C.O.R.N. Newsletter 2006-11

Dates Covered: 
May 1, 2006 - May 8, 2006
Editor: 
Tammy Dobbels

Frost Damage in Alfalfa

Authors: Mark Sulc

We have received a number of calls from producers who are concerned about a sudden change in appearance of their alfalfa fields. Most of these calls have come from the northern half of the state.,I had the opportunity to see a sample from a damaged field in Holmes county just this morning. The alfalfa had some leaf chlorosis (yellowing) and bleached streaks in the upper leaves. The most likely culprit of this damage is cold temperatures. Some parts of the state experienced temperatures at or below 25 F last week for an hour or more, which is certainly cold enough to cause frost damage in alfalfa. One producer who called was concerned that the symptoms looked like disease, but if the change was occurred rather suddenly and alfalfa weevil are not present in high numbers, it is most likely a result of the frost and cold temperatures we experienced. The sample I saw only had the damage on the upper leaves, and the buds where new growth was coming from were not damaged. So I expect the alfalfa to grow right out of this damage within the next couple of weeks. Where damage was more severe, development into the bud and flowering stage may be slowed, so the first harvest may be delayed a few days. Just keep an eye on those stands and call your county agent or me if the appearance does not improve within the next 5 to 10 days.

VERY IMPORTANT also is to check your new legume seedings that were emerged as of last week when the cold nights occurred. Seedling stands of alfalfa and clovers can be sensitive to temperatures that low, and could be killed if the temperature near the soil surface actually fell to the low 20s. But most new seedings are done with conventional tillage, and the dark soil surface absorbs plenty of heat that protects young seedlings near the soil surface. So while established stands may have been damaged in the upper canopy, new seedlings likely did not suffer any damage. If the new seedlings were damaged by the cold temperatures last week, the symptoms should be very evident by now. My new seedings that were planted April 12-13 in western and northeastern Ohio look fine.

Rainfall Concerns - Preemergence Herbicides

Some parts of the state, especially the northwest part of Ohio, are dry to very dry and have received little rainfall during the last two to three weeks. Corn and soybeans have been planted and preemergence (PRE) herbicides applied for greater than 10 days in many parts of the state. For PRE herbicides to be effective, rainfall is needed to incorporate and activate the herbicides. For most herbicides, at least one inch of rainfall is needed for proper incorporation and activation with more being better. Yet, some herbicides require less rainfall for activation, such as Balance, Harness, and Keystone and many PRE herbicides may get by with less depending upon several factors, but certainly is not ideal.

When rainfall has been inadequate to incorporate and activate herbicides, consider rotary hoeing. The rotary hoeing will incorporate some of the herbicide which will activate it and control weeds before they emerge. The best time to rotary hoe is when the weeds are in the “white stage”. The “white stage” means that weed seeds have germinated, but have not emerged and that they are not green in color. Once a weed has emerged, rotary hoeing usually does not control that plant. Rotary hoeing should be done 7-14 days after planting.

Scouting & Managing Leaf Diseases of Wheat With Fungicides

Authors: Jim Beuerlein, Dennis Mills, Pierce Paul

It is time to start scouting wheat fields for leaf diseases. The wheat is now between growth stages 6 (jointing) and 8 (flag leaf emergence). This marks the beginning of the period during which we recommend that field be scouted to determine which disease is present and at what level. Although it has been a fairly dry spring up to this point, leaf diseases are beginning to show up on susceptible varieties in some fields. Fungicides are available to control these diseases in Ohio; however the decision to use these fungicides should be based on the susceptibility of the variety planted, the level of disease in the field, weather conditions, and the yield potential of the field. When the level of disease in the field is high on the top two leaves, wheat growers could benefit from applying fungicides, but in low disease years, fungicide applications would not be economical. Under favorable weather conditions, on susceptible varieties, leaf diseases cause substantial reduction in wheat yield. Yield response to fungicide application is directly dependent on the amount of disease in the field and the susceptibility of the variety to that disease. Resistant varieties rarely benefit from application of fungicides.

Stagonospora leaf and glume blotch, powdery mildew, and leaf rust are the most important yield-reducing leaf diseases in Ohio. Of these, Stagonospora leaf and glume blotchare most common statewide and powdery mildew is most common in the northeast, east central and south central parts of the state. Most years, leaf rust is detected in the state after flowering of the crop and is usually considered too late to cause significant yield loss. The growth stage of the wheat crop when disease develops influences the impact on yield and timing of fungicide application. The earlier the growth stage, the greater the potential to impact yield. Yield losses are greatest when the upper two leaves of the plants become diseased at or before heading. When this happens, yield losses can be as high as 25 to 30%. Hence, the main purpose of making fungicide applications in wheat is to keep the upper two leaves and the head healthy between growth stages 8 (flag leaf emergence) and 10.5.4 (flowering).

