With late planting, don’t switch corn hybrids yet

Medium autum freeze (32oF) date. Half of all autumn freezes will occur before the dates shown on this map and half will occur after (based on 47 years of records, 1949-1995). From the NU NebGuide, Autumn Freeze Probablilities (G96-1312).

Fortunately, although delayed planting shortens the growing season, corn hybrids adjust well to this. Adapted hybrids can be planted into early June without major risks of fall frost injury. But, if planting is delayed until the second week of June, producers should think about switching away from typical full-season hybrids.

As producers weigh their options, a review of Midwest research on the effects of late corn planting dates and fall frosts is helpful. It is clear that delayed planting usually reduces corn yields. A report by Golden Harvest summarized yield across several “northern” Cornbelt locations including Hastings, North Platte and Waterloo, Nebraska. The trials were conducted from 1993 to 2001.

The greatest yield potential occurred with a May 7 planting date. Yield potential declined slowly during mid-May and dropped rapidly in late May and early June. For example, yield potential with a May 19 planting date was about 94% of maximum while that of May 29 was about 83%. By June 9, yields were less than 80% of normal.

Of course, every year is different and planting late in 2004 may actually enhance yield. The Golden Harvest work from all north and south locations also shows that grain moisture contents at harvest increased about 1% for every four- to five-day delay in planting.

In addition to the issue of potentially lower yields with delayed planting, there also is concern about the possibility of frost occurring before crop maturity. One of the NebGuides (G1312) listed in the Sources section below includes data for autumn frost probabilities in Nebraska. A map (right) from the NebGuide shows the median probability of a 32º fall freeze and indicates that in a large portion of southeast and south central Nebraska, half of the freezes would likely occur before October 6 and half would likely occur afterward. Ideally I’d like to have corn mature at least two weeks before this date.

We also should consider measures of crop maturity, which can become somewhat confusing given the variety of measurement systems available. While there is no single standard, researchers Bob Nielsen (Purdue University) and Peter Thomison (Ohio State University) clarified the relationship between hybrid comparative relative maturity (CRM) and growing degree days (GDD).

The CRM system they used is similar to that of Pioneer Hi-Bred International and is thought of as days required from planting to maturity. The equation generated for this relationship was:

Hybrid GDU to black layer = 24.908x - 82.821 (R2 = 0.9273) where x is CRM.

For every day increase in CRM, GDD requirements appear to increase about 25 units. Table 1 shows this relationship too.

Table 1. Relationship between CRM and GDD for days to physiological maturity (black layer) (86/50) for ‘normal’ planting dates. CRM GDD 100 2408 105 2533 110 2657 115 2782 120 2906

Based on this table, a 115 CRM hybrid would use about 2800 GDD to mature with a normal planting date. The last five words are important. Research cited by Nielsen and Thomison shows that:

1. although delayed planting shortens the growing season, corn hybrids adjust well to this, and
2. adapted hybrids can be planted into early June without major risks of fall frost injury.

Many preemergence herbicides restrict replant options and producers should use caution when faced with replanting. One method of planting into soil containing damaging herbicide residues is to set furrow openers on the planter to remove the surface soil. A heavy rain after planting would negate this technique and may result in the crop being “silted under.” Use herbicides only “as needed” on the replant crop. A sound strategy is to keep replant options in mind when choosing a herbicide for a given site.

Corn and beans were snapped off at the ground and most residue was just sucked up like a vacuum cleaner had run over it -- leaving the ground bare and hard. The damage, along with the dirt/silt deposited on the growing points, may later lead to stalk rot. Alfalfa and wheat survived the storm fairly well although earlier drought conditions are becoming apparent. There are lots of white caps, unfilled heads, stunted growth and poor color in wheat. Alfalfa weevil numbers have decreased, but cutworms are being reported in corn.

Jennifer Fleer. Extension Educator in Clay and Webster counties: Clay County was hit pretty hard by this weekend’s storms. Farmers have been busy clearing fields of tree, irrigation pipe, grain bin and other debris blown in from the storms. Corn in the worst areas was broken off at ground level and is visible as rows of dots in the field The amount of damage will depend on how much rot occurs and if corn can grow through the silt and debris covering many fields. Soybean damage is difficult to assess since plants in the worst areas were covered with silt and debris and in some cases. In some cases it’s difficult to tell what fields had been planted or where beans were coming up. Wheat looks normal for the most part. Overall, it’ll take about a week to see how the crops respond to the damage from these storms and if replanting is necessary.

