Pest & Crop


Purdue Cooperative Extension Service


Issue 14, July 2, 2015 • USDA-NIFA Extension IPM Grant


How Late Can I Replant Corn?(Bob Nielsen) -

Even though essentially all of Indiana's 2015 corn crop was planted on the first go around, frequent and excessive rains from late May to date, and the subsequent ponding, flooding, or saturated soil conditions have caused extensive damage to the first planting on tens of thousands of acres around the state (Nielsen's very conservative estimate). Some growers, in desperation, are asking "How late can I replant corn?" in hopes of recouping some lost yield / income potential from severely damaged fields.

Most of the time when I receive this question in the last week of June, my stock answer to growers in the northern half of Indiana is "Perish the thought" simply because there are too few remaining calendar days and, more importantly, Growing Degree Days (GDDs), in the growing season to safely mature most adapted hybrids of corn prior to a killing fall freeze (Nielsen, 2015).

However, "desperate times call for desperate measures" and so one can speculate on whether or not corn could be planted the first week of July and safely mature. One of the primary keys to answering this questions lies with the relative maturity ratings of hybrids and, more importantly, their expected GDD requirements from planting to physiological maturity (Nielsen, 2012b). The common range of relative hybrid maturities grown in Indiana ranges from about 104 to 118 "days" or hybrid GDD ratings from about 2500 to 2800 GDDs from planting to physiological maturity.

We also know from past research that hybrids respond to delayed planting by maturing in fewer GDDs than expected (Nielsen et al., 2002). Our research some years ago indicated that for every day of planting delay beyond May 1, hybrids mature approximately 7 fewer GDDs than expected. That research included planting dates out to mid-June. We can only speculate that the reduction in GDDs to maturity continues beyond that date, but for the sake of argument, let's say that the trend continues. A hybrid planted on July 1 might mature in 420 fewer GDDs than expected (approximately 60 days x 7).

What to do now?What to do now?

If this response to delayed planting holds true out to early July, then the next step is to estimate how many GDDs one might expect from that date to a date of your choosing in the fall. For this, the online U2U Growing Degree Tool offers some assistance in estimating GDD accumulations for specific counties and planting dates. Let's use Randolph County along the eastcentral side of the state where there are currently quite a few acres of severely damaged 1st-planting corn. The GDD Tool indicates that October 21 is the average first killing freeze date in the fall (28oF), so let's use that as our ending date. The U2U Growing Degree Tool estimates that 1963 GDDs would accumulate "on average" from July 1 to October 21, with a range of 1615 to 2123 GDDs.

Now, let's work backward to relate that GDD estimate and the estimate that a hybrid planted July 1 may mature in 420 fewer GDDs than expected to estimate what relative hybrid maturity might have a chance of maturing safely. Get out your pencils...

The estimated 1963 GDD accumulation plus the 420 GDDs "gained" by the delayed planting might be equal to a hybrid maturity with a rated 2383 GDDs to maturity. With that estimate in hand, visit with your seed dealer and find out what relative hybrid maturity that would equate to. For many seed companies, a hybrid GDD rating estimate of 2383 would be in the neighborhood of a 95 to 100 "day" corn hybrid.

What if the remainder of the growing season remains a bit on the cool side (like it has been most of the season so far)? Use the low end of the GDD range provided by the U2U GDD tool and repeat the calculations. The estimated 1615 GDD accumulation plus the 420 GDDs "gained" by the delayed planting might be equal to a hybrid maturity with a rated 2035 GDDs to maturity. This would be equal to a relative hybrid maturity rating of 75 to 80 "days". Quite a difference compared to running the numbers with the "average" expected GDDs from July 1.

Another factor to consider is the consequence of the ending date you choose to run these calculations. I chose the average date of a killing fall freeze for my example. Understand, that a hybrid that simply matures on that date still requires quite a bit of field drydown of the grain before it reaches a harvestable moisture content. If you choose dates earlier than the average fall killing freeze to provide for more days of field drying, that will result in even fewer available GDDs to mature the crop in the first place.

