Corn Silage Resources: For those making corn silage this year, hopefully the following resources can be of help. The multiplier for corn silage value from UNL is 7.65 times the market value of corn grain.
- Making corn silage considerations: https://go.unl.edu/qven
- Estimating a fair value for standing forage (including silage): https://go.unl.edu/sy6j
- Value of Standing Forage excel spreadsheet (scroll to mid-page): https://cap.unl.edu/forage
Spidermites: I’m hoping that the cooler weather and either rainfall/irrigation are helping a beneficial fungus help us in the battle against spidermites. Last week I was showing growers how to distinguish this via a hand lens. We mostly have two-spotted spidermites in fields, which are yellow with two black spots on them. Anytime they start looking different (darker, cloudy, white) where the spots are no longer visible, it can be an indication that they are infected and will die. Unfortunately I didn’t grab any pics from the field. The economic threshold from Colorado State says spraying is no longer beneficial past hard dough. I can appreciate that’s hard with the severity in some upper canopies, so here’s hoping the cooler weather helped with the battle.
Pollination: I sure appreciated seeing and smelling all the pollen shed in these replant fields last week! It was perfect weather for it, hopefully a bright spot in the midst of a difficult situation. Been hearing and seeing complaints about poor pollination in non to less severely hailed areas. I don’t remember smelling pollen this year like I normally do in July, but I also admit most of my time has been spent in this large replant area this year. The following is about poor pollination, not kernel abortion.
What I’ve learned from Dr. Tom Hoegemeyer and Dr. Roger Elmore about corn pollination through the years: Heat over 95F depresses pollen production with prolonged heat reducing pollen production and viability. When soil moisture is sufficient, one day of 95-98F heat has little or no yield impacts. After four consecutive days, a 1% yield loss can occur for each day above that temperature with greater yield loss by day 5 or 6. High humidity, without a drop in humidity during the day, can delay pollination or prevent pollen from leaving the anther sacs. Pollination mostly occurs between 8:30 a.m. and noon. When the temperature is 90°F to 95°F, the pollen is eventually killed by heat and is seldom viable past 2 p.m. Pollination typically occurs over a span of six to ten days depending on variability of growth stages in the field.
So, I did some digging into weather data. I don’t have all the tools that you may have, so do something similar for your operations based on the timing of when your specific fields were pollinating and where you’re located. First, I did a general map of Nebraska showing the number of days over 95F from July 9-19, 2022. The eastern 1/3 of the State only had 0-1 days that fit this criteria.
Perhaps bigger factors may have been humidity and timing of silk emergence compared to pollen shed? We’ve had high humidity. For pollen shed to occur, relative humidity needs to drop between 50-65% and the pollen is no longer viable at 30%. As I look at weather data for different locations in the area, many places had over 65% relative humidity as an average for the day for at least 5 days in the time period listed above. It really comes down to at what time the relative humidity dropped enough during the day to release viable pollen. It’s possible that for several days, the anther sacs dropped without releasing pollen if the humidity didn’t drop in the morning. I also remember mentioning in July about how extra long the silks seemed this year prior to pollen shed. That can be a problem, particularly for pollination on the lower end of the ear. The first silks that emerge from the husk are attached to kernels at the base of the ear and they begin to form 8-10 days prior to R1. Silks then continue to emerge sequentially up the ear with the ear tip silks emerging last. Silks are receptive to pollen anywhere along the silk, but after 10 days, the silk senesces (and they’re most receptive to pollen in the first 4-5 days of emergence). Some drought tolerant hybrids may have genetic X environmental responses which trigger silks to emerge 4-5 days prior to any pollen shed (which can result in poor pollination). Older silks can also get covered up by newer silks and miss exposure to pollen. Drought stress adds an entire other complexity to this discussion. Japanese beetles clipped silks in some areas, but it sounded like most were sprayed timely or the silk clipping occurred after the silks had pollinated (turned brown). I don’t know the specifics of every individual situation. These are some thoughts to consider if you’re dealing with pollination issues this year.
Thank You to all the volunteers; ag society and 4-H council members; Extension staff; and all the youth and families who made the 2021 York and Seward County Fairs successful! It was a joy for me to see ‘normal’ fairs, youth and adults excited to find their projects and show their ribbons, the number of people out attending activities, walking through buildings, and just talking with each other!
