Corn Drydown, Late Season Corn and Soybean Disease Key  08/30/16 10:52:04 AM

THANK YOU FOR ATTENDING OUR FIELD DAY!   Hopefully, all who attended found it to be worth the investment of their time!  We would also like to thank BASF, Bayer, Cargill, Dow, DuPont, FMC, Midwest Labs, Monsanto, Syngenta, CPS, United Suppliers, and Valent for reviewing current products and programs for the coming fall and 2017 season. We look forward to working with you this harvest and winter season.  We hope that we are able to provide you the technical facts, the retail and farmer experience, and the service you deserve to continue your farming success.

How Fast Will This Year’s Corn Dry?

Drydown after black layer formation varies greatly from hybrid to hybrid. Hybrid characteristics such as husk coverage and heavy test weight can have a significant impact on field drying. A general rule of thumb is that 30 GDUs are needed to lower the grain moisture each point from 30 to 25% and 45 GDUs per moisture point are needed from 25 down to 20%. The following table indicates approximate moisture loss at various times during the fall.

Time
Period

Moisture Loss Per Day

 

%

Mid-to-late September

¾ to 1

Early-to-mid October

½ to ¾

Late October to early November

¼ to ½

Mid November

0 to ¼

Late November

0

 

 

 

WHEN ARE SOYBEANS MATURE?  It is not un-common for soybeans to begin senescence during the first week in September.  This is the first sign of the maturing process in soybean plant development.  As in corn, physiological maturity is when the maximum amount of dry matter has been accumulated in the seeds.  This, by definition, would mean they are mature.  The old rule of thumb is if the entire bean plant is yellow, a frost will have little effect on yield.  This is true!  Here is an explanation.  There are three stages of maturity.  Physiological maturity of soybean occurs 2-5 days after 95% of the plants have reached growth stage R7 (one normal pod on the main stem has reached a yellow color).  Visual or full maturity (R8) is reached when 95% of the pods have attained a yellow color (about 32% seed moisture).  And, finally, harvest maturity is when the seed reaches a moisture content of 14%. 

 

When a mature pod has turned yellow it has a seed moisture around 50%.  At this time, leaves and stems begin to yellow due to chlorophyll breakdown.  When this occurs, yield is fixed and cannot increase.  When 65-70% of the plant is yellow, desiccants could be used to accelerate the drying process of the grain if so desired.   When the plant is fully yellow the effects of an early frost are usually not a concern.  Seeds injured by frost will remain green, and, if the seed has a high moisture, germination is reduced.  Immature seed can withstand temperatures of 28 degrees F, and will be killed by a 20 degree F temperature in as little as four hours.  Sometimes, if there has been poor pod set, the stems and leaves may remain green while the pods turn yellow and then mature to their final color (tan or brown).  This is common of plants with male sterility.

Killing Alfalfa Stands—Fall Applications Most Efficient--As an alfalfa stand ages, it becomes less productive and eventually must be replaced.  Two to three alfalfa plants per square foot will produce maximum yields in older stands on dryland.  Stands thicker than this will not produce more forage because the lack of moisture limits production.  Therefore, it is usually best to rotate to another crop for several years before reseeding alfalfa. Fall is an excellent time to kill alfalfa with herbicides in preparation for next year’s row crop.  No-till treatments make this a popular alternative to plowing.  Plowing is an age-old process in which the alfalfa is not always completely killed.  Herbicides are more economical than plowing, very effective, and will leave the soil in a condition which is less susceptible to erosion.  Applying herbicides in the fall will eliminate hurried applications in the spring and possible planting delays due to product label restrictions.

 

An economical, consistent alfalfa control treatment is a combination of 1 qt 2,4-D (4 lb/gal) = 0.5 pt of Banvel per acre.  Make sure that the alfalfa has at least 4” of top growth after your last planned cutting so there is sufficient plant surface area for herbicide uptake.  Applications made in September/October prior to a hard freeze will produce the best results.

 

Wet Weather and Stalk Rots/Lodged Corn—diagnosis is the key

Stresses such as nutrient deficiencies, diseases, insect feeding, excessively wet or dry conditions, high winds, and hail can lead to stalk lodging and happen every year to some extent.  With all the wet weather this year, we are likely to see a couple of developments as a product of the climate we have had since we planted the crop.  A couple of things to remember this fall

1)      Above average rainfall created a nutrient availability question after it was applied.  This question has not gone away since the spring and as the crop nears maturity, areas prone for fertility availability issues are again noticeable and also susceptible to increased vulnerability to diseases and lodging.   

2)      Soil Compacted/Low Organic Matter/Areas where recent Conservation Work took place in fields are “prime” areas for diseases/nutrient deficiencies/lodging to develop. 

Corn Disease Key in and on the Stalks

     (A) Anthracnose stalk rot:
                Contains shiny, black discoloration that can not be scratched off the rind; 

     (B) Charcoal rot:  
                Contains tiny black sclerotia produced inside the stalk give the appearance of charcoal dust; 
    
(C) Diplodia stalk rot:
                Contains tiny, raised black dots (pycnidia) on lower nodes are embedded in the stalk   
                and can not be scraped off; 
    
(D) Fusarium stalk rot:
                Contains pinkish-white fungal growth on outside of stalk, pink or salmon colored    
                discoloration inside stalk, lack of visible reproductive structures, crowns often are
                brown and rotted;
     (E) Gibberella stalk rot: 
                 Contains bright pink to red discoloration at the nodes;
     
(F) Bacterial stalk rot:
                 Contains dark brown water-soaked lesions at base of stem with soft, slimy stalk  
                 tissues accompanied by an extremely foul odor.

