C.O.R.N. Newsletter 2011-12

Dates Covered: 
May 10, 2011 - May 16, 2011
Editor: 
Glen Arnold

The Weather Pattern is Beginning to Change

The weather pattern is beginning to change. As we had discussed since last summer, we had expected a very wet late winter into spring with La Nina and the negative North Atlantic Oscillation and we got it. Now, we expect La Nina to end by June but the effects will likely linger into at least early summer.

The rest of May will see improving conditions from what we saw in April and very early May. The outlook for the rest of May is as follows:

May 9-14 - Temperatures will average about 6 degrees above normal with rainfall near normal. Best chance for rain will be Monday night and Tuesday in the west half and late week into the weekend. Covered will be more scattered and rainfall variability will be much higher than we have seen due to the warmer late spring weather pattern.

May 15-21-Temperatures will average near normal and rainfall above normal. Rainfall normally is near 1 inch for a week. Expect 1 inch west to 2 inches east on average but again variability will be high.

May 22-28 - Temperatures will average 5-10 degrees above normal as a large dome of high pressure builds in shifting the heaviest rains into the western corn and soybean belt. Rainfall is forecast to be below average.

Confidence in the summer outlook has been lowered. One of the best year to analog historically to may be 2008. The outlook will likely be for near normal rainfall trending to drier than normal by late summer. Temperatures are tricky. Near normal is forecast but anything may go. As soon as we gain confidence in the outlook in the next few weeks we will let you know.

Review of the week: What does probability of rainfall mean? When there is a 70% chance of rain, it means that historically at a given point for a given period of time (say 12-hours) 70% of the time with similar weather patterns we saw .01 of rainfall. A 20% chance of rain does not mean less rainfall totals than a 90% chance of rain. You can think of it more like an areal coverage (even though that is not exactly correct either since it is for a given point) for receiving at least .01 inches of rainfall for a given period of time, usually 12-hours. It also does not tell you how long it will rain. A 90% chance of rain does not mean it will rain all day. It simply means for a given say 12-hour period, it is very likely you will receive .01 of an inch or more of rainfall. You may receive .02 inches or 1.12 inches. Often times, rain chances are mis-interrupted.

Wheat Disease Management as we Approach Critical Growth Stages

In spite of a relatively slow start due of cool, wet conditions, the wheat crop has developed well and is now between the jointing (in the north) and boot (in the south) growth stages. At this rate of development, and with warmer weather in the forecast, flowering should begin within the next 10 to 20 days. More rain is also forecasted for later this week and early next week (May 13 – 18). Rain + warmer weather + wheat flowering = increased risk for head scab and vomitoxin. Early flowering fields in southern Ohio may be at risk within the next week or so and growers in those areas should be prepared to apply a fungicide at flowering to suppress scab. However, with flowering still several days away, things could change quickly, either increasing or decreasing the risk of scab. So, keep your eyes on the weather and the forecasting system (http://www.wheatscab.psu.edu) as we approach flowering.

In the meantime, remember, the wet conditions we have had so far this season and temperatures in the 60s and 70s for the next several days are also favorable for foliar diseases such as powdery mildew, Septoria, and Stagonospora blotch. Powdery mildew and Septoria are already very prevalent in some locations. Continue to scout your fields and be prepared to apply a fungicide to prevent these diseases from spreading and reaching the flag leaf, especially if your variety is susceptible and conditions continue to be favorable (wet and humid). Damage to the flag leaf caused by foliar diseases could result in reduced grain yield and quality. A foliar fungicide application between flag leaf emergence and heading usually provides the best control of these diseases; however, this relatively early application WILL NOT provide adequate protection against scab and vomitoxin if favorable conditions occur during flowering and early grain fill. Fungicide application for scab and vomitoxin suppression MUST be made at flowering.

An updated fungicide efficacy chart with a list of products labeled for wheat, efficacy against foliar and head diseases, application rates, and pre-harvest intervals can be found on the field crops diseases website: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf.