Crop Update: Thanks also to the crop consultants and ag industry agronomists who dropped off samples during fair and kept me in the loop with what you were seeing in the fields! Southern rust was also confirmed in Hamilton and York counties this week. Frogeye leaf spot is also showing up on some soybeans with the high humidity and dew on soybean leaves.
Many have asked why the crops aren’t using much water. ET is evaporation from soil and leaf surface + transpiration (process of water lost through leaf stomata) from the crop. The high humidity has kept plants wet, especially soybeans, longer during the day (which is why I think the soil moisture use has been showing up less on soybeans than corn). I know many, including myself, have been trained that crops automatically remove 0.30”+ a day upon tassel and flowering, but that’s just not true. That thinking doesn’t account for the environmental factors at play which change every day of every year. Higher ET occurs on sunshiny days with high heat, higher wind, low humidity. Cloud cover, humidity, and low wind all reduce ET (and we’ve had a lot of these lately). As I’ve worked with farmers through the years, I’ve heard many say how helpful their ET gage was, because it’s such a visual representation of what’s going on with the environment and crop water use. If you don’t have an ET gage, the UBBNRD is sharing daily crop water use from the High Plains Regional Climate Center via email, so you can contact Marie there if you would like this info. each day. Thankfully, the humidity has allowed non-irrigated crops to hang on longer, due to lower crop water demand, in spite of the humidity being harder on us and animals.
Pollination: I realize there’s pockets of really good looking corn out there. And, I also realize that a lot of corn may look good from the road, but there’s concerns and questions about pollination and tip back in fields. As I think about when pollination occurred, the smell of pollen was thick in the air some mornings, and even early evenings when pollen shed was delayed from high humidity. Many fields I walked into had ample pollen shed. There’s a range of pollination dates in the area, so heat/humidity could have played a role for your specific fields. Dr. Tom Hoegemeyer shared the following about high heat and humidity during corn pollination in a CropWatch article, “Just a day or two difference in flowering, or planting, or other factors can make a substantial difference in (kernel) set. Stress during pollination and silking could result in shorter ears, increased tip back and fewer kernels per ear. All of these contribute to less yield potential.”
- When soil moisture is sufficient, one day of heat over 95-98F during pollination has little to no yield impact. After four consecutive days, there can be a 1% loss in yield for each day above that temperature. Greater yield loss potential occurs after the fifth or sixth day.
- Heat over 95°F depresses pollen production. Prolonged periods of heat can reduce pollen production and viability (ability of pollen to fertilize silks).
- High humidity helps reduce crop water demand. High humidity, without a drop in humidity during the day, can delay pollination or prevent pollen from leaving anther sacs. “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.”
I also think about what I’ve seen the past few weeks with all the silk balling, pollination misses, tip back, and what’s being shared with me by others in the field. The July 9 wind event that hit a portion of this area seems to have impacted plants more greatly that were within 1 week of tasseling. With the resources it took to right plants in developing additional brace roots, thickened nodes, etc., I wonder how much of the resources that would’ve been put into “normal” pollination were used for these other purposes instead and how that may have impacted pollination timing, silks pushed out of husks, etc.? A number of agronomists are reporting abnormal ear development they’re seeing in addition to pollination misses and tip back of various levels. This is what’s known from the research regarding wind impacts to yield on lodged plants (however the specific causes of the yield losses are not mentioned):
- Research found lodged plants after a wind event had yield reductions of 2-6% (V10-12 stage), 5-15% (V13-15 stage), and 12-31% (V17 and after stages).
- We’ve also personally observed yield losses greater than this due to abnormal ear development on lodged plants in the area after wind events.
Regarding tip back, it’s important to count kernels long as there may be more kernels than one realizes in spite of tip back occurring. Tip back on corn occurs most often from some sort of stress. One can tell the approximate timing of stress events by the appearance of the kernels. If kernel formation isn’t evident, the stress occurred before or during pollination. If kernels are very small or appeared to have died, the stress was after pollination as the kernels were filling. Japanese and rootworm beetle silk clipping can impact tip pollination. We’ve also had high heat with humidity since pollination in addition to cloudy/hazy days and I haven’t dug into the weather data yet. Hopefully this helps a little for the questions received thus far.
Crop Update: The smell of pollen is in the air! Did you know each tassel contains around 6000 pollen-producing anthers? Two good articles from Dr. Bob Nielsen, Purdue University at https://go.unl.edu/x5tv.
