August 26, 2026

By Becky Wiepz and Dan Kielar

Station Updates

This is a good time of year to check sprayers to line up winter repairs and clean/winterize sprayers for the year.
Maturity testing on early apple varieties will start next week.
Soil sampling to plan fall and spring fertilizer applications can be collected at anytime from now until the ground freezes.

UW Madison/Extension Updates

Historic Growing Degree Day Comparison

Date 8/17	2022	2023	2024	2025	2026	20-year avg.
Base 50	1206	1275.5	1299	1259.5	1731.5	1643

GDD₅₀ is 1-2 days ahead of the 20-year average.

Recent Weather at Peninsular Ag Research Station

Date	Max Temp(℉)	Min Temp(℉)	Max Wind Gust(mph)	Daily Rain Total(in)
8/10	79	62	17.8	0.0
8/11	81	63	11.6	0.0
8/12	80	63	14.5	0.01
8/13	79	63	8.9	0.04
8/14	79	60	15	0.0
8/15	77	63	16.8	0.0
8/16	85	66	16.8	0.0
8/17	81	58	15	0.0

Upcoming forecast will result in continued infection periods for fungal and bacterial pathogens due to predicted rain events and warm temperatures.
If you’d like to see weather data for your area, visit https://wisconet.wisc.edu/

Apples

Growth Stage: Pre-harvest on most varieties. Make your plan for when to apply Stop Drop.
Seasonal Update: Soil sampling for nutrient testing can be done at any time now until soil freezes. Pre-harvest fungicide sprays to decrease storage losses can go out with your last insecticide spray.

Pest	Presence	Notes
European Red Mite	Present throughout Door County.	Monitor now for build up from the hot and dry weather in July, spray only if needed. *Watch the pre-harvest intervals.
Borer species	American Plum Borers still being caught.
Codling Moth	Second generation flight continues.	2nd generation sprays should go out with a follow-up spray 10-14 days later.
Apple Maggot	Still only a few have been caught throughout the County.	Egg laying will start 7-10 days after first catch on yellow sticky traps.
Leaf rollers	Flight continues.	Red banded leaf roller continued high numbers are up and oblique banded leaf roller trap catches decreasing.
Spotted Tentiform Leaf Miner	Present	2nd generation currently active.
Japanese Beetles	Present and building populations.

For more information visit the NEWA Codling Moth Model.

Disease	Presence	Notes
Apple Scab	Lesions detected throughout Door County on leaves and fruit	Primary spore dispersal is complete. If control was good, sprays can be stretched to 10-14 days between applications. If pressure early in the season was high or lesions are evident on fruit continue tighter spray windows.
Fire Blight	New strikes detected throughout the County this week	Orchards should be monitored and strikes should be removed promptly, cutting 12-18 inches past the end of the canker.
Powdery Mildew	Late season active. Strikes detected throughout the County	If present, include a product that specifies control on the label and plan on and early season application of sulfur next year.
Sooty Blotch/Flyspeck/Summer Rots	None detected	Apply preventative sprays before rain events, using NEWA models to determine spray timing.

Cherries

Growth Stage: Harvest is complete.
Seasonal Update: A post-harvest spray for Cherry Leaf Spot may be necessary to retain leaves into September. Hedging and any post harvest limb removal should be done now. Soil sampling can take place now through fall freeze.

Disease	Presence	Notes
European Red Mites	A few adults present throughout the County. Some blocks have increasing population near threshold.	Monitor population build up and spray only if needed.
Cherry Leaf Spot	Very light pressure in most blocks.	Due to less rain events, single post harvest fungicide should be applied to prevent defoliation in most blocks.

Visit the Wisconet Pest & Disease Models page to check Cherry Leaf Spot for a weather station near you.

GRAPES

Growth Stage: E-L Growth Stage 33-35 depending on variety.
Seasonal Update: Shoot thinning and leaf removal to increase light exposure on fruit clusters should be complete now. Also consider netting early varieties due to high bird pressure.

Pest	Presence	Notes
Leaf Hoppers	No
Phylloxera	Some galls observed
Red Banded Leaf Rollers	Yes
Japanese Beetles	Yes	Check Midwest Fruit Pest Management Guide for effective insecticides if damage reveals over 20%

Disease	Presence	Notes
Black Rot	Single lesions observed	Early season fungal control is critical to prevent diseases from reaching economically damaging levels.
Powdery Mildew	None Detected	Risk will increase with current heat and humidity. Scout your vineyard to determine local pressure.
Downey Mildew	None Detected	Risk will increase with current heat and humidity. Scout your vineyard to determine local pressure.

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