June 9 Conference Call

AppleTalk Conference Call Summary
Tuesday, June 9, 2020 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 or send to Josie Dillon, jdillon@ipminstitute.org.

June 9th Call Stream: CLICK HERE

AppleTalk Conference Call Summary

Tuesday, June 9, 2020 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 or send to Josie Dillon, jdillon@ipminstitute.org.

June 9th Call Stream: CLICK HERE

Guest Speaker Schedule Reminder

  1. July 14: Dr. Sara Villani, North Carolina State University presenting on Summer Fruit Rots

Regional update

Location Degree Days from January 1st

 (Base 50°F)

Plum curculio management
Petal fall date Degree Day Accumulation from Petal Fall (Base 50°F)
Eau Claire, WI 459 5/28 229
Gays Mills, WI 502 5/27 271
Hastings, MN 518 5/27 272
Harvard, IL 459 5/28 234
La Crescent, MN 597 5/27 288
Mauston (Northwoods), WI 449 5/29 217
Mequon (Barthel), WI 366 5/30 167
Rochester (Ela), WI 406 5/31 177
Trempealeau (Ecker’s), WI 498 5/26 290
Verona, WI 467 5/29 225

Table 1. Degree-day accumulations as of June 9, 2020 using data reported by Cornell NEWA Network.

Following the heavy rain forecasted for June 9 – 10, the rest of the week will be dry with highs in the 70’s and lows in the 50’s. The weekend low temperatures may drop into the 40’s and evening activity of codling moth and plum curculio will likely drop. Locations along the Mississippi River may receive two to four inches of rain, with less in eastern Wisconsin.

Most locations have accumulated 225-degree days (DD), base 50°F, or more degree days, of the 308-DD base 50°F from petal fall, which track and predict plum curculio movement into the orchard. Plum curculio will typically no longer move into the orchard after 308 DD from petal fall.

Orchards which had a codling moth biofix over Memorial Day weekend began reaching their 250 DD, base 50°F, benchmark to apply the first codling moth larvicide on Friday, June 5th.  Orchards that had a later biofix will likely reach this first benchmark for applying a CM larvicide this week.

The hot weather is making thinning decisions more challenging for growers. Despite the Mother’s Day freeze, thinning is looking good in most orchards and trees generally do not appear to be stressed. Thinners are still being applied and if fruit are at 15-20mm, applications of NAA under extreme, hot conditions, especially when applied with Regulaid, could drop much more fruit than anticipated. There has been a good differentiation in fruit size over the last week, which has made thinning results more apparent. As temperatures begin to cool after the rains this week, thinning rates will need to be adjusted according to the carbohydrate model.  The four-day carbohydrate balance for the rest of the week is showing a surplus and to increase thinning rates 15% to 30%.  Please use your local NEWA station to evaluate how the carbohydrate balance may impact your thinning.

The crop this year is moderate and not very uniform. Some varieties have too much fruit while other varieties self-thinned well in different environments. A reminder that last year’s fruit load will also play a role in thinning this year’s crop. A heavy fruitload last year will relate to more difficulty in thinning, while a lighter fruit load may lead to an easier thinning process.

Disease management
Incidences of apple scab and fire blight have been lower than initially predicted and high-inoculum orchards have not shown the increases in scab lesions that were expected. Continue scouting blocks with a history of scab infections, since lesions may still appear within the next week, depending on when the most recent infection occurred.

After assessing past infections that occurred between bloom and petal fall, several locations may still be waiting for first generation scab lesions to appear. When scab infections occur and temperatures are in the 50s, it can take 12 to 14 days for lesions to appear. As temperatures increase, the days until lesions appear decreases, where infections that occur in the 60sF, only require nine to 11-days to appear.

  • Eau Claire, WI: An infection event occurred on May 23rd that had a 30% ascospore discharge. There was also an infection event that occurred from May 25th, with 10% ascospore discharge.
  • Hastings, MN: An infection event occurred on May 23rd that had a 33% ascospore discharge. There was also an infection event occurring on May 25th, with a 10% ascospore discharge.
  • Mequon, WI: An infection event occurred on May 28th that had a 47% ascospore discharge.
  • Trempealeau, WI: An infection event occurred on May 23rd that had a 22% ascospore discharge.

Note: Where mancozeb has been used on the extended spray schedule, fruit to be harvested on September 1 have until June 15 to make a final 3 lb. per acre application of mancozeb and comply with the 77-day pre-harvest interval. Where the pre-bloom, spray schedule was used, no more mancozeb may be applied. As per the label, the pre-bloom and extended mancozeb spray schedule should not be mixed.

Powdery mildew
Powdery mildew (PM) has been observed at a few orchards in the last two weeks. This disease flourishes in hot and dry conditions. Spores are easily washed from infection sites, but the fungus can grow on terminals, in the absence of rain. At one time, this a rather rare disease in the upper Midwest, but shoot infections are now commonplace. In the southern United States, powdery mildew is much more severe and can spread to fruit and cause russeting. At this point, there is no need to worry if powdery mildew appears on trees other than to note its location for next year. Single-site fungicides and sulfur provide protection against powdery mildew, whereas captan does not. Where there are no active-scab infections, single-site fungicides with efficacy on powdery mildew may be used with minimal concern of losing efficacy for primary scab management. Growers may have new trees that brought in PM or have some resistance. Sulfur may be used as a tank mix to mitigate resistance and organic producers may also use sulfur as a protectant against powdery mildew. Nurseries have different management programs and it is important to keep an eye out for PM on first-year trees and to remember there is potential for this disease to develop resistance.

The spring and fall of the last several years have been notably wet with excess rain leading to overly saturated soils for extended periods of time. This saturation is not a great concern in November, however rainstorms earlier in the fall and in March – May, a time when roots are actively growing, can induce additional tree stress. Orchards which continue to hold moisture and remain oversaturated, are also are at risk of invasions from Phytophthora and water molds. When flooded orchards and soils are saturated for more than a week, the soil biota can become anaerobic. In addition to supplying a conducive habitat for root-injury-causing soil pathogens like phytophthora, water-logged fields pose a severe risk of tree stress and drowned roots. Significant death of tree roots can occur after three weeks of over saturation even without standing water on the soil’s surface. If soils are not drying out, there is little that can be done to mitigate these risks. Applying a phosphorous acid fungicide will offer some protection against these pathogens, but risk of root die-off remains.

Soil moisture may be assessed by digging into the root zone and making a clump of soil with your fist. If the soil remains in a in a clump when squeezed, there could be excess water in the soil.  This is rather subjective and should be completed a week after heavy rains. The phosphorous acid fungicides include Aliette, Fosetyl-Al 80 WDG, ((Aluminum tris (O-ethyl phosphonate)), Phostrol (Mono- and dibasic sodium, potassium, and ammonium phosphites), Rampart (53 – Mono- and dipotassium salts of Phosphorous Acid), after the soil has dried out a little bit. The phosphorous acid fungicides are highly systemic, short acting and all function the same way. They are applied as a foliar spray where they are absorbed into the leaves and are translocated to the roots where the fungicides fight off Phytophthora and soil-based pathogens. Overuse of these fungicides may result in pathogen resistance. Make sure to look at the pre-harvest intervals on these fungicides. Generally, two applications about a month apart are recommended; one application after petal fall and one 30 days later. These products are relatively cheap, at $7-8.00 per acre.

Phosphorous acid fungicides should not be tank mixed with other pesticides and need to be applied alone. These fungicides are formulated to be rapidly absorbed into the leaf tissue, which could pull in other products that are included in the tank mix and result in phytotoxicity injury. Leaf burning from captan would be a good example. The longer the product stays wet on the tree, the more absorption will occur. Even if the soil dries out, roots may be compromised through the rest of the season.

Where orchards are being established on soils that have a high water-holding capacity or are poorly drained, consider using rootstocks with Phytophthora tolerance, e.g., Geneva rootstocks. Other rootstocks like M26, M9 should not be planted where Phytophthora has been documented.

John has been recommending the minimal label rate applied 30 days apart. However, he has been recommending applications per acre, rather than per 100 gallons. These phosphoric acid products are acidic, therefore if another product mixed in is alkaline, it could cause some issues. This can also be an issue if the water pH is above 7.3. If this is the case, a pH modifier should be added to the tank.

