{"id":49480,"date":"2022-12-02T10:02:48","date_gmt":"2022-12-02T10:02:48","guid":{"rendered":"https:\/\/dev.metos.global\/?page_id=49480"},"modified":"2026-05-04T09:39:27","modified_gmt":"2026-05-04T09:39:27","slug":"disease-models-corn","status":"publish","type":"page","link":"https:\/\/metos.global\/en\/disease-models-corn\/","title":{"rendered":"Disease models – corn"},"content":{"rendered":"\t\t
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Corn <\/b>disease models\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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CORN<\/br>LEAF BLIGHT<\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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FUSARIUM EAR ROT -<\/br>Fusarium spp.<\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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GRAY LEAF SPOT -<\/br>Cercospora zea maydis<\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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Corn leaf blight<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Two diseases are summarized under the name\u00a0Corn Leaf Blight<\/strong>. In the moderate and cool climate we will find the\u00a0Northern Corn Leaf Blight<\/strong>\u00a0caused by the disease\u00a0Helminthosporium turcicum<\/em>. Whereas it warmer climate we might find the\u00a0Southern Corn Leaf Blight<\/strong>\u00a0caused by the pathogen\u00a0Bipolaris maydis<\/em>\u00a0(Nisikado & Miyake) Shoemaker, teleomorph\u00a0Cochliobolus heterostrophus<\/em> (Drechs.) Drechs. This disease became famous when it has led to very high losses in the year 1970 in which a very warm summer climate combined with a very successful parent genome widespread in the corn grown in the US at this time.<\/p>

Southern corn Leaf Blight (Bipolaris maydis<\/em>)<\/h3>

\u2022\u00a0SCLB: Biology and Disease Cycle<\/a>
\u2022\u00a0SCLB: Infection Model<\/a><\/p>

Southern Corn Leaf Blight\u00a0is a disease caused by the pathogenic fungus\u00a0Bipolaris maydis<\/em>. This was a minor disease of corn for many years, with no economic effect on yield. In 1970, a highly virulent strain called Race T appeared on corn hybrids with Texas male-sterile cytoplasm. Losses were severe.<\/p>

Symptoms<\/span><\/p>

Symptoms of Race lesions are spindle-shaped with yellow-green halos. They will later have dark, reddish-brown borders and occur on leaves, stalks, leaf sheaths, husks, and shanks. Cob Rot ear occurs as well as ear drop. The fungus overwinters in corn debris and on the seed. Wind and splashing water spread the spores rapidly in the field under ideal conditions, cycling in about 72 hours. Control with resistant hybrids.<\/p>

Biology and Disease Cycle<\/span><\/p>

Southern corn leaf blight\u00a0(SCLB) is favoured by\u00a0warm temperatures (68-90\u00b0F or 20-32\u00b0C) and high humidities<\/u>. Thus, it tends to be a problem in the Southern half of Illinois, although it can be found farther north if weather conditions are favourable. Frequent\u00a0rainy periods<\/u> enhance disease development.<\/p>

The symptoms of SCLB are\u00a0leaf lesions<\/u>\u00a0ranging from minute specks to spots of one-half inch wide and one and one-half inches in length. They are oblong, parallel-sided, and tan to greyish in colour. A purplish to brown border may appear on the lesions depending on the genetic background of the plant. Early and severe infections in susceptible plants predisposes them to stalk rots.<\/p>

The fungus overwinters in corn debris as spores or mycelium.\u00a0Spores are spread by wind or splashing water<\/u> to growing plants. After infection and colonization, sporulation from these primary lesions serves as the source for secondary spread and infections as long as weather conditions are favorable for disease development and living tissues are present. The disease cycle may repeat every few days under ideal conditions. Germination of spores and penetration into the plant can occur within six hours when free water is present on the leaf surface and temperatures are between 15 and 28\u00b0C. Control of SCLB is easily accomplished with resistant hybrids. Although some slight flecking may be found in some hybrids, this is simply a part of the resistant reaction and does not lead to any economic loss.<\/p>