How does heat impact pollination? Dr. Tom Hoegemeyer, former UNL Professor of Practice, shared that high humidity, without a drop in humidity during the day, can delay pollination or prevent pollen from leaving anther sacs. While heat over 95°F depresses pollen production, one day of 95-98°F has no or little yield impact when soil moisture is sufficient. After 4 consecutive days, there can be a 1% loss in yield for each day above that temperature. Greater yield loss occurs after the fifth or sixth day. Thankfully we’re not in a high heat pattern during this critical time of pollination!
My concerns regarding pollination: bent ear leaves covering silks in wind-damaged fields. Seeing a great deal of this. Also seeing silks continuing to elongate and grow through broken mid-ribs to increase exposure to pollen. Will continue to observe impacts.
Preliminary storm prediction center weather data showed a total of 93 wind, 11 hail, and 13 tornado damage reports on July 8th in Nebraska. Univ. of Wisconsin found lodged plants had yield reductions of 2-6% (V10-12 stage), 5-15% (V13-15 stage), and 12-31% (V17 and after stages). For greensnapped plants (below ear), Iowa State found in the worst case situation, yield reduction may range up to a 1:1 percent broken:yield loss. It’s possible these losses will be as low as 1:0.73 or even 1:0.50. We have an article in this week’s CropWatch (https://go.unl.edu/cwy2) with more detailed information. Recovery pics also at https://jenreesources.com.
Southern Rust was confirmed at low incidence and severity in Fillmore, Nuckolls, and Jefferson county fields this past week (probable for Thayer). Received questions on fungicide applications. In conversations, it seems like there’s fear of making the wrong decision and ultimately pressure to apply them. I realize economically it’s easier to justify adding a fungicide with insecticide when insect thresholds are met to save application costs. Most fungicide studies focus on VT applications; however, yield increases with automatic VT applications aren’t consistently proven in Nebraska.
In fact, in 2008-2009, a UNL fungicide timing trial was conducted near Clay Center on 2 hybrids (GLS ratings ‘fair’ and ‘(very) good’) with a high clearance applicator. Timing over the two years included: Tassel, Milk, Dough, 25%, 33%, 50%, and 100% Dent comparing the fungicides Headline, Headline AMP, Quilt and Stratego YLD.
- 2008: No yield difference on GLS hybrids rated ‘good’ at any of the timings (Tassel, Milk, 33% and 100% Dent) nor the check when Headline or Stratego YLD were applied. For the ‘fair’ hybrid, no yield difference for any application timing nor the check for the April 30th planting except for Headline applied at milk stage (increased yield). Low gray leaf spot pressure.
- 2009: No yield difference on GLS hybrids rated ‘very good’ or ‘fair’ nor the check on any timings (Tassel, Milk, and Dough) using Headline, Headline AMP, or Quilt. Moderate gray leaf spot disease pressure.
Thus I’ve recommended waiting till disease pressure warrants the application (have personally recommended apps as late as hard dough in previous years). Hybrids vary in disease susceptibility (thus response to fungicide application). The main ‘plant health’ benefit observed in Nebraska when disease pressure was low (ex. 2012) was stalk strength and that may be something to consider again in this lower disease year. Regarding any improved water use efficiency for drought-stressed plants, the peer-reviewed research published on this was in 2007. The researchers found slightly increased efficiency in well-watered plants, but it was reduced in water-stressed plants. They suggested fungicide use in water-stressed plants could potentially negatively influence water use efficiency and photosynthesis.
Same area of a York County Field taken morning of July 9th (left photo) and morning of July 13th (right photo). Grateful to see how plants are re-orienting themselves in many impacted lodged fields!
Seeing some new growth on some greensnapped plants. Dissecting the growth revealed baby corn ears (they won’t amount to anything). Just shows the resiliency in plants regarding how they’re created to survive and reproduce. I never cease to be amazed by their Creator!
Corn: Corn plants are rapidly growing and at or nearing tasseling soon. One sign of rapid
growth is to look at the new leaf edges. Sometimes there will be a white margin, more transparent look, wrinkles, or notches in them. All of those are signs of rapid growth which take place during cell division.
