Asparagus is a perennial crop historically grown without irrigation in western Michigan for the processing market. Shifts to fresh market production, new hybrids, increased incidence of summer drought, and increased disease pressure, justify evaluation of more intensive production practices including irrigation. Field and greenhouse trials evaluating the impact of drought stress and irrigation delivery system (overhead vs. sub-surface drip) on two varieties (Guelph Millennium [GM] vs. Jersey Supreme [JS]) were initiated to guide Michigan asparagus grower's irrigation decisions. Short-term results from these studies indicate a variety of positive plant responses to irrigation treatments. Asparagus yields increased from 6 to 21% with trickle and overhead irrigation treatments in GM and JS during the 2012 field season. With supplemental irrigation, increases in stem number, light interception, fern height, root carbohydrates, cladophyll weight, and dry fern weight occurred. Cultivar responses to irrigation treatments differed depending on drought stress severity and plant growth stage. Increased yields for GM were attributable largely to increased weight per spear, rather than increased spear number as seen in JS. Results from multi-season greenhouse trials with GM demonstrated that prolonged low-level drought stress reduced fern growth and root weight, while short-duration intense drought stress had greater impact on root carbohydrate concentration and short-term yield. Overall, these results suggest that under weather conditions similar to those of 2011-2012 irrigation increases yield and plant health enough to justify the added costs of irrigation for Michigan asparagus growers.
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