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Corn Newsletter : 2015-14
Watch Wheat for Head Scab and Cereal Leaf Beetle
We are now well into the late-heading and early-flowering growth stages, and understandably, folks are concerned about head scab and vomitoxin. Questions keep coming in about applying fungicides for scab control, particularly when and whether a fungicide is needed. The forecasting system (http://www.wheatscab.psu.edu/) shows that if your wheat flowered over the holiday weekend (May 22- May 25) or is flowering today (May 26), and your variety is moderately susceptible or moderately resistant, the risk for scab is low. Low risk usually means that a fungicide treatment is not warranted. This low-risk forecast is probably due to the fact that it has been relatively dry over the last week or so. Although temperatures have been in the favorable range for head scab development, we have had little rain since May 17. Dry conditions combined with moderate cultivar resistance help to keep the risk of scab down. However, flowering will continue across central and northern Ohio over the next 7 days, so continue to keep your eyes on the weather and the forecasting system to see if the risk for scab increases as your crop begins to flower. A fungicide application could be needed if conditions become favorable.
Questions are also being asked about cereal leaf beetle, as the numbers have increased over the past week. The larvae are the most damaging stage and can cause leaf stripping (already seen in some fields) from their feeding. They are small, dark and moist and closely resemble bird droppings. But don’t be fooled, these larvae can do heavy damage to a field, causing substantial yield reduction, particularly if the flag leaves are badly damaged before grain-fill is complete. To determine if a spray is needed, randomly inspect 50 stems in your field. If the average number of larvae is greater than 1 or 2 per stem, you may want to consider treatment.
Several products are available for both scab and cereal leaf beetle control (see Bulletin 545 for a list of insecticides:http://oardc.osu.edu/ag/images/545_Final_2013(3).pdf ). Tank mixing is an option if your field has both scab and cereal leaf beetle—please review pesticide labels before any application and make sure your products are compatible.
Wheat Flowering Growth Stage
Wheat continues to go through the heading and flowering growth stages across central and northern Ohio. Depending on the weather and the variety, flowering usually occurs about 3-5 days after full head emergence (Feekes 10.5) – earlier under warmer conditions and delayed by up to 5 or more days after heading under cooler conditions. Flowering is marked by the extrusion of anthers from the spikelets; the reason for which this process is also referred to as anthesis. Flowering will continue over the next 7-10 days. The identification of this growth stage is very important for the management of Fusarium head blight (head scab) with fungicides.
1- Closely examine the heads (also called the spike) of primary tillers at multiple locations in the field for the presence of anthers – often seen as a yellowish (or other color) part of the flower hanging from the spikelet;
2- If no anthers are seen, then your wheat may still be at the heading growth stage, Feekes 10.5;
3- If the first few anthers are seen hanging from florets/spikelets in the central portion of the spike, your wheat is at Feekes 10.5.1 - early flowering or early anthesis;
4- If anthers are seen hanging from florets/spikelets in the central and top portions of the spike, your wheat is at Feekes 10.5.2 - mid-flowering or mid-anthesis;
5- If anthers are seen hanging from florets/spikelets along the entire length of the spike, your wheat is at Feekes 10.5.3 - late-flowering or late-anthesis;
Note: When trying to identify these growth stages, based your assessment on the presence of fresh (brightly colored) anthers, since dried, discolored, and spent anthers may remain hanging from the spike well after Feekes 10.5.3 and well into grain filling stages of development. This can be misleading.
Click on the links below for information on management practices that are recommended (or not recommended) at these growth stages: http://ohioline.osu.edu/agf-fact/pdf/0126.pdf
Link to video: https://youtu.be/ybZVW_YbhxY
Residual Herbicide Issues – were they applied, are they working, what to doAuthor(s): Mark Loux
While a variety of rainfall and soil moisture conditions can be found around Ohio, a shortage of rain following application of residual herbicides seems to be common. We are hearing about weeds emerging early in the season even where residual herbicides were applied, which is an indicator of inadequate herbicide “activation”, or lack of downward movement into the upper inch or two of soil where weed seeds germinate. Herbicides vary in the amount of rain required for activity, due to differences in water solubility and adsorption to soil, and whether absorption into the plant occurs via roots or shoots. Ignoring all of this though, the general rule is that a half to one inch of rain is needed within about a week after application to ensure activity. Some considerations for this situation:
- Later rain will cause residual herbicides to eventually become active, but by then weeds may have already emerged through the thin layer of herbicide on the soil surface. There is the possibility of “reachback activity” from some herbicides, where emerged weeds are controlled, due to uptake of herbicide by roots. In our experience, this is erratic and not that reliable unless weeds are very small.
- Escaped weeds will usually require treatment with postemergence herbicides. Applying POST when weeds are small ensures more effective control and prevents interference with the crop. Keep in mind that where residual herbicides have largely failed, we defer to the basic principles of weed removal timing for total POST systems. Weeds in corn should be removed before they exceed 2 inches in height, and in soybeans before they exceed 4 to 6 inches in height (giant ragweed will typically be larger than the rest of the weeds). There is probably some flexibility in these sizes where the residual herbicides had enough activity to substantially reduce weed populations, so this can be somewhat of a judgement call.
