Hop crop report for the week of May 23, 2022
Warm weather next week will kick hops into gear.
Weekly weather review
The week began with cool weather and then warmed up on Friday. There was wild weather Friday afternoon with strong thunderstorms, high wind, and up to baseball size hail across portions of northern Michigan. An EF3 tornado (winds up to 150 mph) touched down in Gaylord, Michigan, and caused significant damage, multiple injuries, and fatalities. It was the strongest tornado in in Michigan in over 10 years. Most of the state received 0.5-1 inch of precipitation over the weekend.
Over the last 30 days, most areas of the state are slightly dryer than normal except for southern Michigan, which has had slightly more precipitation than average. Average temperatures have been higher than normal over the last 30 days with above average GDD across nearly the entire Lower Peninsula.
Beginning Wednesday, there will be breezy conditions from the east/southeast with an area of low pressure beginning to form. There is a chance of rain in southwest and west central Michigan in the afternoon Wednesday and then a prolonged period of rain (0.25-0.5 inches) through early Friday. High temperatures will be in the 60s-70s and lows in the 40s-50s. By Sunday into early next week, we will see warmer and potentially wetter conditions with temperatures in the 70s-80s and a chance of thunderstorms. The NOAA 6-10 outlook predicts above average temperatures and precipitation through June 2.
Stage of production/physiology
Hops across Michigan are in Principal Growth Stage 1: Leaf Development and entering Growth Stage 2: Formation of Side Shoots and 3: Elongation of Bines depending upon growing location.
In the field
Across Michigan, yards are strung, hops are being trained, and growers have applied or are preparing to apply fertilizer. Leaf+ petiole sampling for SAP analysis has commenced. Growers are applying fungicides for downy mildew control. For growers interested in reducing erosion and leaching and/or improving environmental stewardship the voluntary Michigan Agriculture Environmental Assurance Program (MEAEP), may be of interest. Farmers who complete the MEAEP verification may have an advantage for USDA cost-share programs. MSU recently updated their nitrogen fertilization recommendations for Michigan hop producers.
Current recommendations are based upon nitrogen fertility and hop cone quality research conducted by Anne Iskra and colleagues at Washington State and Oregon State Universities. Cumulative nitrogen should not exceed 160 pounds/acre/year and most, if not all, nitrogen should be applied June 1 – July 15. Excessive nitrogen does not improve yields and total oil volume and alpha- and beta-acids has been found to decrease with increasing nitrogen rates.
If you are unsure of what is causing symptoms in the field, you can submit a sample to MSU Plant & Pest Diagnostics. Visit the webpage for specific information about how to collect, package, ship and image plant samples for diagnosis. If you have any doubt about what or how to collect a good sample, please contact the lab at 517-432-0988 or email@example.com.
Grass weeds have taken off and need to be treated when small for optimal control. Refer to the Michigan Hop Management Guide for weed control options.
Downy mildew spikes are visible in some locations. Downy mildew is caused by the fungal-like organism Pseudoperonospora humuli and is a significant disease of hop in Michigan, potentially causing substantial yield and quality losses. This disease affects cones, and foliage and can become systemic; in extreme cases the crown may die. Cool and damp weather during the spring provide ideal growth conditions for the pathogen. Disease severity is dependent on cultivar, environmental conditions, and management programs. Growers should focus on proactive management strategies, including 1) sourcing clean planting stock, 2) clean crown management in the spring, 3) scouting regularly and 4) utilizing a preventative fungicide program. Refer to the Michigan Hop Management Guide section on downy mildew for additional management options.
Powdery mildew of hop (caused by the fungus Podosphaera macularis) is an emerging disease in Michigan that has serious implications for growers. Powdery mildew was confirmed in Michigan in 2014 and has been a concern on greenhouse/nursery plants for years. Seasonal disease severity is dependent on cultivar, environmental conditions and management programs. Focus on proactive management strategies, including sourcing clean planting stock, scouting regularly and utilizing a preventative fungicide management program.
