Michigan hop crop report for the week of May 31, 2021

Dial in your fertility plan now.

Trained hops
Trained hops in southeast Michigan. Photo by Rose Stahl.

Weather

Temperatures last week were 1-4 degrees below normal for most of the state with near freezing temperatures in some locations. There was roughly 0.25-2 inches in precipitation in most areas of the state. Southwest Michigan and some areas of the Thumb are 2-3 inches below normal for April-May. Approximately 79% of Michigan remains in a drought.

Growing degree days (GDD) fell off a bit last week due to below-normal temperatures, but we remain ahead of the five-year average. Continued dry conditions and summer-like heat are on the way for the end of this week and into next week. As a result, water demand will increase. The medium-range forecast suggests above average temperatures and dry conditions through mid-June.

Watch the most recent agricultural weather forecast from Michigan State University state climatologist Jeff Andresen.

may 31 rainfall hops
Accumulated degree day (base 50 F) summary for hop producing areas of Michigan on May 31, 2021, as compared to the five-year average. Data from MSU Enviroweather.
may 31 hops gdd
Accumulated rainfall summary for hop producing areas of Michigan on May 31, 2021, as compared to the five-year average. Data from MSU Enviroweather.

Stage of production/physiology

With warmer weather over the last few days, hops have begun to grow rapidly across most areas of the state. Hops across Michigan are in Principal Growth Stage 2: Formation of Side Shoots (see chart). Most growers have trained and have begun fertilizing.

Average Michigan hop growth stage chart.
Average Michigan hop growth stage based on date. Botanical drawings courtesy of Dodds, Kevin. 2017. Hops, a guide for new growers. NSW Department of Primary Industries.
Timing of hop production chart.
Timing of hop production management activities in northwest Michigan.

Hop growth stage chart.

Crop development

Southeast Michigan

Weather conditions have been ideal. Established plants are 8-10 feet, while new plants are 6-8 feet. Occasional isolated downy spikes have been found. Fungicides are actively being applied.

Hops
Ideal weather conditions have resulted in an excellent start to the 2021 season in southeast Michigan. Photo by Rose Stahl.

Southwest Michigan

Hops are trained and 3-6 feet. Potato leafhopper has been spotted and European corn borer eggs are being spotted across the region. The European corn borer Enviroweather model biofix was May 24-26 in southwest Michigan. Treatments are starting this week. 

Trained hops
Trained hops in southwest Michigan on May 31, 2021. Photo by Mike Reinke, MSU Extension.

East central Michigan

Growers have wrapped up training for the most part. Hop height varies by cultivar from 3-6 feet.

West central Michigan

Despite the cold overnight temperatures over the Memorial Day weekend, no widespread frost damage was reported in hops. Pruned and trained bines are averaging 3 feet in height but are variable by based on management and variety.

Northeast Michigan

Dry conditions persist in northeast Michigan. Plants are 4-5 feet. Growers will be hilling this week to cover up extra shoots. Some leafhoppers have been spotted. There have been no signs of downy mildew although growers have applied a preventative.

Dry hops
Dry conditions persist in northeast Michigan. Photo by Andrew Walawender.

Northwest Michigan

Training is complete in northwest Michigan. Hop growth slowed a bit with the cooler temperatures but should pick up steam again this week. Heights range from 3-8 feet depending upon the cultivar.

Hops
USDA advanced field trial cultivars show promise in northwest Michigan. Photo by Aaron Martell.

Weeds

Minimize competition from weeds, which can compete for water and nutrients. As a reminder, weeds are best controlled when they are small. 

Diseases

Sporadic downy mildew spikes have been seen in southwest Michigan for the past few weeks. Due to the fact that we had a rainy weekend, these may increase and develop into secondary downy mildew on lateral shoots. Most growers have made some form of chemical application already. Several effective foliar fungicides are available and include products in FRAC codes 4, 11, 21, 40, 43, 45 and 49. See the MSU Extension article, “Managing hop downy mildew in Michigan,” for more information on management methods for downy mildew and refer to the Michigan Hop Management Guide. This is a critical time to control downy mildew to prevent the development of lateral downy mildew and additional spikes in the yard.

Downy mildew on hops
Left, downy mildew spike in southwest Michigan on May 25, 2021. Notice the yellowing and stunted growth. Right, dark sporulation on a downy mildew spike in southwest Michigan on May 25, 2021. Photos by Tim Miles, MSU.

