CORN
Crop Observation and Recommendation Network

September 25 - October 1, 2000
C.O.R.N. 2000-32

In This Issue:

A) Does time of day affect herbicide performance?
B) Wheat Planting: Avoid Early Planting and Avoid Problems
C) Diplodia Ear Rot All Too Common
D) Anthracnose and Gibberella Stalk Rots Severe
E) Corn Borer Injury Variable from One Region to Another
F) Slugs Already Active This Fall
G) Harvesting Bean Leaf Beetle Damaged Fields
H) Time to Clean and Store Sprayers Properly
I) A Short Discussion Short Beans

A) Does Time of Day Affect Herbicide Performance? - Mark Loux CORN Questions

For years we have received questions about the effect of time of day on herbicide effectiveness. We have had very little information available to us on this matter to allow us to provide any practical guidance.

Issues that come up:
- Is the presence of dew on the plant a plus or minus?
- Do plants "shut down" under very hot conditions in the middle of the afternoon?
- Is herbicide effectiveness reduced when leaves of some weeds droop in the evening?

We recently came across two studies that addressed this issue, and the results of these may help out with application decisions. 

The first study, conducted in Texas, addressed the effectiveness of Staple (an ALS inhibitor) applied at various times during the day for control of pigweed. When the herbicide was sprayed on pigweed on an afternoon with the temperature above 93 degrees, pigweed was barely affected. Pigweed that was sprayed in the cooler morning was almost totally killed. When the investigators examined response of the ALS enzyme to Staple under laboratory conditions, they found it to be most affected at temperatures between 68 and 93 degrees Fahrenheit. Two years of field studies confirmed the lab results. Their conclusion - farmers might consider stopping herbicide application before the day gets too warm. The temperature at spraying time has the greatest effect on how well Staple works, even though it takes the compound two weeks to kill weeds.

The second study, in Minnesota addressed effectiveness of Liberty and glyphosate on a number of weeds when applied at various times almost around the clock. They applied use rates and half use rates of the two herbicides on large weeds from 6:00 a.m. to midnight at 3-hour intervals (no one was willing to stay up late enough to apply at 3:00 a.m., I guess). Greatest annual weed control was observed between 9:00 a.m. and 6:00 p.m., while significantly less control was observed at 6:00 a.m., 9:00 p.m., or midnight. This was much more noticeable for broadleaf weeds than for grasses. Applying with an adjuvant or increasing herbicide rate resulted in greater herbicide effectiveness, but did not overcome the time of day effect. They could not attribute the time of day effect to any one factor, such as dew, temperature stress, etc., and concluded that the variation was linked to environmental effects and weed species and heights. Plant physiological factors (such as the natural diurnal rhythms) are also assumed to have a role. They're recommendation: consideration should be given to avoid early morning and evening hour applications under cooler environments and on difficult to control or larger weeds. A one-page summary of this research can be found at: www.agro.agri.umn.edu/appliedweeds/

Here we have two studies that appear to tell us two different stories about the effect of time of day on herbicide performance. The key to the difference is probably the extreme heat in the Texas study and its effect on the enzyme, which overrides any other effects of time of day. I assume that environmental conditions in Ohio are likely to be on average somewhere between those in Texas (where armadillos regularly throw themselves on busy highways to avoid the summer heat) and those in Minnesota (10 months of winter and 2 months of mosquitoes and road construction). However, we can certainly have periods of high temperatures during the growing season in Ohio. I would suggest the following might apply to Ohio weed control conditions:

- The effectiveness of foliar-applied herbicides appears to be maximized by applying between the hours of 9:00 a.m. and 6:00 p.m., except when weeds are stressed by high temperatures. This is likely to be most apparent when asking herbicides to perform under less than ideal conditions - large weeds, cool or dry conditions.

- During those summer periods when weeds are subject to extreme high temperature stress, avoid application in the hottest period of the day (1:00 p.m. to 5:00 p.m.?).

- Drift reduction should still be a major goal of all applicators, and may have to take precedence over concerns about herbicide effectiveness in some fields. When applying under decent environmental conditions using labeled rates on small weeds, application in early morning may still be preferred to avoid drift problems.

