Hop fertility applications should be ending within the next two weeks now that we are past the summer solstice (June 21). Keep an eye on plant growth stage in your region and terminate fertility applications once burrs (female inflorescence) are detected (Principle Growth Stage 5: Inflorescence emergence on the BBCH Scale (Hops), Figure 1).
Flowers are typically initiated by the plant within 7-14 days after the solstice as a response to the change in photoperiod (decreasing day length) . The hop plant will shift from vegetative growth to reproductive growth at this point in the season (Figure 2). No additional fertility applications should be required for the remainder of the growing season.
Irrigation, however, is essential at this same growth stage. Growth stages 5 through 7 (Inflorescence emergence to cone maturity) is a critical period for water use in hops (Figure 3). Studies have shown that supplemental irrigation can improve yield and quality of hops and may positively affect alpha acid concentrations. Most recommendations suggest 7.5 L of water per plant per day (~2 U.S. gal/plant/day) is adequate for plant growth, however , some more recent information on Evapotranspiration (ET) rates of hops suggest the plant may require even more water, up to 19 L/plant/day (~5 U.S. gal/plant/day) for optimal plant growth. Always remember to include rainfall amounts when calculating how much supplemental irrigation should be applied.
Agriculture and Agri-food Canada (AAFC) tracks precipitation amounts across the country and develops Accumulated Precipitation maps which are a useful resource to determine rainfall accumulation over the growing season for a particular growing area. Maps like the one in Figure 4 (Accumulated Precipitation, April 1 – June 16, 2014) give us the ‘big picture’ of rainfall amounts for the growing season. Although it appears there has been plenty of precipitation, one cannot base irrigation decisions on this long term chart. A much different and more applicable picture of rainfall status across the province can be seen in the 7 day average in Figure 5 (7 Day Accumulated Precipitation June 10-June 16, 2014) which may be useful when determining the amount of supplemental irrigation one should apply for the week.