitation and Apple Scab.
  3. June 2: Dr. Brent Short, Trecé presenting on Codling Moth Lures and Mating Disruption
  4. 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 459 100 27
Gays Mills, WI 523 129 36
Hastings, MN 510 135 42
Harvard, IL 543 120 28
La Crescent, MN 556 141 43
Mauston (Northwoods), WI 487 96 17
Mequon (Barthel), WI 442 67 13
Rochester (Ela), WI 510 90 19
Trempealeau (Ecker’s), WI 513 121 35
Verona, WI 522 112 22

Table 1. Degree-day accumulations as of April 28, 2020 using data reported by Cornell NEWA Network.

Regional update
Locations further north, e.g., Eau Claire, Hastings, and closer to Lake Michigan and Lake Superior are behind in degree-day accumulation and bud development. Several growers have reported silvertip to ¼ inch green tip in these regions. Orchards along the Illinois and Wisconsin border and near Lacrosse are closer to ½ inch green and tight cluster on Zestar. Up to an inch of rain is expected for most of the upper Midwest on Wednesday and then will be dry the rest of the week.

Note: Remember to record 50% McIntosh green tip dates for better ascospore development readings in NEWA. Some orchards reported 50% McIntosh green tip as early as April 8-10.

Pre-bloom apple scab management
Orchards past green tip in southern Wisconsin, Northern Illinois or Southeast Minnesota are positioned to be impacted by major scab infections when the next rain occurs. After the rain subsides immediately reapplying a protectant may not be necessary. The forecast predicts three to four days of warm and dry weather beginning on Thursday. A lot of leaf growth is expected and with no rain in the forecast it may be best to wait until next week to apply a fungicide and protect new leaf growth.

Development of overwintering ascospores may be tracked by monitoring growing degree days base 32°F from 50% McIntosh green tip. Primary ascospores are considered completely developed after 900 to 1000 DD, base 32°F. The ascospore model is not linear and most spore maturation occurs around or after 900 DD. Ascospore development currently ranges from three percent in Hastings, MN to eight percent in Lacrosse, WI and most other locations are within this range.

Ascospore discharge usually begins within 30 minutes after the rain event begins and is largely completed within three to six hours. When infections occur at temperatures below 40⁰F, the number of days for scab lesions to become visible is unknown. Lesions become visible at or after 17 days for infections between 40⁰F and 50⁰F and when temperatures are above 50⁰F, lesions become visible in 10 – 14 days.

Next week, we will provide more detail and information on apple scab and fire blight management during Dr. Kari Peter’s discussion. Please review the blog posts from April 23, 2019 and April 30, 2019 for more information on apple scab management:

April 23: http://www.ecofruit.wisc.edu/appletalk/april-23-2019-appletalk-conference-call/
April 30: http://www.ecofruit.wisc.edu/appletalk/april-30-2019-appletalk-conference-call/

Organic scab management
Organic producers can manage scab infections by applying sulfur during a light rain in high-inoculum blocks at 7-8 lbs. per acre. Typically, it takes ascospores four to seven hours to invade the leaf, which is why post-infection applications of lime sulfur or potassium bicarbonate also work when applied within 24 hours of the infection period. As more leaf tissue emerges and as temperatures rise, organic producers may begin to incorporate biological fungicides into their spray program.

Fire blight
Severe weather bringing hail and high winds is forecasted in parts of Wisconsin this week, which is usually not a concern this early in the season. However, John observed fire blight ooze in an orchard this week. Typically fire blight risk is closer to bloom, however this was observed at tight cluster. The fire blight was discovered on one-year growth that was affected by cold weather and not pruned off. Copper applied at silver tip or green tip is intended to have activity when these scenarios present themselves and orchards still at green tip can receive a copper application, if this has not yet been done.

Pre-bloom scale and mite management
Over the next week, warmer temperatures will offer excellent conditions to apply oil. John recommends not applying oil once pink is visible and suggests the latest applications should be at tight cluster. Be careful to not expose pollinators to Esteem (pyriproxyfen) applications. The longer pre-bloom period also allows multiple oil applications at lower rates to target San Jose scale (SJS) and European red mites is possible.

At silver tip and green tip, oil performs best when relative humidity is high (65%) and temperatures are warmer than 60°F. When applied under these conditions, the oil and water emulsion takes longer to dry and extends efficacy with a longer period of time to dissolve insect and mite cuticles. When oils are applied at tight cluster and pre-pink, it is best to apply oil during periods of lower relative humidity. The most effective time to target the overwintered, immature San Jose scale is during the delayed-dormant period, from silver tip to half-inch green. Developing foliage will increase spray shadowing as the season progresses, reducing application effectiveness.

