C.O.R.N. Newsletter 2005-28

Potential For Stalk Rot And Lodging in Corn: Drought Effects

Authors: Peter Thomison

Drought conditions this year are likely to increase the potential for lodging and stalk rot problems in corn. When stalk rot occurs late in the season as it often does, it has little or no direct effect on yield. Nevertheless, stalk lodging, which results from stalk rot, can have such an impact on harvest losses that many plant pathologists consider stalk rots to be the most significant yield limiting disease of corn.

For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is subjected to severe drought stress, photosynthetic activity is sharply reduced as leaves roll tightly and plant growth slows. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi. Even mild, early season water stress during the pretassel stage of development can significantly increase root infection by stalk rot fungi and result in greater stalk rot at maturity. As plants near maturity, this removal of nutrients from the stalk to the developing grain results in a rapid deterioration of the lower portion of corn plants in drought stressed fields with lower leaves appearing to be nitrogen stressed, brown, and/or dead.

Other plant stresses which increase the likelihood of stalk rot problems include: loss of leaf tissue due to foliar diseases (such as gray leaf spot or northern corn leaf blight), insects, or hail; injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium; compacted or saturated soils restricting root growth; and high plant populations.

Most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity. It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot. Although a number of different fungal pathogens cause stalk rots, the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium. For more information on stalk rot in corn, consult the OSU Plant Pathology web site "Ohio Field Crop Diseases" (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/) for more details and pictures of the disease symptoms associated with these pathogens.

The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvested promptly. It’s not uncommon to walk corn fields where nearly every plant is upright yet where nearly every plant is also showing stalk rot symptoms! Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds are not will not prevent lodging if harvest is delayed and the crop is subjected to weathering, e.g. strong winds and heavy rains.

A symptom common to all stalk rots is the deterioration of the inner stalk tissues so that one or more of the inner nodes can easily be compressed when squeezing the stalk between thumb and finger. It is possible by using this "squeeze test" to assess potential lodging if harvesting is not done promptly. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present. To minimize stalk rot damage, harvest promptly after physiological maturity (about 30% grain moisture). Harvest delays will increase the risk of stalk lodging and grain yield losses, and slow the harvest operation.

Premature Plant Death in Corn and Effects on Grain Yield

Authors: Peter Thomison

Premature plant death is occurring in parts of Ohio (especially the southwestern and west central regions) which have missed recent rains. Plants that have died or are dying prematurely have lost or are rapidly loosing their green tissue, and have turned sort of a yellowish brown, tan, or brown color. Another symptom of premature corn death is ears that are drooping (ear tips pointing downward) because the shanks connecting the ear to the stalk have collapsed. Normally ears will remain erect until about black layer (physiological maturity) after which they will start to droop downward as the ear shank tissue collapses. However, genetic background also influences ear position as ears of some hybrids remain upright longer than others (possibly due to differences in shank length). Premature ear drooping can also occur as the result of other pre-maturity stresses - such as European corn borers tunneling into the shanks, foliar and stalk rot diseases, late season hail damage, early frosts, etc.

Yield losses in corn plants that have died prematurely vary depending on when death occurs. In studies conducted in Minnesota back in the early 1980's, effects of premature death on yield were simulated by defoliating plants at different kernel development stages. Losses were estimated at 39 to 42% when plants were harvested at full dent following defoliation, and at 11-12% when plants were harvested at late dent following defoliation. Stalk rots are often associated with corn that dies prematurely. Premature plant death increases the likelihood of stalk lodging, and fields with high percentage of affected plants should be marked for early harvest.

Minimizing Harvest Losses in Drought Damaged Corn Fields

Authors: Peter Thomison

This year's widespread drought has resulted in smaller than normal ears, and a much greater percentage of "nubbin" ears in many fields. In some fields, plants are shorter than normal with reduced ear heights. As a result of these conditions, some combine and harvesting adjustments may be necessary. The following are management suggestions from ag engineers and equipment specialists on harvesting drought damaged crops.

