July 21 Conference Call

Posted on 21. Jul, 2020 by in Uncategorized

AppleTalk Conference Call Summary
Tuesday, July 21, 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.

July 21st 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 1347 May 28 181 June 1 988
Gays Mills, WI 1426 May 27 117 May 24 1188
Hastings, MN 1485 May 27 117 June 1 1107
Rochester (Ela), WI 1326 May 31 129 May 24 1135
Trempealeau (Ecker’s), WI 1449 May 26 174 May 24 1189
Verona, WI 1419 May 29 152 May 24 1208

Table 1. Degree-day accumulations as of July 20, 2020 using data reported by Cornell NEWA Network.

Over the next week, highs will be in in the 80’s and lows will be in the 60’s. The weekend will be warmer with highs in the 90’s.

Sooty blotch and flyspeck applications may begin at 175 leaf-wetting hours (LWH) from petal fall. Eau Claire, and Trempealeau are at 175 LWH according to NEWA. Verona is predicted to hit 175 LWH this week and Rochester, Gays Mills and Hastings are still about a week or so away. Relative humidity plays a role in LWH and applications may need to be made sooner if heavy dew in the morning is not registering as wetting periods on leaf wetness sensors.

A few locations have observed second generation codling moth flights, in Southern Wisconsin and in the Mississippi River Valley. Second generation codling moth captures often reflect how well first generation was managed. Therefore, these trap counts will be impacted by those first-generation counts, e.g., missed timing of insecticide application or wash off could impact second-generation populations. John is observing that CM trap counts are variable and any large flights that occur now, if over 1000 DD, are considered second generation. Where trap captures remain low, adding up all trap counts can help to better represent overall population dynamics.

Disease management
Recap of summer disease discussion
The two species Dr. Villani discussed on last week’s call are two variants of bitter rot. Only one species causes the bitter rot that we are familiar with in the Midwest, whereas the Glomerella species does not cause the fruit rots we are managing. The visual symptoms of bitter appear as a orange, slimy mass that is almost salmon-colored, and creates a V-shape into the fruit when cut in half. Her research indicates that most of the fungicides used to control bitter rot are strobilurins and other materials used for summer diseases, e.g., Topsin (thiophanate-methyl), Incognito (thiophanate-methyl), had a significant drop off in effectiveness of bitter rot management. Merivon (fluxapyroxad and pyraclostrobin), Pristine (boscalid, pyraclostrobin), followed by Flint (trifloxystrobin), and then Luna Sensation (fluopyram, trifloxystrobin), offer the best management of bitter rot.  The SDHIs Fontelis (penthiopyrad) and Sercadis (fluxapyroxad) are not labeled for bitter rot and offer no suppression; Aprovia (benzovindiflupyr) is labeled as suppression only for bitter rot.

Bitter rot should be managed differently on Honeycrisp, compared to less susceptible cultivars. Merivon is the most effective strobilurin and works better with the SDHI component. The strobilurin that is in Merivon is also not available as a single active ingredient labeled on pome fruits. Fruit infections can still spread post-harvest and in the cooler, which makes an application of Merivon several days before harvest a good option. Merivon has a zero-day pre-harvest interval (PHI), which makes it the easiest product to use. Sovran has a 30-day PHI and Flint has a 14-day PHI. Dr. Villani’s recommendation is to use the Merivon right up to harvest on Honeycrisp.

Grower question: Currently I am planning to manage summer diseases with a combination of strobilurin and SDHI use. I will apply Topsin, then go in with Merivon as the two last sprays before harvest. Will I have higher risk for bitter rot due to Topsin not offering as much protection?

  • Yes, you may be at higher risk. Topsin does control black and white fruit rots but is poorer at controlling bitter rot. Merivon applied when lesions are very small will not eradicate the infection. The fungicides must be applied before visual symptoms appear. Once fruit are infected, the question is how long the lesion can be kept in check. The longer we can go through the summer with small lesions and prevent them from blooming, the better. Merivon will be applied later which will suppress lesion growth.
  • Villani also mentioned that a ¾ rate of captan provided Merivon levels of control as a protectant, but that does mean reapplying as soon as wash off occurs. A ¾ rate has efficacy for a 10-14-day period.

