Pest & Crop

Purdue Cooperative Extension Service
July 6, 2012 - Issue 15

Pest & Crop Newsletter, Entomology Extension, Purdue University

In This Issue

 

u.s. drought monitor

 

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Misplaced Insects - (John Obermeyer) We’ve had a couple calls of “flea beetles on steroids” feeding on corn and soybean leaves. A call this week of these beetles feeding on corn silks prompts this reminder. During extreme conditions, e.g., drought, loss of food, insects, like any animal, will be found feeding where normally they wouldn’t. In this case, the redheaded flea beetle (Systena frontalis) was found in spots of fields in fairly large numbers feeding on the crops. Normally, this larger flea beetle feeds on weed species, especially giant ragweed. Either the weeds have died from herbicide or lack of moisture, now the beetles are looking for alternatives. This feeding, which catches attention is nothing more than superficial and certainly doesn’t warrant treatment. Let’s hope they don’t take a liking to our crops in the future! Happy Scouting!!!

Redheaded flea beetles on corn silk

Redheaded flea beetles on corn silk (Photo credit: Sara Alford, Helena Chemical)

Redheaded flea beetle feeding scars to soybean leaves

Redheaded flea beetle feeding scars to soybean leaves

Close-up of redheaded flea beetle

Close-up of redheaded flea beetle

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Click here for the Blacklight Trap Catch Report

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Click here for the Western Bean Cutworm Trap Report

 

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plant diseases

Tobacco Growers May Need to Manage Disease – (Kiersten Wise)

Reports from Kentucky indicate that the disease black shank is prevalent in tobacco. Indiana tobacco growers should also be aware of this problem and decide if rescue applications of fungicide are needed. Kenny Seebold from the University of Kentucky has prepared disease management recommendations for Kentucky that will also apply to Indiana tobacco growers. Please read his article from the Kentucky Pest News for more information about black shank and fungicide applications in tobacco: <http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/
kpn_12/pn_120626.html
>

Agronomy Tips

VIDEO: Potassium Deficient Corn and Soybean During Drought - (Jim Camberato) -

Potassium deficiency in corn and soybean is prevalent this year due to dry soil conditions. Potassium availability is reduced by dry soil and its movement to the root is also hindered thereby reducing plant uptake. Unfortunately, potassium’s role in the plant is heightened when moisture is limiting further affecting plant growth and yield. To see the symptoms of potassium deficiency and more details on the role of potassium in plant growth see this video.

 

 

 

 

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Nitrate Analysis is Important for Drought-Stressed Corn Plants Destined for Forage – (Jim Camberato and Keith Johnson)

Pastures are not growing, hay production to date is below average and there is no expectation of another harvest this season, and the corn crop that looked so promising in May is not going to make much grain. The drought-stricken corn could be harvested to feed livestock, but there are concerns about nitrate levels in the corn vegetation that can impact the wellbeing of the livestock. It is imperative that your crop insurance agent be contacted about the possibility of using the corn as a forage resource before any harvest is made.

Why are nitrate levels high? Drought reduces both crop nitrate uptake from the soil and the conversion of nitrate to protein in the crop. If the effects of drought are greater on protein formation than on nitrate uptake, high concentrations of nitrate can accumulate in the crop. Even worse, rainfall on a drought stricken crop can result in a surge of nitrate uptake that may be poorly assimilated into protein for several days.

Nitrate is not evenly distributed in the corn plant. Stalks contain far more nitrate than leaves. The lower stalk has a higher concentration of nitrate than the upper stalk. However, in extremely severe cases even the nitrate concentration of the upper stalk can be high enough to limit utilization as a feed.

It is impossible to guess whether or not nitrate is high in forage. The only way to know the amount of nitrate in the forage is to have it analyzed. Reviewing information collected from the drought year of 1988 supports this conclusion. Based on 70 fresh corn samples, only 18% contained toxic levels of nitrate. In contrast, 71% of the sorghum-sudangrass samples collected contained toxic levels of nitrate.

Obtaining a representative sample of the forage is the most important step in determining forage nitrate. The results received from the laboratory will be meaningful only if you have collected a sample that represents the corn to be harvested. Contact the laboratories that you use for soil testing, tissue testing and/or feedstuff testing to see if they analyze nitrate content in plant tissue. Also inquire about price for an analysis, where to get a sample submission form, what the expected turn-a-round time will be, and their suggestions on sampling procedure. A list of National Forage Testing Association Certified Laboratories can be found at: http://www.foragetesting.org/index.php?page=certified_labs. Agricultural laboratories that perform soil tests may also do forage testing. A list of these facilities can be found at: <http://urbanext.illinois.edu/soiltest/>.