Fungicide Application and Vomitoxin Suppression

Fungicides do suppress vomitoxin, but do not expect 100% control. The best results in term of head scab and vomitoxin reduction are seen when 1) the most resistant variety is planted, 2) wheat follows soybean instead of corn or wheat in the rotation, and 3) a TRIAZOLE fungicide is applied at flowering when the risk of scab is moderate to high. When these three approaches are combined, more than 75% reduction in scab and vomitoxin can be expected, depending on the weather, compared to about 45-60% with fungicide or resistance alone. However, as you would realize, the first two of these management approaches should have been implemented in the fall at the time of planting. Although nothing can be done at this time about variety resistance and cropping sequence to reduce scab and vomitoxin, it is still important to know whether your variety is resistant or susceptible and whether your wheat crop follows corn, wheat or soybean in the rotation. This will help you to assess the risk of having problems with scab and vomitoxin in your field. Of course it all depends on the weather, however, if conditions are wet and humid at the time of flowering, fields planted with a susceptible variety after corn or wheat will be at a much greater risk for scab and vomitoxin than those planted with a moderately resistant variety after soybean.

The only in-season management approach for scab and vomitoxin suppression is fungicide application, and among the fungicides labeled for wheat, the triazoles are the most effective products. However, even the best triazoles, Prosaro and Caramba, only provide about 50-60% suppression when applied at flowering. Depending on the weather conditions, and the baseline level of disease and toxin, 50-60% suppression may be sufficient to avoid or reduce price discounts and dockage. For instance, 50-60% suppression would bring vomitoxin levels from 4-6 ppm to 2-3 ppm, or under more favorable weather conditions, from 8-10 ppm to 3-5 ppm. So, this is what you can expect, suppression, not 100% control. Efficacy is greatly reduced when applications are made before or after flowering, so expect little or no vomitoxin suppression from application made for foliar disease control between flag leaf emergence and heading.

Flowering is when anthers (the yellowish male part of the flower) are seen sticking out of the heads. This typically occurs 3 to 5 days after heading. Anthers first emerge in the central portion of the head – this is called early anthesis or early flowering and is the growth stage at which fungicides should be applied for best results against scab and vomitoxin. If conditions are warm, it takes less time between heading and flowering, however, under cooler conditions, it may take longer, up to 5 or more days after heading, and flowering may last for several days. Main tillers (main stems) usually flower first, followed by secondary tillers (side stems). So, the flowering pattern may vary from field to field, depending on the variety and local weather conditions. This variation affects the risk for scab and vomitoxin and fungicide efficacy against the disease and toxin. In general, a well-timed application to a field with a narrow flower window will likely provide better scab and vomitoxin suppression than a poorly timed application or an application made to a field that flowers over several days.

Adding Insecticide to Wheat Fungicide Sprays

With the wet and cool conditions that growers have been experiencing, we realize there will be a significant amount of fungicide spraying on the wheat crop over the next month. This happening is discussed in other articles by Pierce Paul and Dennis Mills in this issue of the newsletter.  We want to address information we are receiving that many growers will automatically add an insecticide to the mixture because 1) a spray application is already being done and 2) the addition of an insecticide is relatively cheap.

We want to make is clear that this is not a very good Integrated Pest Management, or IPM, approach to managing insect pest populations.  Indeed, in most wheat fields, there are no pests that will even get close to economic levels, assuming that they are in the field in the first place.  Aphid populations are rarely high enough to cause concern, and any virus transmission would have already occurred.  Although we had an initial concern with armyworm, word from Kentucky suggests that they perhaps will not be that high, and an insecticide spray might kill off all the predators and parasitoids that help keep armyworm under control (see adjacent picture for an armyworm with a parasitoid egg).  Cereal leaf beetle problems are still infrequent in Ohio.  And we would point out that all of these pests can be scouted for and managed if necessary.

We still maintain that an IPM approach is the best way to manage pests, protect beneficial insects, and promote good environmental sustainability.   While it is easy and cheap to apply insecticides, we urge growers to think about the overall benefit in NOT applying an insecticide.

They are very capable of surviving these long winters, and in many cases they do not germinate immediately in the spring.  They require a period of time where the soils remain wet for at least 2 weeks.  Based on earlier work at the OARDC, 2 weeks is required to get maximum germination of many of these oospores.  In 2011, in Ohio, we have now had 4 weeks of perfect conditions, to prime, many of these soil borne pathogens.

