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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2007-18

Dates Covered: 
June 19, 2007 - June 26, 2007
Greg LaBarge

Potential for Two-Spotted Spider Mite

Authors: Bruce Eisley, Ron Hammond

As if dry and hot conditions were not enough of a problem, we need to remind soybean growers that these conditions are favorable for two-spotted spider mites outbreaks. Although typically a late summer problem, we have been seeing earlier outbreaks under these conditions the past few years. We would advise growers in areas of Ohio that are extremely dry to begin checking their soybeans for this pest. The easiest way to locate mites is to look for telltale signs of their injury, yellow spotting or stippling on the upper side of leaves. Here are two pictures showing this stippling, both on a unifoliate leaf ( and a trifoliate leaf ( .

There are no thresholds available for mites on soybeans. Treatment is recommended when mites become numerous in the field and begin to cause discoloration of the plants, especially the lower leaves. Growers should take into account future weather predictions, because we do know that continued hot and dry weather will aggravate the mite problem, where as cool and wet weather will tend to lesson it. However, if cooler and wetter conditions arrive, we would still suggest keeping a close eye on this pest.

There are only two materials which are currently available for mite control on soybeans, compounds containing chlorpyrifos at various formulations and rates, and dimethoate at various formulations and rates. Of these two, the chlorpyrifos labels state that “When large numbers of eggs are present, scout the treated area in 3 to 5 days. If newly hatched nymphs are present, make a follow-up application of a non-chlorpyrifos product that is effective against mites”. Compounds containing lambda-cyhalothrin and gamma-cyhalothrin are also labeled for mite control on soybeans but the labels state for “suppression only”. Also note that if treatment becomes necessary within the next few weeks, that soybeans most likely will be in the flowering stage, which brings up the concern about honey bees. Be careful if spraying at flowering so as not to harm honey bees.

Sentinel Plot Report-June 18

Authors: Anne Dorrance

The sentinel plots are progressing and some reached the R1 growth stage (one flower) last week. This is exactly what we like to see in that our sentinel plots, that they are a few days/weeks ahead of the remainder of the crop. For some reason, data from both Brazil and Georgia have indicated that rust does not infect the plant in the vegetative stage during the normal growing season. They have found rust on soybeans in the early vegetative stages during the winter in Louisiana and Georgia, but not in June or July.

We confirmed last week that one of the locations does have frogeye leaf spot. This foliar disease was rare in Ohio and only occurred at the end of the season. This is one of the clear benefits of this sentinel plot program, we can find and detect a disease long before controls need to be implemented. The primary reason why frogeye was so widespread was due to extreme susceptibility to this pathogen from a few soybean cultivars. We scored the Performance trial last year and over 90% of the entries had high levels of resistance. We don’t expect a similar problem this year, but it is good to monitor the situation.

It is too early to spray for frogeye at this time, but it is not too early to scout for it. We were able to document economic returns on fungicide applications ONLY WHEN the disease had reached 1 to 2% leaf area affected by the R3 growth stage (pod is 3/16 of an inch long at one of the four uppermost nodes on the main stem). This growth stage occurs around mid to late July for most of Ohio on normal planted soybeans. Frogeye is distinct from other soybean foliar pathogens in that it has a gray-silver center surrounded by a deep cranberry red border. The soybean rust ID card has a close-up on the inside. Conditions for the next few weeks are predicted to be hot and dry. Frogeye requires moisture/dews and tends to infect young new leaves as opposed to rust which infects older leaves. For the next few weeks we will be surveying the state to determine how widespread this is and if fungicides will be needed.

On the national front, one new soybean rust find in Texas. Again inoculum levels in the southern US are very low and the risk for rust in Ohio is very low for the foreseeable future.

Harvesting Stressed Alfalfa and Other Forages

Authors: Mark Sulc

I have received several calls about harvesting alfalfa that appears to be under stress from dry weather. Alfalfa usually has a strong capacity to continue growth under dry conditions, and we would normally expect alfalfa to be growing better than it is at this stage in a dry cycle. The late spring frost injury combined with the first harvest taken before the crop had a chance to replenish taproot reserves has likely contributed to the weak regrowth now being observed.

Many alfalfa stands were cut in mid- to late-May, which in a normal year is ideal timing. Unfortunately, the late killing spring frost this year resulted in alfalfa plants having to initiate new growth all over again. That required a lot of energy from the plant at a time when taproot reserves were low. So the mid- to late-May cutting was actually like an early harvest stress in terms of the physiological condition of the plant. This has likely contributed to the weak regrowth of many alfalfa stands, especially those that were cut last autumn or have additional stress factors such as suboptimal fertility and pH.

