May 19, 2015
At the station: APPLE are at pink to early bloom, CHERRY are at bloom and GRAPE are at 1-2″ shoot.
With the persistence of cool weather over the past week perennial fruit crops are developing very slowly. At this time of the season we normally move through plant development stages quite rapidly, but this season we are seeing a slow progression. Cool and windy weather may also be affecting pollinator flight. Both of these factors could contribute to poor fruit set or uneven crop development.
The rain and mist over the past weekend resulted in a light apple scab infection at the Sister Bay weather station site (5/17-18). During the same time period, cherry leaf spot infection conditions were recorded at most sites from southern Door north. The risk of infection, however, is dependent on leaf development at this time. Until leaves have completely unfolded they are not susceptible to infection. This is because infection from the cherry leaf spot fungus occurs through the stomates (breathing pores) on the underside of the leaves; stomates do not finish developing until a leaf has unfolded, usually around petal fall.
With the persistence of cool weather over the past week, perennial fruit crops are developing very slowly. At this time of the season we normally move through plant development stages quite rapidly, but this season we are seeing a slow progression. Cool and windy weather may also be affecting pollinator flight. Both of these factors could contribute to poor fruit set or uneven crop development.
Disease Pressure – As we approach bloom, fire blight will become a concern for apple growers. Right now temperatures are not conducive to the development of this bacterial disease, but once blossoms open, and if temperatures rise into the 60’s or higher, bacteria will develop quickly. Any wetting (even rain, fog or dew) can then trigger an infection. Protectant applications of a bactericide like Agri-Mycin or other streptomycin products should be made every 4-5 days during the bloom period.
Apple Scab and powdery mildew continue to both be a concern on apple. Scab can be best managed at this time with 7-10 protectant applications of Captan or one of the EBDC fungicides. However, with a variety like Honeycrisp that is only mildly susceptible to scab but much more prone to powdery mildew infection, an additional fungicide is necessary. For powder mildew control the SI fungicides like Rally and Indar are both still effective along with the stroblurin materials Sovran or Flint. Combination fungicides (SDHI + strobilurin) are also good choices for powdery mildew control. These include Pristine, Luna Sensation and Merivon. The tight cluster through petal fall time period is the most critical for control of this disease.
Insect Pressure – As we progress through the bloom stage of development, it is a good time to start scouting for green fruit worm and oblique banded leafroller larva on blossom clusters. The presence of early hatching European red mites have been high in some orchards on the peninsula. Growers should scout blossom cluster at this time to determine if petal fall miticide applications will be necessary.
Disease Pressure – If the cool moist weather continues, European brown rot will be an issue on blooming tart cherry trees. The Balaton variety is more susceptible than Montmorency, but Montmorency can be infected when conditions are right (cool and wet) . To prevent infection, an application of Indar at the popcorn stage is suggested; a later Indar application during bloom will also help to prevent infection.
Unfolding leaves will need to be protected with fungicide applications before the next cherry leaf spot infection periods occurs. Products containing chlorothalonil (Bravo, Echo, Equus etc) are the fungicides of choice now through shuck split for cherry leafspot control.
Disease Pressure – Once shoot tissue begins to develop, Phomopsis fungal spores may be released during rain events. Protectant fungicide may be needed once flower clusters become visible– when 2-3 leaves have expanded. Powdery mildew can become an issue on susceptible varieties as young shoots develop; however, powdery mildew is not likely to be an issue until later on most varieties and fungicide applications may be better left until the 6-12 inch stage of shoot growth when downy mildew becomes more active and a threat.
Insect Pressure – Watch expanding buds and young shoot and leaf tissue for the presence of grape flea beetles and climbing cut worms. Although damage is often not extensive enough to warrant control, infestations from these insect are often more likely to occur in cool springs.