May 13, AppleTalk Call Summary

AppleTalk Conference Call Summary
Tuesday, May 13th, 2014, 8:00 – 9:00 a.m.
Presenter: John Aue, Threshold IPM.
Moderator: 
Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

May 13th call download:  Click Here

Tree phenology
Zestar near the Wisconsin and Illinois state line are in bloom, with a majority of orchards in southern Wisconsin at tight cluster or nearing pink.  Orchards in the Mississippi valley and north are varied with varieties ranging from green tip to tight cluster. Growers in Bayfield County Wisconsin report trees are still in dormancy.

Tree stress: the impacts of temperature, solar radiation and wet weather
Spring weather can induce a variety of stresses on developing trees.  Trees become especially stressed during warm nights or warm-cloudy days, when photosynthesis is not producing enough sugars to support the rapid leaf development that is taking place.  Fluctuating temperatures and sunlight can be monitored to determine the necessity of a foliar-fertilizer application.  Winter injury will begin to show at this time.

Root diseases should be assessed early in the summer and temporarily saturated soils, in the spring, should not warrant the use of a phosphorus acid systemic fungicide, e.g., Aliette/Linebacker (aluminum tris) or Phostrol (mono- and dibasic sodium, potassium, and ammonium phosphites), for the control of root diseases such as, Phytophthora.  When applied, phosphorus acid fungicides translocate quickly from the leaves to the roots and are effective for a short amount of time.  If a root disease is suspected, fungicide timing needs to allow for the maximum uptake of the product.  Ideal timing is in early summer, followed with another application six weeks later.  A concern with applying these products between green tip and bloom is the potential phytotoxic reaction between copper and phosphorus acids.

Update: Captan and phytotoxicity
Last week we discussed the possible correlation between captan products formulated in China and phytotoxicity.  Further research into this hypothesis shows that a large amount, if not all, captan is currently produced in China and the captan of concern is being imported by a suspect distributor in the eastern United States.  None of the captan we receive in the Midwest is from this distributor. It is still advised to not tank mix captan with other materials for petal–fall applications.

Apple Scab
Heavy rains on May 12 and warm temperatures have most likely resulted in a severe infection for the majority of growers in the region.  The chance of a scab infection increases in orchards that are at tight cluster and bloom, or that did not have a protectant fungicide on, or if it has been more than ten days since their last application.  Also, the probability of an infection increase in blocks with scab-susceptible varieties and high-inoculum levels.  Even if your datalogger registered a severe infection, the actual threat of an infection may be less, because of the frequency of brief showers and cooler temperatures.   The threat of a severe infection is reduced if spores are gradually discharged during light rains, when the leaf surface only stays wet for an hour.  The chances of a severe infection is dramatically increased if it has been dry for the last seven days.

Fungicide redistribution versus wash-off rates
Single and multi-site fungicides break down  at different rates, as a result of  leaf growth and rain events.  Single-site fungicides such as QoIs, e.g., Flint (trifloxystrobin), SDHIs, e.g., Fontelis (penthiopyrad), and APs, e.g., Scala (pyrimethanil), enter the leaf tissue and travel through leaf surface translaminarly.  The benefit of the chemical entering leaf tissue is that they will not wear off as easily, but will not redistribute into new leaf tissue.  Protectant  fungicides, e.g., Penncozeb (mancozeb) or Captan (captan), will redistribute onto new leaf tissue during minor rain events, but are susceptible to wash off during heavy rains.  

Managing apple scab with cultural practices and organic fungicides
In the early spring scab fungi develop fruiting bodies (pseudothecia) on the tops of fallen dead leaves.  During rain events, ascospores are released upward into the tree canopy to colonize on leaf tissue.  Flail mowing the orchard floor can manipulate this life cycle by flipping over leaves and destroying leaf litter.  If conducted in the spring, the development of the fungus will be interrupted and the developing pseudothecia on leaves that have been overturned, will not be able to reorient and create new pseudothecia.  Flail mowing or chopping leaf litter is one of the most effective practices that any grower can do to reduce scab inoculum in their orchard.  Further breakdown of leaf tissue may be completed by applying a 5% urea solution to the leaves in the spring or fall.