Many stands don’t appear to be growing any more, but that does not mean the plants are sitting idle. Alfalfa stems stop elongating during the initial phases of moisture stress, but the plant continues to manufacture carbohydrates and protein that are stored in the root system since they are not being used to produce top growth. Allowing those reserves to accumulate a little longer will benefit alfalfa plant health and longevity. I encourage growers to allow the alfalfa to get close to full bloom stage before taking the second cutting this year. Allow at least a 35-day interval from the first harvest.

Once the alfalfa is well into bloom stage and there is enough harvestable forage to economically justify a hay cutting, then go ahead and harvest it. The forage will probably be higher in quality than normal growth in full bloom because of the stems are short and fine. If fencing is available, controlled grazing of drought-stressed alfalfa stands is a very economical way to utilize the forage that is present, but bloat prevention strategies should be employed.

Other forages are also showing signs of drought stress. Red clover is not as tolerant to the combined effects of drought and heat stress as alfalfa. Cutting during periods of hot and dry weather CAN WEAKEN RED CLOVER PLANTS and may cause stand reductions. If feed is badly needed, red clover stands can be lightly grazed during drought stress.

When cutting or grazing birdsfoot trefoil during periods of heat and drought stress, be extra careful to harvest when plants are at least in mid-bloom stage and leave a full 3-inch stubble. Birdsfoot trefoil maintains relatively low levels of reserve carbohydrates in the roots and crowns during the summer. Cutting or grazing when plants are well into bloom stage and leaving sufficient leaf area will improve its regrowth potential.

Grass growth has also been slowed by dry weather in many areas. Established orchardgrass and tall fescue have better regrowth after first harvest than species like ryegrass or timothy that are less tolerant of dry conditions. Established grass stands can survive through drought conditions and regrow once rains return.

Options for Producing Supplemental Forage

Authors: Mark Sulc

First harvest yield of alfalfa was reduced this year due to the late spring frost and dry spring. If dry weather persists across the Ohio Valley, many producers may be looking for options to produce supplemental forage, particularly in fields after wheat grain is harvested. This article briefly outlines some alternatives for producing supplemental forage for mechanical harvesting. More information on forage alternatives for grazing operations can be found at and

Summer-annual grasses (eg. sudangrass, sorghum x sudangrass hybrids, pearl millet) grow rapidly in summer, and when managed properly can provide good quality forage. All these species can be planted up to July 15 to 20, and will produce 3.5 to 5 tons of dry matter per acre assuming sufficient moisture is present for emergence and growth in the latter half of the summer. 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. I’ve heard that seed supplies are very short for these grasses, so do not delay your search for seed.

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 compared with summer-annual grasses grown alone. The annual legumes included in these mixtures would be present in the first growth only. 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 (eg. soybean meal).

Ohio producers have had success with establishing oats in early August to produce forage for harvesting or grazing in the autumn. This is an economical option for fields coming out of wheat grain. Spring triticale will also produce well in the autumn, but seed cost is much higher than for oats. Wheat, rye, and winter triticale will only produce significant forage in the spring and are poor options for autumn forage.

No-till seeding 2 bushels per acre of oats with 100 pounds per acre of urea can yield 2.0 to 2.5 tons of dry matter/acre by early to mid-October when the oats should be in boot to early heading stage. Oats can be grazed, or made into silage or balage after cutting and wilting. Small grain forage (boot stage) has more energy and about the same crude protein content as high quality alfalfa.

If land is available, corn can be planted in mid- to late June for silage production. Planting corn silage this late certainly carries increased risk, especially if dry weather persists; however, June planted corn with adequate rainfall can produce more forage of greater feeding value than the summer annual grasses. If forage is needed before the ear is formed, corn can be green chopped. Without the ear, feeding value will be at least equal to that of the other summer annual grasses and yields are likely to be higher with corn. For June plantings, select a tall 100- to 102-day relative maturity corn hybrid and plant only on soils with good moisture holding capacity. Nitrate toxicity is a potential problem with drought stressed corn, so be prepared to test for nitrates if the drought persists and limits corn growth.