Fertigation and Irrigation: Some fertilizer is occurring now before tassel. I also recommend 30 lbs of N at brown silk if needed. This is based on research from Purdue University sharing today’s hybrids use 30-40% of their total Nitrogen from flowering through maturity. In the past, some have asked about applying fertilizer during pollination. The following information is from Dr. Tom Hoegemeyer, Plant Breeder and UNL Professor of Practice Emeritus, “Pollination mostly occurs between 8:30 a.m. and Noon. Thus, as a precaution, I would not run a pivot on pollinating corn from 6 a.m. to Noon. When the temperature is 90°F to 95°F, the pollen is killed by heat and is seldom viable past 2 p.m. That leaves lots of time to run pivots, apply N, etc. when it won’t harm pollination. Silks tend to be viable for three or four days at these temperatures, so if a plant isn’t pollinated one day, generally the next day will work just fine. (If nitrogen is needed), I’d recommend that nitrogen go on as soon as practical. Corn nitrogen use is very high during the pre-tassel growth phase and again at kernel growth, from one to three weeks post pollination. About seven to ten days post pollination (before brown silk) lower N will start causing kernel abortion and serious yield loss in corn.” The UNL recommendation for fertigation is to use 30 lb of N with 0.25″ of water or 50-60 lb of N with 0.50″ of water.
Insects and Diseases: Thus far, insects and diseases have been pretty minimal in corn. Seeing some spidermites in low numbers. Japanese beetles are showing up in areas where they’ve traditionally been more of a problem. In corn, the threshold is 3 or more beetles per plant, clipping silks to ½” or less, with pollination less than 50% complete. The hard thing about the beetles is they have a long emergence of 3-4 weeks where they don’t all emerge at the same time…and they live as an adult for 3-4 weeks. The threshold for corn rootworm beetles for silk clipping is similar. Light trap data for western bean cutworm is showing moths are beginning to appear in low numbers. They prefer laying eggs on upper leaf surfaces of corn in late whorl stage to early tassel (however, I’ve seen them lay eggs on the underside of leaves and on leaves closer to developing ears in high heat). The current UNL economic threshold for treatment is 5-8% corn plants with eggs or larvae.
And, often there’s discussion about fungicide applications at tassel time or throwing in a
fungicide with an insecticide (or vice versa) to save an application cost. I shared a great deal about this a few weeks ago; please be very careful with growth stages and what is applied in the tassel time. With uneven emergence, not all plants in the field will be tasseling at the same time, which allows for corn ear abnormalities when NIS in particular is added to the tank (or is in the product formulations) and applied just prior to tasseling. That’s why I prefer to see fungicide applications delayed to at least full brown silk and preferably later if there’s no disease pressure to warrant the application.
Research at UNL South Central Ag Lab showed we can still apply fungicide to dough stage with no yield difference, particularly in low disease pressure years. The research also didn’t show an automatic yield increase with tassel applications. This allows us to account for southern rust which has occurred at some point all but two years of my Extension career. With tight economics, it just makes more sense to me to delay fungicide applications to when disease warrants it vs. applying too early as some have had to repeat applications (when southern rust occurred after applying too early). It’s also just good resistance management to not apply when disease and insect pressure doesn’t warrant it. Also be aware that we can see corn leaf aphids flare after fungicide applications as the fungicide kills a natural fungus that keeps their numbers in check. Aphids also can interfere with pollination by covering tassels.
Soybeans: As soybeans approach R3 (beginning pod), that’s the critical time to avoid
water stress in soybean (similar to tassel for corn). We recommend avoiding irrigating during flowering whenever possible to reduce disease pressure (such as white mold and SDS). Don’t pull insecticide triggers too early for soybean defoliators. UNL recommends 20% defoliation at reproductive stages from all defoliators.
Crop Updates: A great deal of timely information was provided in this week’s CropWatch at http://cropwatch.unl.edu including information about high heat and pollination, applying fertilizer during pollination, western bean cutworm scouting, forecasted yields, etc. Please check it out!