The success of many Organic Material Review Institute (OMRI) listed protectant fungicides are varied.  The strength of host–plant resistance inducers which are said to activate a plants natural defense mechanisms against disease have relatively low efficacy and strength.  These products include Vacciplant (laminarin) and Regalia (Reynoutria sachalinensis).  Protectant/competitor materials like Serenade (Bacillus subtilis) and Blossom Protect (Aureobasidium pullulans) are beneficial organisms that colonize the leaf surface before pathogens are able to infect the leaf tissue.  To be successful, a large amount of these materials needs to be applied before an infection occurs.  Sulfur and liquid-lime sulfur products offer effective control of scab and powdery mildew and could be considered by conventional growers for use on young trees.  All of these products have poor rain fastness and reapplication is necessary to keep a protective layer.

Oxidate (hydrogen dioxide) and Lime Sulfur (calcium polysulfide) are materials often used post infection, though lime sulfur may also be applied as a protectant.  Hydrogen dioxide is effective at sanitizing packing lines and food handling equipment, but is not well proven at eradicating apple scab in an orchard.  Oxidate  rapidly degrades in sun light, and therefore limits its window of effective use.  Lime sulfur may be used pre or post infection, but needs to be applied within 12-24 hours after an infection and can not be used in temperatures above 80⁰F.

Redbanded leafroller (RBLR) and Spotted tentiform leafminer (STLM)
Redbanded leafroller and STLM are two insects that generally have not required insecticide treatments in recent years.  Monitoring helps to gauge populations and time when to begin scouting.  Flights are beginning with warm weather, if traps are not already up, they should be hung as soon as possible.

Obliquebanded leafroller (OBLR)
Obliquebanded leafroller traps are usually hung before petal fall, John has not seen any larvae emerging which may suggest a later than normal flight.

Codling Moth
The first codling moth catch, biofix, has traditionally been around petal fall and growers to hang pheromone traps May first.  We are well past May first, and if the Trece’ long-life lure, CM L2, is being used,  hang traps as soon as possible. The long-life lures last a half season and if  hung May 15 they would be replaced on July 15.  If the standard-red lure is used, wait until McIntosh bloom to hang  traps, and remember they will need to be changed every three to four weeks.  Note: place codling moth traps in the upper 1/3 of canopy.  If mating disruption is used, hang traps, including a CMDA in the trees by bloom.  Note: If you are planning to use mating disruption hang oriental fruit moth (OFM) and lesser appleworm (LAW) traps.  The appearance and damage caused by these two species is very similar to damage caused by codling moth.  Oriental fruitmoth flights begin soon and will have three flights this season and LAW starts around petal fall.

Bores
Borer damage is beginning to show up higher in the graft union.  If you have damage, begin trapping for American plum borer and lesser peachtree borer, as they fly early.  Dogwood borer monitoring should begin in early July.

Thrips invasion
On  Friday, May 9th, John noticed a large population of thrips at an orchard in Sauk County.  He suspects that strong southerly winds and warm temperatures last week allowed the thrips to move into the region.  They were found in tight cluster buds and can cause damage to the fruitlets with their sucking and chewing mouthparts.  Thrips have caused damage in the past and orchards should be scouted for migrant populations.  Hosts may be variety or phenology specific, as large numbers have been found in Cortland, McIntosh, and Golden Delicious.  While scouting, check orchard perimeters and spend a few seconds scanning flower clusters  to pick out small black specs.  If you notice a large population in your orchard, please contact John or Peter.

Captan phytotoxicity: http://www.ecofruit.wisc.edu/appletalk/?p=829

Thrips damage: http://www.ecofruit.wisc.edu/appletalk/?p=826