Historically, apple growers in the Midwest have been using two to three applications of oil up until early pink. In New York, SJS has been a growing problem and has some correlation to the reduction in use of oils. The downside of using oil is eliminating the possibility of using Captan in the early season. Oil can also cause phytotoxicity by dissolving parts of the leaf cuticle, similar to how it works on insects or mites. The later that oil is applied, the higher possibility for oil to cause phytotoxicity. For more information on the components of horticultural oils, visit: https://extension.colostate.edu/docs/pubs/insect/05569.pdf.

Oystershell scale overwinters beneath the dead-mother scale as eggs and cannot be effectively targeted pre-bloom with oil. Oystershell scale (OSS) will begin to hatch at 364-449-degree days, base 50°F. On a normal year this may occur between May 15 and June 1. We will revisit OSS management strategies in the coming weeks.

Dr. Amaya Atucha discussion on nutrient management

  1. Last year, you recommended to amend zinc, with a foliar application of zinc chelate. Most suppliers carry a 9% zinc chelate solution (Zn-EDTA) and recommend using one quart of Zn-EDTA per 100 gal. Suppliers labels are often vague in terms of timing and frequency of application. There are also formulations that supply additional nutrients, e.g., 6-20-0+Zn, whose use seems more limited/complicated because of the N and P supplied. Is this an appropriate base rate of Zn and how frequently should we apply Zn post bloom to address deficiencies in leaf analysis?
    • Foliar fertilization is necessary because many micronutrients are not readily available in the soil, e.g., zinc, boron. These nutrients are needed for pollen tube and early fruit development. Typically, boron deficiencies are also associated with high soil pH. Growers expecting a large crop should apply foliar zinc and boron.
    • Zinc chelate can be applied at 8-9%. Apply at tight cluster, first cover and second cover. If a deficiency is known or likely, apply the first application at ½ inch green with 100 gal. per acre. Even if soil has high organic matter, supplementing zinc and boron may still be necessary.
    • If soil pH is between 6-6.5, applying zinc and boron to the soil is okay. Boron applications to the soil should be applied at 1.5 to 2 lbs. per acre.
    • In a normal year with no deficiencies and fully producing trees, two to three foliar applications of zinc is still necessary. An orchard with a zinc deficiency will require one extra foliar application of zinc around green tip. Zinc chelate is more forgiving and is safe to apply with boron and urea if needed.
  2. Is there an optimum percent organic matter (OM) for high-density dwarf orchards? In established orchards that have low OM, what strategies should growers use to restore or build OM?
    • Incorporating organic matter during preplant and as an amendment has positive effects on soil physical and chemical properties, especially in retaining moisture and increasing porosity. If trees have a very small root systems and poor soil organic matter, any drought will negatively affect the development of the tree. Applying compost to very heavy or sandy soils will help increase OM and will help with tree development. Over time, the extra organic matter will encourage microorganisms to build up activity in the soil.
    • Do not apply any compost with more than 0.5% salt (sodium). The pH should also be similar to the soil pH, typically 6-6.5. When compost is not fully composted it tends to have a higher level of ammonium. The ratio between ammonium and nitrate should be balanced. Too much nitrogen could also lead to over fertilization.
    • The carbon to nitrogen ratio in compost is also important and should be between 15:1 and 25:1. The OM may vary depending on the type of compost as well. When compost is produced, the longer, hotter and more aerobic the conditions, greater amounts of fixed carbon will result.  This is preferred as the fixed carbon OM breaks down slowly, during which time it offers increased H2O holding capacity, increased number of cation exchange sites, and offers a favorable environment for beneficial microbes that assist in nutrient uptake and pathogen suppression.
    • 50-60% OM is a mature compost, which will have a higher carbon to nitrogen ratio and will take longer for microorganisms to break down carbon and release nitrogen in the soil. If the percentage of OM is lower, it means it has likely been mixed with soil. Sometimes, pathogens, e.g., salmonella or E. coli, could be present along with herbicide residues. Make sure the compost is coming from a certified source or has been examined by a lab. Note: Samples of compost may be sent to the same lab used for soil testing, e.g., UW Soil and Forage lab for a standard nutrient analysis, however this would not include testing for herbicide residues or pathogens.
    • Biochar is organic matter that has been burned with the absence of oxygen. The carbon structures in organic matter form a strong bond that the microorganisms in the soil cannot break down, and therefore keeps nutrient levels higher. Biochar has many positive effects, including increasing availability of nutrients in the soil, reducing leaching of nitrogen into groundwater, improving carbon sequestration, increasing water retention, and much more. Biochar has been found to help mitigate peach replant diseases. Adoption of biochar in commercial fruit production is low due its high cost.
  3. How can organic matter be increased in an established orchard and what are the long-term effects of herbicide use on tree health?
    • Once an orchard is established, compost can still be applied. There is a lot of research into the effects of bark and wood chip mulch that is showing positive effects for tree growth, and increased productivity and population of microorganisms in the soil.
    • After 17 years of research in M26 rootstocks at Cornell, the long-term effects of herbicides did have a negative impact on the health of trees. Bare soil will retain a lot of moisture that can lead to root diseases and increases the soil temperature. High soil temperatures, e.g., above 86°F, cause roots to decay and become more susceptible to root diseases.
    • Using bark mulch is much healthier for the tree. The bark mulch must be renewed over time, which requires equipment and labor. However, it is a valid way to reduce herbicide applications. Spot applications of herbicides will likely be needed to suppress perennial-weed growth. Mulch conserves moisture during dry periods, reduces soil temperature allowing better growth during warmer periods, and improves soil structure conductive to good root growth.
    • After shoots have elongated and slowed down their growth in July, weeds do not affect tree growth and health in terms of competition. It is different with new trees and weeds that are present at any time are a problem during the first four years of tree growth. It is important to note that often weeds are kept down late in the season to improve harvest management and prevent the creation of rodent habitat in the winter.
  4. What can we expect from mineralization of soil OM, e.g., muck soils may be high in OM, but are not able to mineralize soil vs. soils with clay, sand and gravel can vary between 1% and 4% OM, but still provide lots of nitrogen. Should a well-drained soil receive different amounts of N vs. a poorly drained silty clay if both had the same amount of soil OM?
    1. Once established, most orchards don’t need to apply nitrogen due to mineralization.  The issue is the timing of the release of nitrogen. In the spring, the tree is generating growth using nitrogen stored from last year. Right now, there is a high demand of nitrogen but the lowest amount in the soil. Even though soil organic matter at 2% to 4% may release 80lbs of nitrogen over the growing season, this release fluctuates making nitrogen availability low in the spring when trees need it. New trees don’t have the nitrogen reserves available yet and need nitrogen in the spring. If nitrogen applications are needed, the best time to apply would be during pre-bloom.
    2. A good range for OM is 2-4%. It is important to note that different levels of OM have differences in ability to retain nitrogen. About 3-5 lbs. of nitrogen per acre per day will be released by soils that have 5% OM, where a peat soil with 25% OM can release up to 20 lbs. of nitrogen per acre per day. As soil temperatures increase, the release of nitrogen will also be greater.
  1. In the New York Fruit Quarterly Article, http://dev.nyshs.org/wp-content/uploads/sites/343/2016/10/5.When-and-How-Much-Nitrogen-Should-Be-Applied-in-Apple-Orchards.pdf, “When and How Much Nitrogen Should be Applied in Apple Orchards”, discusses applying 3 lb. of urea per 100 gal of water for foliar N sprays. Do you have any other suggestions on products, rate, and timing for foliar N sprays on new vs. established dwarf trees? How often and when should a foliar feeding program be used?
    • The best time to apply foliar urea is at tight cluster to pink at 2-3 lbs. per acre and can be mixed with zinc chelate and boron.
    • John typically recommends 5 lbs. of 20-20-20 as a foliar boost especially if cloudy weather occurs during pink and there is carbohydrate stress.

