May 14th Apple Talk Call Summary

Tuesday, May 14th, 8:00 – 9:00
John Aue, Threshold IPM; Patty Mc Manus, University of Wisconsin.
Peter Werts, IPM Institute of North America; questions or comments,

Download the May 14th call recording here

Webinar May 21st
Our first webinar will be Tuesday May 21st.  Peter will be online around 7:30 am to help provide technical support to growers who may have trouble accessing the webinar.

Tree phenology
John has been observing lots of tree stress and trees with nitrogen deficiencies.  Trees are pushing a lot of blossoms out and he is suggesting foliar applications of Urea, 20-20-20, or something else that could go on with boron or a fungicide cover.

Weekly IPM Bulletins and Newsletters

Disease management with Patty McManus, University of Wisconsin
Fireblight management

Unlike the past several years, the hot, wet and humid weather during bloom is creating a perfect storm for fireblight infections of the blossoms, also known as blossom blight.  Fireblight bacteria requires moisture and enters the flowers on the stigma and at the base of the flower.  The infection does not require much extra water and a brief rain shower, fog or heavy dew can often provide enough.  Unlike like apple scab where several hours of leaf wetness and measureable rainfall are required; the fireblight bacteria will be multiply rapidly with hot weather and brief wetting events, such as thunderstorms forecasted across the region through May 24th.  Bees will be pollinating in the hot weather and this will spread the bacteria around.

At this point, there is no confirmed resistance to streptomycin in our region.  Growers in Minnesota and Wisconsin have not used it as intensely in as in Michigan, California and the Pacific Northwest.  Resistance problems in Michigan developed because folks were going out with continues low doses of strep.

When should streptomycin be applied?
Growers should be using a Maryblight, or Cougarblight, to identify risk and guide timing of applications.  Streptomycin applications may begin at 10% bloom and be repeated every four or five days until the end of bloom.  We need to control the early bloom, since these are the largest fruit and need to maintain protection because late blooms still need control.  Growers should only need to use two or three spays of streptomycin to control fireblight.  Growers can expect two to three days of protective activity.  The recommended rate of streptomycin is 50PPM.  In the lab fireblight has been killed with rates as low as 10ppm.  The concern regarding rates is that a heavy dew or rain could easily dilute if it is too low.  The 50ppm equates to 1.5lb per acre.  Streptomycin effectiveness increases with use of Regulaid, and can use 1/3 less streptomycin, i.e., reduce from 1.5 lb to 1 lb of streptomycin.  Since do not have a lot of leaf tissue, growers should use the same water per acre as scab sprays right now.

Can streptomycin be applied up to 24 hours after an infection, does this have same efficacy as when used 24 hours before?
Streptomycin is moderately systemic and it is an assumption that post-infection control could work.  Patty suggests it is worth trying but there is no data to support this.

How should growers be preparing to manage shoot blight later in the season?
Often growers are able to manage fireblight through bloom without infection but can still have shoot blight in June.  This is because fireblight moves internally and the succulent tips are still susceptible.  Damaged shoot tips from hail, wind and rain at night can result in shoot blight.  Split applications of Apogee are better than one big shot.  It takes apogee several weeks to have an impact on growth of plant.  First application is king bloom petal fall.  It could be two weeks after this before someone sees that fireblight has infected the shoots.  It is unknown if there would be utility in reducing shoot blight by applying apogee late.  Bloom applications of apogee are targeting the shoot blight that would appear in several weeks.  For example vigorous cultivars susceptible to shoot blight should receive Apogee now, if they have had shoot blight in the past.

What are options for streptomycin alternatives?
Regarding pesticides to prevent fireblight, there is nothing better than streptomycin and is available for organic producers.  The biological fungicides, e.g., Serenade (Bacillus subtilis) have not been proving as effective.  These can be integrated with streptomycin, but our climate is too variable and these products need to be applied immediately so they can establish and be spread around by bees.

Oxytetracycline will be phased out of organic production, but other streptomycin will be allowed.  The Argument against this is the philosophy regarding the use of antibiotics in food production.  Oxidate (hydrogen dioxide) is a good disinfectant and antibacterial, but applications would have to be made daily or every other day and does not have much staying power on tree.  Messenger (harbin aβ protein), Actigard or Bion (acibenzolar –S-methyl) induce host resistance, are not bactericidal, turn on plant host resistance.  These products have not worked well on woody plants and are more for bacterial infections in vegetable systems.

Scab, powdery mildew and other disease management recap
2012 spring freeze drought scaled back disease control programs for many growers.  Late-summer rains were enough to resurrect scab in some orchards, even though it was put on hold in the summer.  Drought stress on non-irrigated trees can predispose trees to developing cankers.  Trees can’t afford to use water to make callus tissue and last year could have had white rot, black rot and lucastoma getting a hold and could begin to see symptoms in the next several years.  Rosenberger is suggesting connections between roundup, drought and white rot.

Powdery mildew will do quite well in hot dry weather and over winters in the buds.  Temperatures of 10 below zero are required to kill powdery mildew infected buds.  Some parts of the state may have had 10 below once or twice this year.  Duration and number of cold events have an impact and it is not documented if one night of 15 below or a week of 5 below.  Powdery mildew should be taken seriously on young trees and dwarf trees.  Rosenberger suggested spores can travel long distances.  A more mobile fungus than Venturia, i.e., spores in tree pretty much are what came up from ground, and secondary scab spreads within the tree, whereas powdery mildew spores can spread further.  Patty would be surprised if we had powdery mildew resistance in our region.  The fungus has not been as present until more recently, even though we have had lots of sterol inhibitor and strobilurin use.

Insect musings from John Aue
Plum curculio traps can be put up on trees or free standing on orchard perimeters.  This week would be ideal for these traps to function.  By the time petal fall happens, the effectiveness of these traps don’t work as well.  Temps these next few days are ideal for plum curculio migration into orchards.  Place traps along the orchard perimeter and trap data could help influence how we approach plum curculio management

Rosy apple and spirea aphids.  In many years rosy apple aphids are not observed pre-bloom.  This year is different and just as the field guides suggest, stem mothers who give birth to live aphid nymphs are present.  Rosy apple aphid damage appears as leaf curling at base of fruit clusters.  John is seeing predation from lady beetle adults.  There are also many lady beetle egg masses that appear in clusters of 10-12 orange eggs and often found on roof of pheromone traps.  John is also finding small white eggs around fruit clusters that may be the orange Cecidomyiidae fly larva.  These are the orange gall midge maggots and eat aphids.  Often we don’t have predators at the right time to control, but it looks like this year we are seeing good signs that predation of rosy apple aphid is happening in significant numbers.

Codling moth traps need to get up.  We are having nights conducive to flights and it is anybody’s guess if we have a flight.  A flight now would be early as per tree phenology and late according to the calendar.  Rather the codling moth flight is inherently linked to temperature and accumulation of growing degree days, base 50F.