June 1 AppleTalk

AppleTalk Conference Call Summary
Tuesday, June 1st, 2021 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM,
Moderator: Peter Werts, IPM Institute of North America; questions or comments,

 June 1st Call Stream: CLICK HERE


Location Green Tip Date Degree Days

(Base 50°F)

Jan 1 – Present

Eau Claire, WI 4/3 339
Galesville, WI 3/21 377
Gays Mills, WI 4/3 401
Mauston (Northwoods), WI 3/30 400
Mequon (Barthel), WI 4/4 323
Rochester (Ela), WI 3/30 366
Verona, WI 4/3 397
La Crescent, MN 3/23 422
Hastings, MN 4/5 378
Harvard, IL 3/30 406

Table 1. Degree days and ascospore maturity downloaded on 6/1/21 from Cornell NEWA system. Find your local station today: http://newa.cornell.edu.

Regional roundup
Summer must be here, as by June 5 and 6 the temperatures are to reach the 90s and will accelerate insect activity. Expect plum curculio and codling moth to become active during these warm nights.  Other summer pests such as San Jose scale, aphid, dogwood borer, black stem borer will become active too. 297 – 332 DD base 50 for the month of May.

The sky is not falling
We have at least 16 growers in AppleTalk that have been at this for just a few years. This next paragraph is for you! I had a conversation with a trusted grower who returned to the farm to grow apples the same year I started scouting; 14 years ago. They commented that John and I approach every pest with a sense of urgency, as if the sky is falling, when in reality it is not. We take this approach because most advanced IPM strategies using low-risk insecticides have a very narrow window for their effectiveness. The reality is tree nutrition, crop-load management, sales and marketing, are also equally important. Most beginning growers can produce a great crop if they stay focused on codling moth, plum curculio, apple maggot, apple scab and fire blight. One way to set priorities is to ask the question: Will this pest impact my crop quality or my tree health? A pest that will have a minor impact on crop quality or tree health could perhaps get a pass now and then, but not always. Setting the priorities is up to you, we want to make sure that AppleTalk is giving you the right information to do so. Please let us know what topics you would like addressed or additional information you need to set your IPM priorities.

Nutrient deficiencies
Make note of discolored foliage on terminal growth and which cultivars are affected and consider taking pictures for future reference. This may be helpful when collecting leaf samples for nutrient testing.  Trees that are showing excessive symptoms of nutritional deficiencies should have separate samples collected when you take tissue samples for nutrient analysis.

Soil borne pathogens
Most growers do not have to worry about too much water this year, however, those with heavy soils or who frequently irrigate, can be at risk of having too much water. Over watering can cause root death if a hypoxic environment is created, i.e., too much water deprives roots of oxygen. Other problems that can result from too much water include development of root diseases such as phytophthora.  Impaired root function also can appear as discolored, small, or wilting foliage at tops of trees and have begun to appear at the tops of trees.  These abnormalities will appear more intensely due to the heat and high evapotranspiration rates and show up on the tops of trees and are less likely to be present on lower limbs.

Estimate your current water deficit by totaling precipitation from February 1 through May 31 and comparing that to the normal precipitation for those four months. This will establish a baseline for your water needs going forward. If your current needs are being met through timely rains, but you have a deficit of four inches from February through May, begin or continue supplemental watering, so when apples are sizing in August there will be sufficient available water deeper in your soil profile. Even though many orchards have received 3.5 to 5 inches of rain in the last two weeks, the subsoils are still abnormally dry and will cause the surface soil to dry out faster. In our region approximately nine inches of precipitation accumulates between February 1 and May 31, and we have only received six inches to date. Warm weather Friday, June 4 to Monday, June 7 will lead to significant evapotranspiration. Going forward, high density orchards need an inch of water a week either from rain or irrigation.

Return bloom
In the most recent UW Fruit News there is an article about promoting return bloom. One possible reason due to poor return bloom was due to the dry period in the 45 – 90 days after full bloom, which is the time when fruit buds are formed.  This was an excessively dry period and if there was not irrigation, may have resulted in poor return bloom this year.

Crop assessment
While hand thinning or evaluating fruit your fruit load, look for fruit abnormalities due to freeze damage or poor seed-set. Not all freeze damaged apples show a classic “frost-ring”. Fruit may be misshapen, lopsided, have surface spots or discoloration. You can do a seed count in affected fruit to verify freeze/frost damage as the culprit. Symptoms will be more pronounced as fruit sizes beyond 20 mm.  Besides frost rings, other injury can include misshapen fruit or discoloration on the skin.