The bottom line with this discussion is that it may well be possible to replant damaged corn fields in the northern half of Indiana as late as early July with hybrid maturities more suitable for parts of Minnesota or Wisconsin. But, therein lies some more challenges. Such early hybrid maturities are not adapted to the central Corn Belt for several reasons. In particular, one needs to focus on identifying candidate hybrids that have good genetic disease resistance "packages" for our important diseases here in Indiana, especially gray leaf spot, northern corn leaf blight, and some of the ear and stalk rot diseases. Furthermore, I suspect that available seed supplies for these early maturity hybrids may be difficult to obtain, either due to short supply or the logistics of moving seed from the northern Corn Belt to Indiana.

The final comment I would make is that growers who carry crop insurance policies need to visit with their crop insurance agents before taking the risky step of replanting corn this late in the season. There may be unforeseen ramifications to your coverage that would frustrate you later.

This article contains quite a few "ifs", "ands", and "buts". That should give you a hint of the riskiness of replanting a damaged corn crop back to corn at these late dates. But, as I said earlier... for some growers "desperate times call for desperate measures".

Related Reading

Nielsen, R.L. (Bob). 2012a. Heat Unit Concepts Related to Corn Development. Corny News Network, Purdue Univ. [online] [URL accessed June 2015].

Nielsen, R.L. (Bob). 2012b. Interpreting Corn Hybrid Maturity Ratings. Corny News Network, Purdue Univ. [online] [URL accessed June 2015].

Nielsen, RL (Bob). 2015. Hybrid Maturities for Delayed Planting. Corny News Network, Purdue Extension. [URL accessed June 2015].

Nielsen, Robert L., Peter R. Thomison, Gregory A. Brown, Anthony L. Halter, Jason Wells, and Kirby L. Wuethrich. 2002. Delayed Planting Effects on Flowering and Grain Maturation of Dent Corn. Agron. J. 94:549-558.

Useful to Usable (U2U). 2015. Corn Growing Degree Day Tool. Useful to Usable Project, Purdue Univ. [online] [URL accessed June 2015].

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Planting Soybean for Grain or Cover?(Shaun N. Casteel, Soybean Specialist) -

Planting soybean for the first time or as a replant in large flooded areas is under consideration for many this July. Yes, this July. Rainfall totals for June have reached historic levels for the northern half of Indiana. Many areas received 6 to 8 inches more than their monthly average and several counties from the central to eastern portion received 8 to 10 inches more than their average for June (Figure 1). These conditions have prevented planting for many fields and drowned out soybeans and corn in fields that were planted. Field drying is slow and many will not likely be able to plant until after the 4th of July.

Figure 1. Rainfall deviation (inches) from the average for June (May 31 to June 29, 2015). (Indiana State Climate Office, <a href=Figure 1. Rainfall deviation (inches) from the average for June (May 31 to June 29, 2015). (Indiana State Climate Office,

Late Planting For Grain

We recommend shortening the maturity group by 0.5 unit and increase the seeding rates under normal, late planting conditions, which would be June 15-30 for northern third, June 20-July 5 for central third, and June 25 to July 10 for southern third of Indiana. That recommendation is quickly expiring (and really expired for northern Indiana).

If soybeans are to be planted for grain harvest, we need to shorten the maturity group by 1.0 unit relative to the full season for your area and plant at least 200,000 seeds/acre. We will mature about 7 to 10 days faster with that shorter season variety (i.e., 2.5 vs. 3.5 maturity), which is critical for grain production in the northern half of Indiana. High seeding rates are needed to push the plants and first pods higher, produce more nodes on area basis, and canopy faster.

The next and most critical decision is to backdate 90 days from the typical fall freeze (Figure 2). If the fall freeze is typically October 10th, then soybeans need to be planted and emerged by July 10th to have a chance of producing harvestable grain this fall. Soil moisture and temperatures should allow soybeans to emerge quickly (4 or 5 days in many cases). Basically, you could substitute July for October in the legend of Figure 2 to determine the date that soybean should be planted and emerged (plus or minus a couple days).

The soybean could mature completely in some years. While in other years, the soybean is nearing the end of seed fill (R6 – full seed) or leaves are dropping and pods are turning yellow-brown (R7 – first signs of physiological maturity). In the latter cases, the freeze could arrest seed fill resulting in small seeds that are sometimes green in color, but are still harvestable.

Figure 2. Average fall freeze (32<sup>o</sup>F) dates for Indiana. (Indiana State Climate Office, <a href=Figure 2. Average fall freeze (32oF) dates for Indiana. (Indiana State Climate Office, You can substitute July for October to have a guideline for the last opportunity to have soybeans planted and emerged for harvestable grain.

