Monthly Archives: July 2012
While farmers may be tired of irrigating right now, I think all who have irrigation are thankful for it in such a dry year. Honestly, thankfully with our irrigation we have some of the best looking crops in the Corn Belt right now. Even so, with corn that hasn’t been replanted nearing dent or stages of starch fill, you may be wondering how to schedule for your last irrigation.
For those of you in our Nebraska Ag Water Management Network using watermark sensors, the goal is to use them to determine when the soil profile reaches 60% depletion (for silty-clay soils in our area aim for an average of 160 kpa of all your sensors). You may be thinking, “An average of 90kpa was hard enough!” but as Daryl Andersen from the Little Blue Natural Resources District points out, you’re only taking an additional 0.30 inches out of each foot. So if you’re averaging 90kpa on your three sensors, you have depleted 2.34 inches in the top three feet so you still have 0.96 inches left (see the Soil Moisture Depletion Chart). If you add the fourth foot (using a similar number from the third foot), it would bring the water available to the plant up to 1.28”.
At beginning dent corn you need 24 days or 5 inches of water to finish the crop to maturity. If you subtract 1.28 from 5 you will need 3.72” to finish out the crop. Corn at ½ milk line needs 13 days or 2.25” to finish the crop to maturity-so subtracting it from 1.28 would be only 0.97”.
Soybeans at the beginning of seed enlargement (R5) need 6.5”. Soybeans in R6 or full seed which needs 3.5 inches yet for maturity. Subtracting off the 1.28” in the four foot profile would lead to 2.22”. The UNL NebGuide Predicting the Last Irrigation of the Season provides good information on how determine your last irrigation in addition to showing charts on how much water the crop still needs at various growth stages.
Several people I’ve talked to who have been irrigating using watermark sensors aren’t replenishing the second foot, so you may have a few rounds yet to go on corn and beans. For a quick way to know where you’re at, think about irrigating this way as explained by Daryl Andersen at the Little Blue Natural Resources District:
One way to look at this is by the numbers of days left. At 1/4 starch, there are about 19 days before maturity so you can let your sensors average 130kpa on the first week and 150kpa on the next week. If these targets are met during the week, you would put on about 1 inch of water. By going to these numbers, it might give you a higher probability for rain in the next couple of weeks. I’m hoping for many answered prayers that we will see rain in August!
Unfortunately the drought continues to intensify. All Nebraska counties have now been released for haying and grazing of Conservation Reserve Program (CRP) lands. Information and resources continue to be added to UNL Extension’s Drought Resource page at http://droughtresources.unl.edu. Please check it out for drought information for livestock, crops, water, and gardening.
Some have started chopping corn for silage or are about to soon. Dr. Bruce Anderson, UNL Extension Forage Specialist, shares the following information about maintaining silage quality in the future. “After silage has been chopped and piled and packed correctly, it still can be damaged seriously by air and moisture slowly penetrating the outer 3 to 4 feet. Animals often eat less when fed moldy silage and can even experience health problems due to mycotoxins.
Good, well-eared silage can lose over 20% percent of its feed value from fermentation and spoilage under normal conditions. Silage made from corn with little or no grain might have even greater losses. This loss can be cut in half or even more if the silage is kept well covered by plastic.
Cover freshly chopped silage with black plastic immediately after you finish filling the trench, bunker, or pile. Then cover the plastic with something to help hold it down. Old tires are readily available and do a good job of keeping the plastic from blowing away, but they only keep keep pressure on the silage directly under the tire. In between the tires, air can circulate and cause spoilage.
An even better choice would be a solid cover over the plastic, something like freshly chopped forage or weeds or maybe even a 3- to 4-inch layer of manure. This would ensure that the entire surface of silage is fully protected to reduce the chance for air bubbles to form under the plastic which could reduce silage quality. You go to a lot of time and expense to make good silage. Isn’t it worth it to protect that investment?”
In early July, southern rust caused by the fungal pathogen Puccinia polysora was discovered in Hall, Adams, Clay, Fillmore, Thayer, and Burt counties in Nebraska. Most farmers in south-central Nebraska remember the corn season in 2006 walking out of fields orange and the slow harvest due to downed stalks. Since then, southern rust has been a disease of concern and fungicides are used to prevent and also treat it when it’s found in fields.
