Drought and Heat Stress

Source: Dr. Peter Thomison

Drought stressed corn near tassel emergence

One of the corn production scenarios agronomists least like is an exceptionally wet spring followed by a hotter and drier than normal July and August. The spring of 2019 was one the wettest on records throughout much of the state and now, as the dry weather that started in July persists, such a scenario seems to be a possibility in many Ohio corn fields. A combination of warm temperatures and inadequate rainfall is beginning to stress corn fields across Ohio. What’s exacerbating this problem are the marginal roots evident in some corn fields. Several factors, including poor planting conditions, surface/sidewall compaction and/or excessively wet soil conditions in June have inhibited good root development in many fields. With the onset of drier, warmer conditions in July, these small, shallow root systems have been unable to extract water deeper in the soil profile. Cooler weather and the possibility of storms later in the week may ease drought stress, which is important because many late planted corn fields (planted throughout June) are near or entering the pollination period, the stage of development most susceptible to drought. Other fields past pollination are vulnerable to kernel abortion, which drought conditions increase.

Corn is at many different stages of development because of the wide range in planting dates. To estimate the impact of dry hot weather on corn yield potential, let us review the effects of moisture deficits on corn growth and development from the late vegetative stages, prior to pollination, to the dent stage of kernel development. Yield losses to moisture stress can be directly related to the number of days that the crop shows stress symptoms during different growth periods. The following summarizes findings of past Iowa work that shows the potential impact of water stress on yield potential. Continue reading

Grain Fill Stages in Corn

Source:

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.  Throughout the growing season I will discuss the various corn growth stages and management issue at each stage. 

Grain Fill Stages

The grain fill period begins with successful pollination and initiation of kernel development, and ends approximately 60 days later when the kernels are physiologically mature.  During grain fill the plant will do all it can to “pump” dry matter into the kernels, sometimes at the expense of the health and maintenance of other plant parts including the roots and lower stalk.

Kernel Development. The embryo and non-embryo sides of each kernel.

Cross-section of primary ears from R1 to R6. The embryo and non-embryo sides of each ear are shown once they are distinguishable.

 

A stress-free grain fill period can maximize the yield potential of a crop, while severe stress during grain fill can cause kernel abortion or lightweight grain and encourage the development of stalk rot (see table 1). The health of the upper leaf canopy is particularly important for achieving maximum grain filling capacity. Some research indicates that the upper leaf canopy, from the ear leaf to the uppermost leaf, is responsible for no less than 60% of the photosynthate necessary for filling the grain.

 

Table 2 shows the average amount of water needed for each growth stage and the cumulative total for the entire growing season.

 

Are Crops Catching Up?

Source: Peter Thomison, Laura Lindsey, OSU Extnesion

Corn –  Crop development varies tremendously across Ohio because of planting dates that range from late April to early July. According to field agronomists in some areas of the state, it looks like late-planted crops are “ rushing through development” …Unlike soybean, corn development is directly related to temperature, i.e. heat unit accumulation. Above average July temperatures (especially nighttime temperatures) have promoted rapid corn growth and development. After corn reaches the V10 stage (and most of our June plantings are near or beyond this stage), leaf collar emergence occurs at approximately one leaf every 50 GDDs.  See Corn Growth & Development posts on this blog for more detailed information on various corn growth stages.

Late planted corn fields (especially those that have adequate soil moisture and good soil fertility and weed control) may appear to be “catching up” with neighboring fields planted earlier. The rapid growth of late planted corn is associated with greater vegetative growth and faster canopy closure, which will help optimize yields. However, it does not mean that the rate of development of later plantings is greater than earlier plantings.  Corn growth and development have distinct meanings (Abendroth et al., 2011). Growth refers to the increase in size of an individual plant (or plant component) whereas development refers to a plant’s progression from earlier to later stages of maturity based on specific criteria (e.g., numbers of leaf collars).  So, while late planted corn may appear to be “catching up in terms” in terms of vegetative growth, i.e. plant height (probably because of longer internodes), it’s not caught up from the standpoint of development (leaf collar stages).