White rot
It is not easy to distinguish black rot from white rot, and the difference is identified by the appearance of the rot going into the core of the fruit. John describes most of these lesions as black rot due to it being observed every year via the frog eyed leaf spot in leaf tissue. However, white rot may be even more widespread. Captan prevents fruit infection but does not help prevent infections of the trunk, though is possible that captan on the bark might offer some protection. The white rot invasions that Peter observed likely happened last spring after the polar vortex, and while it seems the cankers appeared out of nowhere, the fungi have been present for a long time. When trees become stressed, the trees stop producing compounds that can help prevent the spread of these infections.

If trees have bark injury from herbicides, rodents, weed whips, etc., these trees are at risk of being infected by canker fungi when there is warm, wet weather. Many larger infected trees can withstand and fight off many of these infections for years, but the margin of error on a high-density planting is very small. Trees can likely be invaded in year one if they are not cared for properly.

Black rot
Black rot infections on fruit usually appear at the calyx end and can originate at any wound that penetrates the epidermis, e.g., insect or hail injury. Black and white rot can be difficult to distinguish and spore producing lesions are black for both types of rot. Usually only one spot occurs per fruit, a characteristic that distinguishes black rot from bitter rot. Initial infection becomes brown and stays brown or turns black as it increases in size. A series of concentric rings often forms as the rotten area increases in size and lesions are usually amorphous. The flesh of the decayed area remains firm and leathery, and fruiting bodies will appear on the surface of the rotted tissue.

Fungicides that protect against fruit rots include captan, strobilurins, e.g., Pristine (boscalid, pyraclostrobin) and Flint (trifloxystrobin). Do not apply strobilurins if scab lesions are present. A high rate of captan may provide adequate protection. Note: To reduce resistance concerns always tank mix single-site fungicides with a protectant.

Frogeye leafspot
Symptoms are defined by their purple to red margins around the leaf surface with a brown middle. Lesions appear several weeks after petal fall and will grow to 3-6 mm in diameter. Frogeye leaf spot can be confused with phytotoxicity from pesticide application, use the purple margins as defining characteristics of this disease. Once present on the leaf surface, this disease will not release spores or cause additional infections.

Alternaria leaf blotch
Symptoms appear as brown blotches that are 2-10mm in diameter on leaves and are surrounded by a dark margin. The leaves turn yellow over time and will die prematurely. Fruit appear sunken with small (~2mm) brown spots surrounded by a black border. Alternaria leaf blotch usually affects high value cultivars like Royal Gala, Fuji, Pink Lady and Red Delicious.

Marssonina leaf blotch
Marssonina leaf blotch is a foliar disease with a similar life cycle to apple scab. It overwinters as a fungal spore in leaf litter on the orchard floor. Contrary to apple scab, it is a warm weather disease with infection periods occurring in mid to late summer. A definitive sign is early leaf drop occurring in August and early September. Some cultivars are more susceptible than others.

Fruit sunburn
Fruit sunburn has been increasing over the last several seasons, especially as adoption of high-density plantings increase. Sunburn can occur as early as mid-July and is still a threat through early September. Anecdotal evidence suggests that fruit becomes more susceptible to heat and sunburn injury increases near harvest. Damaged flesh is vulnerable to colonization by various fruit rots, requiring fungicide programs to be modified if symptoms of rot are detected. Sunburned fruit is also susceptible to changes in pigment, restricted coloring, and degradation of internal-fruit quality.

Sunburn occurs when shaded air temperatures are above 86°F and fruit temperatures are above 113°F:

  • Sunburn necrosis is caused by heat and when fruit-surface temperatures reach 126°F for 10 minutes.
  • Sunburn browning is the most common form and results in yellow, brown, or dark tan patch on the sun-exposed side. Threshold is 115 – 120°F for one hour. Cells are not killed, even though the skin loses color.
  • Photo-oxidative sunburn (bleaching) occurs when shaded or partially shaded apples are moved into strong or direct sunlight, e.g., most often occurs when weight of a heavy crop load moves branches and exposes previously shaded fruit to the sunlight.
  • Sunburn bleaching is independent of temperature and is caused by visible light.

Additional environmental factors that may result in sunburn include intensity of solar radiation, cloud cover, humidity, wind, and growing conditions including canopy density, variety, fruit size and water stress. Higher humidity reduces the occurrence of fruit sunburn, while fluctuating temperatures increases the occurrence of fruit sunburn. Sunburn damage can cause fruit to be more susceptible to summer fruit rots, e.g., bitter rot. Varieties at greatest risk of sunburn include Braeburn, Fuji, Honeycrisp, Jonagold, Gala, Ginger Gold, Golden Supreme, Granny Smith, Royal and Zestar.