Soybean can be grown for forage, but it is extremely difficult to make good soybean hay and ensiling soybean also has problems. The high concentration of fat (about 10%) inhibits bacteria in the silage and fermentation is slow and often incomplete. The best approach to using soybeans as a forage is to mix them with corn plants during silo filling. A mixture of 1 part or more of corn to 1 part soybean works well. In large diameter upright silos, adequate mixing usually occurs when one load of corn is unloaded followed by one load of soybeans. In smaller diameter upright silos one-half load of soybeans followed by one-half to a full load of corn will usually result in adequate mixing. For silo bags, mixing is difficult. The ratio of corn to soybeans should be increased and the amount of soybeans put in the silo at one time should be small. The best solution would be to chop about one-fourth to one-half load of soybeans and fill the rest of the wagon with corn.

Use of herbicide-treated soybeans for forage or hay is allowed for only a few herbicides, so check chemical labels before using herbicides on soybeans to be used for forage.

Additional information on annual forages is provided in the Ohio Agronomy Guide. For more information on managing livestock feeding under drought conditions, refer to the 2002 drought website at

Cover Crops & Manure Nutrient Cycling meeting June 26

Authors: Alan Sundermeier

June 26, 2007 from 8:30 am – 10:30 am a cover crop and manure nutrient cycling workshop will be held at OARDC NW Ag Research Station, 4240 Rangeline Road, Custar, Ohio, Wood County.

Any one with an interest can attend. The program is especially for livestock & dairy managers, crop farmers using manure, crop consultants, ag educators, SWCD, NRCS personnel.

Agenda - Learn how to utilize manure nutrients with cover crops. What cover crops work best in Northwest Ohio? Where do I buy cover crop seed? Farmer shared experiences with cover crops. On-farm research needs. Consolidating cover crop seed orders.

Free and open to public. No registration needed.

For more information contact Alan Sundermeier at 419-354-9050 , Wood County Extension Office.

Drought and Heat Stressing Corn

Authors: Peter Thomison

The combination of high temperatures and inadequate moisture has created severe stress in many corn fields across Ohio. As dry weather continues, more corn fields are showing signs of moisture stress with leaf rolling evident during midday hours. In many stressed fields, soil moisture is available but it appears beyond reach of most corn roots. Current weather conditions are inhibiting root development. In addition to water deficits, high soil temperatures are limiting root growth near the soil surface. The corn canopy shades the soil surface and moderates soil temperatures, but many corn fields have yet to canopy. Plants with root systems restricted to the upper four to five inches of the soil profile are stunted. Thunderstorms early this week may bring some relief but forecasts call for more dry weather later.

Yield losses to moisture stress can be directly related to the number of days that the crop shows stress symptoms during different growth periods. Iowa research by Claassen and Shaw on effects of drought on grain yields in corn is widely used in estimating the potential impact of water stress on yield potential. According to this Iowa research, drought stress during early vegetative growth usually has a negligible impact on grain yield. Some corn agronomists contend that mild drought during June may even be beneficial because roots generally grow downward more strongly as surface soils dry, and the crop benefits from the greater amount of sunlight that accompanies dry weather. However, during later vegetative stages, when kernel numbers per ear are determined, plants become more sensitive to stress. According to Claassen and Shaw's findings, four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5-10 percent.

Kernel row numbers on the ear are determined by the 12th collared leaf stage and the potential number of kernels per row is complete about one week before silking (see last week’s article on ear formation online at Corn planted in April and early May will reach the reproductive phase of corn development in about 2 to 3 weeks. This is the period of development (i.e. tasseling, silking and pollination) which is most sensitive to moisture stress. To get a better understanding of why this period is so sensitive to drought, consider the water requirements of corn during the growing season shown below. A corn crop in Ohio typically uses 20 to 22 inches of water during the growing season and water requirements vary according to the stage of development. Corn reaches its peak water use during pollination when plants are silking.

Water Use Rates for Corn at Different Growth Stages.
Growth Stage Water Use Rate (inches/day)
Prior to 12-leaf stage < 0.20
12-leaf 0.24
Early Tassel 0.28
Silking 0.30
Blister Kernel 0.26
Milk 0.24
Dent 0.20
Full Dent 0.18

For more on effects of effects of dry weather during the mid to late vegetative stages of corn development check out the following article
Nafziger, E. 2007. "Good" Stress or "Bad" Stress?the Bulletin: Pest mgmt & crop developmt information for Illinois. Univ. of Illinois. [On-Line]. Available at