I promised when we were first discovering southern rust this year that I’d post pics, so while delayed, here they are! It is often confused with common rust which we see earlier every year. Common rust typically has pustules (raised fungal spores) that are brick red in color, larger, and on the upper and lower leaf surfaces. The pustules tend to be more spread out.
Southern rust typically has very small pustules that are clustered on predominately the upper leaf surface and are tan to orange in color. This year, southern rust pustules tend to be more tan in color than orange but are still distinctively different with their smaller and clustered appearance. Both fungal rust pathogens arrive in Nebraska each year via wind from the south. Southern rust prefers warm, moist conditions which, in spite of our dry spell, is typical within our pivot and gravity-irrigated fields in the area. At this time we are recommending if you find southern rust in your field to consider treating with a fungicide. Please be sure to read and follow all label directions including paying attention to pre-harvest intervals. A list of corn fungicides and efficacy can be found here by scrolling down to the corn section.
Additional information and pictures of these diseases can be found here.
Well, the heat isn’t letting up. Sixty-nine Nebraska counties are allowed to hay and graze Conservation Reserve Program (CRP) lands. In our area these counties include: Hamilton, Hall, Webster, Nuckolls, and Thayer. From Teri Post at the Webster Co. FSA office, this means that: “If it (CRP) is hayed, it cannot be sold and cost to the livestock person cannot exceed the 10% reduction on contract payment. Paperwork MUST be completed prior to anything being done. If you do not have livestock but do have a CRP contract, you can lease your acres to a livestock producer. They have also released CP25 (wildflower mix) for grazing only. If you prefer to sell the hay and you qualify for managed haying, you may do that but you will be assessed a 25% payment reduction rather than the 10% with emergency release. Also keep in mind that use of emergency haying or grazing restarts the time clock for when you can hay or graze next. If you use the emergency hay or graze release, even if you hayed or grazed in a prior year you are now eligible to hay or graze again.”
Nebraska Farmers who have drought damaged corn which could be swathed and baled, chopped, or grazed can list that on the Nebraska Hay and Forage Hotline. The hotline is available free of charge for buyers and sellers to list feed resources. Call the hotline at 1-800-422-6692 to list the forage you have or to list your need for forage. I’ve been contacted by Extension Educators in the Sandhills asking if we have any producers willing to rent cornstalks for grazing this year to please let me know and we will put you in touch with producers in the Sandhills who need forage.
UNL Extension has developed a Drought Resource Web resource that pertains to crop and livestock producers. Some of you have been asking about options for dryland crops right now. Research has shown benefits to the following crop if stubble height is left at least 10 inches tall when haying or cutting silage from drought damaged corn fields. Leaving a higher stubble height will also reduce the nitrate levels in the forage that has been cut.
When it comes to your options on what to do with weather-damaged corn, Dr. Bruce Anderson, UNL Extension Forage Specialist and Tom Dorn, UNL Extension Educator, recommend to consider the following points before harvesting your crop as forage:
- If grain prices remain high, grain yield may not need to be very high to justify selecting grain harvest over forage harvest.
- Sometimes leaving the corn residue can result in increased yield next year and that increase may provide more value than that resulting from forage use. See NebGuide G1846, Harvesting Crop Residues for information on evaluating your situation.
- Check labels of all chemicals applied to be sure they are cleared for forage use and that the minimum harvest interval has been met.
- Check with the USDA Farm Service Agency and your crop insurer to maintain compliance with farm programs and crop insurance requirements.
- Nitrate concentrations can reach toxic levels in weather-damaged corn. The harvest method can affect the nitrate, a particular concern when its being fed to livestock. Leaving a tall stubble (8 or more inches) will reduce nitrate risk but note eliminate it. Choose the harvest method accordingly.
Silage may be the safest method of harvest as fermentation usually (but not always) reduces nitrate levels and risk. Yield is about one ton per acre of silage for each harvested foot of earless corn plant (not counting the tassel). Feeding value is about 70% to 80% of well-eared corn silage. Corn with some grain (less than 50 bushels) tends to produce about one ton of silage for every five bushels of grain with a feed value about 80 to 90% of regular corn silage.