The impacts of fruit sunburn can be mitigated by scheduling frequent irrigation to avoid tree-water stress; avoiding excessive summer pruning, especially before or during hot weather; protecting picked fruit in bins from direct sunlight and keeping fruit cool by improving orchard airflow. It may not be necessary to apply a sunburn material if paying attention to fruit rots.

There are three primary types of protectants that can be applied directly to the fruit to mitigate sunburn. Generally, these all work under the principle of reflecting ultraviolet and infrared radiation which can damage the fruit skin or cause overheating. These include:

  1. Clay based: kaolin clay, e.g., Surround WP.
  2. Calcium carbonate-based: Purshade (62.5% calcium carbonate). Growers that have used Purshade do not usually apply after end of July because it is difficult to wash off harvested fruit.
  3. Wax based: Raynox (water, carnauba wax, organically modified clay, emulsifiers). Growers have noted that it is difficult to mix in the spray tank and there can be issues with the materials clogging nozzles. For more information visit: Raynox Plus applications to prevent sunburn of Honeycrisp apples, Jon Clements, Sunday, December 6, 2015, http://jmcextman.blogspot.com/

Additional resources

Insect management
Obliquebanded leafroller
John, Josie, and Peter have been observing more leafroller larvae in young trees and terminal ends at locations in Southern Wisconsin and the Mississippi River Valley. These are not all obliquebanded leafroller (OBLR) and could be variegated leafrollers. The summer generation of OBLR have begun flying in a few orchards and should begin across the region at any time. The first generation OBLR biofix occurred around June 11 in southern Wisconsin, and there are approximately 1201-degree days (Base 43°F) between first and second generation biofix and we are at 1183 DD base 43°. Most models discuss managing OBLR after eggs have hatched, however this does not prevent fruit injury. Unmanaged leafroller larvae right now will contribute to a flight that could extend into early September. Also, larvae emergence in August can cause some significant injury right at or before harvest. This has caused major problems in Washington and Michigan as leafroller larvae have become resistant to several insecticide classes including the organophosphates and pyrethroids.

Lures and sticky boards for OBLR traps should be refreshed this week, if not already completed. Neonicotinoid applications are often saved for later in the summer to manage codling moth and apple maggot, however these products are not effective on OBLR. A diamide such as Altacor (chlorantraniliprole) or Exirel (cyantraniliprole), or a spinosyn, i.e., Delegate (spinetoram), Entrust (spinosad) or even a Bacillus thuringensis application should be planned in late-August to manage leafrollers. Applications should be made 10-14 days after the peak flight, if the flight continues, a second application may be necessary.

Japanese beetle
A large Japanese beetle (JPB) emergence occurred about two to three weeks ago where Honeycrisp were impacted the most and now JPB activity has slowed significantly. Japanese beetle is very sensitive to heat and may have moved through their lifecycle faster due to the hot temperatures.

Insecticide options for this pest are rather limited. Neonicotinoids, e.g., Assail (acetamiprid), Actara (thiamethoxam), will offer good repellency if applied before large aggregations of JPB begin to appear. If populations are large, applying a “knock-down” or contact insecticide, e.g., organophosphate or PyGanic (pyrethrin), may offer good control. In the past, a combination of 1 – 2 lb. of Imidan (phosmet) tank mixed with a neonicotinoid may give better management of this pest. Carbamates, e.g., carbaryl, also work, but are much more disruptive to biological controls and other natural enemies that may be active in the orchard. If you are avoiding organophosphates, carbamates or pyrethroids, then it is very critical to make an application of a neonicotinoid at the first sign of their feeding injury and before the aggregations appear. If imidacloprid products are applied for AM, e.g., Wrangler, Alias, Montana, these should also offer some repellency and anti-feeding properties for Japanese beetle.

Organic producers have the option of applying neem (azadirachtin) oil products, e.g., Azadirect, Trilogy, or PyGanic. It is important to be aware that a botanical insecticide such as neem may be phytotoxic if tank mixed with other pesticides.

