Corn seedlings in central and eastern Nebraska were getting off to a good start with above normal temperatures last week and the early part of this week. (Photo by Brett Hampton)

May 14, 2004:

Soybeans and alfalfa susceptible to freeze injury

With soybeans, growers should wait three to five days to assess frost or freeze damage and decide whether to replant, said Roger Elmore, Extension crops specialist. They'll also need to contact their crop insurance agent before destroying any crop.

Temperatures in parts of western, southwest, central and northern Nebraska dropped to the upper 20s and low 30s for several hours early Friday morning. Temperatures at ground level and in low lying areas were probably even lower than the reported lows, Elmore said.

Producers urged to wait 3-5 days before assessing damage to soybeans from freeze.

"While these temperatures are concerning, I'm not too worried about the effect on emerged corn," Elmore said. "However, emerged soybeans are most vulnerable and susceptible to a frost now."

The growing point for corn is below the soil's surface until the sixth leaf has emerged, which hasn't occurred yet, Elmore said. Soybean growing points are above ground as soon as they emerge, which makes them more susceptible to a frost than corn. Producers with soybeans that already have emerged may need to replant, he said. If so, seed treatments may be especially beneficial to provide extended protection. As of May 9, 25% of Nebraska's soybeans had been planted.

"If there are fewer than 100,000 surviving plants per acre, the yield potential will be reduced and this may be a reason for replanting," Elmore said. "Also, it's still early enough to plant soybeans and farmers won't lose any yield potential by planting next week."

Assessing alfalfa damage

Alfalfa growers also need to watch for signs of damage in the next few days, said Bruce Anderson, Extension forage specialist. Well-established alfalfa plants that have the top several inches or more wilted and dried out will stop growing. These fields should be harvested as soon as possible or shredded if there isn't enough to harvest. New alfalfa seedlings could have been hit especially hard. Plants frozen all the way to the soil surface will not recover, Anderson said. At least one set of leaves must have escaped damage for recovery to be expected.

"However, seedlings often possess good cold tolerance, so don't give up on them too soon," he said.

The good news is recent rainfall in some parts of the state may have offered some protection to crops, Elmore said. Soil water can increase humidity and keep temperatures at ground level higher. Also, the short-term forecast calls for a warming trend. If a frost is followed by warm, sunny weather, crops will bounce back quicker, Elmore said.

In 1992, the state's growers experienced serious problems associated with a late freeze on May 28. Cool, damp weather followed that freeze, Elmore said. Corn was very slow to recover and some did not survive, but soybeans were not greatly affected.

"It's not a guarantee that we won't lose stand on corn, but we should be in good shape if a frost is followed by good, warm weather," Elmore said. "A lot of different things can happen when you have frost and a lot of different things can make a difference. The only thing growers can do now is just to wait and see how things shape up."

Sandi Alswager
IANR News

Wheat in the west central area had already headed and was most susceptible to freeze injury. A freeze at this stage can kill or damage the pollen-producing anthers, affecting kernel development and possibly causing the plant to become sterile. Under normal conditions, wheat would start to flower about five to seven days after heading. In the Panhandle, temperatures generally were not as low as further east and wheat had not headed yet. Development in the Panhandle ranged from being very close to heading in the southeast to preboot in the north and soutwest. It will be one to two weeks before this wheat heads out.

Both the temperature and the duration of the temperature determine the degree of plant injury. Areas recording temperatures below 32^oF, sometimes for up to five hours Friday morning, include Ainsworth - 28, Alliance - 29, Broken Bow - 28, Chadron - 28, Imperial - 29, Lexington - 29, McCook - 29, North Platte - 26. O’Neill - 30, Ord - 28, Sidney - 30, and Valentine - 26. These temperatures are air temperatures; however, the critical temperature when assessing damage is the temperature at the wheat head. Several factors can influence this microclimate, including density of canopy, soil moisture, humidity, and wind speed.

Determining damage

Producers concerned about possible freeze injury should examine the anthers inside each floret from several wheat heads soon after freezing. The anthers (male flower parts) are more sensitive to low temperatures than are the stigmas (female flower parts). Wheat is self-pollinated so live anthers are needed for development of each kernel. Anthers are trilobed and typically light green and turgid prior to flowering. They become yellow about the time they are extruded from the florets at flowering. The anthers, still green, become twisted and shriveled within 48 hours after a freeze, but they turn white to whitish-brown quickly and will not be extruded from the florets if they are frozen.

