July 27 AppleTalk

AppleTalk Conference Call Summary
Tuesday, July 27, 2021 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM, jgaue@mwt.net
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org.

 July 27 Call Stream: CLICK HERE

Regional update

Location Green Tip Date


Mac Petal Fall


Degree Days

(Base 50°F)

Jan 1 – Present

Eau Claire, WI 4/3 5/16 1523
Galesville, WI 3/21 5/7 1610
Gays Mills, WI 4/3 5/12 1634
Mauston (Northwoods), WI 3/30 5/10 1644
Mequon (Barthel), WI 4/4 5/18 1415
Rochester (Ela), WI 3/30 5/12 1497
Verona, WI 4/3 5/12 1634
Hastings, MN 4/5 5/17 1605
La Crescent, MN 3/23 5/9 1736
Lake City, MN 4/4 5/16 1694
Harvard, IL 3/30 5/11 1606

Table 1. Degree days forecasted for 7/27/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu. Note: Leaf wetting hours for sooty blotch and flyspeck use an estimated petal fall date, unless entered by the station operator. NEWA model allows you to add your last systemic fungicide or petal fall date.

Foliar and soil sampling
Leaf and soil samples for nutrient analysis should be collected no later than the week of August 17th from this season’s growing shoots. The purpose of collecting the samples now is to inform nutrient management for next year. Samples may be sent to AgSource Laboratories (https://www.agsourcelaboratories.com/) or the UW Soil and Forage Lab in Marshfield Wisconsin (https://uwlab.soils.wisc.edu/). The UW lab includes soil and tissue samples for $25. Tissue sample pricing from AgSource Laboratories is dependent on your specific location. Contact your nearest lab for pricing options.

Soil analysis through AgSource includes the following soil-sampling packages:

  • Basic Package ($45) – includes: Soil Health Score, CO2Respiration, C:N Ratio.
  • Routine Package ($55) – includes: Soil Health Score, CO2Respiration, C:N Ratio.
  • Complete Package ($65) – includes: Soil Health Score, CO2Respiration, C:N Ratio

When collecting leaves, examine this year’s growing shoots and select several leaves from the middle of the shoot. Leaves should be collected from a representative sample of the block or variety. About 30 leaves are needed to have one cup of dry leaf material that will be ground up for the analysis. Samples should be separated by variety or by health of the tree. Analysis of unhealthy trees should be kept separate. We are unsure if the results in mixed-variety orchards would be skewed by collecting leaves from multiple cultivars and it is recommended to keep samples limited to specific varieties. Once we see nutrient deficiencies this time of year it may be too late to amend this year and results will be focused toward soil and tree health next year.

Summer Apple Nutrition and Pre-Harvest Stop-Drop Sprays: Recap of Brian Smith’s article in WI Fruit News: https://fruit.wisc.edu/2020/07/22/summer-apple-nutrition-and-pre-harvest-stop-drop-sprays/
Dr. Brian Smith references the most important aspect of tree nutrition is having adequate soil moisture and describes this as maintaining soil moisture at 50-70% of field capacity. This is very relevant as all the nutrition points we discuss in AppleTalk are dependent on adequate soil moisture. Not everyone has irrigated trees, but water can be delivered to these trees, even if it is labor intensive, do it.

Field capacity is an old term in soil science and is somewhat vague. The textbook definition refers to field capacity as the amount of moisture soil can hold after excess water, i.e., water the soil cannot hold, has drained away. The field capacity Brian is suggesting we target is a middle range of soil moisture, where there is no free water and not so dry that roots cannot pick up moisture. Even if there is still some water in the soil, if the soil is too dry, roots may begin to die. A foot of soil can hold upwards of two inches of rain that trees can access. The lighter or sandier the soil, the lower the water-holding capacity and as soil-organic matter, silt, or clay content increases, so does the soils water-holding capacity, which could increase above two inches.

The most easily assessed metric for assessing water stress is to use the evapotranspiration (EVT) models available via local NEWA sites. Considering the EVT rates over the last month, a significant amount of water has been removed from the soil. It is worth the investment in soil tensiometers and other tools that will help assess soil moisture. As a reference point, corn growers often discuss needing an inch per week. This is likely a minimum amount for fruit trees and could require more depending on EVT rates. Therefore, if we have not had four inches of rain in July, the trees are likely under significant tree stress.

