May 26 AppleTalk Call

Guest Speaker Schedule Reminder

1. June 2: Dr. Brent Short, Trecé presenting on Codling Moth Lures and Mating Disruption
2. July 14: Dr. Sara Villani, North Carolina State University presenting on Summer Fruit Rots

Regional update

Location	Degree Days (Base 50°F)	Percent Scab Ascospore Maturity	Percent Cumulative Scab Ascospore Discharge
Eau Claire, WI	206	94	93
Gays Mills, WI	228	98	97
Hastings, MN	244	96	95
Harvard, IL	197	99	94
La Crescent, MN	231	98	98
Mauston (Northwoods), WI	190	95	92
Mequon (Barthel), WI	141	85	40
Rochester (Ela), WI	165	96	80
Trempealeau (Ecker’s), WI	229	98	98
Verona, WI	201	97	97

Table 1. Degree-day accumulations and scab ascospore maturity as of May 26, 2020 using data reported by Cornell NEWA Network.

Most locations are now at petal fall and have accumulated between 190 and 240-degree days base 50°F, minus locations close to Lake Michigan. This week will be hot with highs in the mid 80’s and lows in the upper 50’s and 60’s. Apple scab ascospore maturity is above 94% for most locations and is nearing 100% discharge. Pay attention to the difference in the percent of remaining ascospores to be discharged vs. percent maturity. For example, Mequon, while at 85% maturity, has only discharged 40% of their spores and still has 60% of their primary ascospores waiting to be released.

Winter conditions do not impact apple scab, cedar apple rust and canker diseases the same way as they impact insect populations. The only exception is powdery mildew, which dies at -15°F. Mild winters with minimal days below zero could relate to more insect pressure for pests that overwinter on the tree. Therefore, without too much speculation, this year might experience high pest pressure compared to 2019.

Insect management
Plum curculio
Please make note of the 95% petal fall date and report back to us. Tracking degree days from petal fall may be used to predict when their emergence from overwintering sites ends, which occurs after 308 DD base 50°F have accumulated. These degree days from petal fall will be included in the next summary table if you submit them to us. Without your actual petal fall date, NEWA estimates petal fall based on degree days accumulated from January first, which is likely to be inaccurate.

Injury from plum curculio (PC)has already been observed on the smallest fruit in high pressure orchards in southern Wisconsin. Fruit become susceptible to oviposition injury as the king fruits reach 5mm or larger. When PC first move into the orchard beginning between bloom and petal fall, they must feed and mate for a period of about seven days, before egg laying begins and the typical crescent-shaped scars appear. This year’s hot weather at petal fall offers perfect conditions for PC to begin moving into the orchards and it is essential to scout the perimeter of the orchard and focus on historical hot spots and locations that have the largest fruits.

Spraying perimeters more frequently is one option to reduce cover sprays. If PC injury is found past the perimeter, e.g., first four or five rows of trees, a full cover spray is recommended. In the past, many assume that thinning sprays with carbaryl will offer protection against PC. Thinning with carbaryl at one pint per acre delivers a half pound of actual carbaryl, whereas if carbaryl was used as an insecticide, this rate would be delivering two to four pounds of actual carbaryl per acre. Therefore, the rates used for thinning are not going to deliver insecticidal activity. Reducing rates of carbaryl may help lessen the impact on beneficial insects in the orchard.

Avaunt (indoxacarb) has been the most commonly applied organophosphate alternative to manage PC. Many of the newer insecticides use a combination of contact mortality, systemic activity as an anti-feedant or ingestion, to manage PC. The neonicotinoids Actara (thiamethoxam), Assail (acetamiprid) and Belay (clothianidin) offer a few days of contact mortality and after several days the insecticide penetrates the fruit and acts as an anti-feedant and oviposition repellant. Exirel (cyantraniliprole), a diamide insecticide related to Altacor (chlorantraniliprole), may be used to manage PC and CM. It has similar activity to Avaunt, which requires ingestion.

Note: Belay is very toxic to beneficial insects and pollinators and will remain toxic to pollinators for more than five days after an application. It is critical to wait until bees are out of the orchard and there are zero blossoms left on the trees and minimal bloom in the groundcover before applying Belay.