Leaving a foot or more of the lower stem un-harvested will reduce the risk of nitrate toxicity, but reduces per acre yield. If corn acreage is abundant and livestock number to be fed in comparison is small, it may be advisable to cut more acres at a higher cutting height to get the desired amount needed so nitrate level is reduced. If stalks are mostly barren, an estimate of yield is one ton of 35 percent dry matter forage per foot of stalk, excluding the tassel.

Drought stress on corn just beginning to tassel may result in little grain production because of barren plants. In some cases plant nitrate may be high, requiring a forage analysis to effetively utilize the corn plant as a feedstuff.

Drought stress on corn just beginning to tassel may result in little grain production because of barren plants. In some cases plant nitrate may be high, requiring a forage analysis to effectively utilize the corn plant as a feedstuff.

The best approach to obtain a representative sample is to cut a swath at the desired cutting height through a representative area of the field with a forage harvester. Composite a dozen or so handfuls from the chopped corn, mix thoroughly, and fill a half gallon-sized plastic bag that will be sent to the laboratory.

If a forage harvester is not available, sample at least 25 plants by cutting them at the intended harvest height. Chop and mix them in order to get a representative sample to fill a half gallon-sized plastic bag to send to the laboratory. A yard waste chipper/shredder can be used to chop the sample.

If relatively dry keep samples cold and ship to the laboratory immediately. Avoid shipments late in the week to avoid delayed arrival. If samples have high moisture, they should be frozen before shipping and shipped overnight or taken to the laboratory in a cooler.

Nitrate levels higher than 3,400 to 4,500 micrograms per gram (same as parts per million) are considered potentially dangerous to feed. Levels in green-chopped (direct cut and immediately fed) corn can be reduced by ensiling. During the fermentation process, 40 to 60 percent of the nitrates will be eliminated. Caution is advised as various nitrogen oxide gases produced during the fermentation process are highly toxic to humans and livestock. For the first three to four weeks after ensiling, do not enter a silo without first running the blower for 15 to 30 minutes. Nitrate levels will not be reduced if the corn is baled as hay. Test the forage for moisture content before cutting the corn to make sure that it will store properly. Forage moisture should be approximately 65 percent when harvested for silage. If wanting to make hay, cut the crop and allow to wilt in the field to less than 20 percent moisture. If not dry enough the hay may mold or spontaneously combust.

If nitrate levels are high in the samples submitted, work with a livestock nutritionist to develop rations that can utilize the corn by blending it with low-nitrate containing feed resources.

Ask for forage quality values, too, while you are getting a nitrate test done if the sample submitted (green chop, silage or hay) is the feedstuff to be fed. A basic nutrient analysis should contain the amount of dry matter (DM), energy (TDN or NE), crude protein (adjusted for heat damage), neutral detergent fiber (NDF), calcium, phosphorus, potassium, and magnesium. From this nutrient profile, a diet can be formulated to meet the animals’ requirements in a cost-effective manner to optimize performance. Share the nitrate and forage quality results with a trained livestock nutritionist so a safe ration can be formulated.

If utilizing the corn as green chop there are some items to consider. To further reduce the chances of nitrate toxicity and founder (another animal disorder that is caused by an abrupt change in diet with increased energy) (1) raise the cutter bar to 12 inches the first few days of chopping, (2) gradually introduce animals to green chop, (3) use other feeds that are low in nitrate as part of the ration, (4) feed green chop in small quantities throughout the day rather than large quantities once per day, (5) don’t allow green-chop forage to set on a wagon overnight, (6) feed two to three pounds of grain with high nitrate feeds, (7) nitrate levels tend to increase for two to three days following rain, thus take extra precautions during this time period, (8) as plants mature, nitrate levels decline; also, animals become acclimated, thus chances for toxicity decrease with time.


 

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Million Dollar Rain for Some Fields; Not All – (Bob Nielsen)

This past weekend, storms rumbling through the state left behind much-needed rainfall. The rainfall amounts varied quite a bit as is typical of summer thunderstorm patterns, but some areas of the state have received 1 to 2 inches over the past seven days (Fig. 1).

Figure 1. Seven-day cumulative rainfall throughout Indiana; as of 7 AM on 2 July 2012. Source of rainfall estimates: http://water.weather.gov/precip

Figure 1. Seven-day cumulative rainfall throughout Indiana; as of 7 am on 2 July 2012. Source of rainfall estimates: <http://water.weather.gov/precip>

In the midst of a severe drought, any chance rainfall is welcomed with open arms. However, the optimism generated by the rainfall needs to be tempered by the severity of the drought throughout Indiana (Fig. 2) and the continued short-term forecast for excessively hot temperatures for much of the state during a period of time when many of the acres will be pollinating.

