Michigan hop crop report for the week of July 19, 2021

The Michigan hop crop is progressing nicely.

hopyard
Southwest Michigan hopyard on July 19, 2021. Photo by Rick Kawalski.

Weather

Last week, temperatures were warmer than normal across much of the state. In terms of growing degree days (GDD) base 50, most areas of the state are still in a slight surplus.

Accumulated degree day chart
Accumulated degree day base 50 summary for hop producing areas of Michigan on July 19, 2021, as compared to the five-year average. Data source: MSU Enviroweather.

Many areas across northern lower Michigan picked up rain over the last several days. Plant available moisture is now close to the 25-year average.

Accumulated rainfall summary
Accumulated rainfall summary for hop producing areas of Michigan on July 19, 2021, as compared to the five-year average. Data source: MSU Enviroewather.
Current soil moisture conditions
Current soil moisture conditions in the northeastern United States. Source: NASA.

Looking ahead, temperatures should be in the mid-70s through low-80s across much of the state this week. There will be a slight chance of showers Thursday and Friday and a greater chance Saturday. Next week returns to above average temperatures (mid-high 80s) and drier conditions. The 6-10 day (July 25-29) and 8-14 day (July 27-Aug 2) outlook suggests above normal temperatures and lower than average precipitation.

6-10 day outlook
United States precipitation and temperature forecasts for July 25-29, 2021. Source: NOAA.

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

Stage of production/physiology

Hops range from Principal Growth Stage 5: Inflorescence Emergence to Principal Growth Stage 7: Development of Cones.

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.
Graph
Timing of hop production management activities in northwest Michigan.

Hop stage

Crop development

Southeast Michigan

Hop plants are looking very healthy. Fungicides are being applied to prevent downy mildew. Japanese beetle numbers have been high. With the recent precipitation, growers are actively managing weeds.

Southeast Michigan hopyard
Southeast Michigan hopyard on July 20, 2021. Photo by Rose Stahl.

Southwest Michigan

Cascade, Nugget, Saaz and Bitter Gold are forming cones. Chinook and Cashmere are in full bloom with some cone formation. Mite pressure has been relatively low overall as has European corn borer. Second generation European corn borer flight has started, so growers are actively scouting. Japanese beetle numbers have been high. In terms of disease, growers are spraying for powdery mildew. If the season progresses as it has, growers are looking forward to good yields and high quality.

East central Michigan

Hops are in burr to cone stage. Growers are preventively spraying for downy mildew.

West central Michigan

Hops are flowering. Growers are spraying for downy and powdery mildew. Potato leafhopper pressure is high. Disease pressure is also high. Some growers are struggling to get pesticide applications on due to the weather. Grassy weeds are prevalent.

Northeast Michigan

Growers are reporting full burr stage in northeast Michigan. Pest pressure continues to be light and growers are applying preventative sprays for mildew every ten days. Harvest is estimated to begin in four to six weeks.

Northeast Michigan hopyard
Northeast Michigan hopyard on July 19, 2021. Photo by Andrew Walawender.
Burrs in northeast a Michigan hopyard
Burrs in northeast a Michigan hopyard on July 19, 2021. Photo by Andrew Walawender.

Diseases

Sclerotinia wilt (also known as white mold) is being observed at this time. According to the Hop IPM Field Guide, Sclerotinia wilt affects nearly 400 weed and crop plant species, including green bean, pea, lima bean, canola, carrot, lettuce, potato, sunflower and squash. The disease is caused by a fungus, Sclerotinia sclerotiorum, and is only an occasional problem on hop in wet, cool climates. Sclerotinia wilt can cause damage when soil and plants remain continuously wet and temperatures are mild.

Disease symptoms generally appear in late spring or early summer as soft, watersoaked lesions on bines just below or near the soil surface at the crown. The infected tissue collapses, creating a light brown to grayish lesion approximately 1 to 4 inches long. In some instances, the fungus can colonize stems higher on the plant. During wet weather, fluffy white growth of the fungus may form on the infected tissue.

Small (about 1/16 to 1/8 inch), hardened, black overwintering structures (sclerotia) form on and in diseased bines. As the disease progresses, the lesions expand and may girdle the bine, causing a wilt. Bines with smaller diameter seem more likely to fully wilt than larger diameter bines. Leaves generally remain green until the bine is girdled completely. Disease symptoms may appear similar to those caused by Fusarium canker or Verticillium wilt, however, the presence of fluffy white mycelia and sclerotia are diagnostic for Sclerotinia wilt.