Read the most recent article from Dr. Peter Jentsch, Cornell, discussing plum curculio and codling moth: http://blogs.cornell.edu/jentsch/2020/05/26/plum-curculio-egg-laying-in-ginger-gold-may-26th-2020/

Codling moth
Over the Memorial Day weekend, a strong biofix was observed across southern Wisconsin. Most sites are between the 180 to 250 DD base 50°F from January 1st and is within the required-degree day accumulations needed prior to the first codling moth (CM) flight. Most orchards to the north will likely have a biofix this week. Codling moth traps should be checked nearly daily to establish the first CM flight. Codling moth biofix is marked by a significant biological event, or first sustained flight, where moths are captured multiple days in a row or exceed a threshold of five moths per trap per week. Once a biofix date is established, begin tracking degree-days (base 50°F) and monitor traps weekly. If you are calculating degree-days by hand, be aware that codling moth has a top developmental threshold of 86°F, which means all temperatures above 86°F should be counted as 86°F, e.g., a high of 95°F would be changed to 86°F degrees, if calculating by hand. Degree days are also available from your nearest NEWA station here, http://newa.cornell.edu/index.php?page=degree-days.

Codling moth fly between 6pm and 11pm when wind speeds are between three and five miles per hour and when temperatures are above 62°F, without rain. Assign the biofix date for the warmest, calmest night. When checking traps, fluttering CM had likely flown within the last 48 hours. Most female CM can live for seven to 14 days yet will mate and deposit the majority of eggs on the evening they emerge. Every day that a sexually viable female emerges and is not able to fly, egg fecundity is decreased by 20%.

Orchards with high pressure or a large first flight, e.g., more than ten moths per week, often apply the first larvicide at 250 DD after biofix. If the initial flight is light or inconsistent due to cooler temperatures or rain a stronger flight can occur after the first biofix, e.g., two-weeks later. If this occurs the first larvicide can be applied at 350 DD from the initial biofix. At 250 DD from biofix 3% of the generation’s population will be hatching and this continues to increase exponentially with additional degree-day accumulations, i.e., at 350 DD from biofix, 15% of larvae have hatched and at 450-550 DD up to 50% larvae hatch.

Lure Type	Lifespan for 1st Generation	Lifespan for 2nd Generation
1x red septum1	3 weeks	2 weeks
10x red septum2	3 weeks	2 weeks
Super Lure2	6-8 weeks	6 weeks
MegaLure (Trece)1	6 – 8weeks	6 – 8 weeks
Biolure CM10x (Suterra brand)2	4 – 6 weeks	4 weeks
CMDA combo lure	8 weeks	Probably less than 8 weeks3
Biolure CM1x (Suterra brand)1	6 to 8 weeks	Probably closer to 6 weeks3
CM L21	8-12 weeks	Probably closer to 8 weeks3

Table 2. Codling moth lure lifespan for first and second generation flights.

¹ http://msue.anr.msu.edu/news/using_pheromone_traps_to_monitor_moth_activity_in_orchards1

² http://entomology.tfrec.wsu.edu/stableipm/WorkshopPDFs/cmmonitoring.pdf

³ No data was available on the lifespan during second generation, but we should presume decreased life of these pheromones based on average temperatures in July and August that have potential to decrease duration of pheromone release.

Rosy apple aphid
Extension literature discusses that rosy apple aphid (RAA) become active between pink and petal fall. However, they are difficult to see, and colonies are often isolated at this time. As degree days accumulate, colonies, will become more prolific and visible. Rosy apple aphids can show some preferences for different cultivars within a block, and scouting efforts should focus on blocks or cultivars with a history of damage from this pest. Their feeding injury curls the leaves and can cause stunted fruit growth on clusters. The typical recommendations in spray guides are to control at pink, yet most years, they are very hard to detect at this stage. At petal fall, RAA may be managed with a low rate of a neonicotinoid, Beleaf 50 SG (flonicamid) or Sivanto 200 SL (flupyradifurone). All of these applications require a high volume of water to ensure adequate coverage. Lingering bloom and populations of bees that may still be foraging in the orchard make it hard to treat right at petal fall with a neonicotinoid. Treatment of RAA is further complicated by the secondary lifecycle it has on other plants, e.g., dock and plantain. Do not treat for RAA if trees are in bloom.

