C.O.R.N. Newsletter 2009-13

Dates Covered: 
May 11, 2009 - May 19, 2009
Editor: 
Tim Fine

Wheat Head Scab Forecasting:

Authors: Dennis Mills, Pierce Paul

The wheat crop is currently at Feekes growth stage 10 (the boot growth stage when the heads are swollen in the leaf sheath of the flag leaf) in southern counties and should be heading out and flowering across the state over the next three weeks. Head scab is our biggest disease concern when the crop reaches Feekes growth stage 10.5.1 (the beginning of flowering when anthers are sticking out of the central spikelets). Scab develops best when wet, humid conditions occur during flowering. So, if it continues to rain as our crop flowers, the risk of scab will be high, especially if it warms up. The scab forecasting system is now up and running and should be looked at on a regular basis over the next three weeks to determine what the risk of scab is in your area.

Using The Scab Forecasting System: 1) Go to www.wheatscab.psu.edu and click on “Risk map tool”. The first page will be a user survey. Completing the survey is optional, but by doing so you will be helping the developers (Ohio State, Kansas State, and Penn State) to improve the forecasting system. 2) The next page provides some brief instructions on how to use the system. Read the instructions and then click the “OK” button. 3) Select your wheat class. In Ohio you should check the box next to “Winter” and then hit “OK”. Winter wheat is planted in the fall and begins to head in May. Checking the box next to “Spring” may give incorrect predictions of scab risk in Ohio. 4) Click on the map of Ohio and then 5) Choose the date your wheat field reached flowering on the calendar to the left of the map. For each flowering date you choose, the map will change to show the risk corresponding to that flowering date. Choosing an incorrect flowering date my lead to incorrect scab risk prediction for you field.

Using The Disease Triangle To Understand Scab Forecasting: The scab forecasting system was developed based on knowledge of how scab develops. For scab to develop, three conditions must be satisfied: 1) the wheat variety needs be susceptible to the disease and must be at the susceptible flowering growth stage; 2) the scab fungus (Fusarium graminearum) needs to be present and producing spores; and 3) the weather conditions need be favorable (wet and humid during flowering).

This is usually referred to as the disease triangle, but in our case we will call it the scab puzzle. The crop (the host), the fungus, and the weather are the pieces of this puzzle. The more perfectly these pieces fit together, the more scab you are likely to have. In Ohio, and most of the nearby soft red winter wheat states such as Illlinois, Indiana, Kentucky and West Virginia, weather is most often the missing piece of the scab puzzle. Most of our wheat varieties are susceptible and since corn is grown throughout the state, the fungus is almost always present, however, if it is not wet and humid during flowers, the risk of scab in reduced because weather becomes the missing piece of the puzzle. If it rains well before the crop reaches flowering, like it has been over the past few weeks, the risk will also be low because the host piece of the puzzle will be lacking since the crop is not yet at the susceptible growth stage. Similarly, if it rains during flowering, but a moderately resistant variety was planted and the wheat field was not planted into or next to a field with corn stubble, the risk of scab will be reduced (but not eliminated) because the fungus and the crop pieces of the puzzle will be lacking. If there is a high amount of corn residue in the field this is more favorable for survival of the fungus and development of spores. Remember, the scab fungus also infects corn, causing stalk and ear rot. Cooler than usual temperatures in combination with infrequent rainfall will also reduce the risk of scab because warm, wet conditions during the weeks leading up to flowering are needed for spore to be produced in crop residue.

So, in summary:
1- The risk of scab is greatest when warm, wet conditions occur during the weeks leading up to flowering and frequent rainfall coincides with flowering.
2- Even if it rains during flowering, planting wheat after soybeans instead of corn and planting a resistant variety instead of a susceptible variety will reduce, but not eliminate, the risk of scab. Under prolonged wet conditions, scab can still develop and vomitoxin exceed 2 ppm even when resistant varieties are planted into a field without corn or wheat stubble.

Management of head scab: Understanding how scab develops will help us to understand why a combination of management strategies would be better than a single strategy for suppressing this disease. Several fungicides are available for suppressing head scab. Proline, Prosaro, and Caramba are the most effective. However, none of these will provide 100% control. THEY WILL ONLY SUPPRESS SCAB, and the extent to which they work depends on correct timing and application technique. Fungicides are most effective when applied at flowering when the first set of fresh anthers are seen sticking out of the central portion of the wheat head. Remember, the crop is most susceptible at flowering and the fungus causes the most damage when it enters the heads at flowering. Protecting the heads with a fungicide at flowering will affect the ability of the fungus to cause disease, affecting the fungus piece of the scab puzzle. Like fungicides, resistant varieties are available, but no variety will provide 100% scab control. The overall control of scab is greatest when fungicides are applied at flowering to a resistant variety that is planted in rotation with soybean. This integrated management approach makes the host and the fungus pieces of the scab puzzle less favorable for disease development. Rotation reduces the amount of spores that are available within a field; fungicides kill the spores and reduce their ability to cause disease, resistance makes the crop less susceptible. Hence, combining these three management options will reduce losses due to head scab.