- Be sure the postemergence herbicides fit the weed population. Residual herbicides typically remove many weed species, leaving one or two that are then targeted with POST herbicides (e.g. giant ragweed, marestail, morningglory). Where residual herbicide activity is reduced, the full complement of annual weeds can be present, requiring a more comprehensive POST herbicide treatment.
There are also fields with emerged corn where no herbicide has been applied yet.
Most residual corn herbicides can be applied to emerged corn, and some of them have enough foliar activity to control small, emerged weeds without the need to add postemergence herbicides. In addition, the majority of the corn hybrids are resistant to glyphosate and/or glufosinate (Liberty), which can be combined with residual herbicides to control weeds emerged at the time of application. It’s also possible to mix in some other POST herbicides such as Impact, dicamba, 2,4-D, Capreno, etc to control emerged weeds, instead of glyphosate or Liberty. Some issues to be aware of with regard to postemergence application of residual corn herbicides follow.
- Only Degree and Degree Xtra can be applied using 28% as the spray carrier once corn has emerged. All other herbicides should be applied in water. Degree Xtra and Degree can be applied in 28% on corn up to 6 inches tall, when air temperatures are less than 85 F. Expect some leaf burn from these mixtures.
- There is usually a maximum corn size specified, which can be based on growth stage or corn height. This can be as small as the V2 stage for some herbicides, such as Corvus and Balance Flex. This information can be found in the herbicide description section of the “Weed Control Guide for Ohio, Indiana, and Illinois”.
- Most premixes or tank mixtures that contain atrazine can adequately control small broadleaf weeds, and especially those that contain another broadleaf herbicide (e.g. Lexar, Lumax, Instigate, SureStart). Grasses more than about an inch tall will require the addition of glyphosate, Liberty, or other herbicide with effective grass activity.
- Follow adjuvant recommendations closely to minimize the risk of injury and do not assume that it is always possible to use an adjuvant once corn has emerged.
- Based on our research with this type of approach to herbicide management, herbicides should be applied when weeds are less than about two inches tall to ensure that they have been prevented from causing yield loss.
- We find that herbicide labels can lack enough information on adjuvants and tank-mix partners for this situation. Be sure to check with dealers and manufacturer/distributor agronomists to get specific information when necessary.
The situation in soybeans is vastly different than in corn, since most residual soybean herbicides cannot be applied once the soybeans have emerged. Failure to apply residual herbicides in soybeans typically results in the need to apply POST earlier in the season, which can result in the need for a second POST application to control late-emerging weeds. This can sometimes be avoided by applying an early POST treatment that has some residual. Several residual soybean herbicides can be applied early POST, and several POST herbicides do have some residual activity. These include the following: Pursuit (also in premixes with glyphosate such as Extreme and Thundermaster); FirstRate; Flexstar and the generic equivalents (also in premixes with glyphosate and metolachlor and Pursuit); metolachlor (Dual, Parallel, etc); and acetochlor (Warrant). None of these provide residual control of most marestail populations, and it’s about impossible to obtain enough residual control of all the giant ragweed that can emerge after an early POST application. Making a second POST application is a more effective strategy for giant ragweed usually.
There is a brief in-field video covering POST application of residual corn herbicides on our Youtube site (search for “Ohio State University weed science”), or at this link: https://www.youtube.com/watch?v=njl4MPL5H4I. You can also subscribe to the Youtube page, and be automatically notified of future videos. Another recently added video takes a first look at studies on various strategies for management of marestail in Enlist and Xtend systems.
Corn Planting Nearing Completion – Time to Troubleshoot Emergence Problems
According to the USDA/NASS (http://www.nass.usda.gov/) for the week ending May 24, corn was 87 percent planted, which was 21 percent ahead of last year and 17 percent ahead of the five-year average. Across the state, corn is at a range of growth stages. Some of the corn planted in early May is showing up to three leaf collars but in later planted fields, corn is still emerging.
Troubleshooting emergence problems early is critical in identifying solutions and developing successful replant plans, if needed. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring. (Some of this information has been adapted from a newsletter article written by Dr. Greg Roth, my counterpart at Penn State several years ago).
-No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.
-Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.
-Seed with poorly developed radicle (root) or coleoptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor. Although corn has just started to emerge or has not yet emerged in many fields, growers should carefully inspect seedlings for symptoms of disease, especially in lower lying areas of fields where ponding and saturated soils were more likely. Seeds and seedlings that are brown in color, are soft and fall apart easily while digging are obviously dead or dying. Seeds and seedling roots or shoots with white to pinkish mold growing on them are likely victims of fungal attack and will likely die. Pythium and Fusarium are common fungi that attack plants and cause these damping-off or seedling blight symptoms under wet, cool conditions. It is more difficult to diagnose disease damage on plants that also show abnormal growth caused by cold soil conditions or by crusting of the soil surface. However, dark, discolored roots and crowns, instead of a healthy creamish-white appearance, are typical symptoms of seedling diseases problems. So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet.
- Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.
-Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.
-Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.
-Uneven emergence. May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Shallow planting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.
Note patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.
Don’t forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). This was widely observed in many fields in 2005 when corn planted in mid April did not emerge until the first or second week of May. As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential often reduced.
Purple and Yellow Corn, What is Going On?
Corn seedlings often turn yellow (due to low nitrogen uptake and/or limited chlorophyll synthesis) or purple (reduced root development) under cool, wet conditions. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool. Yellowing or purpling 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. If plants remain yellow then closer inspection and assessment is needed to determine if yellowing is caused by nutrient deficiency or some other factor.
Environmental conditions (high rainfall causing saturated soils) can lead to the appearance of yellow corn. The visual appearance may be interpreted as N deficiency, but this is rarely the case. Excessive water leads to poor respiration of the roots inhibiting nutrient uptake. This results in the chlorotic appearance which resembles N deficiency. After soils dry out, the appearance returns back to normal. If the chlorotic condition persists after the soil dries, the problem should be investigated further. This short-term condition should not affect yield potential of the crop.
When you combine recent cool nighttime temperatures, high radiation levels during the day, and wet field conditions, you are likely to start seeing purple plants in some corn fields. The first thing that may come to mind is a phosphorus deficient soil. This is unlikely the case, especially this early in the year. The purple tint is more attributable to the production of anthocyanins which is a plant response to a stress or a combination of stresses. Cool temperatures, high solar intensity, and water stress (drought and water-logged conditions) combine to inhibit root growth. Other factors including soil compaction, herbicide injury, etc. can make the effect even more pronounced. Purple corn can also be the result of what is known as the “fallow syndrome.” If corn follows a fallow season, a root fungus called mycorrhizae reaches a low population. Mycorrhizal infection of corn aids in phosphorus and zinc uptake. Until the fungal growth is stimulated by the corn roots, which exude starches and sugars, the purple color may persist. Fortunately, the purple tint is short-lived and rarely persists beyond the V6 growth stage. It should not have an impact on the yield potential of the field.
NOAA Lake Erie Algal Bloom ProjectionAuthor(s): Jim Noel
The National Oceanic and Atmospheric Administration has combined data from the National Center of Coastal Ocean Science and Heidelberg University's National Center for Water Quality Research to predict the severity of harmful algal blooms in western Lake Erie. The first projection is as follows:
The severity of the western Lake Erie cyanobacterial harmful algal bloom (HAB) is dependent on phosphorus inputs from March 1st through July 31st, called the loading season. This new experimental product projects the bloom severity based on the combination of measurements of discharge and phosphorus loading from the Maumee River for the loading season to date with historical records from past years to estimate the remainder of the loading season.
Based on 10 weeks of data (March 1- May 3), the extensive severe blooms observed in 2011 and 2013 are not projected to occur this year. The current load is below that of 2014 at this time. However, there is still a large uncertainty in the projection because the loading season is only about halfway through. This uncertainty will reduce over time as the loading season progresses.
This experimental product uses the Maumee River phosphorus load data from Heidelberg University’s National Center for Water Quality Research and the western Lake Erie bloom severity models by NOAA’s National Center for Coastal Ocean Science.
For the full report, please visit: http://www2.nccos.noaa.gov/coast/lakeerie/bulletin/archive/2015/projection_2015-01.pdf
Weather Update May 26, 2015Author(s): Amanda DouridasThe weather pattern will be shifting to a warm and humid pattern with wetter than normal conditions going into June 2015.Temperatures the next 4 weeks will average a few degrees above normal. The maximum temperatures will likely be to close to normal but with increased humidity and cloud cover minimum temperatures will be held up. This will result in overall temperatures being above normal. This will also result in increased dew overnight into the morning hours for extended periods.The risk for significant 90+ degree days will be REDUCED with more cloud cover, rain chances and higher humidity.Rain chances will be above normal the next 3-4 weeks as a southwest flow above the ground will promote a flow of moisture from the Gulf of Mexico. Rainfall patterns will be scattered as are common in the warm season but overall rainfall will be at or above average. Normal rainfall is between 0.75 inches to just under 1 inch per week.June Outlook:Maximum Temperature RISK above 90: Low to moderateMinimum Temperature RISK above 65: HighFlood RISK: Low to moderateDrought RISK: LowRainfall RISK Above Normal: ModerateFrost RISK: NoneNOAA Temperature outlooks can be found here:NOAA Rainfall outlooks can be found here:
In An Instant: Buried Alive
The ABC network television show In An Instantwill be replaying the Buried Alive episode on Saturday, May 30 at 9:00 pm. This episode features Arick Baker, a 23 year old farmer from Iowa, who was completely buried in his grain bin for over two hours and was fortunately rescued. Some farmers who saw the episode during its first run said it was very eyeopening to watch. The episode can also be viewed online at anytime at: http://abc.go.com/shows/in-an-instant.
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.
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