1. Review the operator's manual for suggestions on harvesting a "light crop".

2. With short or lodged corn, run the gathering snouts and chains low. Watch for stones, and be sure stone protective devises are working.

3. Drive carefully and at normal speeds to avoid excessive harvest loss and machine damage from stones.

4. For small ears, set stalk rolls and snapping plates closer than normal to snap off a higher percentage of ears. Do not attempt to snap off barren cobs.

5. If clean shelling is a problem, increase cylinder speed slightly, and if necessary, decrease concave clearance. With a rotary machine, check rotary concave clearance. Avoid excessive damage to kernels from good ears.

6. If cleaning losses are high, open the chaffer and chaffer extension slightly.

7. Initially decrease the amount of air from the cleaning fan. If cleaning becomes a problem, increase the fan blast, and close the lower sieve slightly.

8. Be alert to changes in weather and crop conditions, and make adjustments as necessary.

Importance of Maintaining Optimum pH for Crop Production

Authors: Robert Mullen, Edwin Lentz

As fall fast approaches, soil probes should be dusted off and readied for field use to determine soil nutrient status and lead liming decisions for next year. Unfortunately, soil pH can be overlooked when soil fertility decisions are made, but it is a vital component of a good nutrient management program. I often make an analogy between crop production and automobile maintenance in my discussions on soil fertility. I equate nitrogen with gasoline in the tank (interesting enough both of these continue to rise in cost) because the amount needed in the tank is dependent upon the length of the trip (yield potential of the field). Phosphorus and potassium are like oil in the crankcase. The amount needed is not dependent upon the length of the trip (unless you drive an older model pickup that burns as much oil as it does gas) you just need to make sure the dipstick shows “full” (soil test level is above the critical value). Soil pH is like the air pressure in the tires. If there is no air in the tires, how much gas and oil are needed? Not much, how far can you go anyway? So do not minimize the value of maintaining an optimum pH for production. This is the right time of year for application of lime for crop production next spring.

Why do I stress maintaining an adequate soil pH? This year is a prime example of why. Under high rainfall conditions soils with marginal pH levels can be productive with little if any loss in yield loss even if the soil pH is slightly less than optimal. When moisture is in short supply (like this year) soils with marginal soil pH levels can experience a decrease in soil pH. This decrease in soil pH can lead to macronutrient deficiencies including potassium and magnesium (exactly what happened this year in certain areas). This is why soil pH should be maintained at or near the optimum level for the crop being grown. For additional information on selecting a lime material visit the following link: http://corn.osu.edu/story.php?setissueID=52&storyID=278. A soil pH and liming bulletin will be published this fall, so be on the look out for this new publication.

Weed Management of Wheat Stubble

Authors: Mark Loux

Herbicide treatments for wheat stubble can be varied based on the weed management goal, which can include any of the following: reducing the addition of weed seeds to the seedbank, reducing the population of perennial weeds, and reducing the risk for wheat diseases by controlling volunteer wheat. It is difficult to find a single herbicide treatment, especially with regard to timing of application, that simultaneously achieves all three goals.

Herbicide application timing depends upon the type of weed species for which control is most important. Wheat stubble can contain weeds from any type of life cycle - summer annual, winter annual, biennial, simple perennial (dandelion and curly dock), warm-season perennial (species that die with a light frost, such as johnsongrass, hemp dogbane, etc.), cool-season perennial (species that survive light frosts, such as quackgrass, Canada thistle, etc.), and volunteer wheat.

It is generally too late to control the summer annual species at this time, as they are in full seed production. However, herbicides may still reduce the viability of any seed produced (see related article at http://www.weeds.iastate.edu/mgmt/2005/lateseasonglyphosate.htm - “Impact of late-season glyphosate applications on weed seeds”). Effective herbicide treatments for summer annuals include: glyphosate at 1.5 pounds acid equivalent/A (lbs ae/A) plus AMS; glyphosate at 1.1 lbs ae/A plus 2,4-D ester at 0.75 lbs ai/A.

