May 17, AppleTalk Conference Call

AppleTalk Conference Call Summary

Tuesday, May 17, 2016, 8:00 – 9:00 AM

Guest speaker: Philip Schwallier, Michigan State University Extension educator

Presenter: John Aue, Threshold IPM

Moderator: Peter Werts, IPM Institute of North America; questions or comments,

May 17^th Call download: Click Here

Tree phenology ranges from full bloom/petal-fall to king fruit of early cultivars above 8 mm across the region.  Growers near Lake Michigan and Lake Winnebago reported many varieties in full bloom while growers in the La Crosse, Gays Mills, Madison, southeastern Wisconsin and northern Illinois have most varieties between 6-8 mm.

A region-wide freeze Sunday morning (May 15) appears to have been of short duration (less than two hours), except for a pocket in southeast Wisconsin with sub-freezing temperatures for five to six hours.  The coldest sites had readings of 25°F, although most orchards had low temperatures in the 27-30°F range.  Fruit injury is widespread and varies by variety and site.  Orchards at higher elevations typically had less damage when compared to lower elevation areas.  Injury can be seen when fruitlets are bisected.  Various amounts of brown or discolored tissue and seeds can be seen on the most severely damaged fruit.  There are a number of fruit on the border of areas with heavy injury, i.e., low elevation, flats, with damaged seeds that are off-white, or “brownish” in color.  At this time these fruitlets do not show any other symptoms, e.g., browning tissue/flesh.  Fruit with damaged seeds may not continue to grow or will have severe blemishes.  The flesh of healthy fruit is green, with green or white seeds.

May 15 freeze analysis and discussion on tactics going forward with Philip Schwallier, Michigan State University Extension educator

What advice can you share with growers who are reporting a 100% crop loss?

Fruit may still be viable in the upper portion, or interior of the canopy where they are more protected from low temperatures.  Although these fruit may still be alive, they will likely be severely damaged from the frost, e.g., russeting, frost rings, and will have low-market value.  If fruit are left on the trees it is imperative that the pest management program continues, since insect pressure will likely be high since surrounding wild apple trees will have also lost their fruit.

If you remove the remaining and damaged fruit, check to see if chemically removing the crop will affect an insurance claim.  The timing and rate recommendations for removing fruit are: Carbaryl + NAA at petal fall, and making a second application at 10 mm.  Growers beyond 10 mm can apply carbaryl + NAA + ethrel.

What do we know about using Promalin as a rescue for fruit that have damaged seeds?  Some results suggest that fruit will continue development if an application is made within 96 hours after a freeze.

• Promalin (gibberellins A4A7, 6-BA) does have the ability to set fruit with frost damage, where the ovules in the plant have been killed and won’t develop seeds. Promalin is will not set fruit if the cortex is brown and damaged, e.g., the tissue surrounding the seeds.  Promalin can be applied on fruit ≤ 6 mm and will encourage fruit to set even without the seeds.  It can be applied up to 96 hours after frost; best results can be achieved when applied within 24 hours of the event.  Fruit that has reached 8 mm will not respond to Promalin.

• The recommended application rate is 1 pt. per 100 gal./water per acre. If 100 gallons of water per acre cannot be achieved, a higher concentration of 1 pt. 75 gal./water would be an option.  Other tradenames for Promalin include: Perlain.

• Promalin has the ability to set a large crop, regardless of fruit quality. A grower should begin to assess the crop at 10 mm to determine the utility of chemical thinners.  This is also true for a crop that had light frost damage but did not receive Promalin.  The ideal thinning window would be between 10 and 18 mm.

• Fruit that received Promalin will have storage issues since seeds will be absent. To maximize fruit quality, growers should continue to apply summer calcium sprays and use recent soil and foliar test results to correct any deficiencies.

• One application of Promalin is all that is needed, even if there is a second frost event. Additional applications may have thinning effect.

What are the ideal weather conditions for applying plant growth regulators?

