June 14, 2018
A second female spotted wing drosophila was caught in a cherry orchard in the northern part of Door County. Cherries are not yet susceptible to egg laying, but will be once straw color begins to develop. Growers are advised to begin 7-10 full cover control applications once coloring begins and then through harvest.
Apple scab and cherry leafspot infections were last recorded on 6/2 at all stations in Door and Kewaunee counties. There is a good chance for precipitation over the weekend. The rain events are likely to result in new infection periods here on the peninsula.
INSECT & DISEASE CONTROL
Disease Pressure – Apple scab lesions have been showing up in scouted orchards over the last week or two. Continue early season protectant fungicide applications on scab susceptible varieties like McIntosh & Cortland to protect leaf tissue, as scab spores will continue to be released during rain events over the coming weekend. Scab spores are now 100% mature in overwintering inoculum with 95% or more of those spores already released so far this spring. It is likely the remaining mature spores will be released with any infection periods for apple scab in the next 5-7 days and will mark the end of primary scab season.
Apple growers can begin to increase intervals between protectant fungicides once primary apple scab season is over. Length of intervals can be increased to 2-3 weeks if scab lesions are not present on leaves or fruit. Apple growers who have scab lesions present in their orchards should continue to apply protectant fungicides on a regular schedule. Captan is the fungicide of choice when protecting fruit from secondary scab infections. In cases where early control has not been adequate and numerous scab lesions are present, we have been successful in stopping further spread with two applications of Scala fungicide at 10 oz/acre 10 to 14 days apart. After that, a regular program using Captan every 14 to 21 days through the pre harvest interval should keep fruit infections to a minimum.
Powdery mildew has been an issue is some orchards where there has been an over reliance on Captan and EBDC’s for disease control. If you are growing Cortland, Honeycrisp, or other susceptible varieties applications during the tight cluster through petal fall stage of either strobilurin or sterol inhibitor, fungicides will help to suppress powdery mildew on those varieties that are susceptible. Rally and Indar are a good choice for this purpose as are Sovran, Flint, Luna Sensation, and Pristine.
Insect Pressure – Plum curculio have now been observed actively egg laying on apple. Applications for control should be made with your next spray. Choose a material that will also provide good control of codling moth like Assail or Imidan.
Codling moth continue to be caught in pheromone traps here at the Station and in scouted apple orchards. Young larva will continue hatching during the next 2 weeks. Control applications to reduce damage from 1st generation should have been made the week of 6/3 in Kewaunee and Southern Door areas and early the week of 6/10 in Sturgeon Bay and Egg Harbor. Applications can still be made in Sister Bay and the cooler lakeshore sites through the end of this week. A second application should then be made 10-14 days after the initial application date.
Disease Pressure – Cherry leafspot infections have been found in orchards throughout the peninsula. At this point we are seeing mostly single lesions and no heavy infections. The older fungicides like Orius, Indar, Gem, and Pristine can still be relied upon in many orchards for cherry leaf spot and powdery mildew control. When using these fungicides they should be tank mixed with Captan 80WDG at a 2.5lb/A rate for resistance management. Newer fungicides, like Luna Sensation and Merivon, have provided excellent control of both cherry leaf spot and powdery mildew in tests in Michigan and at the Research Station. Normally a 10-14 day fungicide application schedule is adequate to keep leafspot under control.
Insect Pressure – Once straw color begins to develop on cherries they will need to be protected from spotted wing drosophila infestation. Trap catches have not yet reached the levels that we saw last year during the harvest period, but the earlier emergence that we are seeing this season is likely to result in high populations building prior to harvest. Once straw color begins to develop on cherries they will need to be protected from infestation. Many options for control are available but the most affordable and effective are Imidan and Mustang Maxx (among other pyrethriods). It is highly recommended that these controls be rotated for resistance management. For example, if Mustang Maxx is applied, the next application 7 days later should not be a Mustang Maxx or any other pyrethroid, but Imidan. This pest has short generations time (7-21 days) and by rotating classes regularly we avoid exposing consecutive generations to the same chemistry.
CHERRY PEST ALERT – Plum Curculio PHI (Pre Harvest Interval): Keep a close eye on tart cherries for plum curculio damage. Plum curculio applications should be made no later than 375 degree days base 50ºF after bloom. This means make them by 6/10 south of Sturgeon Bay, 6/14 Sturgeon Bay and on the bay side of the peninsula, and no later than 6/18 lake side (cooler sites). Larva hatched prior to this time will develop and exit the fruit before harvest. Those hatching after 375 DD could still be in the fruit at harvest.
Links to individual Enviro-Weather stations: