- Stalk Rot
Stalk rot seems to show up every year somewhere. The pictures you see are some of the more common stalk rots that may be found out in a corn field. Several fungi and bacteria can cause stalk rots both earlier and/or later in the season. Generally though, most stalk rots will show up later in the season.
Disease development is generally initiated by an early environment that favors kernel set followed by a late environment that is stressful such as (a) lack of moisture (b) nutrient imbalance or deficiency (c) excessive cloudiness (d) nematode, rootworm or other insect damage, (e) hail or other mechanical damage to the leaves, stalks or roots (f) loss of leaf tissue (g) excessive plant population (h) extended periods of very wet or dry periods (i) abrupt weather changes especially several weeks after silking. Other factors associated with stalk rot development include (j) high yields, (k) high N levels associated with low potassium levels, (l) high levels of decaying plant residue and (m) other plant diseases and stresses.
Balanced soil fertility is very important especially when it comes to potassium levels. Research has also shown the importance of adequate nitrogen during the entire season and how it can help reduce the severity of stalk rot. Take this into consideration, especially if nitrogen leaching or denitrification has occurred during the growing/grain production season. Most importantly, do not guess on the fertility needs of your field. Fertilizer application rates should be based on the results of soil tests. Soil tests may save you money in the long run via establishing the fertility needs and limiting excess fertilizer costs and helping to promote better plant health if the correct nutrient rate/balance is provided.
Hybrids vary in many ways and a producer needs to better understand the hybrids he has chosen to grow. Population in some cases may be the major culprit for a stalk rot problem with a hybrid. Some hybrids when planted at excessive rates can result in spindly stalks with reduced standability that may promote stalk rot which in turn probably means yield loss.
Stalk rots cannot be completely controlled but damage can be reduced. Here are several food for thought items to help reduce stalk rot influenced harvest loss. (a) Understand the hybrid you are growing and the capabilities it has, (b) follow a balanced fertility program, (c) control insects (d) plant at the proper rate (e) if you irrigate, avoid putting stress on the plants (f) foliar disease prevention can help with stalk rot potential associated with fungus and (g) good weed control.
Check your fields to make sure that stalk rot will not be a problem. Hybrids that have a thicker rind or other complimenting characteristics may not appear to have stalk rot but they may. Squeeze stalks above ground level to make sure they are not hollow or diseased. If some are hollow, this might be a field which you may want to consider harvesting sooner rather than later.
- Stalk Rot in Corn
What is Stalk Rot?
Corn stalk rot is a family of diseases caused by several species of fungi and bacteria. Severity of the disease changes from year to year due to climatic conditions, agricultural practices, hybrid genetics and stresses such as available water, fertility, plant population, foliar diseases, insect damage and weed competition. Stalk rot causes internal decay and discoloration of stalk tissues which directly reduces yield and standability by impairing water and nutrient uptake which can result in lodging and pre-mature death.
What Are Some Stalk Rot Symptoms?
The two most striking external symptoms are pre-mature death and stalk lodging. Visually, the leaves may appear to turn dull to grayish green while stalks, depending on which stalk rot is developing, may show brown or black or pinkish-red internal and/or external discoloration. A major portion of the pith tissue is usually destroyed and the remaining strands of vascular bundles inside the stalk are usually discolored. Advanced stages of stalk rot leave the stalk spongy, soft and hollow.
When is a Corn Plant Most Susceptible to Stalk Rot?
Stalk rot, in one form or another, can attack the plant as early as the seedling stage or any time there after. The seriousness of stalk rot is dependent on the types of stresses and the timing when these stresses impact the plant. To date, no true stalk rot resistant hybrids are available however; hybrids vary greatly in tolerance to stalk rot. Foliar diseases increase the severity of stalk rot by impairing leaf tissue thus reducing the amount of photosynthetic activity that can be done by the plant for nutrient manufacture, grain production and acrossthe- board survival. Yield is reduced because the plant draws on stored nutrients in the stalk for survival which otherwise would have been used for grain fill / production.
What Are Some of the Most Common Stalk Rots?
Fusarium Stalk Rot is one of the most common stalk rots. Its pathogen survives on crop residue and in the soil. Fusarium infects the plant by the pathogen being splashed on the leaf and washing down the leaf into the sheath and infecting at the nodes. It can also infect directly through the roots causing decay in the roots or lower stalk. Wounds from hail or insect feeding can provide additional sites of entry. Fusarium stalk rot along with Gibberella stalk rot produces a reddish-pink discoloration on the internal stalk tissue.
Gibberella Stalk Rot, which is a pinkish color too, also survives on plant residue or in the soil. Wind blown spores are dispersed to stalks and infect by direct penetration. Infection may also occur through the roots, wounds on the stalk and leaf scars. The spores can also be splash-dispersed and infect the ears and kernels.
