C.O.R.N. Newsletter 2012-09

Dates Covered: 
April 16, 2012 - April 23, 2012
Editor: 
Steve Prochaska

Impact of Low Temperatures on Corn Survival

 Although it’s too early to determine how early planted corn fields will respond to recent weather, the effects of the low temperatures on corn survival will probably be negligible for the most part. In past years, we have observed that early planted corn that was in the process of germinating or as far along as the V1 stage (one leaf collar visible) survived freezing soil temperatures in April with little impact on crop performance or plant stand. Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (six leaf collars visible), and thereby relatively safe from freezing air temperatures. Moreover, the cell contents of corn plants can sometimes act as an "antifreeze" to allow temperatures to drop below 32 degrees F before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees F or lower for even a few minutes. 

Effects of low temperatures on germination are far more serious when combined with snow and freezing rain. When dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. Cold water can cause similar injury to seedling structures as they emerge during germination. Such injury in corn seed ruptures cell membranes and results in aborted radicles, proliferation of seminal roots, and delayed seedling growth. When temperatures remain at or below 50 degree F after planting, damage to germinating seed is particularly severe. When this physiological damage is combined with surface soil crusting, saturated soil conditions, compacted soils, deep seed placement, and seedling blights, you have a recipe for widespread emergence problems.  

To assess the impact of freezing temperatures on emerged corn, check plants about 5 days after the freezing injury occurred (and preferably when growing conditions conducive for regrowth have occurred). New leaf tissue should be emerging from the whorl. You can also observe the condition of the growing point (usually located ½ in to 3/4 in below the soil surface) by splitting seedlings lengthwise. If the growing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good. 

For some pictures of low temperature injury to corn check out the following article by Dr. Bob Nielsen at Purdue University

Nielsen, RL (Bob). 2001. Symptoms of Low Temperature Injury to Corn and Soybean. Corny News Network, Purdue Univ. online at http://www.kingcorn.org/news/articles.01/Frost_Corn_Soy-0418_Gallery.html  

Wheat Growth Stage and Cold Temperature Injury

Wheat Growth Stage and Cold Temperature Injury

The wheat crop is already at Feekes 8, flag leaf emergence, in some parts of southern and central Ohio and will reach this growth stage within the next 7 to 14 days in northern counties. We have had several days of cold temperatures over the past two weeks and more cold weather is forecasted for this weekend. This has prompted some concerns about possible injury to the wheat crop. Once it warms up in the spring and the wheat starts to grow, it loses its cold-temperature hardiness, becoming more prone to injury from freezes. At the current growth stage (between Feekes 6 and 8), the growing point is no longer below the ground protected by the soil, and as such, it is at greater risk for frost damage. However, the growing point is still somewhat protected by the vegetation and its nearness to the soil surface. Wheat is a cool season crop and can tolerate temperatures well below freezing. At this growth stage, wheat can tolerate cold temperatures down to about 24 to 26 degrees F.

Whether or not the crop is damaged by cold spring temperatures and the extent of the damage depend on three main conditions: 1) how cold it gets, 2) the length of time the crop is exposed to the cold temperatures and 3) the growth stage of the crop at the time of exposure. Freezing temperatures are most damaging when the crop is at more advanced stages of development. Injuries are most severe when freezing temperatures occur during the boot and heading growth stages. Based on information coming out of a Kansas State University publication http://wheat.colostate.edu/freeze.pdf, temperatures below 12 F are injurious during tillering, whereas, during jointing (Feekes 6), 2 hours of exposure to 24 F may be injurious. At these growth stages, injuries tend to be greatest if the wheat is lush and actively growing (especially after spring nitrogen application) and are more common in low areas of the field.

To determine if your wheat has suffered freeze injury, walk the field and observe leaves and stems for discolorations and deformations. Between Feekes 6 and 8, leaves and stems on freeze-damaged plants become twisted and turn light green or yellow, with necrosis (darkening) of the leaf tips (Figure 1). These symptoms usually appear about two to three days after freezing. At Feekes 8, the emerging flag leaf appears yellow (Figure 2B) or necrotic (Figure 2C) instead of healthy green (Figure 2A), indicating that the growing point is damaged or killed. Secondary, unaffected tillers will develop and produce grain, but tillers with damaged growing points will stop growing and will not produce a head.        