Powdery mildew resulting from bud infection appears in the spring white stunted shoots called “flag shoots.” Flag shoots are rare, accounting for less than 1 percent of all shoots in a field and making detection at this stage very difficult. Secondary lesions become visible as leaf tissue expands and first appear as raised blisters, which quickly develop into white, round colonies. Infected burrs and cones can also support white fungal colonies or may exhibit a reddish discoloration if infected later in development.
Burrs and young cones are very susceptible to infection, which can lead to cone distortion, substantial yield reduction, diminished alpha-acids content, color defects, premature ripening, off-aromas and complete crop loss. Cones become somewhat less susceptible to powdery mildew with maturity, although they never become fully immune to the disease. Infection during the later stages of cone development can lead to browning and hastened maturity. Alpha-acids typically are not influenced greatly by late-season infections, but yield can be reduced by 20 percent or more due to shattering of overly dry cones during harvest resulting from accelerated maturity.
Late-season powdery mildew can be easily confused with other diseases such as Alternaria cone disorder, gray mold, other cone diseases or spider mite damage. Several weak pathogens and secondary organisms can be found on cones infected by powdery mildew; limiting powdery mildew can reduce these secondary infections.
Scouting for powdery mildew involves monitoring the crop for signs and symptoms of disease and evaluating the efficacy of the control program being utilized. Keep records of your scouting, including maps of fields, a record of sampling and disease pressure, as well as the control measures utilized. Section your farm off into manageable portions based on location, size and variety and scout these areas separately. It is more practical to deal with blocks that are of the same variety, age and spacing. Walk diagonally across the yard and along an edge row to ensure you view plants from both the edge and inner portion of the block. Change the path you walk each time you scout to inspect new areas. Reexamine hotspots where you have historically encountered high mildew pressure. Due to increased humidity, hotspots may occur more often near tree lines or in low-lying wet areas of the yard. Scout as soon as plant or pests become active and continue until the crop or pest is dormant. Weekly scouting is recommended at a minimum.
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.
First flight of European corn borer is approaching. European corn borer overwinters as larvae inside the host plant where it pupates in response to warming temperatures in spring. First generation flight of moths is expected at 450 growing degree days (GDD) base 50, based on a March 1 start date for GDD accumulation. Currently, GDD50 accumulation in the lower peninsula ranges from 92-238 with 450 GDD50 falling outside of the forecast data range currently. Historically first flight has occurred in early June. First generation moth emergence continues for 500 GDD (through 950 GDD base 50) with females laying 200-500 eggs over a period of two to three weeks.
Egg development is driven primarily by temperature, but generally eggs hatch in approximately 12 days. Newly hatched larvae then feed externally on leaves for approximately seven days before boring into stems and petioles where they continue to feed and grow. This larval feeding period is the critical window for control.
Once inside the plant, observations in hop indicate that European corn borer larvae damage vascular tissue, disrupt the flow of nutrients and water and impede plant development. Since 2019, European corn borer larvae have found in leaf petioles, sidearms, cone petioles (strigs) and bines. There are a number of effective insecticides for managing European corn borer and they should be applied to control larvae before they enter the protection of the bine. Growers with substantial infestations should also carefully dispose of crop waste including chopped bines at the picking line. Consider burying or hot composting crop debris both from the processing line and the field to limit carryover into the next season.
For more information on European corn borer management, refer to the MSU Extension article, “Be on the lookout for European corn borer in hops.”
Managing for European corn borer takes a multipronged approach including careful monitoring and targeted pesticide applications. A regular schedule of insecticide applications based on insecticidal residual activity should be maintained from the beginning of egg hatch until two weeks before harvest or when larvae are no longer detected. For more information on European corn borer, refer to the Iowa State University publication, “European Corn Borer – Ecology and Management and Association with other Corn Pests.”
Grower input is needed on disease management in hopyards. Take our MSU hop disease survey.
Save the date for our MSU Hop Research Field Day on July 13.
For more information on hop production practices, sign up for the FREE MSU Hop Chat Series.
MSU Extension sincerely thanks the Michigan hop producers who provide timely input for the Michigan hop crop report.
This work is supported by the Crop Protection and Pest Management Program [grant no 2021- 70006-35450] from the USDA National Institute of Food and Agriculture and the North Central IPM Center. 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.