A week or so after freezing, look for continued kernel development. Sometimes only a few florets are damaged while other times, the entire head is killed. If you have good kernel development you probably had little or no freeze damage.

The most apparent freeze damage to a wheat spike that has just emerged from the boot is chlorosis or bleaching of the awns (beards), which results in a whitish color rather than the normal green color. Low temperatures that damage the awns also may damage the male flower parts.

Wheat in the boot stage probably did not suffer any significant damage unless the temperature was extremely cold for an extended time. If the spikes emerge normally from the boot but remain white or yellow instead of green, some damage occurred. For more information refer to EC 94-132, “Freeze Injury to Nebraska Wheat," available from your local Cooperative Extension Office.

Lack of rainfall takes a toll on wheat

“The wheat crop is maturing ahead of normal with flag leaves beginning to emerge in many fields,” reported Karen DeBoer, Extension educator in Cheyenne County. While few insect and disease problems have been reported, “recent warm temperatures and a lack of soil moisture are causing the wheat to be stressed.” Jim Schild, Extension educator in Scotts Bluff county, shared a similar report regarding the lack of moisture as well as pests.

“In some fields the wheat is starting to head and is only 12 inches tall. A lot of wheat is showing stress from the high temps and winds of the last two weeks. If we don’t get significant rain this week in most of the area, the wheat yields will decline rather significantly.”

Following a mid-week visit to Morrill and Cheyenne counties, Drew Lyon, Extension cropping systems specialist, reported that much of the wheat was already in the boot stage, about two weeks ahead of normal. “Many wheat fields have areas showing drought stress symptoms, including death of lower leaves, curling flag leaves, and a graying or purpling of leaves.”

“Even the weeds are suffering. I saw downy brome and rye plants that had sloughed all their tillers except one or two where they are now putting all of their limited resources.”

“We need significant rainfall soon or our wheat crop will not amount to much in the Panhandle. The cooler temperatures expected during the second half of the week will help, but most wheat fields have or soon will have exhausted the soil water reserve just as the critical time for grain development is about to arrive. Substantial precipitation is needed in the next 7-10 days,” Lyon said.

Last year conditions initially were quite similar to this year’s and average overall yield for Nebraska was good -- 49 bushels per acre, said Ron Stoddard, executive director of the Nebraska Wheat Board.

“That just shows how wheat can endure with a little moisture at the right time. Last year’s moisture came at the time it was needed most,” Stoddard said. For this year’s crop, that time would be soon, in the next 10 days.

“We hope this year’s yield is equal to last year’s yield, but right now we’re just crossing our fingers,” Stoddard said.

Unusually high temperatures and high winds last week and early this week have only intensified the need for precipitation. Much of the state’s wheat is now in the boot stage and using 0.25 inch of moisture a day, if it’s available. Wheat should be heading in the next week or so across much of the state.

Last fall, winter wheat was sown on 1.95 million acres, up 3% from a year earlier and 18% from two years ago. While there has been an increase in irrigated wheat acres, Stoddard estimated the level at just 5% of total acres.

Part of the increase in irrigated winter wheat is due to a shift in crops on irrigated acres likely to receive only limited irrigation water this year. Some producers are planting wheat for a couple years and saving some of their water allocation for when they plant corn, Stoddard said.

Lisa Jasa
CropWatch Editor

Conditions promote growth of powdery mildew in wheat

Powdery mildew in wheat

Infection is moving up in the canopy and could reach the flag leaves in the next week to 10 days. If powdery mildew gets established on the flag leaves this early in the season and we continue to have weekly periods of overcast, wet, humid weather, yields could be threatened. In addition, leaf rust is present and will continue to develop under these conditions as well. At this point in wheat development, both diseases could threaten yields.

For irrigated wheat, particularly seed production fields, it may be advisable to apply a fungicide in the next week or so to protect the upper leaves from infection by mildew and rust. The two most popular varieties in the state, Jagalene and Wesley, are both susceptible to powdery mildew but resistant to leaf rust.