My hope is that you will be able to finish planting soybeans and be able to produce harvestable grain. If this is the case, you will likely produce 50 to 60% of your typical yields from your normal planting periods. If you are not able to plant before these 90-day backdates, the chances of producing harvestable grain decreases substantially.

Late Planting For Cover

Even still, we should plant something in these fields and large drowned out areas to help suppress weeds, take up moisture and nutrients, and to stabilize the soil for this year and next year. We can maintain the course of planting soybeans as a cover after your target 90-day backdates. The need to shorten the maturity group is not needed since the goal would be to produce biomass and cover the ground. We have attempted to plant double crop soybeans in the northern half of Indiana with success in 1 out of 3 tries (keep in mind the soil moisture limited quick stand establishment). In other words, we have planted soybeans as a cover in 2 out of 3 tries with mid-July emergence dates. If you are in the northern half of Indiana, my estimate of biomass production will be around 3,000 to 4,000 lb of dry biomass/acre with approximately 60 to 100 lb of N/ac in the biomass alone. Soybean will have nodulation and N fixation, so additional N will be in the soil as well.

Another option is to be diligent in weed control (herbicide, tillage, etc.), but I prefer to plant soybeans even if it as a cover or look at other crop options – short-term forage or cover crops. You will need to be mindful of restrictions based on previously applied herbicides, which may kill the other options, be off-label, and/or not be allowable for foraging. One more advantage with planting soybean, even as a cover, will be the ability to spray the whole field with your typical herbicide program to control weeds.

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Windshield Splatter: Insect Pest Update(John Obermeyer) -

As many have asked or made note, insect numbers, other than mosquitoes and fungus gnats, seem to be lower. No surprise that the moisture extremes have had an impact on those insects depending on the soil to complete at least a portion of their life cycle.

Japanese beetles are now appearing throughout the state, and will continue to emerge (from grubs in the soil) for several weeks. Even on a “normal” year it is difficult to assess how abundant they are in the state. From my perspective, they seem to be lower so far. Typically this pest is quite spotty in the state, and soybean defoliation and/or corn silk feeding is noticeable, but hardly justified to treat.

Male western corn rootworm beetle waiting for a mate.Male western corn rootworm beetle waiting for a mate.

The week of June 29, we captured our first male western corn rootworm beetle in Tippecanoe County. The males emerge a few days before the females. Beetle emergence will go on for weeks, so this is just the beginning. As stated in an earlier article, we suspect many hatching rootworm larvae drowned, which should equate to a lower beetle population this year. This insect is known as the “silk beetle,” although it has been some years since I have seen them be of concern except in late-market sweet corn. Heavy rainfall events that have trended for many years in early June, has certainly had an overall impact on this “billion dollar” insect in Indiana.

Two weeks ago, our trap cooperators began monitoring for the emergence/flight of the western bean cutworm. This insect spends a considerable amount of time in the soil throughout fall, winter, and spring. Though it is early in the trapping process, catches so far have been very low. The recent catches are reported below. It would not be surprising for the moth catches to remain low, we shall find out!

Happy Scouting!

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Corn Earworm Trap Report.
Corn Earworm Trap Report.

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Western Bean Cutworm Pheromone Trap Report