The time of day effect is likely to vary between weeds and herbicides, and this information is by no means conclusive. Just one more thing to think about as you watch marestail feed into the combine this fall.

B) Wheat Planting: Avoid Early Planting and Avoid Problems - Jim Beuerlein and Pat Lipps CORN Questions

Date of planting is the cheapest and best way to control a number of insect and disease problems in wheat. The most productive and profitable wheat is planted within seven days after the fly-safe date and receives 25 pounds to 40 pounds of starter nitrogen. Soil P levels above 30 ppm are recommended. Liberal application of Phosphate where lower soil test levels exist is also acceptable. See the Agronomy Guide for fertilization recommendations.

Low yields associated with early planting are due to insect and disease problems. The Hessian fly is a small, dark colored fly about 1/8th inch long and resembling a small mosquito or gnat. It's life cycle includes two generations per year. Adults lay eggs on newly emerged wheat seedlings in the fall which hatch and overwinter in a pupa stage under the leaf sheath. The adult emerges in the spring and lays eggs on new, healthy wheat foliage. These eggs hatch into maggots which move to a point just above the ground between the stem and leaf sheath where they draw sap from the plant. This feeding causes weakness and eventually breakage of the stems and loss of yield. After a few weeks of feeding, a pupa stage is formed which eventually turn into adults. These adults start the cycle again by laying eggs on wheat planted before the fly-safe date. The best control method is to plant after the fly-safe date when adults are no longer laying eggs.

Delayed planting of wheat also limits infections from several different diseases. Most important is Barley Yellow Dwarf. Barley Yellow Dwarf is caused by a virus carried by aphids. Aphids travel on wind currents from the South and land on early emerging wheat in Ohio. The aphid can transmit the virus to wheat plants within the first few hours after it lands on them. Infected plants turn yellow or have yellow leaves in the spring. In planting date field trials at Hoytville, Barley Yellow Dwarf reduced yield by 22% in plots planted 10 days before the Hessian Fly Safe date as compared to plots planted on the Fly Safe Date. Wheat spindle streak mosaic and wheat soilborne mosaic virus diseases are also more severe in early planted wheat. Additionally, foliar diseases like powdery mildew, Stagonospora leaf blotch and leaf rust can infect wheat if planted too early. Giving these fungal pathogens an early start in the fall can increase the potential for more severe problems in the spring if they overwinter on the wheat plants.

C) Diplodia Ear Rot All Too Common - Pat Lipps CORN Questions

Some corn producers are finding a lot of Diplodia ear rot in their fields this year. In certain fields the percentage of damaged ears has ranged from 1% to over 35%. Typical symptoms include a thick white to grey mold that covers a large portion of the ear. The mold usually is most visible on the butt end of the ear. The husks on severely affected ears have the appearance of being plastered to the ear making it difficult to strip the husks from the ear. Kernels on ears that have been colonized for a long time become very dark brown and the cob becomes very easy to break. During combining, the cobs break apart and contribute to the amount of foreign matter in the harvested grain. Affected ears have very lightweight kernels.

The fungus that causes Diplodia stalk rot survives from one year to the next on old corn residue on the soil surface. During periods of wet weather the fungus produces spores that are rain splashed up onto the corn plant. Driving rain helps spread spores through the corn field. Corn plants are infected during mid to late whorl stages of development when the spores are deposited in the whorl by splashing rain. The fungus then infects the developing ear through the ear shank, but some research also indicates the ears can be infected through the silks and directly through the husks. Hybrids very greatly in their susceptibility to Diplodia ear rot.

Wet weather from mid June through mid July probably initiated the development of spores and the several heavy rain showers just prior to tasseling delivered the spores to the susceptible parts of the plants. Continued rain in July also favored infection and disease development. Growers that have a high incidence of Diplodia ear rot should consider planting a different, more resistant, hybrid next year. A two year crop rotation with fall tillage to destroy the corn residue will reduce the population of the fungus in the field.

