Michigan hop report – Aug. 14, 2020
Pay careful attention to preharvest intervals as harvest approaches.
Agricultural weather forecast
Southwest Michigan experienced damaging weather Monday evening, Aug. 10, with high winds and heavy rains. Winds are particularly problematic in hopyards at this time, as bines are fully developed and act as a sail, catching wind and stressing trellises. Significant property and crop damage are being reported in southwest Michigan and neighboring states.
The Agricultural Weather Forecast is calling for dry conditions in the short-term forecast, a brief cool down and then a return to unseasonably warm temperatures next week.
With dry conditions persisting, ensure plants receive enough water. In the height of summer, plants can require 16 gallons per plant per week. Amounts will vary based upon local soil and weather conditions. For example, sandy soils have lower water holding capacity compared to clay soils. Irrigate early in the day to keep the water cool, alternate days to allow the soil to dry down, pulse irrigate in sandy soils, and consider using moisture sensors to dial in irrigation rates and timing.
A typical schedule would be: three to four days per week (every other day), one to two times per day, up to 7 hours per day depending on emitters and soil type, and an occasional deep soak to increase deep root growth in mature plants. Do not deep soak directly after fertigation to avoid washing nutrients out of the root zone. On average, hops require approximately 30 inches of water per acre per season.
Finally, consider adopting practices to increase soil organic matter (compost, green manure additions, etc.), which will increase water holding capacity. For more information on irrigation, refer to the Hop Irrigation Best Practices presentation.
In terms of fertility, hop yield has already been determined, so you should have drastically reduced, if not ceased, any nitrogen application. At this time of year, focus management on effective pest and disease control to maintain cone quality.
With cones closed up or rapidly closing, disease management remains a priority. Growers are also working to clean up any potato leafhopper and mite infestations in preparation for harvest. Insecticide selection may be limited at this time due to preharvest intervals.
Downy mildew and powdery mildew fungicide applications should continue in the run up to harvest. Both mildews can affect plant health, cone quality and yield. Foliar powdery mildew infections are being reported on susceptible varieties and downy mildew infections are active and widespread. Lesser cone diseases like alternaria cone blight and fusarium tip blight remain a concern until harvest. Refer to the Michigan State University Extension articles, “Managing hop downy mildew in Michigan” and “Managing hop powdery mildew in Michigan in 2020” for specific recommendations. Carefully estimate your projected harvest dates and select materials with appropriate preharvest intervals.
Twospotted spider mite populations may continue to build with warm weather in the forecast. 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 and are a contaminate issue at harvest.
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 and the 2020 Michigan Hop Management Guide for pesticide options. Keep in mind that many miticides take time to reduce populations, so determine if treatment is justified as harvest approaches. Most true miticides have at least a seven-day or greater preharvest interval, so options may be limited depending on harvest date.
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This work is supported by the Crop Protection and Pest Management Program 2017-70006-27175 from the USDA National Institute of Food and Agriculture. 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.