Should You Be Concerned about Hay Fields That Didn't Get Mowed in Fall?

Many articles answer what happens if forages are cut below the recommended fall 4 inches or harvested too close to frost, read How Fall Forage Harvest Can Affect Spring Stands.

In a wet fall or when frost comes early, the question comes up, "What happens if I don't take my last cut and leave 18 inches of forages on my field?" This article tries to answer some of those questions.

Having these conversations with producers always starts the same "why is the hay still in the field?" This occurs for a variety of reasons.

• It's too late in the year, not hot enough, and too humid to dry and cure the hay. Baleage provides the flexibility to wrap hay at 45-60% moisture, removing the need for low humidity days and curing time. Even if you don't own a wrapper to make your baleage, renting or hiring a contract wrapper will be cheaper than buying supplemental hay from off the farm.
• I don't need the hay (for my operation or to sell). The quality of the forage and its intended use or value should also be considered. If the forage is high quality from a field that has been well managed with fertility and weed control, there is greater value in that crop and more incentive to harvest. The opposite is also true. If the field was not fertilized and has broadleaf weeds and summer annual weeds like foxtail it has limited marketability and value. If it is a high value crop, with invested dollars, consider taking the crop and selling or stockpiling. This will reduce nutrient loss and increase economic potential.
• I got too busy and now the frost is too close. Wait until after the killing frost to cut or rotary mow the field. If mowing for hay, this will remove the residue and provide a forage source. If rotary mowing, this speeds the decomposition process and preps the field for spring regrowth. Whether mowing for hay or rotary mowing, this will also work as a weed suppressant for the perennial weeds present in the field. Fall Alfalfa Harvest – Cut now or wait till after a killing frost? is a good reference from Iowa State University Extension about killing frosts and when it is safe to mow hay after.

In some instances, we just may go into winter with 18 inches of standing forages. Is this an issue? As with most agricultural situations, there are pros and cons. Understanding these will let you decide whether it is best for the forage to be removed (rotary mowed, used as an emergency forage, harvested after frost), or if you are comfortable letting it over winter as is.

Pros of additional residue:

• More residue = more leaf area. If forages are not dormant (growing before killing frost) the grass can still be stockpiling carbohydrates for winter reserves. Better winter reserves can mean better winter survivability. 
• Decomposing residue can add additional organic matter, and some removed nutrients back into the soil.
• Better weed suppression potential, especially winter annuals like dead nettle, chickweed, and henbit. This is especially helpful for thinner stands.
• Vegetative mat can retain heat and lessen chances of winter kill.
• If the area is, or can be, fenced the forage could be grazed in emergency situations. 

Cons of additional residue:

• Additional forage can add habitat for insects and diseases to over winter. This can lead to increased damage by spring insects, or increased retention of pathogens, especially molds and fungi. 
• If large amounts of forage are present, decomposition can be slow. This partially decomposed grass or weed material can become undesired residue in early cuts in the subsequent season.
• This additional residue can smother tillers and lower spring stand density and regrowth.
• Purchased fertilizers, like N and P, can be immobilized (converted from inorganic to organic forms) in this residue. This immobilization means that it will not be plant available in the spring and will need time to convert back to an inorganic form.

It is important to consider all of these pros and cons, as well as determining what works best for your operation based on farm management, cost benefits, and livestock needs.