Control measures for Sclerotinia wilt of hop usually are not needed. Cultural practices that reduce the duration of wetness on plants and the soil surface can reduce disease incidence. These practices may include limiting nitrogen fertilization, removing excess basal shoots and leaves, stripping leaves from lower bines, delaying the first irrigation as long as possible, and timing irrigations to allow the top two inches of the soil to dry completely between irrigations.

For more information, refer to the Hop IPM Field Guide.

Sclerotinia wilt
Sclerotinia wilt. Photo by anonymous.

Basal spikes and lateral infections of downy mildew have been seen in southwest Michigan for the past few weeks. Downy mildew symptoms will likely continue to develop into secondary downy mildew on lateral shoots if left uncontrolled. Most growers have made one to two 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 symptoms on spike
A second flush of downy mildew observed in our experimental yard in East Lansing, Michigan. Photo by Ross Hatlen.
Dark sporulation on hop plant
Notice the dark sporulation on the underside of the downy mildew spike in East Lansing, Michigan. Photo by Ross Hatlen.

We have been observing powdery mildew in southwest Michigan on some specific hop cultivars as early as May 18. Occasionally we saw flagged shoots but now have been seeing more typical symptoms on the foliage. In Michigan, because powdery mildew appears to be more sporadic, using clean planting material when establishing new hop yards 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. 

Foliar symptoms of powdery mildew
Foliar symptoms of powdery mildew from July 2020 in southwest Michigan. Photo by Timothy Miles, MSU.

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: 1) American hop latent virus, 2) hop latent virus, 3) hop mosaic virus and 4) 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."

On May 28, we began to observe foliar halo blight in hopyards. These infections are caused by a fungus. This fungus is a Diaporthe sp. and researchers at Michigan State University have been studying management methods for the past two years. Halo blight can be a serious disease in specific yards and lead to significant cone infections and ultimately shatter during harvest. It appears to have a wider geographic range than previously thought and has been recovered throughout Michigan on both leaves and cones. How the pathogen survives during the winter, spreads, causes new infections is still being investigated. The goal is to provide management tools that can be used to prevent foliar and cone infections in yards. 

Halo blight on leaf
Halo blight. Photo by Timothy Miles, MSU.

Insects

Twospotted spider mite activity continues around the state and mites found during scouting should be treating. 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 numbers have continued to build in untreated areas. 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 has predicted adult moth emergence in all major hop production regions in Michigan at this time.

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.

Japanese beetles are being widely observed at this time. Adult Japanese beetles aggregate, feed and mate in large groups after emergence, often causing severe and localized damage. They feed on the top surface of leaves, skeletonizing the tissue between the primary leaf veins. If populations are high, they can remove all the green leaf material from plants. Japanese beetle may also feed on developing flowers, burrs and cones.

For more information on identification and management, check out this Japanese beetle factsheet and refer to the Michigan Hop Management Guide.

Japanese beetle on leaf
Japanese beetle feeding on hop. Photo by Erin Lizotte, MSU Extension.

Weeds

Grass weed pressure remains substantial this season, especially with recent precipitation. Growers commonly use a selective grass herbicide containing the active ingredient clethodim to manage annual and perennial grasses within the row. Growers utilizing Aim will also get some control of grasses and broadleaf weeds in the row. Aim should not be used on baby hops. For more information on registered herbicides, refer to the Michigan Hop Management Guide.

Virus testing

MSU Plant & Pest Diagnostics is now providing testing for hop viruses and viroids! Please refer to the recent MSU Extension article, “MSU Plant & Pest Diagnostics provides testing for hop viruses and viroids,” for information on costs and protocol for submitting samples.

Fertility

Growers should be dialing down nitrogen fertilization and considering applying micronutrients. Please reference the Nutrient Management section (pages 22-26) of the Michigan Hop Management Guide for fertility recommendations. As hops approach the wire, consider pulling leaf plus petiole samples for nutrient testing (from 1 foot below the wire) to determine if supplemental/foliar nutrient applications are in order. For more information on hop leaf plus petiole sampling, please refer to “The importance of testing hop fertility.”

Soil testing labs

Plant-tissue 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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