Harvest timing is critical with silage to ensure the correct moisture for proper fermentation. Plants probably are about 80% moisture now and the desired moisture level for silage is about 65%. Plants with any green leaves usually are too wet to chop for silage. For proper moisture, most leaves may need to be dead before chopping. The stalk and ear hold amazingly high water concentrations. For corn with no grain, even if all leaves are dead, the whole plant (and silage) moisture can be 70% if the stalk is still green and alive. Once plants actually die they can rapidly dry down. There are several ways to reduce moisture content:
- If corn has pollinated, delay silage harvest until all chances of increased biomass tonnage have passed or plants naturally dry down to appropriate moisture levels.
- Corn can be windrowed and allowed to partially dry before chopping.
- Excessively wet material can be blended with drier feeds such as ground hay, cracked grain, or dried distillers grains. However, this can take a lot of material — about 500 lb of grain or hay to reduce each ton of chopped corn with 85% moisture down to 70% moisture.
- Silage inoculants may improve fermentation and preservation of drought-damaged silage.
Green Chop: Green chop minimizes waste but may be the most dangerous way to salvage corn. If present, nitrates will start to change into nitrites (about 10 times as deadly) as green chop begins to heat. Chop and immediately feed only an amount that animals will clean up in one feeding. Chop and feed two or three times per day instead of providing excess feed from a single chopping. If any green chop remains two hours after feeding, clean out bunks. Never feed green chop held overnight because nitrites can be exceptionally high. Be sure to allow plenty of bunk space (36 inches per cow is recommended) so boss cows don’t overeat and timid cows can get their share.
Hay: Hay may be the most difficult method of mechanical harvest, especially if ears have started to form – the stalk and especially the ears will be slow and difficult to dry. If possible, use a crimper when windrowing. Unlike with silage, nitrate levels do not decrease in hay after it is baled. Some of the nitrate risk can be reduced by cutting to leave a tall stubble, about 8 inches. Tall stubble also will elevate the windrow off the ground, allowing air to circulate better through the forage and aid in drying.
Grazing: Challenges with grazing include acidosis risk for cattle not accustomed to grain if ears have started to fill (smart cows will selectively graze ears), waste from excessive trampling, availability of drinking water, perimeter fencing, and nitrates. Reduce acidosis risk by feeding increasing amounts of grain similar to feedlot step-up rations before turning into standing corn that has much ear development.
Reduce waste by strip-grazing with at least two or three moves per week; daily is best. Back fences are not needed because regrowth is not expected. Water can be hauled in as with winter corn stalks or lanes might be constructed with electric fence to guide animals back to water sites that are nearby. If strip grazing, animals can walk back over previously grazed areas since back fences aren’t needed.
Perimeter fences can be built using the same fencing as for winter stalks. Cows are likely to respect such fencing but inexperienced calves may not remain where desired. To better control calves, use a double strand of electric wire and/or a more visible barrier such as electric polyrope or polytape. Animals not already experienced with electric fences may need some exposure and training before moving them to a corn field.
Nitrates usually are not a problem with grazing since the highest concentration is in the stem base, the plant part least likely to be consumed. Risk increases, though, if animals are forced to “clean-up” a strip before moving to fresh feed and when corn plants are short (probably less than 3 to 4 feet tall) with small, palatable stem bases. Tests for nitrate concentration (whole plant and just the bottom 8 inches of the stem base) can be made prior to grazing to assess risk. If nitrate levels are risky, the hazard can be reduced by offering enough desirable forage to discourage consumption of hazardous plant parts as a major component of diet. Also, delaying grazing until plants more fully mature often lowers nitrate risk. NebGuide G1865, The Use and Pricing of Drought-Stressed Corn, offers additional information.
Windrow Grazing: This method includes cutting as you would for hay and then grazing the windrows rather than baling them. It eliminates the cost of baling, transporting bales, feeding bales, and maybe hauling manure. It also eliminates any flexibility in feeding location and may reduce opportunities to sell the corn forage.
