July 19, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 19, 2016, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 19th call download: Click Here

Fruit sunburn prevention and management
Sunburn of fruit has been a consistent problem for the last several seasons, especially as adoption of high-density plantings increase.  On average we had 1% crop injury from heat or sun across all growers in the IPM Institute scouting program in 2015.  Today we reviewed some information taken from Australia on different approaches to managing risk of sunburn.  You can read the full article, Sun Protection for Fruit, A practical manual for preventing sunburn on fruit – 2011, http://mvcitrus.org.au/mvcb/wp-content/uploads/sites/343/2012/09/Sun-Protection-Manual-for-Fruit.pdf.

Sunburn occurs when shaded air temperatures are above 86°F and fruit temperatures are above 113°F and results in several types of fruit sunburn:

  • Sunburn necrosis: Caused by heat and when fruit-surface temperatures reach 125.6°F for 10 minutes.
  • Sunburn browning: Most common form and results in yellow, brown or dark tan patch on the sun-exposed side. Threshold is 114.8 – 120.2°F for one hour.
  • 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. Does not require infrared or ultraviolet radiation to occur.

Additional environmental factors that can result in sunburn include, intensity of solar radiation, cloud cover, humidity, wind; and growing conditions including canopy density, variety, fruit size and water stress.  Varieties at greatest risk of sunburn include Granny smith, Royal Gala, Honeycrisp, Zestar, Jonagold, Braeburn, Golden Supreme, Ginger Gold and Fuji.  We can mitigate the impacts of sunburn by scheduling frequent irrigation to avoid tree-water stress; avoiding excessive-summer pruning; protecting picked fruit in binds from direct sunlight and improving air flow in the orchard to keep fruit cool.

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:

  • Clay based: Kaolin clay, e.g., Surround WP
  • Calcium carbonate-based: Purshade (62.5% calcium carbonate) or nutrient solutions, e.g., Phoenix (60% calcium carbonate, 24% calcium)
  • Wax based: Raynox (water, carnauba wax, organically-modified clay, emulsifiers)

Influence of temperature on pesticide applications
The forecasted weather for the next week raises regarding pesticide applications in extreme weather.  As a general rule, do not make fungicide, insecticide or nutrient applications when daytime temperatures are forecasted to exceed 85°F because of the risk of volatilization and/ or the increased risk of sunburn when water is drying on the fruit.  If an application must be made, finish spraying by mid-morning so solution has adequate time to dry before high mid-day temperatures.  High humidity when an application is made will increase the drying time.  Use caution when applying adjuvants that act as a penetrant, e.g., Regulaid, LI700, since they can deplete the plant cuticle for one to two days before the plant rebuilds it.  Do not use a penetrant, sulfur or summer oil when high temperatures are forecasted!

Fungicide update
Phosphonate fungicides (FRAC group 33), e.g., Aliette (aluminum tris), Phostrol (phosphorus acid), ProPhyt (potassium phosphite) are systemic and are rapidly translocated through the vascular system into the roots.  This group of fungicides is effective on root rot diseases, e.g., Phytophthora, and summer diseases, although the foliar effect of the fungicide is gone in a few days (check product label for full list of diseases).  It is recommended to make two applications, time the first at the end of shoot elongation (early to mid-July) and make the second application one month later (August).  Symptoms of Phytophthora and other soil fungi include, reddish-tinge to leaves, small, wilting leaves with poor color.  These problems are common in two or three year old trees that do not have an established root systems.  Root diseases may also occur when roots have become dry and then do not recover well when irrigation starts up in July.

Irrigation management
Evapotranspiration vs. soil moisture: Depending on rootstock and soil texture evapotranspiration can be excessive even if soil moisture seems right, since moisture can be lost from both transpiration and evaporation.  This means that trees are losing a lot of water during the day, even if soil moisture seems adequate.  Standard irrigation volumes may not be adequate in extremely hot conditions and erring on the side of overwatering may be beneficial.