For a list of fungicides registered for scab, go to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf

For information on fungicide application technology for scab control go to http://www.smallgrains.org/Ground%20ApplicationFungicideREVISEDNDSU112508.pdf

Cereal Leaf Beetle Thresholds

Authors: Bruce Eisley, Andy Michel, Ron Hammond

We recently sampled a few wheat fields in Wayne County and collected 13-15 adult cereal leaf beetle adults per 10 sweeps. While we do not have thresholds based on adult counts, we believe that this number of adults suggests a potential economic population. Thus, these fields will need close monitoring for larvae and feeding injury which will occur over the next few weeks into early June. We also have reports of the insect being more active than usual in lower central Michigan and other locations in northern Ohio. All of this suggests that wheat growers should begin scouting their fields for potential problems.

Of more importance is the cereal leaf beetle threshold. Ohio has historically used an average of 2 or more larvae per stem as the economic threshold, the time when an insecticide application should be considered. This has been in effect for the past 30-40 years, during which the cereal leaf beetle has not been a major concern. We have recently searched the literature on cereal leaf beetle thresholds on wheat from many wheat growing states, including some of our neighboring states. It became evident that our threshold is perhaps too high; most if not all the other states have a lower threshold of one larva per stem or flag leaf. Thus, we believe it appropriate to lower the threshold for cereal leaf beetle in Ohio to one larva per stem or flag leaf.

As mentioned last week, insecticides for control are available at http://entomology.osu.edu/ag/images/sgiclb.pdf . And for organic growers, remember that Entrust is a spinosad product that is permissible on organic crops, being that it is OMRI listed.

The Good, Bad, and Ugly 2009 Planting Season

Authors: Jim Beuerlein, Pierce Paul, Anne Dorrance

The soil temperature determines how fast things grow during April and until mid-June. At a soil temperature of 40 degrees, corn and soybeans will emerge in 30 to 40 days. At 53 degrees they need 16-20 days and at a soil temperature of 66 degrees they will need 8-10 days to emerge. Soil temperatures around the state were several degrees cooler than normal through April. In northern Ohio the soil temperatures finally got above 55 degrees the first week of May and about a week behind the soil in southern Ohio. So, any crop we planted in April has not grown well due to cold wet soil conditions but should speed up a bit as the soil gets warmer. For soil temperatures between 40 and 90-degrees, the growth rate doubles for each 13-degree increase in soil temperature, which is why later planted crops emerge sooner, grow faster and get taller than earlier planted crops.

Even if the soil temperatures had been higher and if we had a crop in the ground, the combined stresses of the very wet weather and soil borne diseases may have ruined the crop as they did in 2008 when thousands of acres planted to soybeans between May 5 and May 10 had to be replanted in late May and early June because of inadequate plant populations. Various strains of Pythium will infect corn and soybeans anytime the soil is wet and the soil temperature is above 50 degrees. Fusarium is deadly in wet soil at temperatures from 58 to 75 degrees, and Phytophthora becomes very active in wet soil at around 65 degrees. So not having some crop planted by mid-May could be good for most of us.

Finally, if we get corn planted in May and have adequate sunlight and rainfall in August and September, we can have a great crop. If we get soybeans drilled no later than early-June and have good Fall-weather as in 2007, we can have another record yield. Later planted crops have the ability to compensate for delayed planting when blessed with really good Fall-weather. Two really good days in July or August are worth as much as a week in early May. We all may be part of a second running of the Kentucky Derby where the winner was near the back of the pack early, yet finished several lengths ahead of the pack to win the race.

”Mudding in” Corn

Authors: Jeff Graybill

This article recently appeared in the Penn State Field Crop News newsletter. To view that newsletter, please visit http://fcn.agronomy.psu.edu.

The recent wet weather has been a challenge for all farmers. Whether making rylage, planting corn or even applying herbicides, were tempted to wade into the field earlier than we otherwise might. When is it too wet? What penalty will I pay later for planting into wet soil?

One guide for too wet soil is when you can easily make a ball with a handful of soil from the top 2 inches. If the ball falls apart/shatters easily between two fingers, then soil is marginal. If the ball can be handled, and behaves more like clay than soil, it is too wet. Also, in conventionally-tilled fields, excessively wet soil will accumulate on depth and/or closing wheels. However, in no-till with good cover we can easily be compacting the seed zone without soil accumulating on equipment.

No-tillers: if the seed trench is not closing well and you are tempted to put additional tension on the closing wheels even thought the soil is wet and pliable then you are probably causing serious sidewall compaction. Should a wet spring lead into a dry June, normal root penetration and growth will be greatly restricted. My feeling is that a lot of sidewall compaction goes undiagnosed in the form of slowed plant growth (Paint brush roots) and reduced drought tolerance, resulting in reduced standability and yields for serious violators.