All plant growth regulators (PGR) are more effective (tree is more sensitive to thinner) when applied during warm temperatures and slow drying conditions.  Performance is best when temperature is 65°F or warmer on the day of application, and for the next two to four days.

Plant growth regulators should be applied before rain events, 90% of absorption occurs when the material is drying on the leaf surface.  Light rains may help absorption.

What recommendations do you have for growers assessing frost damage and subsequent crop load management and chemical thinning?

• If damage is not visible at this point, growers who experienced critical temperatures for a freeze, can expect symptoms, e.g., frost ring, irregularities in flesh, to develop within one or two weeks. Each operation needs to approach post-frost crop load management differently: retail-based operations may be able to sell the blemished fruit or press the fruit into cider, yet commercial operations may not have an avenue to move damaged fruit.

• It is extremely difficult to achieve good thinning results when the king fruit is lost. If only viable side fruitlets remain, consider thinning at 8-10 mm with a normal rate of thinner, e.g., Sevin 1 pt. + NAA 10 ppm.  If thinning is completed after 15 mm, apply Sevin with 15 ppm of NAA.  If damage is severe carbaryl can be applied without NAA.

• Additional notes on thinners:
  • Carbaryl is a mild thinner that tends to singulate clusters. Carbaryl is not rate dependent, i.e., 1 qt. carbaryl induces nearly the same thinning response as a rate of 2 qt.
  • NAA is a moderate, dose dependent thinner. Increasing or decreasing rates will effect thinning response.  Tradenames for NAA include: Fruitone and Refine 3.5 WSG.
  • NOTE: Apples with frost damage or that received Promalin, will thin easier and rates will need to be reduced.

• If frost damage is moderate, or difficult to assess, spraying the tops of trees with thinner could allow hand thinning in the lower canopy after the crop quality and quantity can be confidently evaluated.

• Growers are encourage to use Predicting Fruitset Model to identify what is happening with the fruit. For more information visit: http://msue.anr.msu.edu/topic/apples/horticulture.  Scroll down to thinning section and review spreadsheet and PDF.

Should growers with a small crop be concerned with excessive vegetative growth?

• Without a crop trees will grow vegetatively and will not need much fertilizer unless there are micro/ macro nutrients which require corrections. Apogee can be applied to suppress vegetative growth; rates should be increased for tree without a crop.

• Apply Apogee at full bloom or when shoot growth is less than three inches in length; approximately a seven to ten-day window beginning at the king bloom petal fall stage. Most years, all varieties can be treated at this time.  Apply a second application two weeks later and a third application two weeks after the second.  A fourth application is optional and need should be determined by assessing crop load and tree vigor.

NAA for return bloom

• Summer NAA will help with return bloom on the interior of trees, especially on trees that have closed or shaded canopies. Timing and rate: NAA can be applied at a rate of 5 ppm, five, seven and nine weeks after full bloom.  The NAA application during the seventh week is most important for return bloom, the second most valuable is five weeks, and the third is nine weeks.  Do not apply NAA if it temperatures are warmer than 85°F.  Phytotoxicity injury can result, and 10% leaf drop can occur.  If hot temperatures are forecasted, it is ok to make the application one week early or late to work around high temperatures.

Management takeaways

• Continue managing the orchard as if it has a full crop. Putting away the sprayer will lead to greater infestations of insects and diseases in 2017.  Take care of high density and high value orchards, e.g., mowing, maintenance, spraying, etc.

• Areas w/o fruit, or areas with small amount of fruit, use larvacide instead of targeting adult moths for codling moth control. Similarly, monitor and manage apple maggot.  Continue to look for powdery mildew and apply fungicides for powdery mildew until terminals set.

• The critical-temperature chart for freeze injury developed by Michigan State University have been developed based on flower exposure for 30 minutes at four to five feet above the ground.

• What are radiation freezes?, Michigan State University Extension http://msue.anr.msu.edu/news/what_are_radiation_freezes