Figure 2. U.S. Drought Monitor map of Indiana drought severit; as of 6/26/12. Source of image: http://droughtmonitor.unl.edu

Figure 2. U.S. Drought Monitor map of Indiana drought severity; as of 6/26/12. Source of image: <http://droughtmonitor.unl.edu>

There is no question that, for some fields, the recent rains have been “million dollar” rains from the standpoint that they offered some relief for fields coming into the pollination period. However, the drought has not yet been “broken” and the state’s corn crop will require timely rainfall in meaningful amounts to avoid serious yield losses this fall.

Corny Trivia: A million dollars does not go far in terms of Indiana’s most important row crop. One million dollars divided by $6.50 corn equals roughly 154,000 bushels. Take that result and divide by the acres of corn produced in, say, White County and that “million doar” rain equals a yield increase of about 1 bushel per acre (bpa) for every acre in White County. A lot ollf money in total, but not much of a yield increase in the big scheme of things.

The latest USDA estimates of corn crop condition indicates the crop is continuing to slide downhill (USDA-NASS, 2 July 2012). As of July 1, only 19 percent of Indiana’s corn crop was rated as good to excellent. That estimate of statewide crop condition is as low as it has been for this time of the season since the “Great Drought of 1988” (Fig. 3).

Figure 3. Percent of Indiana corn rated as good to excellent for select years including 2012 (as of 1 July). Data source: USDA-NASS.

Figure 3. Percent of Indiana corn rated as good to excellent for select years including 2012 (as of 1 July). Data source: USDA-NASS.

The decrease in corn crop conditions around the state reflected in the July 1 estimates, combined with the crop conditions throughout June, would suggest that statewide corn grain yield could average only 140 bpa or 13% below the estimated 2012 trend yield of 162 bpa. That departure from trend, if it comes to pass, would be the sixth worst departure from trend since 1980. For comparison, the five other worst years were 1983 (-34%, drought), 1988 (-31%, drought), 1991 (-27%, drought), 1995 (-15%, drought), and 2002 (-16%, late planting, cool summer and fall).

RLN Note: The estimated trend yield of 162 bpa for Indiana in 2012 is based on a historical trend line beginning in 1955 (R2 = 0.82). The estimate of yield loss is based a simple linear relationship between 19 years of crop condition ratings in June/July (including 1988 and 1991) and the associated grain yields statewide (R2 = 0.51).

As I indicated last week (Nielsen, 2012b), the stress of this year’s “big hot and dry” on the corn crop escalated greatly with the advent of the excessive temperatures in mid-June. The resumption of those hot temperatures in the coming days will continue to pressure this crop, especially in areas that did not receive the welcome rains of this past weekend. Where rainfall was received, pollination may technically succeed, but the risk of kernel abortion in the few weeks following the end of pollination will be high for those fields where severe drought stress continues or resumes.

I also remind growers they can assess the relative degree of success of pollination in individual fields shortly after pollen shed is complete by sampling ears and conducting the simple “ear shake” test (Nielsen, 2012a). Later in the season, growers can estimate grain yield in individual fields by estimating ears per acre and kernels per ear (Nielsen, 2011b). Pray for rain or turn on the irrigation.

Related Reading

National Weather Service. 2012. AHPS Precipitation Analysis. <http://water.weather.gov/precip> [URL verified June 2012].

Nielsen, RL (Bob). 2008. Grain Fill Stages in Corn. Corny News Network, Purdue University. <http://www.kingcorn.org/news/timeless/GrainFill.html> [URL verified June 2012].

Nielsen, RL (Bob). 2011a. Effects of Stress During Grain Filling in Corn. Corny News Network, Purdue Univ. <http://www.kingcorn.org/news/timeless/GrainFillStress.html> [URL verified June 2012].

Nielsen, RL (Bob). 2011b. Estimating Corn Grain Yield Prior to Harvest. Corny News Network, Purdue Purdue Univ. <http://www.kingcorn.org/news/timeless/YldEstMethod.html> [URL verified June 2012].

Nielsen, RL (Bob). 2012a. A Fast & Accurate Pregnancy Test for Corn. Corny News Network, Purdue Univ. <http://www.kingcorn.org/news/timeless/EarShake.html> [URL verified June 2012].

