By Becky Wiepz and Dan Kielar
High winds and rain in the forecast will continue to make spraying difficult in all crops as pressure remains high for both pests and diseases. This week we saw a spike in Leafrollers and Leafhoppers in both apples and cherries. If this pest is in your orchards check your insecticide label before application to be sure they are covered.
Scale pests, both San Jose and Oyster Shell, are in many orchards. According the the NEWA model, most have not yet reached the crawler stage of development so insecticides will not be effective at this point. If pressures in your orchard are high, now is the time to deploy double sided sticky tape traps around limbs to monitor for crawlers and time insecticide applications correctly. This article from Christelle Guédot provides information on San Jose Scale and how to proper monitoring technique.
Spotted Wing Drosophila has been caught throughout the county! Cherries are not vulnerable yet but monitor your closest Wisconet Station to know when your orchard needs protection.
| Date 6/13 | 2020 | 2021 | 2022 | 2023 | 2024 | 20-year avg. |
| Base 50 | 389 | 561 | 379.5 | 505 | 537.5 | 462 |
GDD50 is approximately 3-5 days ahead of the 20-year average.
Apples
Hormonal thinners like NAA and MaxCell are most effective while fruit is less than 20mm in diameter. The Carbohydrate Thinning Model on NEWA can help determine your tree’s responsiveness to chemical thinners. Read more about your thinning options in this article from Amaya Atucha at UW Madison.
As fruitlets exceed 20mm in diameter, hand thinning becomes your only effective tool, so be sure to get as close to your ideal cropload as possible before then to minimize required labor.
Insects
European Red Mite pressure is low in all blocks scouted but some leafhopper nymphs and Green and Rosy Apple Aphid adults were found in a few orchards.
First generation Codling Moth flight is ongoing and most blocks have reached biofix. Insecticide should be applied soon after biofix is reached and again 7-10 days later.
Stink Bug and Tarnished Plant Bug stings have been found on some fruit; orchards with a history of damage should consider treatment using an effective insecticide as referenced in the Midwest Fruit Pest Management Guide.
Peachtree borer flight has started and Leafrollers and Leafhoppers have been found in many blocks. In addition, Rosy Apple Aphid has been caught in small numbers in some orchards.
Disease
Pressure continues to be high for Apple Scab around the county. Now that initial spore maturity is complete, blocks with low initial pressure can consider stretching out their time between sprays to 10-14 days while continuing to monitor the forecast and NEWA’s Apple Scab Model.
Powdery Mildew pressure continues to be high this year and can require different fungicides than those used to manage Apple Scab. Check the Midwest Fruit Pest Management Guide for chemical recommendations.
Remember that fungicides are almost exclusively protective, so it’s important to treat as soon as symptoms are present to prevent infection from moving onto new growth.
Some Honeycrisp blocks are experiencing ‘Rat Tail Bloom’ a second bloom that can emerge from the bourse or vegetative shoot located adjacent to each initial blossom cluster. If your block is experiencing extensive rat tail bloom, you may consider a streptomycin application to prevent fireblight infection while these blossoms are open. The current wet weather and warmer temperatures are ideal conditions for fireblight infection and late blooms are a perfect entry point for the bacteria.
To learn more about the apple scab and fireblight models from NEWA, visit the ‘Newsletters’ section of the Cornell Tree and Small Fruit Extension Resource Blog.
Cherries
Spotted Wing Drosophila continues to be caught throughout the county but cherries are not vulnerable yet, monitor your nearest weather station at wisconet.wisc.edu to time your SWD insecticide application. In parts of the county, fruit is predicted to reach a vulnerable stage in about a week.
Insects
European Red Mite populations are low in all blocks, but avoiding Pyrethroid (IRAC 3A) chemistries can prevent ERM flare ups and will also save that chemical group for SWD management closer to harvest, which will help to prevent resistance development.
Lesser Peachtree Borer was caught in some orchards along with various Leaf Roller Species. Check your insecticide label before application to be sure these pests will be controlled in your block.
Disease
Forecasted high winds will make Cherry Leaf Spot even more challenging to manage. Active lesions are present in many orchards and full cover sprays with rotating of modes of action (FRAC numbers) are needed to limit infection spread.
Powdery Mildew is also present in many blocks and may require different products to manage than your CLS program. The Midwest Fruit Pest Management Guide is a good resource to check product efficacy.
GRAPES
Grapes on the station are at pre-bloom and will reach bloom in the next week or so. Pre-bloom through berry touch is a critical time for fungicide application to protect the rachis of each cluster and prevent cluster rots.
Now is the time to shoot thin your canopy and begin training your vines up if a VSP system is in use.