Lepidopteran complex
Lepidopteran emergence has been behind tree phenology but is now catching up rapidly. If managing spring lepidopterans in coordination with scab and fire blight management, make sure to scout for physical evidence of their activity to prevent an unnecessary insecticide application. Avaunt has efficacy against lepidopteran species along with PC. Altacor and Intrepid (methoxyfenozide) are other options to target lepidopteran species, but do not have activity on PC.

Disease management
Fire blight
The weather during bloom has been some of the most ideal conditions for fire blight in several years and the fire blight model in NEWA is forecasting significant infections. There has not been a bloom period with such extreme fire blight pressure in recent history. The same is true for scab infections. NEWA stations are showing extreme or high levels of fire blight potential, however this is not true if blossoms aren’t open and petal fall is occurring.

Trees are only susceptible to fire blight infections if blossoms are open and moisture is present. These basic parameters need to be met for an infection to occur: 1) Inoculum or signs of fire blight in neighborhood last year, 2) open blossoms, 3) moisture, and 4) warm temperatures of greater than 65°F. Be observant for cankers and bacterial ooze that could spread infections, even as risk decreases. At the current stage of tree growth, transmission down shoots where new tissue can be exposed, is a primary source of fire blight infections. Rapid or easily transmitted fire blight will be a possibility until shoots stop growing.

Streptomycin applied 24 hours before or after an infection period or rain event will provide control for up to 48 hours of bacterial growth inhibition after the infection. The fire blight Epiphytic Infection Potential (EIP), which references bacterial growth, should be tracked starting when blossoms open and restarted when streptomycin is applied after an infection period.

All other bactericides such as copper or Kasumin (kasugamycin) need to be applied before an infection occurs. Copper products like Cueva (copper octanoate) should be applied as the blossoms open. Copper applications may be beneficial on non-bearing trees or trees where fruit russeting is not a concern. This is an excellent time to scout for oozing fire blight cankers that could be painted with copper. Cankers that are not oozing by now most likely are not active fire blight cankers.

Apogee (prohexadione calcium) may also be applied to help minimize fire blight risk and is generally applied at pink, or as soon as possible. Instead of maximizing shoot growth reduction by applying three to four applications, applying once at a higher rate will help maximize fire blight control. Apogee is often applied at 6oz per acre at pink and again at 6-9oz per acre at petal fall to help with fire blight, according to Allen Teach of Sunrise Orchards, Gays Mills, WI. If the rate is too high, it may actually make the fruit “stick” to the trees and will be very difficult to thin. If not applied at pink, apply Apogee at 6oz per acre or slightly less. When applied at king bloom petal fall, Apogee can increase fruit set. Apogee rates based on tree size and tree row volume are discussed in the Michigan and Midwest spray guides

Petal fall thinning and use of the carbohydrate model
Developing fruit are at many different growth stages due to the variable weather conditions during bloom and timing thinning sprays at petal fall will be more challenging. The carbohydrate model is a tool that can be used to help determine application rates of chemical thinners and achieve more reliable thinning. The model takes some of the guess work out of thinning by using the current weather forecast to determine if thinner rates should be increased, decreased, or applied at the standard rate. The model calculates the general carbohydrate balance, which has been found to correlate well with natural drop and decreasing tree sensitivity including sensitivity to chemical thinners. Cool, sunny periods of good carbohydrate supply leads to a natural drop and less response to thinners (increase thinner rate).

Cloudy, hot periods result in carbohydrate deficits and lead to stronger natural drop and stronger response to thinners (decrease thinner rate). The carbohydrate model needs to be consulted at the time of thinning to help determine rates. The grower needs to use their experience with thinning and adjust rates based on what they have applied in the past to the target variety and crop stage. This model does not tell you what product to use or what rate to apply but is particularly helpful when using MaxCel (6-BA) or Fruitone (NAA), which are both dose dependent. Conversely, Sevin (carbaryl) is not dependent and will generally provide the same level of thinning regardless of rate.

Beginning at petal fall and before fruit begin to put on size, is a relatively safe time to thin, since thinners are much less responsive at this time. For example, to achieve a 50% fruitload thinning when applying Sevin (carbaryl) at 10-15 mm fruit, the same application will generate only 25% fruitload thinning at petal fall. Application timing is dependent on variety and level of desired thinning. Since petal fall occurs at different times, Sevin (carbaryl) should only be applied as a spot application. Applications to the entire orchard at petal fall are not advised.