Black rot
The upcoming heat and dry soils will bring out symptoms of old infections from canker fungi, i.e., black rot or white rot, Phomopsis, nectria canker, etc., where we may see collapse of scaffold limbs. There is no urgency to prune and remove these diseased limbs, but they are sources of inoculum and can spread via trauma from wind or hail.

Apple scab
Primary scab season is over! However, most of our infection periods occurred after May 18th and secondary lesions of apple scab which will be visible on both upper and lower leaf surfaces will take another seven to ten days to appear.  It is advisable to keep fungicides on seven-to-ten-day intervals before stretching to a summer schedule.  Once it is certain there is no scab in the orchard, then intervals may be stretched.

Fire blight
Despite the dry weather, there has been excellent shoot growth this spring and growth may slow down if nighttime temperatures remain warm. Warm night temps will cause trees to burn up sugars they accumulated during the day and exhausting these sugar reserves is what slows growth. Vigorous trees and trees that have had lots of growth will be more susceptible to shoot blight infections.  One strategy that some growers have used is to apply Cueva and Double Nickel preventatively from petal fall until terminals set.  However, even though this tank mix is not supposed to cause fruit resetting, the risk is still present.  A Cueva and Double Nickel tank mix will be much more effective if applied preventively and will stop the development and further spread of shoot blight after symptoms appear. Streptomycin should not be used unless you have trauma from hail and must be applied within 24 hours.

Codling moth
In 2020 many orchards experienced an enormous flight at petal fall and then never saw high codling moth trap captures later in the season. This year the codling moth flight began as a trickle and has remained as such. The warm weather may result in a flight, and everyone should check traps on a tighter interval this week to see if there is a bump in the flight over the week.

The codling moth degree day model suggests that at 250-degree days from our biofix 3% of the population is hatching; at 350-degree days, this increases to 15% egg hatch; and between 450- and 550-degree days from biofix is when we have peak egg hatch. There are 1000-degree days in each generation and similarly, by 750-degree days only 15% of the remaining population is hatching and by 900 it is down to 3%. This makes a bell-shaped curve, and the goal is to get the most value out of each larvacide application. This means making sure we are covered at peak egg hatch and then there is some flexibility on the front and backend of the generation, re additional larvacide sprays.

If initial trap captures were more than ten in a week, per trap, the larvacide may be targeted right at 250-degree days. If trap captures were less than ten in a week and right around the threshold of five per trap per week, waiting until 350-degree days will be better.  If the larvacide is timed at 350 DD from the biofix, approximately 60% of the egg hatch will be targeted by one application. If applying at 250 DD only 3% to 30% of the population will be targeted.  Last year orchards that had high numbers right away, it was important to time the larvacide at 250 DD. This year many orchards will be safe waiting until 350 DD to apply a larvacide.

Many orchards are applying their last plum curculio spray this week.  The timing of this application is likely ahead of 250 DD from CM biofix, and likely will not have active residue by the time 350 DDs have accumulated. Insecticides such as Belay or Avaunt are rated as only fair on codling moth. If your codling moth population is low and considering the minimal egg hatch at 250 DD, these insecticides applied for PC may offer adequate protection against codling moth for a few days. If you have caught high populations since biofix, may not want to rely on these insecticides.  Please see last week’s notes for a more detailed discussion on insecticide options.

Plum curculio
The prolonged bloom has made it challenging to use McIntosh petal fall to predict the emergence and duration of plum curculio season. What is the most important thing to remember is an unmanaged population of PC can remain active well into the end of June. All the degree day model helps us understand is when movement of this pest from the surrounding woods and hedges should end. The conditions this year highlight the importance of PC scouting both on the edge and interior.  I have found PC injury in almost every orchard I have been to and in many instances, it was quite hard to find, but it was there. Even if we loosely lean on the degree day model of 308 DD, base 50°F, from petal fall, most orchards will have accumulated enough degree days by early next week that no new PC should move into the orchard. If your current PC insecticide is ten days or more old, reapplying a perimeter or a full cover ahead of these warm temperatures is essential. Another option is to be vigilant with scouting and wait until the earliest signs of new injury appear and then apply a cover. Either way, there is no substitute for PC scouting this next week, so set aside some time in the morning before it gets too hot and look around the perimeter and interior of the orchard for the crescent shaped scar.

