Many hop growers are asking this question as the abnormally mild weather persists across much of the USA. For most growers in northern latitudes; probably not much effect will be noted. Average hop vernalization temperature requirements of 6 weeks below 38 degrees Fahrenheit will still be met, resulting in normal burr and cone development later in the season. Expect an earlier emergence of pests and disease that the milder winter failed to kill.
For growers in more southern latitudes the story could be completely different. Effects on the hops in the southern tier could include: lack of proper vernalization, increased pest pressure, and increased prevalence and severity of hop diseases like downy and powdery mildews.
Hop vernalization requirements vary by hop genotype and varieties that require longer chilling periods may not properly reset back to the juvenile spring phase required to grow and produce a normal yield of cones. One of the first signs of incomplete vernalization is uneven spring emergence of new shoots within plants of the same hop variety. Growers in the PNW have noted that this uneven emergence follows through the entire growing season; affecting cone-set, yield, alphas, and maturity dates. The cone-bearing sidearms may not extend properly and only produce cones on the terminal ends. Many affected hop plants showed up to a 6 week delay of burr initiation and a 30 to 50% loss in total potential yield.
It's All About Balance
Fertile soil is a mixture of well-balanced minerals, high organic matter, humus, humic, fulvic and carbonic acids, good aeration and bountiful microbial life. The biology or life in the soil is at its healthiest when the nutrients are plentiful and balanced, and there is sufficient oxygen and water. The top soil region is the most vital portion of the soil profile; holding about 70% of the life and 70% of the organic matter. In a typical soil, below 6 inches plant roots are feeding on mostly soluble nutrients since the micro-organisms are not able to thrive due to insufficient oxygen levels. Many minerals are tightly bound to the subsoil colloidal particles are only made available to plants through complex soil interactions with organic acids leaching downward from the topsoil. It is critical to maintain the organic matter content in soils for them to remain balanced and healthy.
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No doubt about it, for many new growers hops are a difficult crop to grow well. Fast growing hop plants require lots of balanced nutrients and water with critical timing of applications; making hops a real challenge to keep up with when compared to most other crops. Getting the hops to climb to the top trellis wire and produce fully developed side arms with lots of cones seems to be an unattainable goal sometimes. There always seems to be a guy named Murphy lurking around, ready to throw a wrench in the works; despite a hop grower’s best efforts. Wind, rain, drought, and pestilence... yet there are lots of pretty pictures of hopyards and recorded harvest yields to show it is more than a dream.
It is common to find in many instances, less experienced hop growers do not fully understand many integrated hopyard management practices and how plant nutrient availability and growth is affected. This following discussion covers a few of the issues that have been identified as potentially holding back hop growth and yields. These issues are gleaned from talking to, and working with hundreds of new hop growers and the challenges they have experienced.
These observations and field notes are intended to educate and provoke deeper, more in-depth discussions amongst hop growers and grower groups.
Downy mildew (DM) of hops is a major disease that affects many susceptible cultivars of hops. It can severely damage both the hop plant as well as making the cones unsuitable for harvest. This discussion pertains to using post harvest DM controls to help hopyards recover from a season of high downy mildew infection.
Many hop growers do not understand the importance of controlling downy mildew in their hop yard after harvest is completed. The fungus and the infection are not as visible as springtime symptoms. Many growers consider the season as finished at harvest and leave the yard unattended going into winter. This is a fundamental mistake in controlling DM in infected hopyards. Downy mildew is active whenever conditions permit – it simply doesn't care if it is springtime, summer, or fall. If green plant tissue, moisture and the right temperatures are present, DM will remain active. Post-harvest fungicide applications and controls can be an effective way to manage downy mildew in yards that have had the disease present and reduce the severity of downy mildew spikes that emerge during the following spring growing season.
Downy mildew, like most molds and mildews, persists and spreads during the growing season mainly through air-borne spores which infect new leaves and growth whenever environmental conditions are favorable. In the Fall season, however, downy mildew “morphs” into a different creature; producing a specialized motile spore type called a zoospore. This spore acts much more like a living microscopic worm than a fungal spore. The motile zoospore form helps downy mildew complete its annual life cycle by finding a safe resting place for it to overwinter or by forming protective dormant oospores. These forms of DM exist outside of the plant in the soil where it is outside its host and can be interrupted at this point.
Lynn, the head hop grower at Great Lakes Hops has over 30 years of experience in the horticultural field. Browse the blog articles here to find useful growing information for humulus lupulus, based on personal experience and observations at Great Lakes Hops.