Tom Dorn, Extension Educator in Lancaster County: The southern part of the county was hit with severe thunderstorms, heavy rain, hail, high winds and multiple tornadoes May 22. Almost 300 square miles of the county is estimated to have received more than three inches of rain, with a considerable area receiving over five inches and some six to eight inches.

Most corn was in the four to six leaf stage May 22. Wind and hail ripped and shredded the leaves but in most fields over 50% of the exposed leaf tissue was still attached. Many soybeans had one or two trifoliate leaves. In the hardest hit fields, 75-90% of the exposed leaf tissue was lost, including one or both cotyledons. In many fields standing beans were coated with soil. It is too early to know whether auxiliary buds will activate or whether soil-borne diseases will reduce stands. Nearly all wheat has headed and appeared to be in the best condition of the crops surveyed. It is going to be critical to clear wheat fields of large rubble before combining.

Darrel Siekman, Extension Educator in Merrick County: The county was lucky and mainly suffered wind damage on crops. Merrick has received minimal rainfall with only 0.10-0.40 inch in several showers. Surface moisture is okay, but there is little subsoil moisture. Pastures are not responding well. There is some feed as well as a decent first cutting of alfalfa. Corn and soybeans look good.

Del Hemsath, Extension Educator in Dakota, Dixon and Thurston counties: This area received about four days of rain from storms of differing intensity. Rainfall amounts ranged from 3 to 6 inches. There was some erosion in over-prepared fields with some minor flooding in low areas. Most of the early planted corn is up and some soybeans were planted before the rains began last week. A few alfalfa fields have been cut.

Keith Jarvi, Extension IPM at the Northeast REC, Norfolk: The rain was quite welcome here and the hail wasn’t big enough or lasted long enough to do significant damage. Crops are slow to grow since some of the corn was nipped by the frost, but it is recovering. Some soybeans still need to be planted.

Gary Zoubek, Extension Educator in York County: We received 0 - 1.55 inches of rain Saturday night. We did have some hail damage, but from what I’ve observed, nothing like what occurred in Saline, Gage and Lancaster counties.

Paul Hay, Extension Educator in Gage County: On the field scene water damage, flipped pivots, hail, and field trash are the most significant problems in Gage, Lancaster and Saline counties. Soybeans are the most difficult to assess hail damage and wheat is the most troublesome due to crop damage and junk in the field.

Doug Anderson, Extension Educator in Nuckolls County: Crops are getting a slow start here -- corn is emerged and growing slowly; soybean planting is slow and some of the first planted fields were frosted off; and milo is being planted now. Wheat condition is iffy due to limited precipitation and frost. Yield may be about 30 bushels per acre. The first alfalfa cutting was poor due to drizzle and excessive laying.

Andy Christiansen, Extension Educator in Hamilton County: We are one of the counties that seems to be in the middle of everything and getting nothing. This pattern has been pretty consistent for several years now. Storm systems and all the rain seem to split and go north and south of us. We got less than a 0.1 inch from Saturday’s storm. We have been getting fractions of an inch fairly regularly over the past month – just enough to delay planting but not enough to really recharge the subsoil. Pastures and alfalfa are vulnerable again this year.

Figure 1. Soybean within-row seed spacing for different seeding rates and row spacings.

Obtaining stand counts is the first step to assessing the field situation. Count plants that have a good chance of recovery. Emerged soybean plants can recover from stem damage if the stem is not severed below the cotyledonary (seed leaf) node. This is the first node on the seedling; the two fleshy-like cotyledons are attached to this node. If still present, buds on each side of this node can produce regrowth. If the plant is broken off below this node, it will not survive.

Once stand counts are established, refer to Figure 1 to estimate plants/acre. (For other row widths see table in Crop-sized ring toss story) Although yield is reduced when plant populations fall below 100,000 plants per acre, the yield loss is not proportional to stand loss. A general guideline is to leave a field alone if plant populations are greater than 50,000 plants per acre, the stand is uniform, and the field can be kept weed free. More information on assessing hail loss in soybeans is in Soybean Yield Loss Due to Hail Damage, NU Cooperative Extension NebGuide G762.

Replanting rates

If replanting is necessary, what seeding rates and other practices are recommended? Soybeans planted in June are usually shorter. If you can’t plant until then, use a narrow row spacing if possible and higher seeding rates to hasten canopy closure. Faster canopy closure will suppress weeds. Avoid using very early maturing varieties because they will flower quickly, resulting in short plants. Tall, medium maturing varieties for your area offer the best hope of minimizing potential yield loss from planting late. Planting non-adapted, early-season varieties will not result in optimum yields. These recommendations apply to double-cropped soybeans as well.