 

Wheat Growth Stage and Foliar Fungicide Applications

Wheat Growth Stage and Foliar Fungicide Applications

Cool conditions over the last few weeks have slowed the wheat down considerably, however, the development of the crop is still about a week or two ahead of what is considered to be normal in Ohio at this time of year. Current growth stages range from Feekes 6, jointing, to Feekes 8, flag leaf emergence (Figure 1). However, the different between these growth stages cannot be determined just by looking at the height of the crop from the road, since relatively low temperatures and dry conditions may have prevented some varieties from reaching the height that is expected when the crop is between at Feekes GS 6 and 8. Remember, short-looking wheat does not mean that the crop is not developing and advancing through the different growth stages. Growers who rely on the height of the crop as an indicator of crop development may miss Feekes GS 6, a critical growth stage for herbicide application, and Feekes 8, a critical stage for managing foliar diseases with fungicides. Do not relay on the height of the plants or calendar dates alone to make your management decisions. Walk fields, pull tillers from multiple places, remove the lower leaves, and examine these tillers for the presence of nodes and the emergence of the flag leaf. At Feekes 6, the first node is visible at the base of the stem, about an inch or so above the soil line; at Feekes 7, two nodes are visible, one about 2 inches above the soil line and the other about 3-4 inches above the first; and at Feekes 8, in addition to the two nodes seen at Feekes 7, the tip of the flag leaf, the fourth leaf above the first node, is visible (Figure 1). As shown in Figure 2, plants of different heights and sizes may all be at the same growth stage (Feekes 8 in this case).

Feekes 8 marks the beginning of the period during which we recommend that field be scouted to determine which disease is present and at what level. Septoria blotch is usually one of the first to show up, and it already has been reported in some fields. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete. Like many other foliar diseases such as Stagonospora, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an important yield component that is defined very early in the development of the plant (before Feekes 6). As a result, a foliar fungicide application at green-up or jointing is less likely to be as beneficial for Septoria and Stagonospiora control as an application made at or after flag leaf emergence. An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual effects of the fungicide will not adequately protect the flag leaf. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas, and new infections will occur, even after early applications have been made. In addition, frequent rainfall may also reduce the residual effects of the early fungicide applications, making them even less effective against mid- and late-season foliar disease development. Results from previous studies have shown that the greatest benefits from foliar fungicide applications were obtained when applications were made between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9.

There are several different fungicides available for use on wheat. If powdery mildew is the target disease then Tilt or PropiMax should be applied. Tilt, PropiMax, Quadris, Quilt, Stratego, and Headline have good efficacy against Stagonospora leaf blotch, other leaf blotch diseases and leaf rust. Obtain current pricing of fungicides to determine the most economical control option. Use 20 gal water/A with ground equipment and 5 gal water/A if applying by airplane. Using less water will lower effectiveness. Check labels for application timing restrictions.

Alfalfa Freeze Damage Assessment and Management

Bruce Anderson, Forage Specialist at the University of Nebraska, offers information below on assessment and management of frost/freeze injury to alfalfa.

A "light" frost/freeze where temps don't go below around 28 for very long is likely to singe alfalfa tops a bit and set back growth rates for a while but plants will grow out of it. No need to cut although some growers seeking very high quality might do so if standing yield is high enough to justify harvest with the understanding that plants will be weakened by early cutting and should be allowed extra time to recover before the next cutting.

An extreme freeze around 20 or less like in 2007 likely will freeze plants all the way to the ground and they will collapse soon afterwards. Harvest is warranted if yield is sufficient but must be done immediately; once plants collapse much of the biomass will be unattainable and leaves will shatter quickly from those stems that still can be cut. Experience in 2007 showed little or no benefit to regrowth by cutting or shredding damaged tissue since the freeze was so thorough that plants reacted to the killed tops just as they would if tops were killed by cutting instead of freezing.

A freeze that penetrates about halfway down into the alfalfa canopy makes decisions more difficult. Cutting will weaken plants that weren’t nearly ready to cut anyhow. But uncut plants will be confused, some continuing to grow, others creating new shoots from aboveground stems, and others with new shoots coming from the crown. And much of that regrowth will be slow to initiate. If yield is high enough to justify harvest, probably should be cut, knowing that extra time will be needed for recovery before the next cutting. If yield of standing crop is low, probably best to just wait out the delay in regrowth. It will be hard to justify the time and expense of cutting/shredding with no immediate harvestable crop.

After a freeze that causes visible damage to alfalfa tissue, be extra observant of how the plants respond. In 2007, some regions experienced significantly higher than usual damage from foliar diseases and sometimes, insects, on regrowth following the freeze. It was speculated at that time that weakened plants may have been less able to resist these pests or that the abundant amount of dead alfalfa plant tissue on the ground or surrounding the regrowth provide a more desirable environment for pests to develop.

