C.O.R.N. Newsletter: 2016-12

Is it still worth putting on a fungicide? If so, what would be the best time to put it on? Via phone, email, or in person, these have been the most frequently asked questions over the last 5 days. The short and simple answer is “it depends”. Some fields have been hit by stripe rust while others have been hit by freezing temperatures, all within the last 7 day. Understandably, most people were planning to hold off on making a fungicide application until flowering (anthesis: Feekes 10.5.1) to get the best control of head scab and vomitoxin. Several of the fields affected by stripe rust are still between Feekes 10 (boot) and 10.5 (heading), at least a week before flowering. Since it is never really profitable to make multiple fungicide applications to wheat, the question now becomes, should I apply a fungicide now (at Feekes 10.5) to control stripe rust or should I just wait until Feekes 10.5.1 to target head scab.

You should base your decision on how much rust is in your field, your current growth stage, the scab forecasting system, and the scab resistance of your variety. If stripe rust is on the flag leaf in multiple hot spots across the field, you should consider applying a fungicide since this is a very explosive diseases and the weather is favorable for its spread. You already have rust but do not know if you are going to get scab. If you are close enough to flowering (at 10.4-10.5), you will get some scab suppression if you apply now, but remember that you usually get better scab control with applications at 10.5.1 (early flowering) or 2-6 days after 10.5.1, than with applications at 10.5 (3-5 days before 10.5.1). Keep in mind that high levels of rust before or during flowering usually have the greatest impact on yield. Rust causes losses by reducing the number of kernels per head and the size of the kernels, and by lowering test weight (Factsheet PLPANT-CER-12). Scab, on the other hand, causes losses by reducing the size of the kernels, lowering test weight and contaminating grain with vomitoxin (Factsheet PLPANT-CER-06).

Before making your fungicide decision, take a look at the scab forecasting system (www.wheat scab.psu.edu) to see what the risk is. For wheat flowering today (May 16), the forecasting system says that the risk for scab is moderate on susceptible varieties across most of the state, and will likely decrease over the next few days because of the cold snap. On moderately susceptible and moderately resistant varieties, the risk is low today and over the next three days (Factsheet PLPANT-CER-03). The forecasting system is 80% accurate, meaning that it is correct more than 3 out of 4 times. 

Things to consider:

1- Find out if the variety in your field is moderately resistant or even moderately susceptible to scab, if it is, then the risk for scab is predicted to be low over the next few days. Consider applying a fungicide now to control rust and keep your eyes on the scab forecasting system to see if the risk increases. Moderate scab resistance (or moderate susceptibility) + the Feekes 10.5 application of Prosaro or Caramba for rust control should help to suppress scab, but keep your eyes on the forecasting system.

2- If your variety is susceptible to scab, but you are still at Feekes 10.5 the forecasting system indicates that the risk for scab will likely decrease (due to the cold weather) by the time the crop start flowering. Consider applying the fungicide now to control rust and keep your eyes on the scab forecasting system to see if the risk increases. 

3- If your variety is susceptible to scab and you are already at Feekes 10.5.1, an application made at this time will help to control both scab and stripe rust. 

4. If your variety is susceptible to scab, you are still at Feekes 10.5, and you want to consider making two application (one for rust and second for scab), consider using a cheap but effective rust fungicide (propiconazole for example) and leave your best scab fungicide (Prosaro or Caramba) for the second application at Feekes 10.5.1.

5. At this point, it is hard to tell whether the recent cold snap (May 15) will severely damage the wheat crop to the point of making a fungicide investment worthless. The level of damage will depend on how cold it got, for how long, the specific variety (some are more cold-temperature-tolerant than others), and how much of the field is affected (see Assessing the Wheat Crop for Freeze Damage and Twisted Wheat: Cold temperatures or herbicide damage?). It may take up to 7-10 days before the level of freeze injury can be determined. Whether or not you choose to wait to assess the damaged before applying a fungicide, you can still use suggestions 1 to 4 above as a guide for making the fungicide decision. 