Read more about Phytophthora: https://ohioline.osu.edu/factsheet/plpath-fru-06

Insect management
Plum curculio
More orchards have reported aggressive injury from plum curculio (PC) and more than what has been observed in recent years. Make sure to continue monitoring for fresh oviposition strikes as migration will occur until or possibly past 308 DD post petal fall. Avaunt (indoxacarb) may be used for a final plum curculio (CM) spray, rather than a neonicotinoid as it will have offer efficacy for CM and will have a longer effect on adult PC. Tank mix another product if planning on applying a neonicotinoid, e.g., Assail or Belay, for late PC. John and Peter recommend saving neonicotinoids to target second generation codling moth and apple maggot, and to not expose first generation codling moth to products like Belay and Assail. See the table below.

John is predicting that all growers should expect to see PC injury in the packing line due to extreme heat after petal fall. In the 90’s a similar weather pattern occurred where mated females were hyperactive. A mated female PC on an 80-degree night may have a revved-up system that can allow them to cause a significant amount of damage to fruit before dying. The females may be able to survive adequate insecticide coverage, even when an organophosphate such as Imidan (phosmet) is used, due to enzymes in the body that fight off the effects of the insecticide for a limited time.

When assessing PC injury, the age of the injury is important, e.g., is injury similar or different in size? The size of the injury reflects when PC have entered the orchard. In wild orchards, female PC lay two or three eggs on a fruitlet and then move on. If more PC are entering the orchard afterwards, the fruitlets will often have several different sized scars. Even though most fruit are at 10mm, they typically target the largest fruit.

PC typically overwinter in the fence row, woods, hedges e.g., anywhere with deep cover to overwinter in. Many factors determine when they emerge, and we generally expect they survived the mild winter. The freezing temperatures this spring likely did not cause mortality. Their emergence does rely heavily on soil temperatures, so if the temperatures were more variable, we could see extended emergence. This may mean PC will enter the orchard even after the 308-degree days from petal fall.

Codling moth
The start of the first generation of codling moth was marked by a very strong flight with high numbers in many orchards.  Codling moth captures have declined over the last week and are steady and consistent with what we have observed in prior years. Last fall was cool and wet, which may have impacted overwintering populations. Later emerging second generation larvae, e.g., emerging in October, may have had lower survival rates than the first emerging larvae. Most growers who hung traps early had a relatively substantial biofix and have seen trap catches drop over the past couple of weeks. The lower survival rate of later overwintering larvae may mean the second generation of CM flights may be lower as well.

Typically, when a larvicide is applied at 250 DD (base 50°F) from biofix, this will target 3% of the total population. The percentage of the population being targeted by a larvicide increases to 15% when the spray is delayed to 350 DD. Peak egg hatch where 50% of the population is hatching occurs around 500 DD and after 650 DD is when egg hatch begins to decline. Orchards that are not using mating disruption should still target first applications at 250 – 350 DD if trap captures are high, e.g., 10 or more in a week’s time. Orchards where some traps reach the threshold of five and have other traps that stay below threshold, could delay to 350 DD. Orchards that are using mating disruption should follow the same approach for determining the need for a larvicide. If the threshold of five is quickly reached or exceeded, then an application right at 250 or 350 DD would be necessary. If there is only a slow trickle of one or two moths per week, targeting at peak egg hatch may be a better solution.

The importance of timing right at 250 DD or delaying the first spray is relative to the size of the CM population in the orchard. Where growers have low populations, the first spray may be delayed to 350 DD because there will not be many codling moth larvae hatching right at 250 DD. Fruit from these early hatches often fall to the ground from thinning or June drops and the injury may never be visible. If 15, 20 or 30 moths were caught during the first flight, then 3% represents a lot more eggs that will hatch, than if only caught 1, 3 or 5 moths were captured in a trap. 40% of egg hatch occurs between 350-650-degree days from biofix, which we can rely on due to the strong biofix in most orchards.

Understanding wash-off rates are critical for timing the reapplication of insecticides. Spinosyns, e.g., Delegate (spinetoram), diamides, e.g., Altacor (chlorantraniliprole), Exirel (cyantraniliprole), and Avaunt (indoxacarb) are very rainfast, whereas neonicotinoids, e.g., Assail (acetamiprid) and Belay (clothianidin) are less rainfast. If 0.5” of rain falls on a neonicotinoid in the first week, there will be adequate residue, but an inch of rain within 24 hours of application will require reapplication. No insecticide can be exposed to two inches of rain and effectively control CM or plum curculio.