Management of these soil borne pathogens is best done at the very beginning – First: select soybean varieties with the best disease resistance package -  Rps1c, Rps1k, Rps3a, Rps6, PLUS high levels of partial resistance for Phytophthora sojae.  The second:  put a seed treatment on – at the right rate.  The low rate of Allegiance or Apron XL won’t touch Phytophthora.  Our field data suggests, that the best return on the seed treatment investment for Phytophthora is the high rate at 1.5 fl. oz/cwt of metalaxyl or 0.64 fl oz/cwt of mefenoxam.  At this rate, we have gotten a yield benefit over several years and locations of testing.  We will evaluate this again in 2011, in a couple of locations.  Note:  this is for the fields that historically have to replant due to seedling damping-off not submergent issues.

We also know from our data, that metalaxyl and mefenoxam are not effective against the full spectrum of watermolds.  In some cases, a strobilurin can help knock some of them back.  Different companies have different strobilurins – each of these also have a bit different spectrum of control.  We are currently confirming this in field evaluations.

Conditions are also right for Rhizoctonia, Macrophomina (charcoal rot), Fusarium virguliforme (SDS) and Fusarium graminearum (head scab of wheat/seedling blight of soybean).  The strobilurins will provide some reductions on all of these but do not provide total control; but Fludioxinil (Maxim) has the best data at the moment.  I don’t have Ohio data, but others are reporting that ipconazole is effective towards Rhizoctonia as well as Fusarium graminearum.

The best seed treatment is a mixture of several active ingredients that target each of the different types of seedling pathogens.  Here is a link http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/seed%20treatments%20April%202011.pdf, to our seed treatment sheet.

Supplemental Forage Options for Planting in Spring to Mid-Summer

Planting cool-season perennial forages may not be in the cards for many of us this spring, unless the rains turn off this week. Unfortunately, that doesn’t look likely. Last week I suggested May 15 as the cutoff date for trying to plant most cool-season perennial forages this spring. Planting later than that carries considerable risk of establishment failure from weed competition and summer stresses. But we do have several warm-season annual forage options that can be planted from late May to early July.

For anyone considering forages for silage, corn should be the first choice because of its high yields and energy content. Corn can be planted as late as mid- to late June for silage production, although planting late carries increased risk, especially if dry weather develops. Planting in May is of course much better. Nevertheless, June planted corn with adequate rainfall can produce more forage with greater feeding value than other summer annual grasses. If forage is needed before the ear is formed, corn can be green chopped. Even without the ear, the feeding value of corn will be at least equal to that of the other summer annual grasses and yields are likely to be higher.

Summer-annual grasses (eg. sudangrass, sorghum x sudangrass hybrids, pearl millet) grow rapidly in summer. When managed properly, these grasses can provide good quality forage. All these species can be planted from late May up to mid-July and will produce 3.5 to 5 tons of dry matter per acre assuming sufficient moisture is present for emergence and growth. Soils should be at least 60 to 65F before planting these species. Pearl millet is essentially free of prussic acid poisoning potential, while the sorghum species have the potential for prussic acid poisoning which varies by species. Nitrate toxicity is possible with all summer annual grasses. Refer to the Agronomy Guide for how to reduce these risks and for more details on establishment and management (http://ohioline.osu.edu/b472/0008.html).

Mixtures of summer-annual grasses and legumes such as field peas and soybeans are marketed by some seed dealers. The legumes generally improve protein content but only in the first growth when they are present. Because the legumes usually increase the seed cost, evaluate the cost to benefit ratio of purchasing mixtures with legumes vs. supplementing livestock with other protein sources.

Teff is a new warm-season grass option that can be used for hay, silage, or pasture. It has become popular among horse owners. In our test plots it produced about 3 to 4 tons of dry matter per acre from 3 cuttings (http://oardc.osu.edu/forage2008/table14.asp, http://oardc.osu.edu/forage2009/table11.asp). It too must be planted when soils are warm. It can tolerate drought-stressed as well as waterlogged soil conditions. For more details on managing this forage, see an excellent factsheet from Cornell University found at http://nmsp.cals.cornell.edu/publications/factsheets/factsheet24.pdf.

 

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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.