The decision to treat dryland wheat with a fungicide is not as clear cut as it is for irrigated wheat. In the eastern Nebraska stands look good and yields could be similar to last year’s excellent numbers. The one difference is that this year April was dry and the crop needs rain to maintain yield potential. This week’s rain will help, but the crop will continue to need added moisture through May and into early June. If we knew we were going to get the key rains and moderate temperatures needed for the wheat to finish in good condition, then treatment with a fungicide to protect the upper leaves from mildew and rust would likely pay off. However, if the weather the next six weeks turns predominately hot, dry and windy, yields are going to decrease and the beneficial effects of fungicide treatment will not be as attractive. Unfortunately, none of us has a magic crystal ball that will accurately forecast weather conditions for the next two months.

To help dryland growers make this decision, if the stand and yield potential are good, and powdery mildew is currently present above the middle leaves of the plant but not yet on the flag or flag-1 leaves, applying a fungicide to protect the yield potential could be a good investment. The products Headline, PropiMax and Quadris can be applied up to heading or flowering, so growers do have a little more time to make the decision. However, don’t wait too long because the purpose of treatment is to keep the flag and flag-1 leaves along with the head free of infection or at least keep it to a low severity. Treatment costs range from $16 to $20 per acre. With wheat at $4 per bushel, the treatment cost is a little more attractive than when wheat was at $3 per bushel.

The early loss of flag leaves to powdery mildew and or leaf rust could easily reduce yields by 10% or more. For example, if a field has a 70 bushel per acre yield potential, a 10% loss due to disease would be 7 bushels which at $4 per bushel would be a $28 per acre loss. If it costs $18 per acre for the fungicide treatment, then the net gain of protecting the yield would be $10 per acre. Weather conditions from now through grain fill will be the overriding factor for both disease development and yield.

Producers considering tillage should weigh the very real advantages of not tilling — saving fuel, tractor time, topsoil and perhaps most importantly this year, soil moisture — against their reasons for tilling. Straightening rows or rebuilding ridges in a ridge till system or controlling a flush of early season weeds are common reasons given.

Tillage may provide a short-term solution in some of these instances, but often simply adjusting management practices will address these problems. Then, you can start building a foundation for improved soil structure that pays long-term rewards in wet years and dry years.

Those sharing reasons were Tom Dorn, Roger Elmore, Paul Hay, Paul Jasa, and Mark Schroeder, all of the University of Nebraska-Lincoln.

Send us your suggestions

Over the next two issues of CropWatch, we’ll share these contributions — some made in jest and others made in earnest. We also would like to invite you to share some creative or humorous reasons for tillage.

When deciding whether to use a crop as a forage, consider your short-term and long-term options. Do you expect water limits to continue for several more years?

If so, a perennial forage would eliminate the cost and time of establishing a new crop each year. Switchgrass is a good choice because it is less expensive to plant, its primary water needs occur in early summer when water is available, and it can be managed successfully for hay or pasture.

Other good warm-season grass options include big or sand bluestem and indiangrass, especially for grazing. Some of the wheatgrasses and bromegrasses as well as alfalfa can work with limited irrigation, but these cool-season plants respond best to water applied in spring. Some irrigators, however, won’t have water available until after the most efficient time has passed.

Of course, annual forages like pearl and foxtail millet, cane, and sorghum-sudangrass are relatively water efficient and will yield proportionately to the amount of water they receive. Small grains like rye, triticale, and oats can be planted for fall and spring forage if you have moisture at those times.

Maybe it’s not what you hoped for, but growing forages under limited irrigation will help you make the best out of a bad situation.

Being aggressive on the first cutting is critical if high forage quality is needed. Alfalfa’s forage quality changes faster during the first spring growth than at any other time of the year. Plants are maturing and temperatures are increasing, both of which will cause alfalfa quality to decline.

If quality hay is needed, be careful not to delay the first harvest as you finish up other crop work. However, if you’re harvesting the alfalfa for feed for beef cows, that might be a little different story, especially if you need to rebuild hay reserves.

Normally you can get your highest total yield by waiting until alfalfa is near full bloom. This uses what soil moisture is available for most efficient alfalfa growth. In dryland fields you may need quite a bit more rain for good summer and fall harvests since deep subsoils remain dry, but with a good first cut you at least will have hay good enough to feed your beef cows next winter.

Timing of hay harvest is important whether your needs are for high quality or high yield. With alfalfa nearing the time for its first cut, remember to time harvest according to your use and what’s best for your operation.

