The cool, wet spring followed by rainy weather well into the summer has delayed hay cutting schedules across much of Ohio. The delayed cutting schedules will likely mean that many fields won't be ready for a last harvest until we are into the critical fall rest period for alfalfa, considered to be from September 7 to 15 to late October in Ohio. Careful consideration is warranted if this is the situation.
Cutting during the critical fall rest period if often practiced in Ohio without great harm to the stand, but it always carries risk to stand health. The fall period is when alfalfa and other tall legumes like red clover undergo many physiological responses to the cooling weather in preparation for the winter. Carbohydrate and protein reserves are stored in the crowns and roots and cold-hardening occurs that makes the plants more resistant to cold temperatures. Interrupting this process by cutting carries the risk of the plants having inadequate energy and protein reserves to make it through the winter and for initiating vigorous regrowth next spring. It also may interrupt the cold acclimation process.
A number of factors affect the level of risk incurred cutting during the critical fall period. These include overall stand health, variety disease resistance, insect pests during the summer, age of stand, cutting management, fertility, and soil drainage.
A vigorous, healthy stand is more tolerant of fall cutting than a stressed and weakened stand. Protection from potato leafhopper stress during the year is important for maintaining strong and vigorous plants that are able to withstand a fall cutting stress. Alfalfa varieties with improved disease resistance and good levels of winter hardiness will be more tolerant to negative effects of a fall cutting because there is less total stress on the plant. Adequate fertility, especially soil potassium levels, increase plant health and plant tolerance to fall cutting effects. A high soil pH of 6.8 to 7.0 will also reduce the risk of fall cutting. Stands under 3 years of age are more tolerant of fall cuttings as compared to older stands where root and crown diseases are setting in.
A significant risk factor to consider when making a harvest during the critical fall period is the number of times the stand has been harvested. Alfalfa that has been cut three or more times before a fall harvest has a higher risk factor for injury due to fall harvest than one cut only twice. In other words, the cutting frequency during the growing season can affect the energy status of the plant going into the fall. Frequent cutting (30 day intervals or less) results in the plant never reaching full energy reserve status during the growing season. This makes the critical fall rest period more necessary for plants to accumulate adequate reserves before winter.
A final factor is soil drainage. Alfalfa stands on well-drained soils tolerate later fall cuttings better than alfalfa on moderately or poorly drained soils. Low plant cover going into the winter from late cutting increases the risk of winter heaving on many Ohio soils. We observed significant heaving this past winter in NE Ohio, and many of those stands had been harvested during the previous fall.
Cutting alfalfa during the critical fall period is sometimes necessary due to the need for forage or weather patterns like we've experienced this year. It often does not cause great harm to the stand, but there is always risk of reduced vigor with some yield loss next year, or even significant stand loss depending on the winter. So carefully assess the condition of your stand and the risk factors discussed in this article. If you do cut during the fall critical rest period, leave some uncut strips in different areas of the field so you can compare the regrowth next spring. You might be surprised by what you learn.