Honeycrisp chlorosis
Honeycrisp chlorosis appears to be related to light crop loads and is a genetic characteristic that develops in the leaves when there is a partial blockage of carbohydrates moving from the leaf into the tree’s vascular system.  This blockage causes a buildup of carbon in the leaf and reduces photosynthesis.  The changing leaf colors are likely a result of this reduced photosynthesis.

European red mites and two-spotted spider mite
This upcoming weather will have a serious impact on insect populations, as we can have pretty high mortality when temperatures are in the upper 90s.  However, mites thrive when temperatures are this hot.  These temperatures dramatically shorten days in a generation and complete a life cycle from egg to adult in less than a week.  Beneficial arthropods, e.g., minute pirate bugs, thrips, lace wing larvae, predator mites, that may have been keeping the mite population in-check, often cannot keep up with these short generations and mite populations can flair.

In orchards that routinely apply miticides, we are not seeing the response we expect when the mode of action switches.  A miticide with a new mode of action, Kanemite (acequinocyl), has been registered for a few years, but local supply has been limited.  If you have already applied a miticide, e.g., Envidor (spirodiclofen), Nexter (pyridaben), Nealta (cyflumetofen), and it did not perform, consider using this new product.

Wooly apple aphid, late season management options

  • Movento (spirotetramat), seven day pre-harvest interval (PHI), typical recommendation is to make application before shoot elongation ceases, but could be used later in the season as a rescue material although it will not deliver long-term impact.
  • Diazinon (diazinon), 21 day PHI, organophosphate that we don’t use anymore, it is still registered and expensive.
  • Beleaf (flonicamid), 21 day PHI, unique mode of action, low toxicity on beneficials, but it is not readily available in the United States.

Apple maggot
Orchards which had hail in 2015 are more likely to be catching apple maggot (AM) than orchards with no hail.  Some orchards that had hail last year and did not clean up the crop are catching more AM than orchard that removed as much damaged fruit as possible after the hail.  If you experienced hail and were not able to remove all the fruit, you will likely have more AM pressure than orchards who did clean the orchard of all hail-damaged fruit.

The results from a rainfastness trial conducted by John Wise, Michigan State University, show that Assail is not very rainfast and after one inch of rain insufficient insecticide residue remains to control codling moth.  Field evidence suggest that there are differences in rainfastness of Assail based on the pest, and that Assail may still protect against AM for 14 days if there was one inch of rain after seven days.

Neonicotinoid alternatives for AM

  • Exirel (cyantraniliprole), same IRAC group (28) as Altacor (chlorantraniliprole) and Belt (flubendiamide), will also control codling moth, leafrollers and white apple leafhopper.
  • Avaunt (indoxacarb), is a non-organophosphate or neonicotinoid that has been historically used for plum curculio. Apple maggot need to consume Avaunt treated apples before oviposition to be effective.  The label recommends tank mixing with a spreader sticker.
  • Carbaryl (carbaryl), has limited efficacy and dramatic effects on beneficials, yet has a three-day PHI and is effective for seven days.

Apple maggot: To bait or not to bait?
The threshold for AM is one fly on an unbaited trap and 5 flies on a baited trap.  Keep this threshold ratio in mind if 15-20 AM are caught on a baited trap, it is comparable to catching 3-4 AM on an unbaited trap.  Contrarily, if 15-20 AM are caught on an unbaited trap (75-100 AM on baited) suggests extreme pressure.

The treatment threshold from Cornell University is to take an average of the traps in an area.  For example: a 10 acre block has three traps, two have caught an AM and the third has not, the average is less than 1, so there is no need to treat.  If this recommendation is used the average number of captures should be 1 (unbaited) or 5 (baited) to treat.

Second generation codling moth (CM)|
Flights have started in some areas.  A good indicator that second generation has begun is if trap captures have been low and begin to increase or exceed threshold, 900 to 1150 DD, from first generation biofix.  Note: If a neonicotinoid, e.g., Belay (clothianidin), was used to treat plum curculio and the treatment overlapped with first generation codling moth management, use caution about exposing second generation codling moth to neonicotinoids alone or without an effective tank-mix partner, e.g., Altacor.  The need to control second generation can often be variable and dependent on how well first generation was controlled and/or pressure populations in neighboring wild trees.