Questions on soil moisture and fruit drop: Will watering help to stop premature fruit drop?
Yes, frequent watering should help to prevent this early drop. Additionally, fruit low in Mg or high in K or B, are more likely to be at risk of dropping.

Bitter pit
Calcium (Ca) is important and necessary to maintain fruit quality. The majority of Ca is absorbed into the fruit during the cell expansion phase lasting from petal fall to the end of July (~50 days after petal fall). After this period, the xylem in the fruit losses efficiency, especially in the calyx end. Calcium does not easily move into the fruit from the soil and is relatively immobile within the tree. Concentrations can vary between foliage, fruit, and soil.

Note: Foliar Ca levels will be greater than what is in fruit because leaves have a high transpiration rate and accumulate more Ca material. The following factors can influence Ca levels and incidence of bitter pit: Nutrient imbalances with nitrogen (N), potassium (K) and boron (B), soil moisture levels and fruit size.

Strategies for reducing bitter pit

  1. Submit foliar, fruit and soil samples for nutrient and pH analysis. It is recommended to test samples for all available macro/micronutrients as many complex interactions exist. For example: an excess amount of magnesium (Mg) or potassium (K) will compete with Ca for uptake.
  2. Keep soils adequately hydrated throughout the growing season.
  3. Reduce excessive vegetative growth. Reducing vegetative growth will redirect the transport of Ca from foliage to fruit. Apogee (prohexadione calcium) can be applied to curb vegetative growth. The pre-harvest interval for Apogee is 45 days.
  4. Lite crops or excessive thinning can result in large fruit. Calcium levels can be diluted in large fruit; Ca concentrations typically vary from stem to calyx end (location where bitter pit symptoms are most pronounced), excessively large fruit usually have exacerbated symptoms.
  5. Calcium sprays can begin at petal fall and continue to end of August; up to six applications may be necessary. Coverage is important – Ca must contact fruit to be effective. The recommended rate is one-to-two pounds of Ca per 100 gallons of water. If visible symptoms of bitter pit are present, it is not too late to apply Ca to prevent further injury.

Plant growth regulators
ReTain (AVG-HCl) reduces amount of ethylene produced to prevent the abscission layer from forming between the fruit stem and spur. The general recommendations for use of ReTain on Honeycrisp are to apply a half rate 30 days before harvest. Other recommendations would allow a ¼ rate to be applied within 14 days of harvest or to include NAA, e.g., Fruitone, at 10 PPM with the ¼ or ½ rates. Honeycrisp does not produce a lot of ethylene and therefore is more sensitive to Retain. This means that a “half rate” is essentially a full rate. The use of Retain with NAA can extend harvest another seven to ten days. The combinations can continue to promote ripening and inhibits separation at the abscission zone.

It is not recommended to apply these materials in complicated tank mixes and to also read product label for compatibility statements. When first using these materials experiment with application timing and rates for specific varieties to help determine what works best for your orchard.

Blush (prohydrojasmon) can enhance color development, especially on the backside of the fruit that does not color well. Blush does not accelerate ripening. Some growers prefer to not apply blush to Honeycrisp, so pickers can use visual cues based on harvest parameters.

Insect management
The first obliquebanded leafrollers (OBLR) of the second-generation flight were observed in the last week, however many locations are still likely waiting on the flight to begin. The second-generation of OBLR will hatch in mid-August and can continue into September. This generation typically feeds on ripening fruit rather than on vegetative tissue. The OBLR larvae will only grow to a few millimeters in length before developing a pupa and going into diapause, where the OBLR’s growth and development is suspended until spring.

Redbanded leafrollers have a wider set of host species, fly further, and traps can capture a lot of males. We often times don’t see a lot of larvae hatching out in correlation with trap captures. This is not the case with OBLR, as female moths are more commonly captured.

The CM larvicides, e.g., Delegate (spinetoram), Altacor (chlorantraniliprole), will control these larvae, whereas the neonicotinoids, e.g., Assail, Admire Pro (imidacloprid), do not. The application rate for these insecticides is typically the same that is used for codling moth. Imidan (phosmet), had a real ability to become resistant to OBLR. We get little resistance with RBLR because of their wide-host range. Managing the second generation now, will reduce the overwintering population that may need to be controlled next spring. Three to five percent injury is possible at harvest and scouting needs to be used to determine if a treatment is warranted. A mistake with OBLR may discount an apple from US Fancy grade but is not usually a problem when selling pick-your own fruit since the injury is very small and there is no worm in the apple. Two traps per 20 acres is adequate to determine where treating is necessary.

