To Determine The Proper Cutting Height For Your Forages

On June 03, 2019

To Determine The Proper Cutting Height For Your Forages

Whether you’re taking the crop as haylage or dry hay, it’s important to pay attention to forage cutting height.  One of our goals as farmers is to maximize our yield; however, cutting a crop too low can lead to several negative issues.  Extension Agronomist Dwane Miller explains the introduction of the disk-type mowers (discbines) allows for cutting very close to the ground.  Miller has seen many fields that have been “scalped” right to ground level.  This differs considerably from the older sickle bar mowers (haybines), whose technology required some level of stubble height remain.  Stand longevity can be compromised when the crop is cut too low.  As a general rule, alfalfa can be cut closer to the ground than our grass crops.  We need to think about where energy reserves are stored in the crop.  For alfalfa, carbohydrates are stored below the ground in the taproot.  Grasses store their energy above ground in the stem base or tillers.  Frequent mowing at a close height will continue to deplete these energy reserves, resulting in stand longevity issues.  

The second consequence for mowing too close to the ground is increased ash content of the forage.  All forage has a natural ash content of approximately 6%.  However, mowing too closely with disk mowers can add soil to the crop, and increase the ash content by as much as 10-12% (18% ash content in total analysis).  If we all had table-top smooth fields, it would also be much easier to make a closer cut across all fields.  However, things such as groundhog holes and the unevenness of fields can add to increased ash content of our harvested forage.

So, the million-dollar question is how low can you go?  The best answer is…it depends!  The first question to ask is – is it a solid stand or a mixed stand?  If you have grasses involved, you must keep cutting height higher than a pure stand of legume, if you want to keep the grass in the stand.  Keep in mind these are minimum recommendations; it’s ok to mow higher than the numbers below.  Remember these are minimum cutting height recommendations.

For Alfalfa or Clover 2” is minimum.  Some literature shows a cutting height of 1” will not reduce stand longevity but remember the increased ash content issue.  Also, keep in mind that frequent cutting at early maturity will continue to deplete carbohydrate reserves.  One cutting of alfalfa should be allowed to reach the bloom stage each year. For Cool Season Grasses (Orchardgrass, Timothy)  4” is the minimum during the establishment year and 3” minimum during production years.  This is where we see most of our stand longevity issues.  Frequent cutting of cool season grasses at a low height will continue to deplete energy reserves.  

For mixed stands you must manage for the predominant species.  Do you have a grass stand with some alfalfa, or an alfalfa stand with some grass? For Alfalfa with some grass use a 2.5” minimum. For grass with some alfalfa use a  3” minimum (if you want to keep the grass stand!)

To Scout For Black Cutwork Damage

Penn State Extension’s Black Cutworm Monitoring Network has detected five significant flights of black cutworm moths in our pheromone traps. Extension Agronomist Anna Busch suggests in these areas, one should expect an elevated risk of cutting damage by caterpillars. A second pulse of moths was reported for some locations. Black cutworms migrate in the spring from the Gulf Coast in April and May. This second pulse of moths is most likely due to a second migration.

Table 1. Details of significant flight of black cutworm moths detected so far this season.

Nearest municipality PA County Date of flight Degree day accumulation by 23 May
Ulysses Potter 19 April 99
North Cornwall Lebanon Approx. 19 April 330
Montoursville Lycoming 27 April 222
Lemasters Franklin 2 May 245
Souderton Montgomery 14 May 105

Cutting damage from black cutworm caterpillars tends to occur about 300 degree days after these flights. Lebanon County reached 300 degree days on Tuesday and there have been reports of cutting damage. Over the weekend or by early next week, Franklin and Lycoming counties will also hit 300 degree days. We recommend scouting for black cutworm damage in these regions that are at a high risk, but all growers should be cautious this season and scout their fields. 

We recommend scouting fields every 7-10 days. This “regular” scouting should detect black cutworm damage. When scouting your fields, note that black cutworm caterpillars can damage corn from first emergence up to V4 or V5. For young plants, cutworm damage can look like a series of symmetrical holes through the leaves. Remember that if cutting damage is found, rescue treatments are usually the most efficient and economical tactic for managing black cutworm. For more information, see this black cutworm article: 

Quote Of The Week: A lie doesn’t become truth, wrong doesn’t become right, and evil doesn’t become good just because it is accepted by the majority.” Booker T Washington