July 14 Conference Call

AppleTalk Conference Call Summary
Tuesday, July 14, 2020 8:00 – 9:00 AM
Guest Speaker: Dr. Sara Villani, North Carolina State University
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.

July 14th Call Stream: CLICK HERE


Guest Speaker Schedule Reminder

  1. July 28: Wisconsin DATCP presentation on Spotted Lanternfly

Regional update

Location Degree Days from January 1st

(Base 50°F)

Petal fall Date Leaf Wetting Hours (LWH) from Petal Fall Codling Moth Biofix Date Degree Day Accumulation from Codling Moth Biofix (Base 50°F)
Eau Claire, WI 1188 May 28 139 June 1 847
Gays Mills, WI 1243 May 27 99 May 24 1028
Hastings, MN 1305 May 27 93 June 1 947
Rochester (Ela), WI 1144 May 31 104 May 24 975
Trempealeau (Ecker’s), WI 1279 May 26 136 May 24 1039
Verona, WI 1237 May 29 120 May 24 1049

Table 1. Degree-day accumulations as of July 13, 2020 using data reported by Cornell NEWA Network.

Over the next week, highs will be in the 80’s and lows will be in the 60’s. Sooty blotch and flyspeck applications may begin at 175 leaf-wetting hours (LWH) from petal fall. Most locations are at 90 to 140 LWH from petal fall. Eau Claire and Trempealeau are predicted to hit 175 LWH later this week.

First generation coding moth flights are coming to an end. There are many sites past 1000-degree days base 50°F from the first generation biofix and a few hovering around 950-degree days. Eau Claire and a few northern locations are at 850-degree days from biofix. One grower in southern Wisconsin had a second-generation flight this week. Where traps went over threshold in the last seven to ten days, there may be CM larvae hatching, even as farms pass 1000 DD from biofix. Higher trap counts moving forward will likely indicate the beginning of second-generation flight. If lures have not been replaced, they should be refreshed now.

Since the beginning of June, several orchards have captured their first apple maggots. The threshold is an average of one fly per trap when using three unbaited traps per ten acres. If using baited spheres, the threshold increases to an average of five per trap. Growers may use spot applications to target blocks or locations that go over threshold. Captures have been more widespread across the region, though numbers have remained low.

Secondary insects
San Jose scale
Currently, San Jose scale (SJS) are in the “white cap” phase. This white appearance is due to the secretion of a waxy white substance. This white substance will turn darker towards the end of the first instar life phase.

For more information, please visit: https://www2.ipm.ucanr.edu/agriculture/almond/San-Jose-Scale/

Wooly apple aphids
WAA populations have been very low this summer and have only been observing occasional small colonies. Please refer to the June 30th blog post for further information on WAA: http://www.ecofruit.wisc.edu/appletalk/june-30-conference-call/

Weather over the past few weeks have been very ideal for mites. Growers should keep an eye out for flair ups and note any presence of predatory mites. Please refer to the June 30th blog post for a more extensive discussion on mite management: http://www.ecofruit.wisc.edu/appletalk/june-30-conference-call/

Potato leafhoppers
Potato leafhoppers (PLH) have been much more persistent this year than they have in the past. John, Josie, and Peter have observed PLH since the beginning of June, with several orchards now showing leaf curling and hopper burn. Growers should continue to scout for these symptoms as well as actual PLH presence. Materials including PyGanic (pyrethrin), Avaunt (indoxacarb) and neonicotinoids, e.g., Assail (acetamiprid), or Alias and Wrangler (imidacloprid) are effective against PLH. Terminals on trees will remain susceptible until they stop growing for the season.

Japanese beetle
Japanese beetle populations, while isolated, have increased drastically over the past two weeks in orchards with historic pressure. Generic imidacloprid, Assail (acetamiprid) and neem products will work as an antifeedant and repellent when applied at first sign of JPB presence in a block. Management of JPB should consider impacts on apple maggot and or second-generation codling moth. Please refer to the June 30th blog post for more information on JPB management: http://www.ecofruit.wisc.edu/appletalk/june-30-conference-call/.

Summer fruit rot discussion with Dr. Sara Villani, NC State

  1. Can you discuss your latest research on Glomerella leafspot vs. bitter rot; how this pathogen overwinters and how its lifecycle allows for transmission; and how early in the season can infections occur? What are the differences between these two pathogens? Are there climate conditions, e.g., rainfall or hours of relative humidity that trigger infection periods?
    • Glomerella leafspot (Colletotrichum gloeosporioides species complex) and bitter rot (Colletotrichum gloeosporiodes, acutatum and Glomerella cingulata) are related fungi, but not the same. With traditional bitter rot (BR), there is no cultivar that is resistance or tolerant. Cultivars with Golden parentage, e.g., Golden Delicious, Gala, Pink Lady, have some resistance to Glomerella leafspot (GLS).
    • Traditional BR is hardier and can withstand colder temperatures whereas GLS is more adapted to warmer, more humid conditions. Active conidia have been observed inside of the buds as early as tight cluster or pink-tip in for typical BR in the south, which suggests it overwinters quite well in moderate climates. However, GLS has not been received from buds until petal fall. Infected fruit can dry up on the tree and become fruit mummies and BR can overwinter within these fruit mummies. Growers should scout cultivars prone to mummy retention, e.g. Fuji and Cortland, and remove them.
    • Deadwood, June drops and hand thinned fruit are also another source of inoculum. Sara recommends scouting the lower canopy around June drop or during hand thinning. Weeds are also another source, e.g., Virginia creeper and several grass species. It is unclear how far rain splash can carry these spores, though Sara believes it is relatively localized.
    • Spores of BR and GLS are released when temperatures are warm, wet and humid. There only needs to be a few hours of leaf wetness, where lower temperatures in the 60’s can trigger an infection event. Infections can occur as early as June depending on the season. However, relatively high humidity and temperatures between 80 – 90°F, are when most infections occur.
    • Other vectors or enablers of GLS and BR infections potentially include insects, e.g., fruit flies and stink bugs. Additionally, sunburn is associated with bitter rot infections, and cooling the fruit with sunburn protectants may help prevent infections.