Windrowing tends to preserve forage quality better than allowing plants to stand. Usually it is easier to strip graze windrows than standing corn because building fences and estimating strip size are easier. Snow cover rarely causes problems if animals already know the windrows are there. They will use their hooves and face to push snow aside to access the windrow. Thick ice, however, can cause a significant barrier. Follow appropriate management recommendations listed earlier for hay and grazing for best utilization and safety.
Fair time is a special time of year. It’s the one time in the year where people from all parts of the county come together for the youth. Yes, there’s healthy competition involved, but 4-H and FFA are building life skills in our youth. Families congratulate each other and are excited for a youth’s job well done. It’s the one time in the year where people from all parts of the county come together for the youth.
It’s always fun for me to watch the fairgrounds come alive Wednesday night as youth bring in their static exhibits and livestock entries. People are smiling and most youth-particularly the younger exhibitors-are excited. Many people, including me, checked the weather forecast throughout the fair in hopes of rain. This is the first fair in a long time that it didn’t rain Wednesday night or anytime during the fair. Thursday is a busy day with exhibits being judged, livestock being weighed in and the beginning of livestock shows. Something I always enjoy is family fun night on Thursday night. Clouds appeared and families enjoyed kiddie games, shelling popcorn, an obstacle course, and roasting hot dogs and marshmallows. Friday and Saturday continued with the remaining livestock shows and plenty of heat. Sunday brought a fun beef-fitting contest where youth of various ages and clubs worked together. It also brought smiles watching the young children tell their stories and show animals in the Rainbow Classic, watching all our top showmen compete in the Round Robin Showmanship Contest, and wonderful support from all our buyers at the Livestock Auction; we’re thankful for your support.
While probably most people are hot and tired by fair’s conclusion Sunday evening, it’s always a little saddening to me to watch the fairgrounds become empty so quickly again. Deanna and Holli in our office spend a great deal of time preparing for it as do all the youth, parents, grandparents, and 4-H leaders; thank you for all you do and the time you all invest in our youth! Thank you to the Fairboard members who spend countless hours preparing the Fairgrounds and always take care of things during fair with a smile-no matter how often they have to plunge the toilets! Thank you to 4-H Council for your help on various committees, your work with the food stand and BBQ, and for all you do. Thank you to all our superintendents and to all our volunteers; without you our 4-H program and fair wouldn’t be possible. Thank you to Tory and the Clay Co. News for all your support and coverage of our fair. We have something so special in our county and I truly feel blessed to work in Clay County! We may not have big-time entertainment at the fair, but I love our fair. I love how the focus is on our 4-H and FFA youth and families; many other counties would love to have that. Our numbers and entries are similar to counties much larger than us and I appreciate the quality brought to the fair each year from our youth. Thank you to everyone for making the 2012 Clay County Fair a success!
A follow-up to my last blog post predicting corn yields for our local area this week in south-central Nebraska. Here’s some 2012 yield predictions for throughout the corn belt from an article my colleagues in Agronomy and Horticulture and I posted this week’s CropWatch newsletter.
July 10, 2012
Forecasted Corn Yields Based on Hybrid-Maize Model Simulations
Most Sites, Except Northeast, Dip Below Long-term Average Yields
The weather is hot, dry, and windy. Corn is pollinating in much of the state and growers are asking how the weather will impact potential corn yields for 2012. To answer this, we ran in-season corn yield predictions using the Hybrid-Maize Model developed by researchers in the UNL Department of Agronomy and Horticulture. This model simulates daily corn growth and development and final grain yield of corn under irrigated and rainfed conditions.
The Hybrid-Maize model predicts yields based on no nutrient limitations, no disease or insect pressure and an “optimal management” scenario. Hybrid-Maize is helpful in understanding how current in-season weather conditions are affecting corn growth and potential yield for the current year and in comparison to previous years.
Hybrid-Maize model can be used during the current crop season to forecast end-of season yield potential under irrigated and rainfed conditions. To do so, Hybrid-Maize uses observed weather data until the date of the yield forecast and historical weather data to predict the rest of the season. This gives a range of possible end-of-season yields. This range of simulated yields narrows as corn approaches maturity.
