Michigan hop crop report – May 18, 2023
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EmailDowny mildew is active and visible in Michigan hopyards.
Weekly weather review
From mid-February through mid-April, temperatures were slightly higher than average for the Lower Peninsula. From mid-April through mid-May temperatures were slightly below normal until last week, when temperatures climbed well above normal. The record highs and record lows that we experienced across most of the state in March and April seemed to have narrowed into a more “normal” range as of late.
In terms of growing degree day (GDD) accumulation, most areas of the state are very close to average to a bit above average.
Looking ahead
Medium range guidance suggests a transition back to warmer than normal temperatures and near to below normal precipitation.
New long lead outlooks suggests warmer than normal temperatures and normal to above normal precipitation.
View the most recent MSU agriculture weather forecast.
Stage of production/physiology
Hops across Michigan are in Principal Growth Stage 1: Leaf Development (from re-growth after burn back) and entering Growth Stage 2: Formation of Side Shoots and 3: Elongation of Bines depending upon growing location.
In the field
Across Michigan, growers have applied a fungicide drench and plants are coming back nicely after burndown prune. Training is underway or will begin soon for more northern farms. Most growers have or will soon apply an initial foliar fungicide, which is timely since downy mildew spikes have been spotted. Finally, many growers are spreading dry fertilizer and getting irrigation ready for the season.
Pest report
Weeds
The window for applying early season, non-selective herbicides like glyphosate is closed. It was a narrow window again this year and broadleaf weeds may be an issue this season. Grass weeds are taking off and need to be treated when small for optimal control. Refer to the Michigan Hop Management Guide for weed control options.
Diseases
Downy mildew spikes are visible in some locations. Downy mildew is caused by the fungus-like organism Pseudoperonospora humuli. It 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. 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’s section on downy mildew for additional management information.
Insects
First flight of European corn borer is approaching for growers in southern and central Michigan. 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 GDD base 50, based on a March 1 start date for GDD accumulation. Currently, GDD50 accumulation in the Lower Peninsula ranges from 193-328 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. 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.
In hop, European corn borer larvae can be found in leaf petioles, sidearms, cone petioles (strigs) and bines. Their location and prevalence in the plant dictates the severity of damage. The most severe damage observed in Michigan hops occurs when hopyards are infested by first generation flight in June during bine elongation and subsequent sidearm and cone development stages. This early infestation greatly reduces yield and leads to variable cone maturity dates.
For more information on European corn borer management, refer to the Michigan State University Extension article, “Be on the lookout for European corn borer in hops.”
Focus on scouting for adults and eggs to allow for corrective management before larvae enter the bine. European corn borer eggs are smaller than the head of a pin but are laid in visible groupings. Eggs are white when first laid but change to yellow and then develop a black spot (the larval head capsule) just before hatching. Eggs are likely deposited on the underside of hop leaves in masses of 20 to 30 and covered with a waxy film.
If available, you may have better luck spotting eggs in adjacent corn fields. European corn borer larvae are light gray to faint pink caterpillars with a dark head and have dark spots along the sides of each segment and a pale stripe along the back. They grow to about 1 inch but start out very small at hatch and feed briefly on leaf tissue before boring into hop bines, and even hop leaf petioles.
European corn borer pupae are smooth, reddish brown, cylindrical and about a half-inch long and found inside bines.
The European corn borer moth is about 1 inch long and light brown with wavy bands across the wings. The male is slightly smaller and darker. The tip of the body protrudes beyond the wings. Adult moths are most active in grassy areas before dawn.
Small European corn borer larvae are the intended target of insecticides, so monitoring for adult moth flight is critical to predicting the start of egglaying and subsequent window of egg hatch. Begin monitoring and trapping well before predicted flight (450 GDD50) to avoid missing the beginning of flight. Simple wing or bucket traps used for other field crop moths cannot be used to trap European corn borer; instead, wire Hartstack or cloth Heliothis traps are used. These traps are cumbersome and expensive and must be positioned carefully in action sites or grassy locations where European corn borer gather to rest and mate. Use sweep nets in fallow, grassy areas at dusk and dawn.
Farms may also consider establishing a cooperative trapping and monitoring system with neighboring hop or corn growers to increase the amount of monitoring information for all. In lieu of trap data, careful crop scouting based on the Enviroweather prediction model can be used as a loose guide.
Other news
Sincere thanks to the Michigan hop producers who provided timely input for the Michigan hop crop report.
For more information on hop production practices, please sign up for the MSU Extension Hop & Barley Production Newsletter, the free MSU Hop Chat Series and continue to visit Michigan State University Extension’s Hops website or the MSU Hops News Facebook.
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.