Herbicide treatments for control of warm-season perennials and volunteer wheat should be applied by mid-September or before a light frost. If grass species are not present, consider an application of glyphosate at 1.1 to 1.5 lbs ae/A plus 2,4-D ester at 0.75 lb ai/A. If grass species are present, consider applying glyphosate at a rate of 1.5 lbs ae/A or higher.

When targeting cool-season perennials, winter annuals, biennials, and/or simple perennials, apply in mid-October or after a light frost. Apply glyphosate at a rate of 1.1 lbs ae/A or higher. Higher rates will provide more effective control with the exception of winter annuals, which can be controlled by 0.56 to 0.75 lb ae/A of glyphosate. Dandelion and marestail/horseweed control can be greatly improved with the addition of 2,4-D to the glyphosate.

GVM Field Day/OSU Extension – September 8th

Authors: Steve Prochaska

A field day featuring the latest technology in pesticide and fertilizer application equipment will be held September 8th from 8:00 am to 4:00 pm at GVM West 4941 Sandhill Road, Bellvue, Ohio. In addition to field demonstrations of equipment, an update on soybean aphids and glyphosate resistant weeds will be presented by OSU faculty Ron Hammond and Jeff Stachler respectively. Core, 2A, and 2C pesticide credit will be offered along with 2 hours of CCA credit in Pest Management. RSVP to GVM West at 1-800-848-8460. Contact Steve Prochaska (prochaska.1@osu.edu) on questions regarding pesticide or CCA credit.

Pre-harvest Tune-up Field Day at Farm Focus – September 12th

Coming up on Monday, September 12, 2005, the Farm Focus committee in conjunction with Ohio State University Extension and the Ohio Agricultural Research and Development Center (OARDC) will host a Field Day at the Marsh Foundation Farm (Farm Focus site) in Van Wert, Ohio. The chosen topic “Pre-harvest Tune-up” will encompass a number of activities aimed at getting farmers ready for fall harvest, and all the field work that follows harvest.

Registration for the afternoon activities begins at 12:30 p.m. Planned activities include combine clinics, a fall weed control workshop, and wagon tours of the various research plots at Farm Focus.

Local implement dealers will have their combine technicians on hand to walk farmers through a checklist of things they can do to make sure their combines are set properly to achieve the most efficient and effective harvest of their corn and soybeans.

With the increase of no-till and reduced tillage conservation practices, learning to deal with increased weed pressures from a number of persistent perennials and winter annuals is becoming an issue for farmers. Dr. Mark Loux, OSU Extension weed specialist, will be at Farm Focus to talk about fall herbicide options available to help control these weeds.

One of the most popular events at past Farm Focus shows was the wagon tours of the research plots. This tradition will be continued at the September 12th field day. Visitors will have the opportunity to see and hear about some of the newest products and technology available in agriculture as they ride past the 18 different trials at the site. There are studies on corn row spacing and population, crop rotations, insecticides and fungicides for soybeans, fertilizer programs utilizing animal waste, foliar fertilizers, weed control for non-GMO corn and soybeans, and many others.

Additional financial sponsorship of the Farm Focus Field Day is being provided by several local agribusinesses. These include Farm Credit Services; Kennedy-Kuhn, Inc.; Violet Implement Sales, Inc.; Wellman Seeds; Wells Fargo Bank; and Williamson Insurance Agency.

The Farm Focus Field Day on September 12 from 12:30 p.m. – 4:00 p.m. is free and open to the public. The event is handicap accessible.

For more information about the field day visit the Farm Focus website at http://www.farmfocusshow.com. Or call the Ohio State University Extension, Van Wert County Extension office at 419.238.1214.