Find more information in part three of Amaya Atucha’s paper published on pg.11 here, https://go.wisc.edu/3s74m8.

The carbohydrate model is available on NEWA under the crop management section, http://newa.cornell.edu/index.php?page=apple-thin.

Thinning discussion with Allen Teach
The weather forecast over the next three days with cloudy days and warm nights will mean trees are respiring overnight and burning up sugars, which will lead to carbohydrate stress. If a thinner is applied after a three to four-day period of carbohydrate stress, the thinner will work better. This Friday-Saturday will have high temperatures in the upper 60’s and cooler nights in the 50’s. It may be more beneficial to thin over the weekend. Fruit are sizing quickly, and fruit will approach 8-10mm before it cools off this weekend. This will be a cultivar by cultivar situation, especially considering freeze damage. There will not be one methodology that can be applied to the entire orchard.

Many fruitlets are at 2-3mm and may not survive if freeze damage occurred. The Malusim fruit growth model will help determine the number of fruitlets that will drop without a thinner. Allen collected samples of blossoms of each variety and each block. Some blocks had 0% freeze damage and others had 90% freeze damage. Allen will use these numbers to determine thinning conditions in each block and variety. At pink, blossoms were counted on about 65 trees, and this week he will go out to mark fruit clusters to get the first measurement of the fruitlets. He will also recount fruitlets to determine freeze loss and need for thinning. This year, Allen marked fruit clusters with numbered clothespins to keep data more accurate and recounting easier to follow. It will take four people two days at eight hours per day to complete these measurements. Allen will go out after four to five days to recount clusters. It sounds like a lot of work but helps save investment on thinning needs.

It has become apparent the effectiveness, or aggressiveness, of the thinner will depend on last year’s crop. If there is a biannual variety, e.g., Honeycrisp, with a heavy crop last year, they will be more difficult to thin year. Allen has also seen this in Gala’s and believes this will be true for most varieties. Thinning a lighter crop from last year will likely require less aggressive thinning. There are also other stress factors that may not be visible that impact disease susceptibility and overall health of the tree. Trees with long-term stress suffered more freeze damage.

Check out this Michigan State University Extension publication for more information on predicting apple fruit set model: http://nyshs.org/wp-content/uploads/sites/343/2015/03/15-20-Schwallier-Pages-NYFQ-Book-Spring-2015.eg-3.pdf

Development of a Fruitlet Growth Model to Predict Thinner Response on Apples: https://journals.ashs.org/hortsci/view/journals/hortsci/48/5/article-p584.xml

Recommended rates of chemical thinners based on the target variety are published in the Midwest and Michigan commercial tree fruit spray guides. Please consult these resources for specific rates. Note: These rates are based on a healthy and undamaged fruit set. The Midwest Fruit Pest Management Guide is available online for free and thinning recommendations may be found on pages 36 – 38: https://ag.purdue.edu/hla/Hort/Documents/ID-465.pdf

Grower Questions:

The bees only flew for two days and do not know how much fruit will set based on freeze and lack of pollination. There are a lot of yellow fruitlets and lost petals in about one day, which may relate to more freeze damage than originally thought. Last year had a lighter crop on Honeycrisp and the orchard is also the highest point in the whole county.

• Even under these conditions the fruit-growth model could still be used. Theoretically you will have time to go out and mark trees, then come back over the weekend to get a data set of what fruit will actually set. Considering you had a relatively mild freeze event compared to other locations nearby, at 27-28°F, freeze damage will be less severe. Locations within each block in terms of elevation will vary in freeze damage.
• Thinning demands careful observation and reflection on past experience. The best approach is to perform fruitlet counts and measurements and wait for the right weather to thin. There is a potential with overthinning with Sevin. A grower applied Sevin when it was damp and over the next couple of days it never dried out. It is best to wait and get three days of dry weather before applying a thinner. In terms of NAA, Allen once applied NAA about thirty minutes before an inch and a half of rain fell and had no issues with thinning. Note the differences between these products in terms of conditions needed for success.
• Phillip Schwallier, PGR’s and Thinning Strategies: https://williamshane.weebly.com/uploads/2/7/0/7/27077603/thinning_stratiges_2018.pdf