Last week, we received a few reports from northwest Ohio of twisted wheat flag leaves.  Twisted wheat leaves could be a result of either cold temperatures or 2,4-D herbicide damage.  To determine the cause of the twisting, consider patterns in the field, recent weather, and herbicide program.

Cold Temperature Damage.  Three things to consider about a freeze event: How cold was it? How long was it cold? and What growth stage was the crop?

A frost is when a layer of cold air settles into low areas, reducing temperatures below the dew point, often just above or below 32°F.  This causes water to be released from the air and freezes on cold surfaces.  A freeze is when a body of cold, dry air moves in and temperatures drop below freezing, often accompanied by a breeze.  In wheat a hard frost can often burn leaf tips, but a freeze can damage leaves, heads, stems, and even kill the growing point.  The length of the freeze can also increase the severity of the damage.  

As wheat breaks from winter hardiness, it loses cold tolerance with each growth stage.  In our current freeze study, wheat plants were collected from the field at different growth stages and subjected to five different temperatures: 39°F (control), 27°F, 21°F, 14°F, and 5°F.  At Feekes 5 (erect growth) and 6 (first node), it could endure temperatures as low as 5°F and 14°F.  At Feekes 8 (flag leaf visible), wheat was able to tolerate temperatures of 24-25°F.  The picture on the left is wheat subjected to 27°F for 15 minutes at Feekes 9 (flag leaf fully emerged). Ten days after the freeze, more than half of the flag leaves were severely damaged with twisting, yellowing, and death.  The flag leaf accounts for 75% of the plant’s photosynthetic source for seed fill, so depending on the extent of damage, yields may be reduced.  Another common symptom of freeze damage at this stage is the head becomes lodged in the leaf sheath and breaks as it is forced out. This can impact seed formation and seed fill, also reducing yield. This damage starts to occur at 30°F. Producers are urged to monitor the health of the flag leaves after any freeze to determine crop damage.  

Herbicide damage.  Late applications of 2,4-D can cause injury to wheat and yield loss.  Some 2,4-D labels specify that application should occur before jointing, but others allow application after jointing but before early boot stage.  In our limited research on this, we have not observed yield loss from 2,4-D applied prior to early boot stage, except when UAN was used as the spray carrier.  It is possible to have yield loss occur from a late application, without really seeing symptoms such as leaf twisting. 

Reference.  Shroyer, J.P., M.E. Mikesell, and G.M. Paulsen.  1995.  Spring Freeze Injury to Kansas Wheat.  Agricultural Experiment Station and Cooperative Extension Service.  Available at:  http://www.ksre.k-state.edu/bookstore/pubs/C646.PDF

Cold, wet conditions have delayed corn planting throughout Ohio. According to the USDA/NASS (http://www.nass.usda.gov/), for the week ending May 15, corn was 34 percent planted, which was 37 percent behind last year and 20 percent behind the five-year average.

Long term research by universities and seed companies across the Corn Belt gives us a pretty good idea of planting date effects on relative yield potential. The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. In the central Corn Belt, estimated yield loss per day with delayed planting varies from about 0.3% per day early in May to about 1% per day by the end of May (Nielsen, 2015). These yield losses can be attributed to a number of factors including a shorter growing season, greater disease and insect pressure and higher risk of hot, dry conditions during pollination.

