With first cutting alfalfa down, now is a good time to review some management guidelines for fields headed into summer. Here are a few management principles to keep in mind:
Water Management: Alfalfa is a relatively drought-tolerant forage, and as such, does not have specific growth stages when it is less sensitive to water stress. If water is not available, the plant will slow or stop growing and go dormant. Then, when water becomes available, growth resumes.
While alfalfa’s long growing season means it uses more water annually than other crops, it can be over-watered resulting in alfalfa plant injury and possibly weed invasion. Maintaining water use efficiency can be complicated due to multiple harvests preventing irrigation for about 7 to 10 days per growth cycle and frequent heavy equipment traffic compacting soils. To reduce compaction, stop irrigating 2-3 days before cutting the alfalfa and begin irrigating again after hay has been removed and plants have initiated regrowth.
Generally, the most yield impacting irrigation occurs just before the second cutting followed by the third and fourth growth periods typically requiring 6 to 7 inches of irrigation. Peak water needs are typically in July and August at 1/3 inch per day. However, hot, windy and dry days can move the maximum water demand up to ½ inch per day; so ET scheduling can provide economic benefits.
Pest Management: You may have seen alfalfa weevil damage during this first growing period. Typically, alfalfa weevils are cool-weather insects. During this time of year adult insects would be exiting alfalfa fields seeking cooler spots for over-summering in nearby shady areas or under leaf litter.
A second flush of these 3/16” green caterpillar larvae with a white back stripe may be feeding under windrows. So, what management strategies are recommended for late spring alfalfa weevil infestation?
In heavy infestations, chopping alfalfa for silage can reduce field cover for the insects. Usually, weevil development is controlled by hotter temperatures, so those who have already harvested may want to maintain an active scouting regime to decide if follow up treatments are required. Remember that these cool-weather insects seek shelter during the heat of the day, so scouting can be a challenge when they move into the alfalfa crowns seeking shade.
After scouting, insecticide treatments with pyrethroids (active ingredient ending in “thrins”) may be needed following harvest to aid alfalfa regrowth. Remember pyrethroid insecticides can also have detrimental effects on any beneficial insects present, so field scouting is still encouraged before making final treatment decisions. You can find economic threshold recommendations in our Nebraska Extension Guide for Weeds, Insecticide and Fungicide Management (EC130).
Proper post-harvest management for first cutting alfalfa can put us in a position for success throughout the rest of the growing season, while mismanagement can easily set us back. After this year’s first harvest, make sure your field is in the best position possible for a great year.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu