What to Look for When Alfalfa is Scouted in the Early Spring

Now that alfalfa has broken winter dormancy, it is time to assess the wellbeing of the crop. It is important to scout the entire field and not just one location as differences in soil types can change conclusions made about alfalfa health. The winter was definitely a roller coaster of temperatures and soils were and remain saturated today. These conditions in late winter can predispose alfalfa to root heaving, the movement of the taproot out of the soil. There has been some root heaving noted in Indiana this year. Heaving results in injury to the root system. This injury can lead to pathogen invasion that reduces plant yield and persistence. Make sure that the mower-conditioner’s cutting height is set above heaved crowns or plants will be gone forever if cut below the crown.

Thin and weedy stand of alfalfa in the spring

Thin and weedy stand of alfalfa in the spring.

Another good reason to scout alfalfa fields is to note what is really growing. From the field’s edge, one could falsely assume that all that is green is alfalfa. If you are fortunate, that may be the case, but it could be that some of that green could be attributed to winter-annual weeds like henbit, chickweed, yellow rocket, cressleaf groundsel, downy bromegrass and many other weeds. Herbicide choice is more limited after dormancy break, but there could remain a chemical control strategy if herbicides are applied soon. Always read the herbicide label for complete details about what crops the herbicide can be applied, weeds controlled, timing of application, rate of application, grazing and machine harvest restrictions, crop rotation interval, personal protective equipment, concerns about drift to sensitive plants, and much more.. A better time to scout an alfalfa field for presence of winter-annual weeds is in the late fall so you can be more proactive with control as compared to being reactive when the weeds are first noted in the early spring.

As temperatures become more consistently spring like, April is a time that alfalfa weevil larvae can be found, too. The larvae are pale green with black heads, and have a white stripe on their back that runs the length of their body. Initially the larvae will be quite small, but they can grow to 3/8 inch in length. First sign of larvae damage is pinholes in the developing buds found at the top of the plant. If there are three or more larvae per stem or pinhole feeding can be found on at least half of the stems, application of an approved residual insecticide should be considered or harvest occur if the alfalfa is at or beyond mid-bud floral development. As was the case with the herbicide label, read complete details about use of the selected insecticide. Always return to the field several days after harvest and check to see that regrowth is occurring. If it is not, it is possible that some remaining alfalfa weevil larvae and adults are enjoying a meal of the young and developing second harvest.

If you have not done so, make sure harvest equipment is in top shape so you will be ready to mow, ted, rake, bale or process the alfalfa as silage. You do not want to be fixing equipment when you should be harvesting a high quality crop when the sun is shining.

Always be on the lookout for nutrient deficiencies. After first harvest is a great time to apply recommended nutrients, such as phosphorus and potassium, as noted by soil test. Alfalfa removes approximately 12 pounds of P2O5 and 60 pounds of K2O for each ton of dry matter harvested. Sulfur deficiency has been noted on some soils in Indiana so be on the watch for assessing how much sulfur is in alfalfa tissue. Areas of lighter green alfalfa could be an indicator of a sulfur deficiency.

To summarize, in the very early spring be on the lookout for heaving, winterkill, winter-annual weeds, alfalfa weevil and nutrient deficiencies. Scouting alfalfa on a weekly basis throughout the growing season for potential yield, quality and persistence concerns is very important. If concerns are noted early, steps can be taken to reduce losses.

Listen to Keith’s podcast about alfalfa.

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