Storm Impact on Alfalfa

Stormy conditions have impacted crop fields across the state recently. With the potential for severe weather with us until the end of summer, what impact do strong storms and hail have on your alfalfa crop?

Strong storms, especially those that bring hail events, have the potential to completely strip and lodge alfalfa fields depending on their severity.  The actual impact will vary depending on damage done, but alfalfa due to its growth form is particularly vulnerable to hail damage.  Because alfalfa plants grow from the terminal or highest potion of the plant, any damage or defoliation can result in terminated growth and the plant having to start growth again from new shoots.

In all situations, estimating the amount of terminal damage is key to making management decisions.  With less than 50% terminal damage, the best option is to wait for normal harvest.  When damage levels get over 50%, we need to look at our harvest calendar to decide what to do next.  Fields damaged more than 2 weeks before planned harvest should be left alone and harvested normally, although expect timing to be a bit delayed. 

If the hail event occurs less than two weeks before planned harvest, harvest immediately as additional growth will be limited. In extreme cases, damage may be so severe that the yield is not worth the effort.  In these cases, allow the plant to regrow and manage the regrowth normally.

Lodged fields should delay harvest 3-4 days to allow plants time to recover somewhat.  Cutting against the lean and adjusting the mower forward will help pick up lodged crops. 

Just like the level of damage, impact from storms can vary. Research from the University of Wisconsin has shown that the biggest impact of hail is in loss of production.  In alfalfa stands averaging 2.25 tons of dry matter per acre, each percent of defoliation resulted in losses of around 35 lb. dry matter per acer in 2nd and 3rd cuttings when the hail event is within two weeks of planned harvest. 

Forage quality also takes a hit as leaves and top portions of the plant are damaged, but if yield is enough to warrant harvest, the impact is usually minimal.