D) Anthracnose and Gibberella Stalk Rots Severe - Pat Lipps CORN Questions

We have many reports of severe stalk rot and lodging from various locations in the state. We expect that certain fields will have very high levels of stalk rot and growers should scout each field individually. It appears that in some counties nearly all fields have high levels of stalk rot and in others only certain fields are severely affected. The amount of stalk rot and lodging will vary with the hybrid and the field. Scout your fields now for stalk rots!

Why is stalk rot severe this year? More than 10 years of stalk rot research and an in depth review of the research literature indicates that the weather conditions that occur during the growing season has more to do with the overall severity of stalk rot than any production practices growers use today. The potential for stalk rot will vary according to several factors including weather, other stresses, and the hybrid planted. Variable rainfall, with some parts of the state too wet and others too dry, has contributed to the overall level of stress on the plants. Shallow root systems that developed in response to the wet weather early in the season have made plants prone to water and nutrient stress. Those plants that endured dry weather early have not developed adequate roots either. It is fortunate that we have received sufficient rainfall throughout the summer to keep these plants going this far. Stressed plants utilized the daily food reserves produced in the leaves to fill the kernels on ears and do not maintained adequate nutrition in the roots or stalks during the latter part of the growing season. Severe leaf damage due to leaf diseases like common rust, gray leaf spot or Stewart's bacterial leaf blight have also predisposed plants to higher levels of stress. Other stresses can include high plant populations, nitrogen deficiency, low levels of Potassium and European corn borer infestation. Additionally, hybrids differ greatly in their ability to endure stalk deterioration. Some, with thick rinds, are able to stand even though the internal pith is severely rotted.

Anthracnose leaf blight was very common in fields during May and June and provided the spores necessary to initiate the stalk rot and top dieback phases of the disease. Anthracnose leaf blight and stalk rot is more common in continuous corn fields, especially those in reduced tillage. The anthracnose fungus survives in old corn residues and infects the leaves of the plants. Spores are rain splashed onto stalk surfaces where the fungus infects the stalks. Shiny black streaks or spots on the surface of the stalk is characteristic of anthracnose stalk rot. Gibberella stalk rot is also very common in fields. Like the antrhacnose fungus, the Gibberella fungus survives from one crop to the next on corn residues. However, it enters the stalks via the roots and moves into the stalks when plants become stressed. The pith inside the stalks begins to disintegrate causing weakened stalks. Gibberella stalk rot can be identified by the pink discoloration of the pith when the stalks are split open.

Scout fields now and harvest those that have weak stalks soon before they fall down. Record the hybrids planted and the level of stalk rot in each. Plant hybrids that have good stalk lodging resistance next year. Secondly, watch those high plant populations! In fields that have moderate fertility and are prone to drought stress, plant only moderate populations. The key to managing stalk rots is to avoid plant stress as much as possible.

E) Corn Borer Injury Variable from One Region to Another - Hal Willson CORN Questions

During the past few weeks, we have been evaluating plots in a number of locations of the State for corn borer injury. Most of the plots are part of a statewide study to compare Bt-corn hybrids to equivalent non-Bt isolines. Plots at the Western and Northwestern branch stations were replicated, plots in a number of counties were non-replicated.

The most severe corn borer (ECB) infestation observed to date was 4.8 cavities per plant in our plots at the Northwestern Branch Station, Wood County. ECB infestations at the Northwest Branch Station during the past three years have ranged from 0.1 to 1.7 cavities per plant. This year the ECB injury at the branch exceeds that observed in 1996 of 3.9 cavities per plant.

The next highest level of ECB injury observed in our plots was at an on-farm trial in Highland County where an ECB infestation of 1.8 cavities per plant was recorded. Observations of ECB injury at five locations around central Ohio have ranged from 0.2 to 0.9 cavities per plant. During the forthcoming week, three additional sites in western and northwestern Ohio will be inspected.

Corn borer injury observed to date on non-Bt hybrids is presented in the following table.

Hybrids included at all sites: Asgrow RX601, Asgrow RX730, Dekalb DK585 & Dekalb DK618.