Corn plants can “adjust” their development in response to a shortened growing season. As was noted in a recent C.O.R.N. newsletter article (https://agcrops.osu.edu/newsletter/corn-newsletter/2019-12/will-planting…), a hybrid planted after late May will mature at a faster thermal rate (i.e. require fewer heat units) than the same hybrid planted in late April or early May. One of the consequences of delayed planting is that thermal time (GDD accumulation) from the dent stage (R5) to “black layer” or physiological maturity (R6) is shortened, “though this may simply reflect a premature maturation of the grain caused by the cumulative effects of shorter daylengths and cooler days in early fall or by outright death of the plants by a killing fall freeze” (Nielsen, 2018). Moreover, instead of a grain moisture content of about 30% at black layer, typical for normal planting dates, grain moisture at black layer for late plantings may be as high as 40%, which may require longer field drying and harvest delays.

Soybeans – Continue reading

Below Normal Rainfall Favored Until at Least Mid-August

Source: Jim Noel, NOAA

The weather pattern is not real supportive of rainfall. The weather models continue to try and support rainfall of normal or slightly above normal, however, current topsoil conditions along with a west to northwest flowing weather pattern does not support that. The last 7 days shows dry conditions across most of the corn and soybean growing areas.

In light of that, we expect 0.25-0.50 inches of rain per week the next two weeks on average with the range from near none to 2 inches in isolated areas. Normal per week about 0.75 inches. Hence, total rainfall for the next two weeks is forecast to average 0.50-1.00 inches with normal being about 1.50 inches for two weeks.

There is some indications that a more normal rainfall pattern will return for the second half of August but still much of Ohio will end August normal or below normal rainfall due to the quite dry first half.

Temperatures for August will average normal to slightly above normal but most maximum temperatures will be 80s to near 90 in the coming week or two.

The latest NOAA/Climate Prediction Center 2-4 week and monthly outlooks can be found at:

https://www.cpc.ncep.noaa.gov/

For the latest on the expanding dry areas in Ohio visit The Drought Monitor at:

https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?Midwest

We expect to see the dry areas expand this week across the corn and soybean belt including Ohio.

One Month Outlook Precipitation Probability

One Month Outlook Precipitation Probability

Accumulated Precipitation

Delayed Corn Planting the Disease Risk in Corn

Source: Dr. Pierce Paul, OSU Extension

Disease Risk

In Ohio, several foliar diseases are of greater concern in late-planted corn for a number of reasons, including: 1 – for diseases like gray leaf spot (GLS), northern corn leaf blight (NCLB), and eye spot that are caused by pathogens that overwinter in corn stubble, delayed planting allows more time for inoculum (spores) to buildup, especially in no-till, corn-on-corn fields and 2 – for diseases like common and southern rust that are caused by pathogens that do not overwinter in Ohio, planting late allows more time for spore for blow up from southern states. So, with late planting, not only are more spores likely to be available to infect the crop, they are also more likely to infect the crop at an earlier growth stage and under conditions that are more favorable for disease development. Let us use gray leaf spot as an example. In a “normal” year, although lesions may develop early in the season, this disease typically takes off and spreads after pollination (VT/R1) when the number of spores in the air is high and the weather becomes favorable for infection. Depending on where you are in the state, VT/R1 usually occurs sometime in mid-July. Planting late does not prevent spores from building up or conditions from becoming favorable for the gray leaf spot fungus to infect plant in mid-July, however, the primary difference it that instead of infecting plants at the VT/R1 growth state, the fungus will be infecting plants at a much earlier growth stage, V8-V12, for instance. If the hybrid is susceptible and conditions become favorable, high levels of infection at V8-V12 will result in greater and more rapid diseases development, and consequently, greater damage to the upper leaves before grain-fill is complete. This is also true for NCLB, eye spot, and southern rust.