Grower questions

  1. After attempting to de-fruit the tree and establish a new leader, a grower is asking for other suggestions on getting a three to five-year old dwarf tree that is runted and over-cropped to put on new vegetative growth?
    • It could be harmful to prune heavily and apply heavy amounts of fertilizer according to research. Amaya recommends approaching the situation more moderately. The tree should be de-fruited for two to three years to promote vegetative growth. Keep the leader and prune lateral branches that are competing with the leader.
  1. At last summer’s WAGA field day, one of the presentations discussed reducing the tree canopy of bareroot trees by 1/3 to compensate for the loss of the root system that occurs during transplanting of new trees from the nursery to the orchard. What is the best approach for reducing size or number of scaffold limbs or leader to accomplish this 1/3 canopy reduction?
    • Amaya does not agree with this practice, which has been discussed in other fruit crops, e.g., grapes, about below ground vs. above ground growth. If the above ground growth is being reduced, the amount of leaf material that is producing carbohydrates through photosynthesis is also being reduced. Trees with long, but few feathers can be headed back to improve the tree structure, however reducing the canopy by 1/3 does not make sense. Adding some nitrogen will help support production of chlorophyll and will send more nutrient to the roots. Heading oversized feathers is a good idea, but do not touch the leader.
  1. 3. Would urea pose risk for bitter pit later in the season?
    • No, not if applied at 2-3lbs per acre at tight cluster to pink. If there was a lot of shoot growth last year and nitrogen levels are a bit high, Amaya recommends skipping urea applications.