The corn borer injury observed has been a combination of 1st brood and 2nd brood injury. In general, most of the injury has been 2nd brood as indicated by the presence of ECB larvae. At most sites, a high proportion of the larvae have been found in the ear zone - especially in the ears and the ear shanks.

Stalk quality has been very poor at the number of sites sampled. Stalk quality has been primarily linked to hybrid, since poor stalk quality has been observed in some hybrid lines regardless whether the hybrids included the Bt trait with no ECB injury or the non-Bt trait with or without significant ECB infestations. It should be noted that some fields are exhibiting serious stalk breakage due to stalk rots that may or may not be linked to presence of ECB infestations. Where heavy ECB infestations are present, stalk breakage may be more severe.

In general, we have observed very little difference in ECB infestations between non-Bt hybrids. Where we did have a significant drop in ECB infestation in a given hybrid, the stalk quality was so poor the ECB larvae preferred not to remain in the deteriorating stalks.

F) Slugs Already Active This Fall - Ron Hammond CORN Questions

With the onset of cool and wet weather, slugs have become active in many parts of Ohio, much earlier than normal. A double-cropped soybean field that had been no-tilled into wheat stubble was found in NW Ohio that had a >60% stand loss. This field had over 50 gray garden slugs per beer trap, which is the highest density we have ever found.

Because of the large populations of slugs in some fields and their increased activity, fall plantings of wheat and alfalfa (and perhaps other crops) where no-till practices are in use should be checked for possible slug problems. In those situations where on ongoing problem is occurring, a molluscicide application might be warranted.

This is also a good time to determine if your fields have a population of slugs for next spring. Research has shown that the presence of slugs in the fall gives a good indication of potential problems the following spring. A visit to your fields at dusk or in the early morning while dew is still present will reveal the presence of slug slime trails on the leaves, and perhaps the presence of slugs. During times of rainfall or heavy mist is another time when slugs will be active. Although research does not currently have specific numbers as to what constitutes a problem, slugs are being found in densities that suggest that many fields will have a significant potential for problems next spring.

G) Harvesting Bean Leaf Beetle Damaged Fields - Ron Hammond CORN Questions

Because of the cool and wet weather occurring in parts of OH, growers should be aware of soybean fields with significant bean leaf beetle pod damage. Secondary seed pathogens can enter the pod through feeding scars from the beetle. Although the insect injury has already occurred, seed diseases can become potential problems. Research has shown that the incidence of certain seed diseases increases the longer the field remains unharvested during periods of cool and wet weather. Thus, growers should be encouraged to harvest fields having bean leaf beetle pod damage as soon as conditions allow.

H) Time to Clean and Store Sprayers Properly - Erdal Ozkan CORN Questions

Sprayers are used only a few weeks in a year. When not in use, protect them against the harmful effects of snow, rain, sun, and strong winds. Moisture in the air, whether from snow, rain, or soil, rusts metal parts of unprotected equipment. The sun helps reduce moisture in the air, but it also causes damage. Ultraviolet light softens and weakens rubber materials such as hoses and tires and degrades some tank materials. The best protection from the environment is to store sprayers in a dry building. Storing sprayers in a building gives you a chance to work on them any time during the off-season regardless of weather. If storing in a building is not possible, provide some sort of cover. Remove the hoses, wipe them clean of oil, and store them inside a building. Do not hang them over a nail or sharp object. This causes a permanent crease that reduces flow through the hose. Coil hoses around a basket or other large round object to prevent sharp bends. When storing trailer-type sprayers, put blocks under the frame or axle and reduce tire pressure during storage.

A few other things have to be taken care of when it is time to store the sprayer.

1. Add 5 to 20 liters of light weight (non hazardous) oil, depending on the size of the tank, to the rinsing water before the final flushing. As water is pumped from the sprayer, the oil leaves a protective coating inside the tank, pump, hoses, and other parts.

2. To prevent corrosion, remove nozzle tips and strainers, dry them, and store them in a can of light oil such as diesel fuel or kerosene.