Secondary insect pests
San Jose scale
An economically significant pest, yet not a problem at all orchards, infestations of San Jose scale (SJS) result in fruit injury and a slow decline of the tree over time. Feeding on the fruit induces local red to purple discoloration around feeding sites and results in a blemish. There are two generations per year and crawlers from the first generation will be emerging soon.  Dormant oil applications are important to targeting scale, in addition to mites. If SJS has been a problem in the past and oil was not applied this year, monitoring this pest should be a priority. If you have never had an issue with SJS, keep an eye out for this fruit injury.

Monitoring sites maintained by Michigan State University began catching males in pheromone traps two weeks ago. Typically, we have not monitored the males using pheromone traps and rather rely on monitoring crawlers using tape. Monitoring with tape is more useful, as insecticides for crawlers have a narrow window and monitoring with the pheromone trap is not an adequate substitute for monitoring crawlers. Based on the MSU captures, it would suggest SJS will be hatching in the next two weeks. Scale and mites have a higher temper threshold for their development, so similar to using an upper limit of 86 for codling moth, scale and mites have an upper limit in the low 90s for their growth and development.

Monitor known hotspots with black electrical tape applied to infested scaffold branches. Place the adhesive side towards the tree and wipe a thin layer of petroleum jelly on the outside of the tape. Double-sided tape can also be used. If populations are high, concentrate a few tapes on younger limbs (2-3” diameter) in areas with greatest pressure and on the sickest looking trees. Last year’s scale will be concentrated near newer growth and increasing the number of monitoring sites may help eliminate false negatives. Low-trap captures do not reflect overall pressure, i.e., false negatives, rather they may indicate the beginning of the hatch. First generation SJS hatches over a narrow period, while second generation hatches over a longer period. Use a hand lens with at least 10x magnification to scan tape for oval, bright-yellow crawlers. Catches of 10-15 crawlers in a couple of days or 10 crawlers on one tape, may warrant an application for management of SJS.

If a special application for SJS is warranted, e.g., evidence of crawlers, Esteem (pyriproxyfen), Sivanto (flupyradifurone) or Centaur (buprofezin), may be applied. Esteem is an insect-growth regulator and will manage OBLR, CM and RBLR. Do not treat at first-crawler detection, rather at 150-200 DD after crawler emergence.

Organic SJS Management
Nothing really changes for organic growers needing to manage SJS, except the insecticide selections, which have been limited up until now. Typically, SJS is not as much of a problem in organic systems, yet plenty of organic growers have mentioned SJS issues over the years. If you are one of these, consider using Grandevo. Trials conducting at Cornell in 2017 showed very similar levels of SJS control when compared to conventional insecticides. There is a supplemental label for SJS management, meaning you will not find SJS on the regular Grandevo label.  Supplemental label: https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Grandevo_2EE1j.pdf.

Obliquebanded leafroller (OBLR)
OBLR have two generations per year and overwinter as larvae and emerge in the spring. The young larvae then feed on leaves and protect themselves by rolling leaves with webbing where they are concealed from outside threats. Once the larvae have reached 4th instar, pupation will then occur inside the rolled leaf and lasts 10-12 days. In the past week, pupae have been observed and flights will likely occur soon. Moths then emerge from Mid-June through Mid-July and will quickly mate and lay eggs. Females can lay up to 900 eggs in a weeklong oviposition period. Eggs take 10-12 days to incubate and emerge at 350-400-degree days base 42F from initial trap biofix. The second flight typically occurs in mid to late-August.

If OBLR traps have not been hung, one or two traps per orchard should be placed this week. Once the OBLR flight has been observed, additional larvicides for CM should consider efficacy against this generation of OBLR. Obliquebanded leafrollers are like CM in that they are poor fliers and therefore may need extra traps in the orchard. Most growers only deploy one or two OBLR traps, which may not be enough to accurately capture the population density and pressure. However, this is not often a concern, when larvacide for codling moth are being applied.  Where mating disruption is used and there is a goal to minimize additional insecticides, more OBLR traps should be hung in the orchard to adequately sample the pest. Typically, the second generation can cause injury at harvest and larvicides applied during their first generation can significantly reduce summer populations.  If trap counts are high, e.g., more than 50 in a week, then larvicides for OBLR may need to be applied.  Note: There is no threshold for OBLR traps, this is just a nominal number based on what we typically observe under high-pressure scenarios.