 

In general, stalk rots are favored by late season stresses. A number of fungi and bacteria cause stalk rots in corn which can lead to stalk lodging. In addition, stresses such as nitrogen deficiency and blighted leaves from foliar diseases can inhibit the production of carbohydrates, causing plants to remobilize or move sugars from the stalk and leaves to fill the kernels. This process is referred to as stalk cannibalization and can make corn plants more susceptible to physiological stalk lodging.

For detailed information on each stalk rot disease, see the University of Nebraska Extension article Common Stalk Rot Diseases of Corn found at http://ianrpubs.unl.edu.

Push or Pinch Test. Scout fields periodically to check for stalk rot and lodging issues. Walk a zigzag pattern through the field and test stalk firmness by squeezing or pinching each stalk at one of the lowest nodes above the brace roots. Healthy stalks are firm and cannot be compressed. If a stalk feels soft, it is likely prone to lodging.

A second method for determining potential stalk lodging is to push each stalk about 5 to 8 inches from upright (approximately a 45° angle) and note whether the plant springs back, remains tilted, or breaks.

If more than 10% of the stalks sampled in a field are rotted or prone to lodging, consider scheduling the field for early harvest. In severe instances, it may be more economical to harvest early and dry the grain post-harvest as opposed to accepting significant losses.

Preventative Measures for Next Season

·         Manage for optimal soil fertility, particularly nitrogen and potassium, to prevent nutrient deficiencies which can lead to stalk cannibalization.

·         Choose products with good standability ratings.

·         If disease is a problem, choose seed products that are rated for resistance or tolerance to the specific disease. Refer to AgSeedSelect.com for seed product disease ratings.

·         Depending on the disease, tools such as tillage, crop rotation, product placement, or fungicide applications can be used in the following year to help reduce disease pressure.

·         Insect feeding creates entry wounds for pathogens to colonize plant tissues. In some cases, planting products with insect resistance such as Genuity® SmartStax® RIB Complete®, Genuity® VT Double PRO® RIB Complete®, or Genuity® VT Triple PRO® RIB Complete® corn blends can reduce the incidence of stalk rots.

 Sources: Jackson, T. A. et al. 2009. Common stalk rot diseases of corn. EC1898. University of Nebraska-Lincoln Extension. http://ianrpubs.unl.edu. 140725100201

Why do stalk quality/stalk rot problems develop almost every year?

 

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 to meet demands of grain fill. When corn is subjected to stress, photosynthetic activity is sharply reduced and carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by remobilizing carbohydrates from the leaves, stalk, and roots to the developing ear. While this “cannibalization” process ensures a supply of carbohydrates for the developing ear under stress conditions, the removal of carbohydrates results in premature senescence and death of the pith cells in the stalk and root tissues which predisposes plants to root infection by stalk rot fungi.

Stresses which increase the likelihood of stalk rot problems in corn include drought, loss of leaf tissue due to foliar diseases, insects (grasshoppers) or hail injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium in the soil, compacted or saturated soils restricting normal root growth; and high plant populations. Several of these stress conditions occurred this season and occur every season..

Late-Season Soybean Diseases Soybean diseases such as sudden death syndrome (SDS), brown stem rot (BSR), charcoal rot, Rhizoctonia stem rot and Phytophthora root rot are all soybean diseases, which can cause early senescence.   Although late, with all the recent wet weather, many of these are just beginning to develop this year.  From a distance, the symptoms of yellow or chlorotic soybeans appear similar in the field. The first symptoms to appear are yellow or chlorotic areas in-between the leaf veins that turn tan to brown. Eventually, plants will defoliate early leaving stems, petioles and pods. Determining which pathogen is responsible can be a challenge.

 

Here are some key characteristics to look for to determine which disease may be causing the problem:

  1. Sudden death syndrome is caused by Fusarium solani f. sp. glycinea. The tap root is very discolored and there are few, if any, secondary roots. A blue stain may be present on the root. The pith is white. As leaves drop, petioles will remain attached to the plant.
  2. Brown stem rot foliar symptoms are similar to sudden death syndrome, but the tap root is not discolored. When stems are split, the pith is intact but chocolate brown in color. Leaves will wither and stay on plants.
  3. Charcoal rot is associated with high soil temperatures. Light gray or silverish lesions first develop on the tap root. Microsclerotia will form under the epidermis of the stem tissues, giving it a grayish black color resembling a "sprinkling of finely powdered charcoal".
  4. Rhizoctonia stem canker will have a brick-red sunken lesion at the base of the stem.

5.      Phytophthora stem rot symptoms include a dark brown discoloration of the stem progressing up from ground level. Internally, the stem pith will be discolored.

 

Preventative Measures for Next Season

 

Most if not all pathologists would agree that genetic selection is the most economical and efficient way to fight diseases within your crops—especially soybeans.  If you have problems within a field with certain genetics, consult your agronomist or seedsmen for proper genetic placement for the environment you plant into each year. Many companies can tell you they are the best in yield.  They usually fail to mention how they perform when growing conditions are less than optimal. Quality seed placement for your acres can pay you big dividends throughout the entire year.

 

 

 

 

 

 

 

 

John W. McNamara

Agronomist

Wiles Bros. Inc.

606 Wiles Road

Plattsmouth NE. 68048

(402) 298-8550--Office

(402) 499-3870--Cell

(402) 298-7174--Fax

 
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