3. Drain all cleaning water from all parts to prevent freezing.

4. Pumps require special care. After draining the water, add a small amount of oil, and rotate the pump four or five revolutions by hand to completely coat interior surfaces. Make sure that this oil is not going to damage rubber rollers in a roller pump or rubber parts in a diaphragm pump. Check the operator's manual. If oil is not recommended, pouring one tablespoon of radiator rust inhibitor in the inlet and outlet part of the pump also keeps the pump from corroding. Another alternative is to put automotive antifreeze with rust inhibitor in the pump and other sprayer parts. This also protects against corrosion and prevents freezing in case all the water is not drained.

5. Cover openings so that insects, dirt, and other foreign material cannot get into the system.

6. Finally, check the sprayer for scratched spots. Touch up these areas with paint to eliminate corrosion.

I) A Short Discussion Short Beans - Ed Lentz CORN Questions

We have received many questions from Northwest Ohio on why this year's soybean plants are so much shorter than normal. Keep in mind that soybeans basically have four periods of growth. I call these phases: 1) germination and emergence 2) vegetative growth before flowering 3) vegetative growth during flowering and 4) end of vegetative growth. Vegetative growth before and during flowering accounts for most of the plant's height. Nodes are made during vegetative growth. At each node, leaves, flowers and branches may develop. Generally, the more nodes per plant, the greater the yield potential.

The first growth phase is germination and emergence, which is greatly dependent upon soil temperature and moisture. This phase determines the number of plants per acre, which later will determine the number of nodes per acre, an important component of yield. Population will determine length of internodes (distance between nodes) and affect height. Lower populations tend to have shorter internodes and more branches than higher populations. Disease and poor growing conditions reduced our populations this year, which were accentuated by poor seed quality and lack of seed treatments.

The second phase is vegetative growth. This period is dependent upon photo-period, moisture and temperature. All of the plant's energy is put into vegetative growth until flowering, which generally occurs after the summer solstice (June 21). Shorter days (longer nights) trigger plants to flower. This vegetative growth before flowering lays the groundwork or makes the factory that will later determine yield. In general, the more days that leaves are present in good growing conditions before flowering, the greater the yield. Thus, soybeans planted in early May usually have greater yields than those planted in June. This would also hold true for soybeans planted in April providing growing conditions were good. This year the below normal temperatures in the last half of May greatly reduced growth and made plants more susceptible to disease.

The third phase occurs when flowering begins. Since our soybeans have indeterminate growth characteristics, vegetative growth continues after flower initiation. However, the plant has to divide its energy between vegetative and reproductive growth. The amount of additional growth is dependent upon moisture and temperature. This indeterminate growth habit allows soybeans to recover somewhat from dry periods in July by producing additional flowers after rainfall. Several weeks of dry weather in July this year reduced growth in some areas until rains returned at the end of July and first part of August.

The last growth phase occurs during bean fill (generally first part of August in Northwest Ohio). The shorter days and aged root system signal the plant to puts its remaining energy into seed development. Very little vegetative growth occurs after this point. Thus any flowers or pods that abort at this time will not be replaced.

In summary, we had several events to occur that may have reduced the height and possibly the yield potential of this year's soybeans. These events started with average to poor seed lots, which affected germination and emergence. Slower emergence caused by poor seedling vigor allowed more time for diseases to attack vulnerable plants. Lack of seed treatments allowed Phytophthora to ravage many fields, reminding us why it is historically the number one soybean disease in Northwest Ohio.  And finally, the below normal temperatures that occurred the last part of May followed by large amounts of rain greatly restricted growth during the vegetative phase, and also made plants more susceptible to disease. Stands were either lost to Phytophthora or stopped growing until better conditions returned. Thus plants not killed by disease behaved like plants that had been planted two or three weeks later than the actual planting date, and fields planted two or more times because of disease behaved like typical June plantings. All of these conditions resulted in shorter plants and may have reduced yield potential. In conclusion, poor quality seed, lack of seed treatments, and poor growing conditions between Mother's Day and Father's Day may have reduced the height of this year's soybeans.

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

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