If reseeding is needed, consider rotating out of alfalfa for a year. Alfalfa produces compounds that inhibit the growth of other alfalfa plants. If an old alfalfa stand is rotated back into alfalfa, there is significant potential for the growth of the new seedlings to be inhibited by these compounds produced by the older plants. Recent research from the University of Wisconsin demonstrated that when seeding alfalfa into a recently killed current stand (plowed or herbicide application), the new alfalfa usually germinates, emerges, and survives, but yields tend to only be about 75% of normal. Basic recommendations are to rotate out of alfalfa for at least one year. If you must maintain a forage stand by seeding into a current stand, and you can't interseed some other forage (red clover, ryegrass), then it is probably best to plow down the old stand, wait at least 3 weeks, then seed the new stand. Even so, you can expect about a 10 to 30% yield reduction from the life of this stand compared to a rotated stand.

Time to Scout for Alfalfa Weevils in SE Iowa

North of I-80, scouting for the pest should begin at about 250 degree days (DD) base 48  starting January 1. South of I-80, scouting should begin at 200 degree days. This threshold was reached last week in SE Iowa. In EC Iowa it will be reached around April 21. Scouting consists of using a sweep net on alfalfa and looking for the small, black headed pale green larvae that have a white stripe the length of the body.  If you find larvae, collect 30 stems and count larvae in the upper leaves by shaking the stems in a white plastic 5-gallon bucket, and gently pulling apart the newest leaves. Economic thresholds depend on alfalfa height and estimated hay value. For pictures and additional information go to:
http://www.ipm.iastate.edu/ipm/icm/1998/4-27-1998/aweevil98.html.

Biennial Thistle Control

Biennial thistles, such as bull and musk thistle, are easier to control in early spring before the plants bolt and produce a flower stalk. Go to the following article on the Weed Science page for a summary on biennial thistle control: 
http://www.weeds.iastate.edu/mgmt/2003/biennials.shtml.

Corn Planting Tips

With this week's warm weather, corn planters will likely be in the field soon. Taking some time to properly operate the corn planter can mean big yield increases at harvest time. On the other hand, getting into too big of a hurry at planting time and making little mistakes can lead to big problems later in the season. A few things to keep in mind:

Time of Planting

Although April 20 to May 5 is usually the ideal window for planting corn, cutting corners to get all of the corn planted by May 5 will likely result in larger corn yield losses than planting corn a week or two later than ideal. Make sure soil conditions are not too wet. Planting a day or two before the soil is fit can lead to problems with "sidewall compaction or smearing." This can lead to later problems with root development where roots cannot grow through the compacted soil and grow in a narrow slot parallel to the direction of the row. Poor root development can mean uneven corn and problems with nutrient uptake, especially potassium. This is especially common in no-till if it becomes dry soon after planting. To check on current soil temperatures, check out:
http://mesonet.agron.iastate.edu/agclimate/daily_pics/soil-hilo-out.gif.

Depth of Planting

Make sure you are planting at least 1.5 inches deep. I have seen many more problems with planting too shallow than planting too deep. In most cases its best to shoot for a 2-inch depth. Shallow planting can lead to poor secondary (nodal) root development. The roots will emerge close to the soil surface where the soil may be too dry for proper root development. A common result can be "stress induced potassium deficiency", especially if the surface soil is dry at the time the nodal roots are developing.

With very shallow planting (an inch depth or less), the nodal roots may emerge above the soil, resulting in "rootless corn syndrome", where the corn will fall over. This also sometimes occurs when planting into "fluffy" soil. If the seed is planted 1.5" deep and the soil settles half an inch after planting, the corn seedling "sees" a planting depth of an inch. Planting depth is also important with certain herbicide programs. The herbicide Balance Pro can occasionally cause corn injury if the corn is planted less than 1.5" deep or is planted when the soil is too wet.

Rate and Accuracy of Planting

Optimum yields are usually obtained with final stands of about 30,000-34,000 plants per acre. Plant about 10% more than the desired final stand. Inaccurate seed spacing (skips and doubles) will reduce yields. Too fast of a planter speed can increase problems with seed spacing. A good source of information on planting corn is the Corn Planting Guide (Pm-1885) at http://www.extension.iastate.edu/Publications/PM1885.pdf.

 

If you have any questions, please feel free to contact the Iowa State University Extension Office.

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Last Update: April 14, 2004
Contact: Jim Fawcett fawcett@iastate.edu

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