Hybrid-Maize was used around July 1 to predict 2012 end-of-season corn yield potential throughout the Corn Belt, including locations in Nebraska, Iowa, South Dakota, and Illinois (Figure 1). Sites in Nebraska include Holdrege, Clay Center, Mead, Concord, and O’Neill. Separate yield forecasts were performed for irrigated and dryland corn for those sites where both irrigated and rainfed production is important (in Nebraska: Clay Center, Mead, and Concord). Underpinning inputs used for the simulations include weather data provided by the High Plains Regional Climate Center (HPRCC) and the Illinois Water and Atmospheric Resources Monitoring Program (WARM) and site-specific information on soil properties and typical crop management (planting dates, hybrid maturity, and plant populations).
Corn Yield Potential (Yp) forecasts, as well as the underpinning data used for the simulations, can be seen inTable 1. The long-term, predicted yield potential based on 30 years of weather data (fourth column from the right) is then compared to the range of predicted 2012 corn yield potential (three columns on the right), which includes the yield potential simulated under the most likely scenario of weather expected for the rest of the season (median) and for relatively favorable and unfavorable scenarios for the rest of the season (75th and 25th percentiles) based on historical weather data.
In general, when comparing the median predicted yield for 2012 to the long-term, 30-year average yield potential, 2012 yields are trending lower than the long-term yields (Table 1). Below-normal rainfall coupled with high rates of daily water use due to high daytime temperatures, are the factors leading to the below-average yield potential predicted by Hybrid-Maize for dryland corn across the Corn Belt. An exception is Brookings, S.D. where rainfall has been favorable so far and rates of water use are relatively low compared with other locations.
In the case of irrigated corn in Nebraska, the model is predicting a median yield potential six to seven bushels below the long-term average irrigated yield potential at Holdrege, Clay Center, and Mead due to above-normal temperatures which hasten crop development and increase night respiration. However, this is not consistent throughout the state. Predictions of irrigated corn yield potential are only slightly below (Concord) or even above (O’Neill) the long-term average in northern Nebraska due to cooler weather.
These are simulations and again are based on optimal conditions for crop growth, that is, no limitations by nutrients and no incidence of diseases and insects. Nevertheless, they provide an idea on how in-season weather conditions can impact corn yield potential under irrigated and rainfed conditions. Last year, we saw a similar situation when in-season yields dropped off from the long-term average due to extreme high temperatures by late July and then climbed back up with cooler night temperatures and a long grain-filling period in August. These yield predictions are based on a snapshot in time. Actually, in the current 2012 season, there is still a good chance of having a near or above-average corn yield potential at locations where weather conditions are favorable during the rest of the season as indicated by the 75th percentile yields shown in Table 1. However, if hot, dry conditions continue through much of July, we would expect yield predictions to fall. We will follow-up with predictions later on in the season.
Patricio Grassini, Research Assistant Professor, UNL Department of Agronomy and Horticulture
Jenny Rees, UNL Extension Educator
Haishun Yang, Professor, UNL Department of Agronomy and Horticulture
Ken Cassman, Professor, UNL Department of Agronomy and Horticulture
Table 1. 2012 In-season Yield Potential Forecasts using UNL Hybrid-Maize Model
|Location, state||Water regime||Soil type¶ & initial water||PP¶ (ac-1)||RM¶ (days)||Planting date†||Long-term yield potential (bu/ac)‡||2012 forecasted yield potential (bu/ac)|
|Holdrege, NE||Irrigated||Silt loam||32.4k||113||April 27||248||257||241||228|
|Clay Center, NE||Irrigated
|Silt clay loam
|Silt clay loam
|O’Neill, NE||Irrigated||Sandy loam
|Brookings, SD||Rainfed||Silt clay loam
|Sutherland, IA||Rainfed||Silt clay loam
|Monmouth, IL||Rainfed||Silt loam
|DeKalb, IL||Rainfed||Silt clay loam
|Bondville, IL||Rainfed||Silt clay loam
|¶ Simulations based on dominant soil series, average planting date, plant population (PP) and relative maturity (RM) of most widespread hybrid at each location (Grassini et al., 2009), assuming 100% available soil water in the top 40 inches at the beginning of the growing season. ‡ Average (20+ years) simulated yield potential (Yp)|
The past few weeks I’ve received questions on how the weather conditions are impacting corn yields. One way to help predict this is by running the Hybrid Maize model developed by researchers in the Agronomy and Horticulture Department at UNL. I ran Hybrid Maize model simulations for various planting dates in the Clay Center, NE area. This model predicts corn yields using weather data under “perfect conditions”-nothing such as nutrients or water is limited and there is no disease or insect pressure in these simulations. Reality is that all these things do occur. To use the model, I input current season weather data from the High Plains Regional Climate Center which allows me to compare the current growing season weather conditions and potential yield impacts to a long term median 30 years worth of weather and yield data.