Apple maggot: Effective life of maggot sprays
Apple maggot are more widespread this year than they have been in the past few years. Trap capture numbers have been low, but John has been observing them more commonly. Early captures of apple maggot may be targeted with imidacloprid products through July, as these will prevent crop injury through their ability to repel feeding and egg laying.  However, sprays applied closer to harvest need to kill the adult population before sprays cease to meet pre-harvest interval requirements and Assail or Exirel are the best organophosphate alternatives that could be applied. Apple maggot traps need to be kept clean, otherwise it will be more difficult to identify trap captures. If growers want to manage apple maggot with lower numbers, they can apply spot sprays. Imidacloprid remains a good tank mix option as a repellent and anti-oviposition material that can be included with Altacor or Delegate.

The neonicotinoid class of insecticides has become our primary organophosphate alternative for managing apple maggot. Unlike pesticides such as Imidan (phosmet) that offer excellent contact mortality against adults, neonicotinoids are absorbed into the skin of the fruit and act as a repellant or a systemic antifeedant and larvicide. These systemic properties of the neonicotinoids give the insecticide a long lifespan and boosts rainfastness up to two inches (or one inch if the rain event was within 24 hours of application). Assail and Altacor, for example, can last up to 21 days with very low rainfall. Pesticide rainfastness is much more of a concern for codling moth, but for apple maggot and Japanese beetle, we may achieve adequate control of these pests even as we reach the maximum of two inches of rain.

Apple insecticide precipitation wash-off re-application decision chart. Expected codling moth control in apples, based on each compound’s inherent toxicity to codling moth larvae, maximum residual, and wash-off potential from rainfall.
Insecticides Rainfall = 0.5 inch Rainfall = 1 inch Rainfall = 2 inches
*1 day *7 days *1 day *7 days *1 day *7 days
Imidan Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Asana Sufficient Insufficient Insufficient Insufficient Insufficient Insufficient
Assail Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Proclaim Sufficient Insufficient Sufficient Insufficient Insufficient Insufficient
Rimon Sufficient Sufficient Insufficient Insufficient Insufficient Insufficient
Delegate Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient
Altacor Sufficient Sufficient Sufficient Sufficient Insufficient Insufficient

Apple maggot: Opportunities for spot sprays
Both baited and unbaited-red spheres are effective for attracting AM. Apple maggots are highly mobile pests and are attracted to fruit both visually and through olfactory senses. When unbaited spheres are used at three traps per ten acres, the threshold is one fly per trap, while baited spheres have a threshold of up to five flies per trap. Maggot flies are sometimes only caught in isolated sections of orchards. If we are using a good density of traps, we can rely on this trap data to determine what part of the orchard needs to be sprayed. This can help us effectively use spot treatments to manage AM and is particularly useful if codling moth does not need to be treated. Spot sprays can be an excellent option for AM control, especially in orchards with variable pressure looking to limit insecticide costs or toxicity effects. Ultimately, it may not be necessary to make an orchard wide application.

The most common management strategies employed by organic producers include trap out with red sphere, applications of Surround (kaolin-clay) and a limited range of insecticides.  Products like the GF-120 Fruit Fly Bait (spinosad) have been around for a long time and used with some success.  The GF-120 bait is a spinosyn baited with sugar to encourage feeding by the apple maggots.  Newer products such as Grandevo (Chromobacterium subtsugae) or Venerate (heat-killed Burkholderia spp. Strain A396 and spent fermentation media) are available but their ability to manage apple maggot is not well established and their use is not widely adopted. Grandevo has been proven to be effective at managing populations of spotted wing drosophila and may be promising for apple maggot.  We welcome feedback from organic producers using any of these chemistries.

Even though harvest is still six weeks away, it is not too early to think about harvest management. Applications of ReTain tank mixed with NAA can extend harvest seven to ten days. The combinations can continue to promote ripening and inhibit fruit separation at the abscission zone. This may be advantageous for growers wishing to extend pick-your own harvest or if fruit are beginning to drop before the anticipated harvest. 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.

Pre-harvest intervals for late season sprays

Product Pre-harvest Interval
Actara (thiamethoxam) 0 – 2.75 oz./acre: 14 Days
2.75 – 5.5 oz./acre: 35 Days
Altacor (chlorantraniliprole) 5 Days
Assail (acetamiprid) 7 Days
Avaunt (indoxacarb) 14 Days
Captan 80WG (captan) 0 Days
Delegate (spinetoram) 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
Pristine (boscalid, pyraclostrobin) 0 Days
ReTain (-trans-2-Amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride 7 Days
Topsin (thiophanate-methyl) 1 Day

Table 2. Pre-harvest intervals of commonly used pesticides.
*Note: This table is only a reference, always refer to the product label.

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