Recommended soybean seeding rates, stand assessment and replanting rates based on Nebraska field research are discussed in Soybean Seeding Rates, NU Cooperative Extension NebGuide G99-1395.

Much of the wheat is flowering or in early grain fill. Freeze damage is evident in some fields, but the damage appears to be restricted to a few florets in scattered heads throughout the affected fields. Drought is definitely a larger concern in the Panhandle than the freeze of a couple weeks ago.

With western Nebraska in its fourth to fifth year of drought, subsoil moisture is limited and has not been recharged. Since January 1, the northwest reporting district has received only 67% of normal precipitation. The southwest district has received only 82% of normal since Jan. 1 and only 71% since Sept. 1, 2003. Wheat is currently estimated to be using as much as 0.30 of subsoil moisture a day for this growth stage, although with cooler temperatuares, use has dropped significantly.

Grazing wheat, even if it has headed out, can provide feed for cattle as well as help you delay grazing your other pastures until later in the season. This will allow them to use limited soil moisture more efficiently and develop the highest carrying capacity they can during a dry year. If you do graze your wheat, be sure to feed a magnesium supplement to avoid potential problems with grass tetany.

Wheat hay can be harvested whenever it becomes convenient, but I recommend cutting before much grain fill occurs or leaves start to turn in order to maintain good forage quality from the leaves and stem. Before feeding the wheat hay, make sure you have it tested for nitrates, especially if plants experience much drought stress before harvest.

A poor wheat field doesn’t need to be a total loss. If you have a use for forage, it can help you extend the field’s value.

Soybean seedling damping off caused by Pythium. (Photo courtesy of X.B. Yang, Iowa State University)

The most common fungi involved in seedling diseases in Nebraska are species of Fusarium, Phytophthora, Pythium, and Rhizoctonia. All four are capable of killing soybean seedlings or at least causing damage sufficient enough that it affects the ability of the plant to achieve its full yield potential. Diagnostic characteristics of common soybean seedling diseases are described in Damping off, Root Rots, and Vascular Disorders of Soybean, Extension Circular EC99-1877-B. Cool, wet weather favors a couple of our most common fungi causing seedling disease problems. Those, which I predict to be a problem this year, are Pythium and Phytophthora. Of the two, Pythium is usually the most common. In fields with a significant stand loss after the wet conditions that have a history of replant anytime wet weather occurs near planting, Phytophthora should be the number one suspect.

At least five species of Pythium cause seed decay, damping off, and root rot of soybean. Although these fungi are capable of infecting the soybean plant at any developmental stage, early infections on seedlings are the most damaging. Seed rot and seedling diseases caused by Pythium spp. develop early in the season under cool temperatures and wet soil conditions. In cool (50° to 60°F) and wet soil, they, like Phytophthora, produce zoospores that move through soil water to seed or roots where they infect the plant.

Seedlings are the most susceptible to infection and the soybean plants become progressively more resistant as they age. Look for seeds rotted in the soil that are soft and slimy to the touch or overgrown with other fungi and bacteria, giving the seed a fuzzy appearance. Infections that cause seedling blights occur after the seed has germinated but before or just after emergence. Infected roots have a brown color and appear wet, or they may have brown lesions on the hypocotyl. If seedlings are infected after emergence, leaves have a gray-green cast, wilt and then die within a day or so. For Phytophthora, seedlings infected after the unifoliate leaf stage (VC) will typically have a visible discoloration in the stem center which is evident when the stem is cut. Many times these plants will have an externally visible dark discoloration of the stem which extends from the soil-line upward into the canopy.

Description

The aphid is light green to pale yellow, less than 1/16 inch long, and has two black-tipped cornicles (cornicles look like tailpipes) on the rear of the abdomen. It has piercing-sucking mouthparts and typically feeds on new tissue near the top of soybean plants on the undersides of leaves. Later in the season the aphids can be found on all parts of the plant. It is the only aphid in North America that forms colonies on soybean.

Life cycle and soybean injury

Soybean aphid

The seasonal life cycle of the soybean aphid is complex with up to 18 generations a year. It requires two species of host plant to complete its life cycle, common buckthorn and soybean. Buckthorn is a woody shrub or tree and is the overwintering host plant of the aphid. Soybean aphids lay eggs on buckthorn in the fall. These eggs overwinter and hatch in the spring, giving rise to wingless females. These females reproduce without mating, producing more females. After two or three generations on buckthorn, winged females are produced and they migrate to soybean.