Dry weather and Postemergence Glyphosate Management

Authors: Mark Loux

Mid-season reports on the effectiveness of postemergence glyphosate applications in corn indicate that the dry weather is affecting glyphosate activity in some fields. We have reports of reduced control of lambsquarters and giant ragweed, which lead us to believe that we are likely to experience problems with control in soybeans as well. Many of the soybeans in the state were treated within the last week or so, or are being treated this week. Problems with glyphosate performance usually become evident within 10 days to 2 weeks after application. The droughty conditions we have been experiencing in many areas can be a contributing factor to reduced glyphosate activity for several reasons:

1. Weeds that are actively growing under adequate soil moisture conditions are most readily controlled by herbicides, and conversely, drought-stressed weeds are generally more tolerant of herbicides;

2. Dry weather causes weeds to grow more slowly, so it takes them longer to reach the size at which may applicators apply glyphosate. So, weeds are older and have been subject to drought-stressed conditions for a long period of time, which generally makes them less sensitive to herbicides; and

3. We have a working theory that some weed populations are developing a low level of resistance to glyphosate. This resistance may not be expressed when weeds are small and conditions are favorable, but could be expressed when weeds are large and growing under stress from drought or other factors.

Rain forecast for today may alleviate some of the drought stress and result in improved postemergence herbicide activity. Our general suggestions with regard to postemergence glyphosate applications and the current dry weather follow.

1. Increase glyphosate rate to 1.5 lbs of glyphosate acid in soybeans. In corn, apply the maximum postemergence rate allowed in a single application based on the glyphosate label and type of glyphosate-resistant corn. Our research with glyphosate resistance clearly shows that in any situation where glyphosate activity could be reduced (large weeds, drought stress, low level resistance), most effective control results from using a high glyphosate rate in the first postemergence application, and following with a lower rate in a second application if needed. Using a low rate in the first application and then trying to “bail out” the resulting poor control with a second application at a higher rate will have a much lower rate of success.

2. Where a second postemergence glyphosate application is needed to control plants that survived the first application, our research indicates that about three-week interval between application may result in the best control. This provides time for plants to resume growth after the first application so that glyphosate can have activity in the plant, but does not allow time for plants to regrow to a large size. Waiting until enough regrowth occurs so that plants can be seen above the crop from a road survey is not the best approach. Applying the second glyphosate treatment too soon after the first is also not optimum, since plants that have not recovered from the first application cannot respond to the second.

3. Include AMS in all applications and be cautious of AMS substitutes without a proven performance record. In soybeans, avoid mixing other herbicides with glyphosate unless there is a good reason to do so (something more substantial than “it seemed like a good idea at the time”).

4. In corn that is not too large, glyphosate can be mixed with Status to improve control of large, drought-stressed weeds. There are certainly other tank-mix possibilities, but glyphosate and dicamba have historically worked well when applied in combinations.

5. Glyphosate activity can increase when applied in low spray volumes, but this has to be balanced against the need for penetration of spray into dense weed/crop canopies or to obtain better coverage of large weeds. For the latter situations, it’s possible that spray volumes of 15 to 20 gpa may be more effective than 10 gpa or less. Be cautious also of using too many drift-reduction measures, such as combinations of low drift nozzles and drift-reducing agents. This can result in too few droplets of too large a size, which can reduce control.

Controlling Kochia and Palmer Amaranth in Warm-Season Grasses

Authors: Mark Loux

Small infestations of kochia and palmer amaranth developed in areas of the state last year seeded with warm-season grasses as a result of the presence of weed seed in certain lots of grass seed. NRCS and OSU cooperated to develop a fact sheet on the control of these weeds, “Controlling kochia and Palmer amaranth in warm-season grass stands and in cropland”. This is available through NRCS and at the OSU weed science website,

We seem to be hearing more about kochia than Palmer amaranth. Kochia is one of the tumbleweeds that are abundant in the west. At one site in Knox county last year, the kochia was present in a warm-season grass field, and at the end of the season the kochia plants broke off at ground level and rolled with prevailing winds to spread seed for quite a distance into adjoining crop fields.

Now is an appropriate time to apply herbicides in warm-season grass stands to control small kochia plants. Effective herbicides for kochia control include dicamba and fluroxypyr (Starane, WideMatch), and also Aim if plants are small. 2,4-D is not effective on kochia. The bad news is that all of these herbicides will injure or kill forbs in the field, but this is probably better than allowing kochia to get a foothold in the state.

Nutrient Deficiencies Popping-up

Authors: Edwin Lentz, Robert Mullen

Some areas of the state are reporting sporadic nutrient deficiencies and the question is what can be done about it?