The degree-day model for OBLR is based on a lower developmental threshold, 42-43°F. Using this lower-base threshold will allow degree days to accumulate faster. The important consideration is that no trap threshold exists to help time sprays. Typically sprays for OBLR are applied after large flights. Since OBLR have a narrower-host range and will not fly very far, trap captures are a good reflection of pressure within the orchard. Low captures of five or six OBLR, do not signify a problem. Captures of 15+ should be followed up with a typical spray we use for codling moth.

Michigan State and the Utah IPM program have similar degree-day models for OBLR. Utah suggests the first-generation flight occurs at 1025-1175 DD from January, 1 base 43°F. The flight for the second generation in Utah begins at 1100 and hatch begins at 1500. Michigan suggests that OBLR biofix occurs around 900 DD from January 1 base 43F. The peak moth flight for second generation OBLR will happen at 2300 from the biofix date and egg hatch will start at 2750 DD base 43°F.

The OBLR degree-day model is explained in the following two articles:

European red mites (ERM) and to a lesser extent two-spotted spider mites (TSSM) have continued to be a problem in orchards where predators have not been successful at managing the populations. The threshold for August is 7.5 mites per leaf and while it is relatively easy to count ERM, populations of TSSM can be much more difficult to assess due to their webbing and size and do not have a specific threshold. The predator complex will be more effective with the cooler weather this week. The cooler weather will also allow for applications of oil.

Organic producers do not have many options for mite control, though many oils are OMRI approved. Oils should be applied in cooler temperatures, and most days in July were likely too warm for an application. Some larger growers have had problems with resistance developing to most of the miticides that are commercially available. As a result, one grower has experimented with summer oils this year and used a product called JMS Stylet oil, which is a paraffin based mineral oil. It is approved for organic use and has been in use since the 1960’s. Nutrien in Galesville, WI does have this product. Apply at a 1-2% rate per acre and John recommends using more water as it will increase the chance that the mite will suffocate. Keep in mind that when using oils, it will also kill predator mites. Oil is considered another mode of action, so a miticide used several years ago and have made several years of oil applications, it is okay to use it again as a spot or cover spray.

If bronzing is still occurring while mite populations are below threshold, action is required to prevent further economic injury to the plant. This happens when a population of predators have remained active long enough to keep populations below threshold, yet enough mite feeding has occurred to cause leaf bronzing. Once leaf bronzing occurs, economic injury is happening to the tree and a miticide should be applied. This scenario is referring to what we call mite days, where the duration of mite activity is just as important as the actual population. If we reach threshold and still cannot see significant damage on any leaves, we may be questioning whether we need to make a miticide application.

Pre-harvest interval reminder

Product Pre-harvest Interval
Actara (thiamethoxam) 0 – 2.75 oz./acre: 14 Days
2.75 – 5.5 oz./acre: 35 Days
Acramite 7 Days
Altacor (chlorantraniliprole) 5 Days
Assail (acetamiprid) 7 Days
Avaunt (indoxacarb) 14 Days
Captan 80WG (captan) 0 Days
Delegate (spinetoram) 7 Days
Envidor (spirodiclofen) 7 Days
Esteem (pyriproxyfen) 45 Days
Exirel (cyantraniliprole) 3 Days
Flint (trifloxystrobin) 14 Days
Indar 2F (fenbuconazole) 14 Days
Luna Sensation (fluopyram, trifloxystrobin) 14 Days
Merivon (pyraclostrobin, fluxapyroxad 0 Days
Nealta (cyflumetofen) 14 Days
Portal (fenpyroximate) 14 Days
Pristine (boscalid, pyraclostrobin) 0 Days
ReTain (-trans-2-Amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride 7 Days
Topsin (thiophanate-methyl) 1 Day
Wrangler (imidacloprid) 7 Days

List of pesticides and pre-harvest intervals http://cpg.treefruit.wsu.edu/pesticide-intervals-impacts/preharvest-intervals/