For the simulations I ran right now using Clay Center weather data, I found that overall, we are trending below the 30 year median average yields for both irrigated and rainfed corn. Right now the long-term median yield for all irrigation simulations is trending towards 259 bu/ac at planting populations of 32,000 seeds/acre with 113 or 115 day relative maturities. The following are a few simulations and please check out this week’s CropWatch to view simulations across the Corn Belt. Click on the images below to view them closer up. Compare the 2012 median yield line (in red) to the long-term median line (yellow).
- Mar. 27 planting date, 115 day rm: Best yield 300 bu/ac. Predicted mean is 241 bu/ac.
- Apr. 15 planting date, 113 day rm: Best yield 293 bu/ac. Predicted mean is 242 bu/ac.
- Apr. 15 planting date, 115 day rm: Best yield 200 bu/ac. Predicted mean is 253 bu/ac.
- May 1 planting date, 113 day rm: Best yield is 286 bu/ac. Predicted mean is 248 bu/ac.
- May 1 planting date, 115 day rm: Best yield is 293 bu/ac. Predicted mean is 252 bu/ac.
- May 15 planting date, 113 day rm: Best yield is 310 bu/ac. Predicted mean is 253 bu/ac.
The best comparison is the predicted mean to the long-term median so right now we’re seeing a slight drop below the long-term median for all the planting dates and relative maturities run in these simulations. However, if we receive cooler night-time temperatures and a longer fill period like last year, we may see these yield trends turn up.
For rainfed conditions, I did not run optimal simulations. I ran real-time water limited situations assuming full soil moisture from 0-40” into the profile at the beginning of the season. Here are the results for a planting population of 22,000 plants/acre with 113 day relative maturities:
- Mar. 27 planting date, 115 day rm: Best yield is 202 bu/ac. Predicted mean is 140 bu/ac vs. long term median of 163 bu/ac.
- April 15 planting date, 113 day rm: Best yield is 224 bu/ac. Predicted mean is 146 bu/ac vs. long term median of 167 bu/ac.
- May 1 planting date, 113 day rm: Best yield is 223 bu/ac. Predicted mean is 152 bu vs. long term median of 167 bu/ac.
- May 15 planting date, 113 day rm: Best yield is 250 bu/ac. Predicted mean is 161 vs. long term median of 165 bu/ac.
Here’s a good post from Elizabeth Killinger, UNL Extension Educator, regarding all the tomato troubles we are currently seeing in the garden. You can also check out the following YouTube video by Sarah Browning, UNL Extension Educator.
Vegetable gardening has become more and more popular. It is a way to relax, if you consider pulling weeds relaxing, and is also a way to grow your own groceries. Tomatoes are grown in over 86 percent of gardens in the United States. There are many common diseases and problems that can plague tomatoes in the home garden. With a little help you can keep your tomatoes in tip top shape.
Early blight is a common tomato disease. It is caused by a soil-borne fungus. Rain water, or overhead irrigation, can cause the soil and fungi to splash onto the lower leaves of the plant. The infection starts as leaf spots on the lower leaves then causes yellowing then eventually causes the stems to turn brown. The infection works its way up the plant causing the foliage to die.
