Is it time to irrigate my hops?
It continues to be hot and dry across the province with little to no rainfall in the last 7 days. Agriculture and Agri-food Canada (AAFC) tracks precipitation amounts across the country and develop 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 A (Accumulated Precipitation, April 1 – July 19, 2011) give us the ‘big picture’ of rainfall amounts for the growing season. Although it appears there has been enough precipitation for hop yards to date, we cannot base our 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, Figure B (7 Day Accumulated Precipitation, July 13-July19, 2011).
Similar to the ‘big picture’ weather maps, studies report that hops require approximately 700-800 mm of water during the growing season, however, there are two critical periods when hops require water for adequate growth and yield. The first critical period occurs in early spring as hop plants begin to grow and the second critical period occurs just before flower initiation through to cone development. Much of the hop crop in Ontario is currently at the second critical stage and irrigation should be considered during these hot, dry periods. Studies have shown that supplemental irrigation can improve yield and quality of hops and may positively effect alpha acid concentrations. Supplementing rainfall with irrigation to achieve approximately 25-35 mm of water twice per week during hot and dry conditions should be adequate for crop growth in established hop yards. Some studies have reported irrigating a total water volume of 3-8 L of water per plant twice per week during dry periods. It should be noted that first year hop plantings typically require more frequent water applications but in lesser amounts.
Drip (trickle) irrigation is commonly used to supplement rainfall in hop yards. Other irrigation methods can be employed but caution should be taken to prevent long durations of leaf wetness which could favour conditions for foliar diseases. Scheduling your irrigation in early morning will help decrease the time of leaf wetness and thereby reducing the incidence of disease development.
You can conserve water in your hop yard by various methods including irrigating deeply and infrequently to promote deep root growth, minimizing tillage to prevent soil moisture evaporation, and applying mulch around the base of the plants which may reduce weed populations and their competition for soil moisture. Drip irrigation also assists in water conservation by placing water directly on the row instead of over the entire yard as would occur with sprinkler irrigation systems.