Nielsen, RL (Bob). 2012b. Hot & Dry: Stress on the corn crop escalates. Corny News Network, Purdue Univ. <http://www.kingcorn.org/news/articles.12/HotDryMidSeason-0625.html> [URL verified July 2012].

Nielsen, RL (Bob). 2012c. Next Big Hurdle: Pollen Shed and Silking. Corny News Network, Purdue Univ. <http://www.kingcorn.org/news/articles.12/Hurdle-0617.html> [URL verified June 2012].

Nielsen, RL (Bob). 2012d. Resources for Managing or Assessing Drought-Stressed Field Crops. Corny News Network, Purdue Univ. <http://www.kingcorn.org/cafe/drought> [URL verified June 2012].

USDA-NASS. 2012. Crop Progress. USDA Nat’l Ag Statistics Service. <http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1048> [URL verified June 2012].

 

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Recovery From Hail Damage to Young Corn – (Bob Nielsen)


As is usual in Indiana, early summer thunderstorms rumbling across the state often include damaging hail. Looking out the kitchen window the morning after such a storm can be one of the most disheartening feelings in the world to a corn grower.

Two days after hail storm (Mostly minorinjury)

Two days after hail storm (mostly minor injury)



Yield loss in corn due to hail damage results primarily from 1) stand reduction caused by plant death and 2) leaf area reduction caused by hail damage to the leaves (Vorst, 1993). Assessing the yield consequences of hail damage in corn therefore requires that the severity of each of these factors be estimated.

Click for Hail Damage Photo Gallery

As is usual in Indiana, early summer thunderstorms rumbling across the state often include damaging hail. Looking out the kitchen window the morning after such a storm can be one of the most disheartening feelings in the world to a corn grower.

Yield loss in corn due to hail damage results primarily from 1) stand reduction caused by plant death and 2) leaf area reduction caused by hail damage to the leaves (Vorst, 1993). Assessing the yield consequences of hail damage in corn therefore requires that the severity of each of these factors be estimated.

Assessing Plant Survival

As with most early-season problems, evaluation of hail-damaged fields should not be attempted the day after the storm occurs because it can be very difficult to predict survivability of damaged plants by simply looking at the damage itself. Young corn has an amazing capacity to recover from early season damage but patience is required to allow the damaged plants enough time to visibly demonstrate whether they will recover or not. Damaged but viable plants will usually show noticeable recovery from the whorl within 3 to 5 days with favorable weather and moisture conditions.

One thing you can do shortly after the storm, however, is to evaluate the relative condition of the main growing point area of the stalk. The growing point, or apical meristem, of a young corn plant is an area of active cell division located near the tip of the pyramid-shaped top of the stalk tissue inside the stem of the plant (Nielsen, 2008a). The growing point region is important because it is responsible for creating all the leaves and the tassel of a corn plant.

Initially, the growing point is located below ground but soon elevates above ground beginning at about the 5th leaf collar stage. Slicing a stalk down the middle and looking for the pyramid-shaped upper stalk tissue can identify the vertical position of the growing point. If hail has damaged the growing point or cut off the stalks below the growing point, then those plants should be counted as victims and not survivors.

Remember that yield loss in corn is not directly proportional to the reduction in the number of plants per acre when the damage occurs early in the growing season (Table 1). The surviving plants surrounding an absent plant can compensate by increasing their potential ear size or by developing a second ear. A 25 percent reduction in plant population should reduce yield by less than 10 percent. A 50 percent reduction in plant population should reduce yield by less than 25 percent.

Click for Hail Damage Photo Gallery

Assessing Defoliation Severity

Leaf damage by hail usually looks worse than it really is. Tattered leaves that remain green and connected to the plant will continue photosynthesizing. It takes a practiced eye to accurately estimate percent leaf death by hail. With that caution in mind, percent damage to those leaves exposed at the time of the hailstorm can be estimated and used to estimate yield loss due to defoliation alone.

The effects of leaf death on yield increases as the plants near silking, and then decreases throughout grain fill. Therefore, the grower needs to determine the leaf stage of the crop when the hail damage occurred.

Remember that leaf staging for the purposes of hail damage assessment is slightly different than the usual leaf collar method. The yield loss estimates listed in Table 2 are based on leaf stages as defined by the “droopy leaf” method (Nielsen, 2010). If you are walking damaged fields many days after the storm, you can stage the crop that day and backtrack to the day of the storm by assuming that leaf emergence in corn occurs at the rate of about 1 leaf every 80 GDDs from emergence to V10 (ten fully visible leaf collars) or every 50 GDDs from V10 to the final leaf (Nielsen, 2008c).

