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Corn Illustrated: Purdue specialists weigh in on starter fertilizer and rootworm questions.

Tom J Bechman 1, Editor, Indiana Prairie Farmer

June 4, 2019

4 Min Read
dust blowing in dirt field
SKIP STARTER? If it’s super-late before you can plant corn and applying starter slows you down, skipping it this year might make sense, agronomist Jim Camberato says.

Questions that might never arise in a “normal” year are suddenly important if you’re still struggling with deciding to plant corn, planting corn or dealing with late-planted young corn. Here are two such questions:

First, should you skip starter fertilizer so you can speed up corn planting if you’re still planting? Second, do you still need to worry about corn rootworms, even if you’re planting a substitute hybrid without rootworm protection?

The Purdue Pest & Crop Newsletter published by Purdue Extension Entomology weekly during the growing season is carrying tons of information to help you through this challenging season.

Starter fertilizer question

Jim Camberato, Purdue Extension agronomist, addresses the starter fertilizer question in his article “To quicken corn planting, should starter fertilizer be skipped?” in the May 24 issue. Here is Camberato’s article:

“To facilitate speedy planting between rain showers, many growers are skipping starter fertilizer. What might be the consequences?

“Our recent research has shown in continuous corn [CC] that 25 pounds per acre each of N and P2O5 in 2-by-2 placement increased yield at one-third of the site-years by an average of 8 bushels per acre. In corn rotated with soybeans [CS], increased yield occurred at half the site-years and averaged 7 bushels per acre. Pop-up, 3 gallons of 10-34-0 per acre, had little benefit in CC and was not tested in CS.

“Most of the yield responses to 2-by-2 in CC were in no-till fields, but yield increases occurred with different tillage practices in rotation corn. Averaged over both non-responsive and responsive site-years, yield increases were less than 3.5 bushels per acre for either crop rotation. Early planting and cool soils were not related to whether a site responded to starter fertilizer.

“We found yield response to vary considerably from year to year for the same field. For example, at the most responsive field, yield increases ranged from zero to 17 bushels per acre. In contrast to yield, starter consistently increased the rate of crop development so maturity was reached sooner. Grain moisture was less with starter than without starter — 1.2% and 0.6% for CC and CS, respectively.

“If the rain stopped today and all the corn could be planted before the next rain, the earlier maturity and potential for a small increase in yield might be more beneficial than the slightly lengthier time it takes to plant. If planting continues to progress in fits and starts between rain events, then planting without starter may be the better decision.”

Rootworm issues

John Obermeyer, Purdue Extension entomologist, addresses potential rootworm considerations for very late-planted corn in his article “Switching to hybrids without rootworm protection,” also in the May 24 Purdue Pest & Crop Newsletter. Here is his complete article:

“Desperate times calls for desperate measures. As delayed planting conditions persist … we can’t anticipate all likely miscues that will play out in the next few weeks. One brought to mind, prompted by [agronomist] Bob Nielsen, is that some producers may be attempting to switch to shorter-day hybrids — those without desired insect traits, especially rootworm.

“What is the rootworm risk, especially to central and northern Indiana fields? Bottom line, if one did not scout cornfields during corn pollination last year, or sample soybean fields during August for the presence or absence of rootworm beetles, then the localized risk is unknown. However, Indiana as a whole has seen lower rootworm beetle populations for several years.

rootworm on finger

SURVIVE OR STARVE: If corn rootworms hatch early enough and corn is planted very late, a larva like this one may starve before roots are available for feeding.

“First, [consider] the worst-case scenario. The 2002 year had a horrendous start to the growing season. First, planting was delayed by excessive rains, followed by a long, hot dry spell. That year, producers pushed the window and planted into wet soil, creating sidewall compaction. Producers were so hurried that inputs such as soil insecticides for rootworm protection were neglected in some cases. When drying finally occurred, the top inches of soil baked, becoming rock hard.

“The result was that even a rootworm population that was not excessive caused high levels of damage by feeding upon puny, misshapen and slow-growing roots, causing ‘floppy corn,’ ‘small corn-tall corn’ and sometimes plant death — meaning, it took very few rootworm larvae to cause devastating damage to these already challenged root systems.

“[Now the] best-case scenario. Today, seed-applied insecticides are applied to virtually all corn seed, though rates vary. Low and moderate rates are not labeled for corn rootworm control, but this year, because of the close proximity in timing to rootworm hatch, they will likely help. Rootworm egg hatch typically begins in later May in central counties, plus or minus several days for soil temperature differences from one end of the state to the other.

“Although egg hatch occurs over multiple weeks, lower rates of [seed-applied insecticides] may help long enough to protect early root development. Too, the statewide risk today from rootworm is not like it was back in 2002.

“To put a positive spin on the extreme delays in planting this season, rootworm larvae [which hatched May 23] or before, will likely starve to death in fields yet to be planted.”

About the Author(s)

Tom J Bechman 1

Editor, Indiana Prairie Farmer

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