Several called me asking about applying fertilizer during pollination. I shared that while
I wasn’t aware of research, I personally was concerned about anything potentially interfering with pollination and that I do recommend 30 lbs of N at brown silk if needed or if you were originally planning split nitrogen apps. This is based on research from Purdue sharing today’s hybrids use 30-40% of their total Nitrogen from flowering through maturity. After discussing with Dr. Tom Hoegemeyer, Adjunct UNL Professor of Practice, he offered the following insights: “Pollination mostly occurs between 8:30 a.m. and Noon. Thus, as a precaution, I would not run a pivot on pollinating corn from 6 a.m. to Noon. When the temperature is 90°F to 95°F, the pollen is killed by heat and is seldom viable past 2 p.m. That leaves lots of time to run pivots, apply N, etc. when it won’t harm pollination. Silks tend to be viable for three or four days at these temperatures, so if a plant isn’t pollinated one day, generally the next day will work just fine. (If nitrogen is needed), I’d recommend that nitrogen go on as soon as practical. Corn nitrogen use is very high during the pre-tassel growth phase and again at kernel growth, from one to three weeks post pollination. About seven to ten days post pollination (before brown silk) lower N will start causing kernel abortion and serious yield loss in corn.” The UNL recommendation for fertigation is to use 30 lb of N with 0.25″ of water or 50-60 lb of N with 0.50″ of water.
Last week also brought questions regarding thresholds and difficulty in finding Western Bean Cutworm egg masses with moth flights at their peak. You can view light trap data from UNL’s South Central Ag Lab thanks to Terry Devries at: https://scal.unl.edu/ltr2018.pdf. There’s also a great article in this week’s CropWatch on how to scout for them, insecticide options, and additional recommendations. Thresholds for western bean cutworm are 5-8% of corn plants in the field containing egg masses or larvae. Egg masses can be difficult to find during pollination with pollen hiding them. ‘Typically’ egg masses are found in the top third of the plant on the upper sides of leaves and near midribs or leaf axils. However, with higher heat, I tend to find them closer to the ears and have even seen masses laid on the ear husks and on the backsides of leaves (not common). While larvae are generally known to move up the plant to feed at the tassels, I’ve seen high heat force larvae into ears earlier. It typically takes 5-7 days for larvae to hatch and the egg masses turn purple just prior to hatching. A number of insecticide options are available for both aerial application and via chemigation; these products are listed in the CropWatch article.
With insecticide applications occurring in corn for both western bean cutworm and also corn rootworm beetles, many have also called or talked with me about the recommendation of fungicide applications. Right now, I haven’t found gray leaf spot above 3 leaves below the ear leaf in several counties. There’s been some mis-diagnosing bacterial leaf streak as gray leaf spot. Southern rust was just confirmed in a Kansas county this week, but we still have yet to confirm it in Nebraska. Even the longest residual products won’t get us through August if a fungicide application occurs now. I can appreciate that economics are tight so the thought is to save an additional application cost by applying a fungicide now with the insecticide. And, I can appreciate economics are tight regarding why apply a fungicide right now when disease pressure doesn’t warrant it? Perhaps, at least those of you with the ability to chemigate could consider waiting till disease pressure warrants it for your field, if it does. Always in the back of my mind is the need for late-season protection with southern rust eventually showing up and gray leaf spot often worse then.
My perspective is from a resistance management and research-based one. We have 5 total modes of action for fungicides with 2 of them being in nearly every fungicide product we use in corn, soybean, and wheat because they work against foliar fungal pathogens. At some point, our pathogens will also adapt, as we’ve seen our weeds and insects do…it would be like losing our ability to control gray leaf spot and southern rust similar to palmer amaranth on the weed side. In Nebraska, Dr. Tamra Jackson-Ziem’s research has not shown an automatic yield increase to fungicide application in the absence of disease. And, it has also not shown an automatic yield increase when applied at tassel. In a high heat and low disease year like 2012, there were no statistical yield differences with fungicide application vs. the untreated control. Even in years with some disease pressure such as 2008-2010, she found no statistical yield differences between when various products were applied from Tassel through Dough stages. In high disease years, her research shows the benefit of fungicide application for reduced disease pressure and increased stalk strength. Fungicides are great tools to help us with disease pressure and stalk strength. Just would encourage all of us to consider when we really need to apply them and to understand that research in Nebraska does not automatically show increased yields with the use of them or with the timing of Tassel/Silking vs. later in the year. Also, hybrids may vary in their response due to disease susceptibility and other factors. Not all her data is listed at this site, but you can view it for yourself at: https://go.unl.edu/ni3y.
Bagworms: I’ve been seeing shelter belts and various trees turning brown from heavy
bagworm infestations. Please be checking your trees if you are noticing them turning brown. Additional information can be found at: https://go.unl.edu/rgju.
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.”