So, what should I do:

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A more normal pattern ahead into August

Source:  : Jim Noel

June and July together for Ohio will go down as 1-2 degrees warmer than normal and rainfall will go down on average as 100-175% of normal. However, details and timing matter. Looking at July only, rainfall will go down as 75-100 percent of normal over the southwest part of the state while the northern and east will down down as 100-150% of normal.

Average Temperature: Departure from Mean June 1, 2019 - July 27, 2019

Accumulate Precipitation: Percent of Mean June 1, 2019 - July 28, 2019

Over the next two weeks rainfall will be at or slightly below normal in the 1-2 inch range. Rainfall is expected into Tuesday July 30. After that rain event, the next will not occur until about August 6 or 7. The good news is temperatures will be close to normal over the next two weeks. There will be a burst of above normal temperatures this coming weekend though.

Accumulated Precipitation: Percent of Mean June 1, 2019 - July 28, 2019

Corn of Many Colors

Source: Alexander Lindsey, Steve Culman, Peter Thomison, OSU Extension

As corn is emerging and beginning to grow, we are again seeing many colors present. In any given field, corn can appear dark green in sections, while other sections are yellow and occasionally purple. Yellowing (due to low nitrogen or sulfur uptake and/or limited chlorophyll synthesis) or purpling (reduced root development and/or increased anthocyanin production) of corn plants at this stage of development generally has little or no effect on later crop performance or yield potential. If it’s induced by environmental conditions, the yellow or purple appearance should change to a healthy green after a few sunny days with temperatures above 70 degrees F (and as soils dry). If plants remain yellow then closer inspection and assessment is needed to determine if the yellowing is caused by nutrient deficiency or some other factor. Cooler wet conditions often increase the appearance of these different colors. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool.

 

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Mid to Late June Prevented Planting Decisions

Source:Ben Brown, Sarah Noggle, Barry Ward, OSU Extension

Consistent rains across Ohio and the Corn Belt continue to delay planting progress as the June 17 USDA Planting Progress report showed that 68% of intended corn acres and 50% of intended soybean acres have been planted in Ohio. Nationwide, roughly 27 million acres of corn and soybeans will either be planted or filed under prevented planting insurance. Across Ohio, the Final Plant Date (FPD) for soybeans is June 20. Soybeans can be planted after the FPD, but a one percent reduction in the insurance guarantee occurs. This brief article outlines economic considerations for soybean prevented planting under three scenarios: planting soybeans on corn acres, planting soybeans late, and taking prevent plant soybeans. There are three sections to this article: a brief market update on corn and soybeans, a policy update on Market Facilitation Payments, and then finally the scenarios listed above. This article contains the best information available as of release, but conditions may change. Farmers should check with their crop insurance agents when making prevented planting decisions. OSU Extension is not an authorizing body of federal crop insurance policies.

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How to store treated seed

Source: Anne Dorrance,  OSU Extension

Let me say upfront that much of the information in this piece is based on a study published (Crop Science 53:1086-1095 in 2013) by Dr. Susan Goggi’s lab and others at Iowa State University, Dept. of Agronomy & Seed Science Center. As a scientist, we store both untreated and treated seed over years, but it is healthy and it is in cool and always dry conditions.  But this year we have several issues.  The seed raised in 2018, due to the rains through our long drawn out harvest, left a lot to be desired.  Last week, we had one day to plant and now we are making decisions on what to do with the seed we purchased that is treated.  Treated seed cannot enter the market and must be disposed of through planting, incineration, or burial based on the label. All of these are costly.

In a study at Iowa State, they compared 24 different seed lots which were treated with a fungicide, fungicide plus insecticide and not treated under 3 conditions: 1) a warehouse; 2) a climate controlled cold storage (50 F, ~60% RH); or 3) warm storage (77 F, ~31 % RH). The seed itself was high germination (95 to 98% germination), dry (<8%), and there was a very low percentage of seedborne pathogens.

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