Multiple generations of wingless female aphids are produced on soybeans until late summer/fall, when winged females and males are produced. They migrate back to buckthorn, where they mate. The females then lay eggs on buckthorn, which overwinter, thus completing the seasonal cycle. Although a few aphids have been found this spring on a buckthorn plant in Lincoln, I have not found any on the buckthorn plants I have been monitoring in northeast Nebraska. It remains to be seen how successful the aphid will be at overwintering and colonizing soybean in Nebraska.

Soybean aphid populations can grow to extremely high levels under favorable environmental conditions. Reproduction and development is fastest when temperatures are between 70-80oF. Aphids die when temperatures reach 95oF. When populations reach high levels during the summer, winged females are produced and they migrate to other soybean fields. Like a number of other insect species (e.g. potato leafhoppers), these migrants can be caught up in weather patterns, moved great distances, and end up infesting fields far from their origin. I believe these summer migrants were the major source of infestations in Nebraska during the last two years.

Soybean aphids injure soybeans by removing plant sap with their needle-like mouthparts. Plant symptoms include yellowed, distorted leaves and stunted plants. A charcoal-colored residue also may be present. This is sooty mold that grows on the honeydew that aphids excrete. Honeydew in itself makes leaves appear shiny. Soybean plants appear to be most vulnerable to aphid injury during the early reproductive stages. Heavy aphid infestations during these stages can cause reduced pod and seed counts.

Management

The soybean aphid is new to North America and our experience with it is limited. As we gain more experience, recommendations will be refined and developed to manage the aphid under Nebraska conditions. Following are our recommendations:

With the advent of transgenics (Herculex) and systemic seed treatments (Gaucho, Poncho, and Cruiser), farmers have alternatives to use at planting time rather than the traditional liquids (pyrethroids like Asana, Pounce, Warrior, Mustang Max, Baythroid , and also the organophasphate Lorsban). However, transgenics and seed treatments require that the plants be fed on, since most control is obtained through systemic activity. This leads to some nervous moments for growers as they see the feeding damage on corn leaves. We have little data to give us insights as to how these new technologies work on overwintering cutworms, since most cutworm data is obtained by artificial infestation with black cutworms. While our gut feeling tells us that they should work, we would appreciate any feedback from “real-life” situations where these technologies have been used to learn how they fared against cutworms.

Alfalfa weevils are larger now and some damage is being observed in alfalfa fields. The damage in most areas is not economic and even if it were, the best solution at this time would be to harvest the alfalfa as soon as possible. However, regrowth after the first cutting needs to be carefully watched to see if the weevils (adults or larvae) hold back the new growth.

Dr. Irmak received his Ph.D. degree from the University of Florida Department of Agricultural and Biological Engineering in Gainesville, Florida; his ME degree from the Mediterranean University in Antalya, Turkey Agricultural Structures and Irrigation Engineering Department and his BS degree from Cukurova University, Adana, Turkey Agricultural Structures and Irrigation Engineering Department. His areas of interest include soil and water resources engineering; surface and pressurized irrigation systems -- design, management, and optimization; crop water requirements (evapotranspiration: direct measurement and modeling, and use of climate information in agricultural water management); crop water use efficiency; and soil physics.

Dr. Irmak shared the following:

“I’m in the process of planning and establishing my long-term research and extension programs. I have statewide research and extension responsibilities with an emphases in south central Nebraska. I’ll be carrying out a significant portion of my research projects at the South Central Agricultural Laboratory (SCAL) near Clay Center.

Some of the research and extension projects that I’ll be conducting this summer include:

1. Subsurface drip irrigation (SDI): Developing best management practices for subsurface drip irrigated corn. We’ll quantify the nitrogen leaching from subsurface drip irrigated corn as compared with the furrow-irrigated plots. We’ll quantify crop growth and yield, water application, water use efficiency, and nitrogen leaching. I’m working on this project with Richard Ferguson.
2. Measurement of crop evapotranspiration of corn and soybean using low-cost modified atmometers.
3. Calibration and error analyses of various types of soil water content and soil matric potential sensors and their use in irrigation scheduling.
4. Direct measurements of crop water requirements using Eddy correlation and Bowen ratio techniques.
5. Predicting soil temperature: a modeling approach and its experimental verifications for dominant soil types in Nebraska.

The open house will be from 9:30 a.m. to 4 p.m. June 3. Visitors will be able to observe the installation of a subsurface drip irrigation (SDI) system and talk with UNL scientists about the technical details of installing and operating the system.