Given these planting date effects, do yield losses associated with late plantings translate into lower statewide yields? Not necessarily. Let’s consider some previous growing seasons that were characterized by a “late start” and what impact this had on crop production. For the purposes of this discussion I’ll consider “late start” years as those in which 40% or more of the corn acreage was not planted by May 20. Since 1980, there have been significant planting delays associated with wet spring weather in nine years – 1981, 1983, 1989, 1995, 1996, 2002, 2008, 2009, and 2011. Table 1 shows the percentage of corn acreage planted by May 20 and May 30, the 50% planting date (the date by which 50% of the corn acreage was planted), yield, the state average yield for the previous five years, and the departure from the yield trend in each of those years. Of these nine years, the greatest delays in crop planting occurred in 2011 when only 19% of the corn acreage was planted by May 30. In five of the nine years (1981, 1983, 1996, 2002, and 2008) average state yields were markedly lower than the state average yield of the previous five years (In six of the  nine years, average yields were five bushels per acre or more below the yield trend line for Ohio). In one of these years, 2002, the average corn yield dropped to 88 bushels per acre (nearly comparable to the record low of 86 bushels per acre for the major drought year of 1988). However, in four of the nine years, yields were similar or higher than the statewide average yield of the previous five years, and in one of these years, 2009, a record high corn yield, 174 per acre, was achieved. 

This comparison of statewide average corn yields from past years indicates that lower grain yields are not a certainty with late plantings. While delayed planting may cause yield loss relative to early planting, planting date is just one of many factors that influence corn yield. Figure 1 shows grain yields associated with dates by which 50% of the corn acreage was planted in Ohio from 1980 to 2012 and it does not suggest a strong relationship between planting date and yield. There are other factors that are of greater importance than planting date in determining grain yield. Weather conditions (rainfall and temperature) in July and August are probably the most important yield determining factors. Favorable weather conditions subsequent to planting may result in late planted crops producing above average yields as was case in 2009. However, if late planted crops experience severe moisture stress during pollination and grainfill, then crop yields may be significantly lower than average, with 2002 being the most notable example in addition to 1981, 1983 and 1996. 

References
Nielsen, R.L. 2015. The Planting Date Conundrum for Corn.  Corny News Network, Purdue Univ. [online] https://www.agry.purdue.edu/ext/corn/news/timeless/PltDateCornYld.html [URL accessed May 16, 2016].

Getting our first cutting of forages this year seems to be shaping up to be another frustrating experience, although we can only hope it won’t be as bad as last year. The outlook for the end of May does not look very promising for a nice stretch of dry weather. While the recent cool weather has slowed development and growth of our forage crops, in central Ohio forage grasses are entering or already well into the heading stage and alfalfa is beginning to show buds. So it is time to start thinking about that first harvest soon, along with getting corn and soybeans planted!

Last year in the midst of very rainy weather I urged hay producers to “be patient, to make sure their hayfields were dry enough to support their equipment before they try to get out on them once the sun starts to shine again.”  I heard how some tore up their fields and lost stands. The alternative is to be patient and to lose forage quality as the stand matures. But I still think the complete loss of the value of one cutting is a better choice than ruining a forage stand for the remainder of its potential productive life by running equipment on ground that is too soft, especially if it is a younger stand. So let me repeat what is indeed easy for me to say, but super hard to put into practice – be patient, take the long look and wait until the field is dry enough to support the equipment without damaging the forage stand.

There are some management steps that can reduce the field curing time once the hay is cut. First, adjust your mower to lay as wide a windrow as possible in order to maximize the surface area exposed to the sun. The picture accompanying this article shows narrow windrows, which is not what you want. Try to get windrows that cover 65-70% of the cutting swath. Follow the manufacturer’s guidelines to adjust the crimping rollers or the clearance of the flails on flail conditioners. Do not assume the mower is adjusted correctly for this spring’s crop, check it and make sure the mechanical conditioner is doing a good job. Tedding soon after mowing (usually the same day or early the second day) can also be a good option to maximize forage surface area exposure to the sun. Tedding is especially a good option for grasses because it does not cause the leaf loss in grasses that can result with legumes.

Using chemical desiccants this time of year tends to be risky because they are less effective under cool and moist conditions than under good drying conditions. A more reliable option in the spring is to apply a proprionic acid preservative as the crop is being baled because it allows you to bale at slightly higher moisture contents. Follow the manufacturer’s guidelines for recommended rates (product formulations vary), but you should be applying the equivalent of 10 lbs of actual proprionic acid per ton of forage being harvested.

