EC & SE IA Crops Newsletter

June 8, 2011

HAIL

Hail has danced across the area, varying from none to light to severe.

To assess injury to corn and options to consider, see http://www.extension.iastate.edu/Pages/eccrops/hailcorn.html.

To assess injury to soybean and options to consider, see http://www.extension.iastate.edu/Pages/eccrops/hailsoy.html.

As corn fields begin to recover, many are noticing whorls “tied up in themselves.” The vast majority of those plants will recover and become normal plants.

Roger Elmore has two more detailed articles in the ICM News at http://www.extension.iastate.edu/CropNews/2008/0607LoriAbendrothRogerElmore.htm and http://www.extension.iastate.edu/CropNews/2009/061901.htm.

CORN

Striped Corn Leaves

Many corn fields have plants that are showing striping on the upper leaves. Most commonly, the symptoms are most consistent with Sulfur deficiency; see page 3 of IPM – 42 “Nutrient Deficiencies and Application Injuries in Field Crops” http://www.extension.iastate.edu/Publications/IPM42.pdf.

Our soils generally have quite sufficient amounts of sulfur available, so this phenomenon is generally an indicator of lack of root function. As root function improves, new growth should not exhibit the striping. However, on extremely sandy soils, soils that are severely eroded, and soils that have been adulterated while installing terraces or other structures, sometimes a true sulfur deficiency does exist if the area has not had manure applied recently. Soil tests for sulfur are quite unreliable. Adding a sulfur compound to some of the area while leaving another area untreated and then making visual observations can help establish or eliminate this as a possibility. Elemental sulfur is not quickly available, so use a sulfate compound instead.

Stalk Borers on the Move

According to Growing Degree Day accumulations, base 41, stalk borers are starting to move from grassy areas into nearby corn fields along and south of I-80 and will soon start to move from grass into nearby corn fields north of I-80. However, Tom Hillyer noted some movement close to I-80 back on May 28.

Information on scouting and management can be found at the ICM News article at http://www.extension.iastate.edu/CropNews/2011/0602hodgson.htm. Note that the recent heat is moving the projected dates on this article’s map forward.

Local Growing Degree Day accumulations are shown at http://www.extension.iastate.edu/Pages/eccrops/stalkborer.html.

You can get an early “heads up” of the size of potential movement of stalk borers into corn by examining the grass for dead heads; the vast majority of dead heads will have been killed by stalk borers who are outgrowing the grass plant and moving into nearby corn. The more dead heads you find, the more stalk borers may be poised to move into corn. Tom Hillyer provided the following pictures.

Smooth bromegrass head killed by a stalk borer.

Stalk borer hole in the stem of smooth bromegrass.

Stalk borer still in the smooth bromegrass stem but about ready to head for corn.

Corn Rootworm Eggs are Hatching

Corn rootworm eggs are now hatching. As you examine roots for health, look for signs of feeding and the presence or absence of rootworm larvae on the roots or in the soil. Remember, however, that if you find some rootworm larvae, that does not automatically mean your management strategy has failed; insecticides and Bt CRW are designed to protect roots and some larvae may be present even though roots are being adequately protected. Rootworm larvae are less than 1/8 inch long at hatching and grow to about 1/2 inch long before pupating. They are white with a dark head and a dark plate on top of the tail section. They have three pairs of small legs just behind the head.

Corn rootworm larvae. (Marlin E. Rice)