Once percent leaf damage and crop growth stage have been determined, yield loss can be estimated by using the defoliation chart provided below in Table 2. This table is a condensed version of the season-long table published in the Purdue Extension publication ID-179, Corn and Soybean Field Guide or in NCH-1, Assessing Hail Damage in Corn (Vorst, 1993).

Click for Hail Damage Photo Gallery

Assessing Consequences of Whorl & Stem Bruising

The eventual yield effects of severe bruising of leaf tissue in the whorl or the stalk tissue itself in older plants are quite difficult to predict. Consequently, it can be difficult to determine whether to count severely bruised plants as survivors or whether they should be voted off the field. The good news is that observations reported from an Ohio on-farm study suggest that bruising from hail early in the season does NOT typically result in increased stalk lodging or stalk rot development later in the season (Mangen & Thomison, 2001).

Early season bruising of leaf tissue or stem tissue may, however, have other consequences on subsequent plant development; the occurrences of which are hard to predict. Areas of bruised whorl leaf tissue often die and can then restrict continued expansion of whorl leaves, resulting in the type of ‘knotted’ whorl reminiscent of frost damaged plants. These same bruised leaves would be more susceptible to secondary invasion by bacteria contained in splashed soil that might have been introduced into the damaged whorls if the hailstorm was accompanied by driving rains.

If the plant tissue bruising extends as deep as the plant’s growing point, that important meristematic area may die; thus killing the main stalk and encouraging the development of tillers. If the plant tissue bruising extends into the area near, but not into, the growing point; subsequent plant development may be deformed in a fashion similar to any physical damage near the hormonally active growing point (stinkbug, stalk borer, drill bits used by malicious agronomists).

Click for Hail Damage Photo Gallery

Example of Assessing Damage

Let’s say that your field of corn was at the 7-leaf stage (approximately V5 by the leaf collar method) when hail damage occurs. After walking the field several days later, you determine only 20,000 of your original 30,000 plants per acre will survive the hail damage. Let’s further assume that your original planting date was 25 April. Your surviving stand of 20,000 now has an upper yield potential of 92% of “normal” (Table 1). Therefore, the yield loss due to plant death itself would be about 8%.

Let’s also assume that you estimate the average percent leaf death by defoliation to be 50% (which to most of us would look devastating). The combination of leaf stage and percent defoliation would translate into an additional 2% yield loss (Table 2), resulting in a total estimated yield loss due to both stand reduction and defoliation of approximately 10%.

 

Click here to go to Table 1.

 

Table 2. Estimates of percent yield loss in corn due to leaf defoliation at selected leaf stages.
Leaf Stagea Percent Leaf Defoliation
25 50 75 100
Approximate % Yield Loss
7-leaf 0 2 5 9
8-leaf 0 3 6 11
9-leaf 1 4 7 13
10-leaf 1 6 9 16
11-leaf 1 7 12 22
12-leaf 2 9 16 28
13-leaf 2 10 19 34
14-leaf 3 13 25 44
aLeaf stage according to the "droopy leaf" method (see Nielsen, 2004a). The corresponding leaf stage according to the leaf collar method would be approximately 2 less than the "droopy leaf" values shown above (e.g., 7-leaf~V5).
Adapted from the National Crop Insurance Association's "Corn Loss Instruction" (Rev. 1994).

 

Related References

Mangen, Todd and Peter Thomison. 2001. Early Season Hail Damage in Corn: Effects of Stalk Bruising and Tied Whorls. Ohio State Univ. Cooperative Ext. Service Special Circular 179-01. [On-Line]. Available at <http://ohioline.osu.edu/sc179/sc179_16.html> [URL accessed July 2012].

Nielsen, RL (Bob). 2010. Determining Corn Leaf Stages. Corny News Network, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/timeless/VStageMethods.html> [URL accessed July 2012].

Nielsen, RL (Bob). 2008a. Growing Points of Interest. Corny News Network, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/timeless/GrowingPoints.html> [URL accessed July 2012].

Nielsen, RL (Bob). 2008b. Tips for Staging Corn with Severe Leaf Damage. Corny News Network, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/timeless/VStagingTips.html> [URL accessed July 2012].

Nielsen, RL (Bob). 2008c. Use Thermal Time to Predict Leaf Stage Development in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at <http://www.kingcorn.org/news/timeless/VStagePrediction.html> [URL accessed July 2012].

Vorst, J.J. 1993. Assessing Hail Damage to Corn. Purdue Univ. Cooperative Ext. Service Publication NCH-1. [On-Line]. Available at <http://www.ces.purdue.edu/extmedia/NCH/NCH-1.html> [URL accessed July 2012].

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