Hazardous Algae Blooms – What Are They, Why The Public Concern and What Is Their Relationship to Ohio Agriculture?

Hazardous Algae Blooms (HAB) are actually caused by a form of a bacteria; cyanobacteria.   Even though they are called blue/green algae, they are different from filamentous algae commonly found in many Ohio ponds and lakes. Examples of cyanobacteria that may constitute HAB include: Anabaena, Aphanizomenon and Microcystis.  These organisms have the ability to produce toxins that can be quite harmful to people, fish and animals.  For example:  Microcystin, anatoxin, saxitoxin and domic acid are all toxins produced by cyanobacteria and these toxins can be neurotoxins, heptatoxins, endocrine toxins or tumor promoters and have also been linked to ALS.   As a side note to understanding these toxins, there are a number of farm crop fungi that under certain environmental conditions and a susceptible host may produce toxins.  Examples of the fungi and associated toxins are:  Fusarium which may grow on corn or wheat and produce vomitoxin and Aspergillus flavus which may grow on corn and produce the carcinogenic toxin, aflatoxin. 

HAB (along with some of the above toxins) have been documented in the major Ohio water resources of Lake Erie and Grand Lake St. Marys.   In Ohio, the drinking water advisory for a HAB toxin is 1 part per billion (PPB).  An example of a PBB is 1 second in 32 years.   The swimming level for HAB toxins has been set at 20 PPB.  Hence, because of human health threats (and other adverse effects), there rightly has been concern by state officials over HAB outbreaks in major Ohio water resources.  

What is the relationship of Oho Agriculture (production practices) to HAB blooms?   First, HAB outbreaks have been associated with phosphorus loading of water.  Many studies have been conducted that link agricultural field phosphorus losses to the increase in phosphorus loading of Ohio water resources. The final report of the Ohio Lake Erie Phosphorus Task Force stated, “The majority of annual phosphorus loading to Lake Erie has been documented to be from storm-pulsed runoff from the landscape into the tributaries that drain to Lake Erie.”    Further, it has been documented that biologically available phosphorus levels in Lake Erie have been increasing since about 1995.  This type of phosphorus (biologically available) has been linked to HAB.

Certainly, agriculture is not the only source of phosphorus loading into our water resources. Further, major storm events have also contributed very significantly to the loss of both sediment bound phosphorus (soil erosion) and biologically available phosphorus (field runoff and tile discharge) and these events may be increasing in number.   

Significant research is now being conducted to further study the relationships between modern agricultural production practices and loss of phosphorus from farm fields and drainage tiles.  To read more about this issue, go to the report from ODA, OEPA and ODNR that contains a plan of future actions that focuses on mitigating agricultural field/tile losses of phosphorus.  http://corn.osu.edu/newsletters/2012/2012-06/#7 .  Also, review the BMP’s for reducing agricultural phosphorus loading at: http://corn.osu.edu/newsletters/2011/2011-38/#2 .

 

Weather Outlook

While rainfall was limited across the north half of the state to generally 0.10 to 0.40 inches, the south half of the state received 0.50 to 1.00 inches over the last week with some spots in southwest Ohio over 1.5 inches. Most of this rain fell Saturday. Normal weekly rainfall is between 0.75 to 1.00 inches and decreasing. Therefore, rainfall was below normal in the north half to near normal in the south half of the state.

Looking ahead, this week April 16-22 will feature temperatures close to normal (above normal during the week and below normal on the weekend). Normal temperatures feature highs in the 60s and lows in the 40s. Rainfall will generally be at or below normal. After a few showers Monday it will be dry until late week into part of the weekend when a slow moving system will move across the area. Rainfall totals for the week should average 0.25 to 0.75 inches.

Next week April 23-29 will feature more of the same with a drier week until late week or the weekend when rain chances will return. Temperatures will start cooler than normal but return to above normal for the second half of the period. Rainfall will likely fall into the 0.50 to 1.00 inch range but again most of that coming late.

In summary it looks like we may be getting into a pattern that is dry for much of the work week with rain chances late week or on the weekend for the next few weeks. Temperatures will average close to normal the next two weeks with rainfall normal to slightly below normal. A widespread hard freeze looks unlikely at this point but some frost is still possible. The best chances in the next two weeks looks to be either Sunday April 22 or Monday April 23 but there is a lot of uncertainty if it will happen as our weather models are all over the places with temperatures at that time. North of I-70 is most at risk.

 

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.