If you find problems, immediately start to plan how to deal with them. For instance, if you have too much pennycress or mustard or downy brome in your first cutting, consider spraying dormant herbicides next fall to kill these weeds.

Are stands getting thin? Can you determine why? Is this why weeds may be more of a problem this year? Maybe it’s time to rotate to another crop. If you have other good options, most dryland alfalfa fields should be rotated every four to five years and irrigated fields every five to six years.

If some field areas don’t produce well, but the stand is still thick, check for problems like dry subsoil, compaction, or inadequate fertility. When you know what’s causing the problem, then you can address it. Also assess how the alfalfa plants look when they’re cut. Are lower stems dark colored with many leaves on the ground? Spring blackstem may be a problem. Do most plants have open blossoms? Or are new shoots starting to grow and getting cut off by your mower? In all these examples, earlier harvest might be wise next year.

Take some time to look closely at first cut alfalfa and use what you learn to become an even better manager.

Ralph Kulm, Extension educator in Holt and Boyd counties: Dry weather continues to be a major concern here. Dryland alfalfa is very short and starting to bud. Producers are wondering whether they will just clip it or try to graze it off as much of it is too short to pick up with a baler. Brome is very short and starting to head. Some dryland farmers haven’t planted corn, feeling that it would be a waste of time while others are going through the motions, buying crop insurance. Irrigators are concerned that they will again be pumping +1500 hours (like last year) with much higher fuel costs. Pastures are looking very short and many producers are selling livestock to compensate.

Andy Christiansen, Extension Educator in Hamilton County: I caught European corn borers moths Monday night at Aurora, a little earlier than normal. We might have caught them even earlier than that, but I just turned on the trap Sunday (May 9). For the last four years, the first catch in my trap was May 18, May 24, May 16, and May 16 for 2003, 2002, 2001 and 2000, respectively.

Jennifer Chaky, Coordinator of the UNL Pest and Plant Disease Diagnostic Clinic: Diagnostic sample report for May 3-7:

Alfalfa — Rhizoctonia crown rot from Lincoln County and Rhizoctonia root and stem rot from Cass County.

Wheat -- powdery mildew from Adams County; Tan Spot and Wheat Streak Mosaic Virus from Red Willow County and High Plains Virus and Leaf Rust from Saline County.

Dr. Stephen Baenziger, Eugene W. Price distinguished professor of small grains breeding and genetics, will present variety trials containing over 50 experimental lines and blends in the State Variety Trial. Participants also will see some of the university’s Clearfield wheat experimental line evaluation trials plus winter barley and triticale varieties.

Dr. John Watkins, UNL Extension plant pathologist, will discuss ongoing wheat disease management trials. Participants will see 15 treatments in the wheat fungicide plot. Most will be registered products and include BASF’s Headline, Bayer’s Stratego and Folicur, and Syngenta’s Tilt, Quadris and Quilt.

Soybean planting progressed to 25% complete, 10 days ahead of last year at 5%.

Sorghum planting advanced to 7% complete, ahead of 2% last year and 4% average.

Wheat condition rated 11% very poor, 18% poor, 36% fair, 32% good, and 3% excellent, below last year and average. Fields were 82% jointed, about a week ahead of last year at 68% and average at 58%.

Sugar beet planting was virtually complete.

Alfalfa conditions rated 4% percent very poor, 11% poor, 34% fair, 43% good, and 8% excellent. First cutting activities were underway with 2% harvested to date.

National prospective

Of the 18 top corn-producing states 84% of the 2004 corn crop has been planted, compared to 63% last year and for the five-year average. This is about one week ahead of last year.

These same states report about 36% of the crop has emerged, compared with 21% at this time last year and the five-year average of 24%.

With soybeans 35% of the crop has been planted, which compared to 14% last year and a five-year average of 21%.

This publication covers uses, general agronomics, seedbed preparation; planting; soil fertility; weed, disease and insect management; irrigation; harvest and storage; marketing and sample production budgets.

About Crop Watch | Agricultural News | Events | Archives | Markets Ag Links | Weather | Photos | Search Lisa Jasa, Crop Watch Editor | Publications | IANR

Copyright 2004 by the University of Nebraska

Published by University of Nebraska Cooperative Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture

The University of Nebraska-Lincoln does not discriminate on the basis of gender, age, disability, race, color, religion, marital status, veteran's status, national or ethnic origin, or sexual orientation.