Most neonicotinoids (Assail, Belay, Actara, Imidacloprid) will not suppress populations of OBLR. Belay (clothianidin) is one exception and is labeled for OBLR, but not other leafroller species. Belay has been a popular neonicotinoid to use, where plum curculio and first-generation codling moth management overlap. Growers who have used Assail (acetamiprid) or other neonicotinoids for plum curculio or first-generation codling moth should note these will not manage populations of OBLR or other leafrollers. Two popular classes of insecticides which will manage codling moth plus the spectrum of leafrollers and other internal-feeding lepidoptera, e.g., oriental fruit moth and lesser apple worm, include spinosyns, i.e., Delegate (spinetoram) and Entrust (spinosad) or the diamides, i.e., Altacor (chlorantraniliprole) and Exirel (cyantraniliprole). A good option for organic growers would be to apply Bacillus thuringiensis (Bt) for OBLR plus the codling moth, e.g., Virosoft or CYD-X (Cydia pomonella granulovirus).

Dogwood borer
Borers are an occasional, yet problematic pests of apple trees and especially dwarf trees.  Some semi-dwarf orchards live for many years with significant DWB infestation and yet show no signs of decline; and conversely, DWB can easily take down a dwarf tree if left unmanaged. Usually, DWB injury is found right above or around the graft union. DWB have also been observed in the scaly bark that is not covered by tree guards, e.g., winter injury or herbicide injury, or even on pruning cuts just above the tree guards. Small diameter dwarf tree, e.g., three to six-years old, are more prone to girdling that can be caused by continuous infestation; feeding often needs to happen for several years before trees shows decline in vigor and possible death. Even if feeding does not impact the vigor of the tree, it can produce an entry point for disease, e.g., black, or white rot.

Pheromone traps for DWB should be placed in 2–5-year-old trees at height of 3′-4′. The DWB pheromone casts a very wide net and attracts multiple species of native clear-wing moths. If moths are caught in traps, they need to be appropriately identified to confirm species. There is not a trap-based threshold for DWB, rather if you are catching DWB adults you need to be looking for evidence of DWB larvae, e.g., frass around the graft union. Initial stages of DWB infestation may be random, damage may not affect tree immediately but four to five years down the road trees will begin to decline. Trapping gives us an early warning system to begin scouting, rather than waiting for visible symptoms.

Management options are limited and a trunk spray of chlorpyrifos is the currently the best option for suppressing existing infections.  Trunk sprays require large volumes of water and high pressure to thoroughly coat the bark. If good coverage is achieved effective protection can be achieved for 2-3 years. Low pressure backpack sprayers are not suitable for this application, and neither is using the bottom nozzles of an airblast spray.  Applying chlorpyrifos with a hand-wand attachment to the main sprayer is the best option.

Spider Mites
The approaching heat will accelerate development of European red mites (ERM) and two spotted spider mites (TSSM). The ERM have dispersed from the sites where they hatched and are beginning to disperse through the canopy. Right now, the priority is to scout historical hot spots or varieties that did not receive an oil application. Keep an eye out for orangish-red or amber colored mites or eggs, as these are predatory mites (the good guys).

Orchards that did not have good opportunities to apply oil and may see more mite activity this year and may be a problem sooner rather than later this year. Do not delay mite observations if oil was not applied and since most miticides don’t take down large populations, early intervention when populations hit their threshold is important.

Black stem borer
Black stem borer is an ambrosia beetle that has slowly been growing in prominence as a pest of economic importance in the northeast United states.  Mostly a problem in non-bearing trees, BSB only attacks trees that are stressed to the point where they begin to produce ethanol. Adult females are attracted to this ethanol and hollow a gallery in the trunk of the tree several inches above the graft union. Young larvae do not feed on the tree, rather on a fungus that grows within the gallery.  Tree decline is caused by the females which essentially girdle the trunk from their tunneling.

In 2020 traps placed at 18 orchards throughout WI caught high numbers in many locations, yet no one has reported wide-spread tree decline.  Some of the highest numbers came from orchards that mostly have semi-dwarf trees that are quite mature with a large trunk diameter.  It may be possible these trees are thriving despite an infestation of this ambrosia beetle.  Monitoring was completed using an ethanol pouch and it may also be possible the trap drew in these beetles from the surrounding woods

The best strategy is to prevent BSB infestations through proper tree nutrition, irrigation and crop-load management, as if trees are not stressed, they will not attract BSB.

BSB was monitored in the following counties:

County Confirmation of BSB presence
Walworth Yes
Racine yes
Rock Yes
Kenosha Yes
Dane Yes
Eau Claire No
Chippewa No
Rock Yes
Calumet Yes
Richland Yes
Vernon Yes
Trempealeau Yes
Lafayette Yes

Japanese beetle
Very warm soils have resulted in early flights of June beetles and John is predicting an early emergence of Japanese beetles.  Monitor wild grapes if available or Honeycrisp for early signs of JPB.  This will be addressed in greater detail in the coming weeks.