County Cooperator WBC Trapped
Week 1 
Week 2 
Adams Kaminsky/New Era Ag 0 0
Adams Roe/Mercer Landmark 0 0
Allen Anderson/Syngenta Seed 0 0
Allen Gynn/Southwind Farms 0 0
Allen Kneubuhler/G&K Concepts 0 0
Bartholomew Bush/Pioneer Hybrids 0 0
Boone Campbell/Beck's Hybrids 0 0
Clay Bower/Ceres Solutions/Brazil   0
Clay Bower/Ceres Solutions/Bowling Green   0
Clinton Emanuel/Boone Co. CES 0 0
Clinton Foster/Purdue Entomology   0
DeKalb Hoffman/ATA Solutions    
Dubois Eck/Purdue CES 0 0
Elkhart Kauffman/Crop Tech Inc. 1 1
Fayette Schelle/Falmouth Farm Supply Inc.   0
Fountain Mroczkiewicz/Syngenta 0 0
Fulton Jenkins/N. Central Coop-Rochester 0 1
Fulton Jenkins/N. Central Coop-Kewana 1 2
Gibson Schmitz/Gibson Co. CES 0 0
Hamilton Campbell/Beck's Hybrids 0 0
Hamilton Truster/Reynolds Farm Equipment 0 0
Hendricks Nicholson/Nicholson Consulting 0 0
Henry Schelle/Falmouth Farm Supply Inc., Millville   0
Jasper Overstreet/Purdue CES 0  
Jasper Ritter/Brodbeck Seeds 1 0
Jay Boyer/Davis PAC 0 0
Jay Shrack/Ran Del Agri Services 0 0
Jay Temple/Jay County CES   2
Jennings Bauerle/SEPAC 0 1
Knox Bower/Ceres Solutions/Freelandville   0
Knox Bower/Ceres Solutions/Vincennes   0
Knox Bower/Ceres Solutions/Frichton   0
Lake Kleine/Kleine Farms   0
Lake Moyer/Dekalb Hybrids, Shelby 0 2
Lake Moyer/Dekalb Hybrids, Schneider 1 0
LaPorte Rocke/Agri-Mgmt Solutions, Wanatah 0 5
LaPorte Rocke/Agri-Mgmt Solutions, LaCrosse  0 2
Miami Early/Pioneer Hybrids   0
Miami Myers/Myers Ag Service   2
Montgomery Stine/Nicholson Sonsulting  0 0
Newton Moyer/Dekalb Hybrids, Lake Village 0 1
Porter Leuck/PPAC 0 1
Putnam Nicholson/Nicholson Consulting 0 0
Randolph Boyer/DPAC 0 0
Rush Schelle/Falmouth Farm Supply Inc.   0
Shelby Simpson/Simpson Farms 0 0
Sullivan Bower/Ceres Solutions/Sullivan   0
Tippecanoe Bower/Ceres Solutions   2
Tippecanoe Nagel/Ceres Solutions 0 0
Tippecanoe Obermeyer/Purdue Entomology   0
Tippecanoe Westerfeld/Monsanto 0 0
Whitley Walker/NEPAC 0 0

* = Intensive Capture...this occurs when 9 or more moths are caught over a 2-night period

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Armyworm Pheromone Trap Report

County/Cooperator Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 Wk 6 Wk 7 Wk 8 Wk 9 Wk 10 Wk 11 Wk 12 Wk 13
Dubois/SIPAC Ag Center 0 0 1 0 2 1 0 4 0 3 1 5 6
Jay/Davis Ag Center 0 0 2 0 4 1 0 0 0 0 3    
Jennings/SEPAC Ag Center 0 0 0 0 1 0 0 2 4 0 3 11 9
Knox/SWPAC Ag Center   0 0 0 1 0 0 2 3 1 1 4 0
LaPorte/Pinney Ag Center 0 0 3 0 17 35 29 5 0 11 87 88 108
Lawrence/Feldun Ag Center 0 2 0 1 0 11 3 5 7 12 19 37 13
Randolph/Davis Ag Center 0 0 0 0 0 0 0 0 0 0 6 2 1
Tippecanoe/Meigs 0 0 1 0 0 0 0 0 0 0 2 13 21
      7 548 406 58 13 7 93 256 496 270
Whitley/NEPAC Ag Center 0 1 5 2 17 25 4 0 5 3 9 5 27
Whitley/NEPAC Ag Center (Hartstack)           792 404 137 103        

Wk 1 = 4/2/15 - 4/8/15; Wk 2 = 4/9/15 - 4/15/15; Wk 3 = 4/16/15 - 4/22/15; Wk 4 = 4/23/15-4/29/15;
Wk 5 = 4/30/15-5/6/15; Wk 6 = 5/7/15-5/13/15; Wk 7 = 5/14/15-5/20/15; Wk 8 = 5/21/15-5/27/15;
Wk 9 = 5/28/15-6/3/15; Wk 10 = 6/4/15-6/10/15; Wk 11 = 6/11/15-6/17/15; Wk 12 = 6/18/15-6/24/15; Wk 13 = 6/25/15-6/30/15

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total precipitation

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average temperature

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Purdue Extension Entomology
901 W. State Street
West Lafayette, IN, 47907
(765) 494-8761

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