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Alfalfa Faces Stress
Hay yields were only about half of what we would expect in the first cutting because the plants essentially needed to start over after the April freeze. The re-growth has been very slow because we have been so dry and the plants have used their root reserves to come back after the cold. If you took your first cut on about May 25th, it would probably be best to wait until about July 5th to harvest the second cutting. We would recommend you allow at least 35 days after the first cutting before you take a second cut; let the alfalfa go until it is in full bloom.
Alfalfa is infested with potato leaf hopper every year in Butler County. Treatment usually just depends on how many are present and how quickly the hay is growing. As you might expect, the leafhopper is going to be a problem this year on many fields. Damage has been done by the time you see the characteristic triangle shape yellow/purple color at the tip of the leaf. You have lost more than enough yield potential to pay for treatment when the signs show up; treat before.
Since it has been so dry and since we need to allow the alfalfa to replenish root reserves, the economic threshold should be lower this year than normal. We would normally treat when you catch more leafhoppers, per ten sweeps, than plant height. So if the alfalfa is 6 inches tall and in ten sweeps you catch seven leafhoppers, you should treat. This year we are suggesting you lower that threshold by a third. If the plant is 6 inches tall and you catch 5, treat. If the plant is 12 inches tall and in ten sweeps you catch 8, rescue the crop. For potato leafhopper-resistant varieties of alfalfa, the economic threshold is three times as many leafhoppers.
There are a number of good products you can use. Be sure to watch the harvest restrictions. You sure don’t want use a product that has a thirty-day harvest restriction if the hay is 12 inches tall. The latest recommendations are in Control of Insect Pests of Field Crops, Bulletin 545. You can get your copy from the OSU Extension Office or go on line to: http://ohioline.osu.edu/b545.