Insecticide options for codling moth and plum curculio
Trade name (active ingredient) Plum curculio Codling moth Notes
Avaunt(indoxacarb) X X Less long-term control of codling moth compared to Delegate or Altacor.  Rated as ‘fair’, reapply after 7-10 days.
Actara(thiamethoxam)* X Apply with CM insecticide, e.g., Altacor, Delegate.
Altacor(chlorantraniliprole) X Apply with PC insecticide, e.g., Avaunt, Actara.
Delegate(spinetoram) X Apply with PC insecticide, e.g., Avaunt, Actara.
Exirel(cyantraniliprole) X X Same insecticide group (28) as Altacor
Belay(clothianidin)* X X Use only if CM pressure is low, e.g., less than 10 moths/week/trap.  If Belay is used and pressure is high tank-mix with CM specific insecticide.
Assail(acetamiprid)* X X
*Note: If a neonicotinoid is used exclusively for PC and first-generation CM control it cannot be used alone for second generation CM and apple maggot (AM) control.  An imidacloprid, e.g., Admire Pro, Montana, Wrangler, tank-mixed with Altacor or Delegate or applying Exirel alone will offer AM control and mitigate resistance concerns for CM; do not treat more than one generation of a target pest with any of these insecticides.

Obliquebanded leafroller
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 will not suppress populations of obliquebanded leafrollers (OBLR), which should be flying very soon. 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 appleworm, 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).

Several traps in the last few years have captured an OBLR mimic that has gray to dark gray banding. This could possibly be fruit tree leafroller. These traps can bring in other insects, e.g., redbanded leafroller, as well. Many times, other moths will get pulled in but are not pests that growers need to worry about.

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.

Dogwood borer
First flights are occurring at about 300-degree days from CM biofix. Traps should already be deployed. 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. John caught DWB in an orchard that filled the trap from the first week in June to early September. Last year there were larger flights, so will be interesting to see what the population looks like this year. If trees are less than 10 years old, growers should have at least one dogwood borer trap up.

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.

When applying chlorpyrifos as a trunk spray use large volume 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.

For more information and photos visit:

What Wood Borers Do? – What’s in the Trunk?, Scaffolds Fruit Journal, April 17 2017, http://www.scaffolds.entomology.cornell.edu/2017/SCAFFOLDS-4-17-17.pdf

Potato leafhopper
Potato leafhoppers (PLH) come to the region during spring storms where warm air masses from the Gulf of Mexico pick them up, as the system moves north. To date, numbers reported in other host crops, as per the Wisconsin Department of Agriculture Trade and Consumer Protection Pest Bulletin, were still relatively low. The first large leafhopper immigration into orchards tends to occur after the second cutting of hay.

Potato leafhopper adults and nymphs will inject a toxic saliva that causes damage to the leaf tissue. The first sign of leafhopper feeding includes the cupping of leaves. Further damage appears as a yellowing “hopperburn” of young terminal leaves. Hopperburn can be described as a triangular yellowing or browning of the leaf tip. This injury develops more rapidly during hot, dry weather and most of the damage come from nymphs.

Leafhoppers often move in a lateral fashion and will quickly jump to the underside of the leaf if disturbed. Growers should be most concerned with PLH nymphs, and if needed, an application should wait until nymphs are more commonly observed, instead of targeting the adults. The main priority is to monitor PLH on leaf terminals in younger trees. The threshold for PLH is one or more nymph per leaf when hopperburn symptoms is appearing. For more detailed information, please visit: http://labs.russell.wisc.edu/vegento/pests/potato-leafhopper/

Questions/requests for growers

  1. John has had reports of phytotoxicity issues when tank mixing Captan 80 and Exirel. If any growers have had this issue, please submit pictures.
  2. Currently, a lot of herbicides are being applied. What are grower’s largest obstacles to adopting mulching as a cultural practice as a long-term weed reduction strategy?
  3. What are your experiences with compost teas? John would like to explore this method of diversifying micro-biota on plant surfaces as an aid to mid to late-season fungal spread.