There are ways to help prevent the spread of this fungal…
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With the high heat, lack of rainfall, and pollination occurring in many fields or just around the corner, questions have been rolling in regarding how high heat affects corn pollination. Dr. Tom Hoegemeyer, UNL Agronomy Professor of Practice wrote the following article and I’m sharing it for the excellent info. Hybrid Maize simulations will be shared in this week’s CropWatch and in next week’s news article.
“Corn was originally a tropical grass from the high elevation areas of central Mexico about 7,400 feet above sea level, 2,000 feet higher than Denver. Today, corn still prefers conditions typical of that area — warm daytime temperatures and cool nights. Areas that consistently produce high corn yields share some significant characteristics. These areas — central Chile, the west slope of Colorado, etc. — are usually very bright, clear, high light intensity areas with cool nights.
This year, in the prairie states and in the Cornbelt, conditions have been dramatically less than optimal. Corn maximizes its growth rate at 86°F. Days with temperatures hotter than that cause stress. In the high yield areas, cool night temperatures — at or below 50°F — reduce respiration rates and preserve plant sugars, which can be used for growth or reproduction, or stored for yield. These are optimum conditions for corn, and interestingly, are fairly typical for areas around central Mexico where corn is native.
In years when we get high day and nighttime temperatures coinciding with the peak pollination period, we can expect problems. Continual heat exposure before and during pollination worsens the response. Daytime temperatures have consistently stayed in the upper 90s to low 100s.The high humidity, which helps reduce crop water demand, also increases the thermal mass of the air—and provides extra stored heat and insulation at night.
Corn pollen is produced within anther sacs in the anther. The plant releases new, fresh anthers each morning, starting from near the top of the tassel, on the first day of shed, and proceeding downward over several days. The process of releasing the pollen from the anthers is called “dehiscence.” Dehiscence is triggered by the drop in humidity, as the temperature rises. However, when it is extremely humid and the humidity falls very little, dehiscence may not occur at all, or it may be delayed until late in the day. If one has breezes, while the humidity is still very high, the anthers may fall to the ground before pollen is released. If the temperature rises too high before pollen dehiscence occurs, the pollen may have reduced viability when it is shed. A person experienced at hand pollination in corn will often see this happen. There will be anthers in a “tassel bag,” but little pollen. The usual solution to this is to wait a couple hours until the temperature rise reduces the humidity. However, last year we had some conditions where pollen was never released from the anthers. This can impact silk fertilization, particularly in open-pollinated situations.
Corn is a “C4 Photosynthesis” plant, making it extremely efficient at capturing light and fixing CO2 into sugars. One drawback of this system is that with high daytime temperatures, the efficiency of photosynthesis decreases, so the plant makes less sugar to use or store. High nighttime temperatures increase the respiration rate of the plant, causing it to use up or waste sugars for growth and development. This results in the plant making less sugar but using up more than it would during cooler temperatures. Heat, especially combined with lack of water, has devastating effects on silking. If plants are slow to silk, the bulk of the pollen may already be shed and gone. Modern hybrids have vastly improved “ASI” or anthesis-silk interval (the time between mid-pollen shed and mid silk). Regardless, in some dryland fields we see seed set problems because of “nick” problems between pollen and silking.
Even in some stressed areas within irrigated fields (extreme sandy spots, hard pans or compaction areas where water isn’t absorbed and held, and some “wet spots”) we can see stress-induced slow silking and resulting seed set issues. Historically, this has been the most important problem leading to yield reduction, particularly in stressful years. Once silks begin to desiccate, they lose their capacity for pollen tube growth and fertilization.
Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen. This is a bigger problem when humidity is low and on hybrids that silk quite early relative to pollen shed. Even with dew points in the 70s, when temperatures reach the high 90s to the100s, the heat can still desiccate silks and reduce silk fertility.
Heat also affects pollen production and viability. First, heat over 95°F depresses pollen production. Continuous heat, over several days before and during pollen-shed, results in only a fraction of normal pollen being formed, probably because of the reduced sugar available. In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. Research has shown that prolonged exposure to temperatures reduced the volume of pollen shed and dramatically reduced its viability. For each kernel of grain to be produced, one silk needs to be fertilized by one pollen grain.”