Dry soil conditions can result in nutrient issues that manifest themselves as deficiencies in a crop. A good example of this is manganese deficiency in soybean. Dry soil conditions cause manganese to form manganese oxide that is unavailable to plants. Extended periods of dry conditions can cause this to be serious enough that the crop exhibits the deficiency symptoms. The symptoms are typically found on the well drained areas of the field or on the high spots or ridges. Manganese deficiency symptoms are also usually associated with high soil pH. Foliar application of manganese solutions can help overcome the deficiency with yield benefits, but it may take more than one application of the foliar solution to solve the problem (unless of course it starts to rain).

Dry soil conditions also lead to other more exotic problems that we are not accustomed to seeing in Ohio’s agricultural fields. One such deficiency is magnesium deficiency. There have been reports of magnesium deficiency in Northwest Ohio this year. Soils that are exceptionally dry can cause soil pH to drop and induce a magnesium deficiency. To identify the cause of the problem, tissue sampling and soil sampling should be conducted from both unaffected and affected areas of the field. In all likelihood, a soil pH problem will be revealed through soil testing. Soil pH issues will have to be rectified this fall through the application of lime.

These two examples illustrate that nutrient deficiencies are not necessarily due to a simple absence of the nutrient in question, but the deficiency is most likely due to some other underlying factor like low soil moisture (or high soil moisture) or soil pH issues.

Sidedress Nitrogen and Crop Response

Authors: Edwin Lentz, Robert Mullen

A few weeks ago we discuss sidedress application of nitrogen and whether it was a good idea to do so or not For those who did supply nitrogen, the corn crop may not have greened as quickly as it has done in the past, so the question is why not?

Soil nitrogen in the nitrate form is moved by mass flow with soil water (as water goes so to does nitrate-nitrogen). In periods of dry weather, soil water availability is decreased and the nitrogen that has been supplied is not able to make its way to the plant roots by the mass flow mechanism. Therefore the crop does not green up as quickly as it would have if adequate soil moisture were present just after the application of nitrogen. Do not panic though, nitrogen supplied below the soil surface in the form of urea-ammonium nitrate (UAN – liquid 28) or anhydrous ammonia has not been lost (unless it was applied poorly). That nitrogen will simply wait in the soil until it has the opportunity to become mobile.

Lack of moisture has resulted in stress conditions on some well drained soils. If you have not supplied sidedress nitrogen and the crop is exhibiting signs of drought stress, you may want to consider decreasing you nitrogen rate slightly. Data collected at Ohio State shows that years with significant drought stress can be less responsive to nitrogen, so you can reduce your rate.

Agronomy Field Day July 10

Authors: Harold Watters

Producers and industry specialists alike will want to visit the Western Agricultural Research Station in South Charleston, Tuesday, July 10, from 2-5 p.m, to take part in the newly revived Agronomy Field Day. Offered once again, this event provides the latest information on Ohio field crops, this year featuring research on corn production and weed control issues. The field day is free and open to anyone in the field crop industry.

Talks will be given while touring research plots, allowing participants to discuss with state specialists exactly what the crop has suffered through so far this year. Certified Crop Advisor CEUs will also be available at this event.

Topics include:
• Phosphorous and potassium management and nitrogen use requirements from Robert Mullen, OSU Extension, state Soil Fertility Specialist.
• Corn weed control issues from Mark Loux, OSU Extension, Weed Control Specialist.
• Foliar disease of corn and foliar fungicides from Pierce Paul, OSU Plant Pathologist for corn and wheat.
• Corn insect update from Bruce Eisley, OSU Extension Research Associate, Department of Entomology, corn insect specialist.
• Emerging Corn Production Issues from Peter Thomison, OSU Extension, Corn Production Specialist.

For more information contact Harold Watters, OSU Extension in Champaign County at 937-484-1526, or Joe Davlin, Research Assistant, Western Agricultural Research Station, 937-462-8016,

The Western Agricultural Research Station is located at 7639 South Charleston Pike, just south of I-70 on SR 41 between Springfield and South Charleston in Clark County.


Archive Issue Contributors: 

Anne Dorrance, Pierce Paul,and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Robert Mullen (Soil Fertility). Extension Educators: Woody Joslin (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Steve Prochaska (Crawford), Todd Mangen (Mercer), Gary Wilson (Hancock), Harold Watters (Champaign), Greg LaBarge (Fulton), Steve Foster (Darke), Steve Ruhl (Morrow), Wesley Haun (Logan), Ed Lentz (Seneca) and Jim Lopshire (Paulding).

Crop Observation and Recommendation Network

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.