  1. Every year John scours fruit in June and July for early signs of fruit-rot, and every year is confronted by small lesions (<1mm) whose cause cannot be determined in the field. Is there a way to do this? Can fruit rot infections be distinguished in the field prior to their enlargement and production of spores?
    • Many of these small lesions could be early black rot, spray injury, or insect damage. Bitter rot will have multiple small legions on the fruit and is more indented, e.g., a sunken lenticel. These small lesions will also be without sporulation. Sporulation is typical with scab lesions and has a “fuzzy” appearance. Black rot will usually see one or two lesions concentrated on the calyx end. It can be difficult to determine initially and one option is to collect samples and incubate them.


  1. What are the current fungicide options for managing these fruit rots and what are the best strategies for managing their potential to develop resistance? Does captan offer an adequate tank mix for resistance and if so what rate?
    • Bitter rot cannot be completely eradicated because the inoculum is latently present within the orchard. Fungicide applications targeting BR should be applied before predicted rain and do not need to be applied orchard-wide and can target certain varieties. Sara has adapted spray programs to target highly susceptible varieties.
    • An application of Merivon (pyraclostrobin + fluxapyroxad) or Flint (trifloxystrobin) would allow for extended spray intervals, as opposed to only using captan to prevent infections. Once symptoms appear, infections tends to be more widespread and will spread from fruit to fruit. The DMI’s and SDHI’s have not had much efficacy against BR and should not solely be relied upon for BR control. Where strobilurins have been used for many years, it is possible to see strobilurin resistance and a multi-site protectant fungicide should be included to help prevent resistance, e.g., captan. For early season sprays, use mancozeb according to the extended spray schedule to allow applications up to the 77-day pre-harvest interval. Use maximum rate of a single site fungicide and mix with a half rate of captan later in the season.
    • Pre-harvest sprays of Merivon will help manage fruit through harvest and should be saved for the last two applications, ten days before harvest then one day before harvest. Merivon has a zero-day pre-harvest interval and will help prevent symptoms from appearing while fruit are in storage. Captan can provide Merivon levels of control using a ¾ rate. A short rain can wash off a majority of residue. These applications should target fruit with a history of bitter rot or that are prone to bitter rot, e.g., Honeycrisp, Evercrisp, Cortland, Gala. Captan residues do not last very long and the active ingredient in Merivon has a much longer half-life than captan, which will prevent rot in storage.
    • Topsin (thiophanate-methyl) is not a good option for bitter rot, but does work well on black rot, white rot and sooty blotch and fly speck.
    • An application of Surround (kaolin-clay) or other sunburn protectants, e.g., Raynox, will help cool fruit down and can help prevent sunburn. Surround is likely not as effective in the south due to consistent warmer temperatures. Calcium is directly toxic to bitter rot, make sure to include it in every cover spray.
    • OMRI Options: Lime sulfur applied early in season along with cultural control can help reduce inoculum, e.g., remove mummies and June drops. Regular elemental sulfur will work well, though cannot be applied in high temperatures. Appropriate timing for sulfur applications remains important, e.g., before rain or later in the evening.
    • Sara had two trials that consisted of harvested fruit without any symptoms, compared to fruit with some small lesions. Across these two trials, the Strobilurin restrained the rot from development. Read more about Sara’s research here: https://cals.ncsu.edu/entomology-and-plant-pathology/people/smvillan/.


  1. We had a question from a grower re summer management of fire blight. What are your thoughts on the following: Common advice is to cut off strikes below the visible infection, cutting into 2nd year or older wood, flagging the cut, leaving a stub, and then cutting the stub off during dormant pruning. Many sources recommend removing any trees with fire blight infections that “reach the leader.” In mature 5-10-year-old high-density trees, it is all too common to have a strike on a first year shoot that is growing from a renewal pruning cut. There may be very little or no older wood between the affected 1-year old shoot and the leader. If the strike is near the top of the leader it is possible to cut off the leader a bit below the strike. But what if the infected shoot is near the bottom of the leader? Not really feasible to do the pair of cuts described above. How should one handle this? As I understand the bacteria have probably travelled down the vascular system into the leader by the time the strike is discovered. Cut the tree out? Break off the infected shoot at the base?
    • This is generally the correct approach. Sara would suggest applying Apogee (prohexadione calcium) as soon as a strike is observed. This would potentially help slow down how quickly the bacteria travels within the tree, though it is unknown how vigor impacts rate of travel. Once the infection reaches a central leader, Sara recommends removing the tree.
    • For organic growers, cut back on fertilizer applications and consider making a maintenance application of copper, especially after making any pruning cuts. Sara had marginal success with Actigard (acibenzolar-S-methyl) and LifeGard (prohexadione calcium). LifeGard has worked better via foliar application and Actigard as a drench application.
    • An application of Cueva + Double Nickel is also an option to reduce spread of fire blight.