Diplodia Stalk Rot usually occurs three to six weeks after silking. It Is distinguished by internal brown stalk discoloration and dry rot in the lower two internodes of the plant. The pith tissue is usually shredded and black spore forming structures are commonly found on the surface of the lower stalk. Spores can be transferred by wind, rain and insects. As the disease progresses, small brown / black reproductive structures form on the stalk surface near the nodes. Anthracnose Stalk Rot has three components (A) leaf blight (B) stalk rot (C) top die back. Prolonged periods of high temperatures and humidity are conducive to this stalk rot. Top die back occurs mid to late summer and affected fields appear to have a green band across the middle of the plants because the lower leaves are drying up due to normal senescence and the upper leaves are dying from anthracnose. Anthracnose has black discoloration on the inside of the stalk as well as on the surface.
Charcoal Stalk Rot is caused by a fungus which attacks the roots, enters the crown and eventually disintegrates the pith leaving only the vascular bundles. Numerous small dark specks called sclerotia form on the bundle strands and can easily be seen when the stalk is split. Sclerotia develop in dry areas where soil temperatures are high and soil moisture is low.
Pythium Stalk Rot occurs under warm wet conditions. Unlike most stalk rots which occur after tasseling, Pythium stalk rot can appear at any time. The rind and pith may become soft, brown and water-soaked and the decayed tissue may have a strong odor. The stalk typically twists and falls over, but the plant may remain green for several weeks because the vascular tissue is not destroyed. Pythium stalk rot may also cause top die back.
- Gray Leaf Spot in Corn
Gray Leaf Spot is an economically important disease in many midwestern and eastern corn belt states. It was initially detected in the southeastern coastal corn growing states of Virginia, Georgia and the Carolinas in the 1920s. In those states it was limited to the corn grown in foggy, humid, mountainous valleys where the warm weather and high humidity created a perfect environment for the disease to increase and spread. GLS has become a major problem across wide areas of the corn belt during the past three or four years.
Gray Leaf Spot, or GLS, is only known to affect corn. The symptoms of the disease vary with the severity of the infection and stage of corn development at which the infection occurred. The disease is first detectable as small grayish lesions on the lower leaves, which run parallel to the veins. As the disease progresses the lesions may coalesce (grow together) and cause the entire leaf to turn brown or gray. The lesions may also appear on the ear husks. Spores, commonly known as inoculum, that overwinter on the residue of the previous year’s crop spread the disease. Wind and surface water movements move these spores. In order to infect the plant, the GLS pathogen requires a moisture film on the corn leaf that lasts from twelve to thirteen hours or more. Then, if air temperatures remain in the 70 to 85 degree F range, the spores germinate and grow into the cuticle of the leaves. The disease moves up the plant with each successive generation. The disease can reach the top of the plant with as little as three generations. Once infected, the disease destroys the plant’s green tissue. This results in kernel abortion, shallower grain fill, reduced plant health, and reduced stalk and root quality. If the disease kills the leaf tissue late in its development cycle, the effect will be minimal. If the plants are infected early and a high percentage of the leaf tissue is lost for most of the growing season, yield losses could reach 30 to 50 percent.
As the advent of no-till and reduced tillage created higher residue situations over the corn growing area from Ohio to Nebraska, a perfect environment was created for inoculum to perpetuate itself from one season to the next. Plant pathologists also believe that the disease mutated slightly and became able to flourish under drier conditions. The climate in the western corn belt has changed since 1987 and many parts of Iowa and Nebraska now receive three to four more inches of rainfall than in the previous years. Pivot irrigation has become more popular in the more arid corn growing areas. The so called “opportunity time” mist emitted by the low pressure systems are also thought to create the 12 to 13 hour long moisture film on the leaves allowing entry by, and a rapid spread of, the foliar disease. True resistance to GLS is seen in some inbreds. However, none of these inbreds are currently being used in commercial hybrids. Currently, the best resistance is from inbreds developed in the southeastern states or from those deprived from tropical germplasm.
Chemical control of GLS is possible by applying one of several fungicides currently on the market with applications generally best around 5 days post tassel. Control of the disease to acceptable levels will take an effort on many growers’ part. The best defense against GLS is to plant hybrids with good GLS tolerance. This means that some corn producers may have to abandon their favorite hybrid. Good tolerance to GLS is available in different hybrids that also yield and perform well under other stresses. It is best to choose 3 to 4 hybrids of different genetics, and flowering dates, each containing good GLS tolerance. However, no hybrid is completely immune to GLS. If high levels of inoculum from the previous year, or an infected neighboring field are present, and weather conditions are perfect, even the immune system of a good hybrid can be overwhelmed. Therefore, the best management program should combine hybrid selection with a tillage program to bury the disease inoculum. All Hoegemeyer corn hybrids have a GLS rating listed in our seed guide as well as on individual hybrid tech sheets which are available on line at www.TheRightSeed.com
3% Early Pay Discount on all products until March15th
-
Save the Date! Hoegemeyer Homecoming on August 9, 2012 at Hooper, Nebraska
A forum to discuss farming in the Western Corn Belt – with advice from our team of experts.
get the dirt here >