What can I do? Correct decisions require one to weigh the options and have good information. What are the negatives of delayed planting? Looking in the http://agguide.agronomy.psu.edu, we see some excellent advice and information. Mudding in corn can have immediate negative effects on stands and emergence. Late planting delays harvest, slows drydown and we start to lose about a bushel per day after May 10th. However, http://agguide.agronomy.psu.edu/cm/sec4/table1-4-8.cfm in the Agronomy Guide shows us that planting and obtaining a stand of 30,000 ppa on May 19th will still return 91% of your expected yield; by May 24th this drops to 86%. Clearly, uniform stands can return very high yields up through most of May. So, when in doubt get off the planter, squeeze some soil, evaluate and examine the seed trench there is still time to do it correctly. We dont want to make a bad situation worse.

What about switching to a shorter season hybrid? It will depend upon your situation and the RM of your hybrids. Grain growers would naturally consider this before silage farmers. Here is a quote from the Agronomy Guide. In most areas, switching to shorter than adapted hybrid maturities should not be considered until at the least the last week of May.

Fields for Soybeans – be sure that it is not too many years in a row

Authors: Anne Dorrance

Another rainy week and we will be behind again in planting. As producers are contemplating what should go where – don’t forget your field history. Fields with soybean cyst nematode – should really be on an every other year planting schedule for soybeans; and for high populations of soybean cyst nematode – 3 year rotations are even more effective. Fields where soybeans were replanted last year – should go to corn. This keeps the Phytophthora populations from building up. Many Pythium spp., a water mold, can infect both corn and soybeans so rotation is not as critical, but seed treatments are. For fields with replanting issues – seed treatment is the best means to minimize this damage. However, when flooding occurs to the point where plants are submerged, seed treatment is really not going to help.

Soybean Rust Status in the Southern US

Authors: Anne Dorrance

Soybean rust has made an early appearance on kudzu in the pan handle of Florida, Georgia, Alabama and Louisiana as posted on the website: http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi . This is the earliest soybean rust has been found in some of these locations. To date, no soybeans are infected. The southern states are having challenges very similar to ours – there soybeans are late going in due to heavy rains and many areas are looking at replanting. The early sentinel plots are flowering this week in some parts of the deep south that are closest to the gulf. Florida is reporting hotter temperatures, it is reaching 90 F and this will slow rust development down. The best time to assess if soybean rust will have any risk for Ohio, will be the fourth of July weekend. Especially in a year when our soybean planting is so delayed.

Alfalfa Weevil Update

Authors: Bruce Eisley, Andy Michel, Ron Hammond

We are getting reports from across the state of fields with alfalfa weevil larvae needing spraying. Although alfalfa looks great from a pickup truck, growers should realize that the only way they can determine the presence and densities of weevil larvae is to get into the field and scout for the insect. Seeing the feeding injury from the road for the first time is seeing it after economic damage has been done. See http://corn.osu.edu/index.php?setissueID=287,article C for an article that discusses how to sample and when to treat. Also, remember that the closer we get to the first cutting, the best management tactic often becomes early harvesting. We normally recommend early harvesting when the alfalfa is over 16 inches in height and more than 4 larvae per stem are present.

Weather

Authors: Jim Noel

Much of what we talked about last week is on track. We expected 0.3 to 1.0 inches of rain for the past week. This is what fell for the most part with 0.3 inches in the northwest and most of the state getting 0.5 to 1.0 inches. The isolated higher totals we talked about fell in mainly in the southern half of the state with 2+ inches in the far south.

We also talked about a drier week this coming week then wetter next week. Things have sped up a bit.

We now expect a dry start to this week to turn rather damp from Wednesday to early Sunday. Two weather systems will affect the area. The first will arrive Wednesday into early Thursday and the next late Friday into early Sunday. Rainfall will average 0.50 to 2.00 inches with isolated 3" totals not out of the question especially in the west and south. Temperatures will average slightly above normal this week. One note, a chilly Tuesday AM with some frost possible mainly in northeast Ohio. Lows for the far north and northeast Tuesday AM may be around 32° and 45° for the southwest.

Week 2 should be a much cooler and drier week with mostly rain free conditions now until the Memorial Day weekend. Temperatures will average several degrees below normal.

Week 3 will feature slightly below normal temperatures and near normal rainfall.

Right now summer - June - August looks slightly cooler than normal with near normal rainfall.

One final note: there is a 40-50% chance for 2 inches or more of rain for the next 2 weeks in the north and 70-90% chance in the south based on our ensemble forecasting system predictions. Normal is about 2".

Archive Issue Contributors: 

State Specialists: Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Peter Thomison (Corn Specialist), Jim Noel (NOAA). County Professionals: Suzanne Mills-Wasniak (Montgomery), Tim Fine (Miami), Jonah Johnson (Clark), Harold Watters (Champaign), Roger Bender (Shelby), Wesley Haun (Logan), Glen Arnold (Putnam), Bruce Clevenger (Defiance), Alan Sundermeier (Wood), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Ed Lentz (Seneca), Steve Prochaska (Crawford), Mike Gastier (Huron), Howard Siegrist (Licking), Jeff Graybill (Lancaster PA)

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.