Consider making balage or silage rather than dry hay on first cutting if at all possible. For upright silos or bags, wilt the crop to 30 to 50% dry matter (50 to 70% moisture) and for balage to 40 to 55% dry matter (45 to 60% moisture). This significantly reduces the curing time compared with drying down to 80 to 85% dry matter (15 to 20% moisture) that is necessary for dry hay, depending on the hay bale size. When making hay crop silage or balage from legumes in the spring (alfalfa and clover), consider using a lactic acid bacteria (LAB) inoculant to improve fermentation. Naturally occurring populations of LAB can be too low when legume crops are wilted under cool and/or short wilting periods.

Producing seed of forage species is not common in Ohio, because our climate is not as conducive to high yields of high quality seed of forages as in western and northwestern states. But each year around mid-July to early August I usually get a few questions about how best to produce red clover seed here in Ohio. Although seed produced by reputable seed dealers out west is of higher quality than what we can produce here in Ohio, there are a few management steps that will help improve the yield and quality of seed produced here in our region. Some of those steps begin with the first cutting of the year, which will soon be upon us. I will highlight a few key steps in this article, but for more details please refer to a factsheet from the University of Kentucky entitled “Producing red clover seed in Kentucky”, available online at http://www2.ca.uky.edu/agcomm/pubs/agr/agr2/agr2.pdf.

Cutting management – It is best to harvest seed from a red clover stand in the first full production year after a spring seeding (in second or third year of the stand). In the year you want to produce seed, the first crop should be harvested for hay because it will have too much vegetative growth for good seed yield and spring conditions are usually too wet for producing good quality seed. Timing of the first hay cutting is very important – first cutting should be made no later than 10 to 15 days after the first sign of blooms appear in the field. Delayed cutting will weaken the stand and reduce the seed yield produced later in the summer. The seed harvest should be made on either the second or third harvest when summer conditions are usually more conducive to seed production in Ohio.

Weed management – Many broadleaf weed seeds are difficult to clean from red clover seed, so areas harvested for seed should be as free of weeds as possible. About the only broadleaf herbicide option available for red clover is 2,4-DB and it does not control well-established broadleaf weeds and has a limited range even for seedling broadleaf weeds. So it is important to establish and maintain a vigorous red clover stand from the beginning if seed is to be harvested from the field. It the area to be harvested for seed is relatively small, the most feasible way to keep weed seeds out of the clover seed is to rogue them out by hand prior to seed harvest.

Pollination – Seed production in red clover is highly dependent on insect pollination, which occurs primarily through bumblebees in Ohio. It is important to use insecticides cautiously to prevent reducing the population of pollinators. It might pay to set a couple hives of bumblebees near the field during flowering.

Harvesting seed – You can thresh the heads in your palm to check the condition of the seed, but it will be ready for harvest when the majority of the seed heads are brown or black. Seed can be harvested by combining directly or after windrowing. Results from University of Kentucky trials indicate that there is no great advantage to using chemical desiccants provided the seed heads are dry and the combine screens and airblasts are set as recommended by the manufacturer. Chemical desiccation (e.g. with paraquat) might be advisable if the field is excessively weedy.

Seed storage and processing – It is critical that seed be dry enough to prevent heating. Heating will dramatically reduce the germination of the seed. Seed cleaning is also very important because seed harvested by combine will not be clean enough for planting. Refer to the factsheet referenced below for more details on these two important management steps.

Reference

Taylor, N.L., D.M. TeKrony, and J. Henning. 1996. Producing red clover seed in Kentucky. Univ. of Kentucky Coop. Ext. Serv. Factsheet AGR-2. Available online at http://www2.ca.uky.edu/agcomm/pubs/agr/agr2/agr2.pdf.