We observed a few flagged powdery mildew shoots in southwest Michigan on May 18. These are hard to spot shoots covered with white sporulation. In Michigan, because powdery mildew appears to be more sporadic, using clean planting material when establishing new hopyards can be a very useful strategy since it is readily spread via nursery stock. Please consult the MSU Extension article, “Managing hop powdery mildew in Michigan in 2020,” for more specific details about how to manage powdery mildew using other cultural practices and chemical applications.

Now is a great time of year to look for viral disease symptoms on new growth. On June 1, we observed a 'Centennial' plant that is known to be infected with four viruses: American hop latent virus, hop latent virus, hop mosaic virus and hop stunt viroid. The best way to control viruses is to utilize sanitation practices prior to planting (e.g., using virus tested stock, destroy heavily symptomatic plants). For more information about hop viruses, please check this article, “Virus visible in Michigan hopyards.”

Mosaic virus symptoms
Mosaic virus symptoms observed in East Lansing, Michigan, on June 1, 2021, on a plant infected with four known hop viruses. Photo by Timothy Miles, MSU.

Insects

Twospotted spider mite activity has begun but remains at low levels and tough to spot. Twospotted spider mite is a significant pest of hop in Michigan and can cause complete economic crop loss when high numbers occur. Feeding decreases the photosynthetic ability of the leaves and causes direct mechanical damage to the hop cones. Leaves take on a bronzed and white appearance and can defoliate under high pressure. Intense infestations weaken plants, reducing yield and quality. Dry, hot weather provides ideal conditions for outbreaks.

Scout carefully for mites season long and treat while populations are at low levels when mites are most effectively managed. Refer to the Twospotted Spider Mite Factsheet for more information on identification and management.

Twospotted spider mite adult
Twospotted spider mite adult along hop midvein under magnification. Photo by Erin Lizotte, MSU Extension.

Potato leafhopper have arrived from Gulf states where they can overwinter but are still at low numbers. Like many plants, hops are sensitive to the saliva of potato leafhopper, which is injected by the insect while feeding. Damage to leaf tissue can reduce photosynthesis, which can impact production, quality and cause death in baby plants. Refer to the Hop Potato Leafhopper Factsheet for more information on identification and management.

Adult potato leafhopper on hop leaf.
Adult potato leafhopper on hop leaf. Photo: Erin Lizotte, MSU Extension.

European corn borer remains a concern this year, particularly on sites with infestations in 2019-20. European corn borer has been a minor pest of hop in Michigan over the last decade. Other Midwestern states have experienced more substantial damage from this introduced moth. Unfortunately, damaging levels of European corn borer larvae were present in some Michigan hopyards for the last two years. The Enviroweather corn borer model is predicting that first generation flight began as early as May 24 in southwest Michigan and May 30 in southeast Michigan. First flight is forecast to begin on June 2 in west central Michigan and June 6 in northwest Michigan.

Regardless of location, scout for adults, eggs and larvae now. For more information on European corn borer, refer to the MSU Extension article, “Be on the lookout for European corn borer in hops.”

6-2 Hop report 9 web
European corn borer egg mass ready to hatch. May 31, 2021. Photo by Mike Reinke, MSU Extension.

Fertility

Growers that fertigate have begun to spoon feed nutrients. As a reminder, please reference the Nutrient Management section (pages 22-26) of the Michigan Hop Management Guide for fertility recommendations. MSU recommends submitting soil samples each spring around the same time (now would be a good time if you have yet to do so). Please refer to lab sampling and submission instructions prior to sending in samples.

As hops approach 8 feet in height, consider pulling leaf plus petiole samples for nutrient testing. Many soil testing labs also offer plant nutrient testing as well. For more information on hop leaf plus petiole sampling, please refer to “The importance of testing hop fertility”.

Soil testing labs

Comprehensive soil health testing labs

Stay connected

For more information on hop production, visit the MSU Extension Hops website. Also, Michigan State University Extension is hosting a series of interactive Hop Chat Zoom meetings this 2021 season to allow easy communication between producers and MSU faculty. These informal weekly sessions run every Wednesday at noon from May 4 through Sept. 7 and include crop and pest updates from MSU Extension’s Rob Sirrine and Erin Lizotte. In addition, MSU faculty will drop in to address timely issues and provide research project updates. Bring your field notes, too! We want to hear what’s going on in your hopyard. Registration is free but required. Sessions will not be recorded. Register here!

This material is based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2017-70006-27175. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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