Subsurface drip irrigation has the potential to apply water more efficiently than other methods, such as center pivots, sprinkler systems or furrow irrigation, said Suat Irmak, extension water resources engineer. ”More efficient irrigation means water, fertilizer and energy savings,” Irmak said.

An SDI system delivers water to crops at the root zone using polyethylene tubing buried below the soil surface. The system allows little or no soil wetting, significantly reducing evaporative water loss. For more information about the open house, contact the South Central Agricultural Laboratory at (402) 762-4403. A light meal will be provided.

Walk into your alfalfa field before cutting and look closely at the base or crown of the plants. Do you see short, new shoots starting to grow? If so, these new shoots are the new plants that your alfalfa plans to turn into your second cutting.

How tall are these new shoots? Are many of them two or three inches taller than the stubble height you usually cut at? If you cut these new shoots off along with the first growth, your alfalfa plants will have to start a whole new set of shoots for regrowth. This could cause a delay in second cutting regrowth by as much as one week. Raising the cutting height just a couple inches to avoid clipping this new growth will give you a head start toward the next harvest and since the stubble you leave behind has quite low feed value, you’re mostly sacrificing just filler.

Another option is the use of preservatives containing organic acids. Tests show that the only products that permit consistent, reliable, safe baling of hay above 25% moisture -- hay definitely too wet to bale -- are organic acids like propionic acid. These acids must be applied uniformly at correct rates to work properly.

Acid treatment isn’t perfect, though. Acid-treated hay will still heat some and become discolored. And large, densely packed bales need to be stored so they can cure or sweat before storing tightly. Otherwise the acid protection will dissipate while hay is still wet so spoilage will occur. Acids can corrode equipment unless it is washed and greased almost daily. Odors can be offensive, too. Fortunately, buffered acids can cause less corrosion and have less odor.

Corn planting was nearing completion with 98% planted, about one week ahead of last year at 87% and average at 93%. Eighty-eight percent of the crop was emerged, ahead of last year at 47% and average at 63%. Condition rated 1% very poor, 3% poor, 31% fair, 54% good, and 11% excellent.

Soybean planting jumped to 70% complete, about a week ahead of last year at 38% and 4 days ahead of average at 55%. Thirty-nine percent had emerged, ahead of last year at 9% and average at 22%.

Sorghum planting advanced to 39% complete, ahead of last year at 14% and average at 33%. Eleven percent had emerged, ahead of last year at 2% but the same as average.

Wheat condition declined and rated 17% very poor, 23% poor, 31% fair, 27% good, and 2% excellent, below last year and average. Fields were 67% headed, a week and a half ahead of last year at 27% and average at 39%. Fields had started to turn color in the Southwest and Southeast Districts.

Oat condition rated 7% very poor, 14% poor, 34% fair, 39% good, and 6% excellent. Eight percent of the oats had headed, ahead of last year at 2% and average at 1%.

Dry bean planting was underway with 16% seeded, ahead of last year at 6% and average at 9%.

Alfalfa conditions rated 6% very poor, 16% poor, 30% fair, 40% good, and 8% excellent, below last year and average. First cutting activities were 13% harvested, ahead of last year at 9% but the same as average. Insect pressure in alfalfa fields was growing. Wild hay condition rated 13% very poor, 13% poor, 34% fair, 37% good, and 3% excellent.

Livestock, pasture and range: Pasture and range condition rated 19% very poor, 21% poor, 31% fair, 27% good and 2% excellent, below a year ago and average. Grass growth remains a concern for western producers as cattle return to pastures.

“Organic Farming in the New Century” will be held from 9 a.m. to 4 p.m. at The Grain Place, 1906 North Highway 14, near Marquette. Participants also will tour The Grain Place, a nationally recognized organic specialty grain and product processing plant at the David and Don Vetter farm.

The workshop is free to the public. Lunch and a binder of organic recommendations and regulations will be provided.

To reserve a place, contact Chuck Francis, Extension Sustainable Agriculture Specialist, at (402) 472-1581 by June 14.

The clinics offer individual and confidential information and education on farm finances; the laws, regulations and policies governing Farm Services Agency (FSA); debt restructuring and other legal options; and how the mediation program can help work with lenders to find an agreeable and workable solution. The Farm Hotline (1-800-464-0258) must be contacted to make an appointment and to learn the clinic location for each town.

Beatrice - June 1

Grand Island - June 1

Alliance - June 3

Norfolk - June 7

North Platte - June 8

Lexington - June 15

Valentine - June 24

Norfolk - June 29

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