Scout wheat fields during the months of May and June to determine the need for fungicide application. The first disease to be detected is usually powdery mildew. This disease is important during the month of May and early June in mild seasons with high relative humidity. Randomly collect 30 to 50 tillers from throughout the field and look for the small white pustules on the lower leaves and leaf sheaths. If powdery mildew is present in a field planted to a susceptible variety you should watch its development over the next week or so and decide whether fungicides should be applied. Fungicides should be applied for powdery mildew control (on susceptive varieties) when 2 to 3 pustules are detected on the leaf (leaf two, counting from the top) below the flag leaf (the top-most leaf) anytime between growth stage 8 (flag leaf emergence) and 10 (boot).

Stagonospora leaf and glume blotch is most severe when frequent rains occur during the months of May and June. Scout fields between growth stages 8 (flag leaf emergence) and 10.5.4 (flowering) and if 1 to 2 lesions are detected on the leaf below the flag leaf on a susceptible variety, fungicide should be applied.

There are several different fungicides available for use on wheat. If powdery mildew is the target disease then Tilt or PropiMax should be applied. Tilt, PropiMax, Quadris, Quilt, Stratego, and Headline have good effectiveness against Stagonospora leaf blotch, other leaf blotch diseases and leaf rust. Obtain current pricing of fungicides to determine the most economical control option. Use 20 gal water/A with ground equipment and 5 gal water/A if applying by airplane. Using less water will lower effectiveness. Check labels for application timing restrictions.

Help in diagnosis can be obtained from OSU Extension or other crop consultants. OSU Extension Agronomic Crop Disease Fact Sheets provide descriptions and pictures of the common diseases in the state. These Fact Sheets can be found on at
http://www.ag.ohio_state.edu/~ohioline/ac_fact/index.html
http://www.oardc.ohio-state.edu/ohiofieldcropdisease.

For updated information on wheat variety reactions to disease visit Ohio Field Crop Disease web site at
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/Wheatreactions05.htm

A Checklist for Corn Emergence Problems

Authors: Peter Thomison, Pierce Paul

Diagnosing 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.
(I’ve adapted some of this information from a newsletter article by Dr. Greg Roth, my counterpart at Penn State).

-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, 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 that have a weft of 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. Given a chance to emerge with warmer soil temperatures many of these plants will likely survive. It is best to check these seedlings very closely for dark brown or soft areas on seedling roots and on shoots next to the seed. These immature plant structures should be white to creamy white in appearance. 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. This may be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above.

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 last year when corn planted in mid April did not emerge until the first or second week of May. As long as stands were not seriously reduced, delayed emergence in most fields did not have a major negative impact on yield. However, when delayed emergence was associated with subsequent crop development, yield potential was reduced.

Surface Lime Applications and Nitrogen Management and Pelletized Lime

Authors: Robert Mullen, Edwin Lentz

If you have recently made a surface lime application (in the last six months) for no-till row crop production or a pasture operation you should avoid surface applications of urea-based nitrogen fertilizers. Surface applications of lime result in high pH levels at the soil surface that can increase the loss of nitrogen by volatilization. Because lime is not extremely soluble, it will remain at the soil surface for quite a while. When urea is applied to any soil it is broken down from an organic molecule to form ammonia in the presence of water and the enzyme urease. If adequate moisture is not present, the ammonia gas can escape from the field and float away into the atmosphere. The formation of ammonia is affected by pH, and the higher the pH the more ammonia formed and the greater the amount of N that can be lost. This is exactly why surface N applications should not be made too soon after a surface application of lime. Lime and a urea-based fertilizer should never be mixed for a surface application.

Pelletized lime can seem like an attractive alternative to typical aglime because it exists in a pellet form that can ease application, but can you apply dramatically less pelletized lime than typical aglime and see similar results? The answer is no. Pelletized lime is made up of smaller particles than typical aglime (that is important for determining the neutralizing power of lime), but that does not mean you can apply a fraction of the lime recommendation and observe the same field results. When you are comparing lime materials, find out what the effective neutralizing power (ENP) of the lime material is. Once you know the lime requirement, based upon your soil’s buffer pH, use the following equation to determine how much of a specific lime material you have to supply:

Lime material recommendation = (Lime requirement ton/acre ÷ (ENP ÷ 2000)).

For example, assume the ENP of a pelletized lime source is 1860 and the lime requirement (based upon soil test) is 1.5 tons per acre, how much lime do you need to apply? The answer is 1.6 tons of pelletized lime per acre. By comparison, assume an aglime source has an ENP of 1100, how much aglime do you have to supply to meet the 1.5 tons per acre recommendation? You would have to apply 2.7 tons of the aglime to meet the recommendation. Notice that even with the pelletized lime you need to supply at least a ton and a half to achieve the desired liming result. Four hundred or five hundred pounds of pelletized lime applied will not adjust soil pH to the desired level.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Jeff Stachler (Weed Science), Peter Thomison, (Corn Production), Ron Hammond (Entomology), Mark Sulc (Forages), Robert Mullen, Maurice Watson (Soil Fertility). Extension Educators: Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Steve Bartels (Butler), Steve Prochaska (Crawford), Bruce Clevenger (Defiance), Gary Wilson (Hancock), Tammy Dobbels (Montgomery), Todd Mangen (Mercer), Ed Lense (Seneca), Alan Sundermeier (Wood), and Keith Diedrick (Wayne).

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.