Burial of crop residue is helpful where erosion is not a problem. Crop rotation is especially suggested where no-till is used or where heavy crop residues are found. Since this fungus overwinters on debris, the planting of corn into such residues may result in earlier infection and poor seedling performance. Foliar fungicides are useful in seed production fields. For optimal control, it is important to control foliar disease during the period from 14 days before tasselling to 21 days after tasselling. Research has shown that this four-week period is the most critical for leaf blight damage and that yields and quality are most affected if susceptible inbred are not protected at this time.<\/p>

Infection Model<\/span><\/p>

This disease needs free water (leaf wetness) to infect plant tissue. Therefore conditions for starting an infection are:\u00a0leaf wetness and temperatures warmer than 15\u00b0C<\/u>. The infection will be finished after we can accumulate 100 degree hours (temperature and leaf wetness hours).<\/p>

START SCLBinfection: if leaf wetness > 0 and air temperature >= 15 then begin<\/p>

INCREASE of INFECTION: SCLBinfection actual hour =SCLBinfection former hour + (air temperature * leaf wetness period in minutes)<\/p>

STOP: if conditions are not given (no leaf wetness, temperature below 15\u00b0C), or if SCLBinfection > 100*60 \u00b0C (= degreeminutes) then SCLBinfection = 100*60 (in sum 6000 degree minutes or 100 degreehours (wich is for example about 6hours leaf wetness at 15\u00b0C or 5hours leaf wetness at 18\u00b0C), of leaf wetness at a temperature higher than 15\u00b0C is the maximum).
(If Temperature is higher than 15\u00b0C and leaf wetness for more than 100*60\u00b0C accumulated Temperature per minute infection is complete)<\/p>

These models have been designed following the Report on Plant Diseases 202 \u2013 Common Leaf Blights and Spots of Corn by Mohammad Babadoost.<\/p>

Extension Specialist in Fruit and Vegetable Diseases, Department of Crop Sciences, the University of Illinois at Urbana-Champaign.<\/p>

Northern Corn Leaf Blight (Exserohilum turcicum<\/em>)<\/h3>

Northern corn leaf blight (NCLB)<\/u>, caused by the fungus\u00a0Exserohilum turcicum<\/em>\u00a0previously called\u00a0Helmithosporium turcicum<\/em>, can cause yield losses in humid areas where corn is grown. In moderate humid climate the disease can occur everywhere, but usually does not appear in fields before silking. This disease rarely causes significant yield losses during dry weather, but during wet weather periods it may result in losses of over 30%, especially when established on the upper leaves at the silking stage of maize development. If leaf damage is only moderate or is delayed to about 6 weeks after silking, yield losses are mostly minimal. Northern corn leaf blight also predisposes corn to stalk rot by increasing stress on the plants.<\/p>

Infection model<\/span><\/p>

Exserohilum turcicum<\/em>\u00a0is able to infect the leaves of the corn plant when temperature and leaf wetness conditions are given. The time span to infect plant tissue is depending on the\u00a0actual air temperature and leaf wetness period.<\/span> The infection can take place, if temperature is ranging from 13\u00b0C to 28\u00b0C.\u00a0At a temperature of 18\u00b0C it will need 18 hours for infection<\/u>. If the temperature is lower it will need even longer time and if it is warmer it will need a shorter leaf wetness period.<\/p>

START of the calculation of a NCLBinfection: If (leaf wetness > 0) and (air temperature >= 13) and (air temperature <= 28) INCREASE: NCLBinfection actual:=NCLBinfection of the former hour +((air temperature-13)*leaf wetness duration in minutes). STOP: no leaf wetness, temperature not in the optimal range or if NCLBinfection > (18-13)*18*60 then NCLBinfection = (18-13)*18*60. That means that in sum 5400 degreeminutes (= 90degreehours) could be reached then an infection is fulfilled (= (18\u00b0C- 13\u00b0C)* 18hours leaf wetness in minutes (18*60). At 18\u00b0C it needs 18hours of leaf wetness for an infection. If the temperature is higher or leaf wetness periods are longer it is still 5400 (all values above are 100% infection).<\/p>

These models have been designed following the Report on Plant Diseases 202 \u2013 Common Leaf Blights and Spots of Corn by Mohammad Babadoost.<\/p>

M. Babadoost is an Extension Specialist in Fruit and Vegetable Diseases, Department of Crop Sciences, the University of Illinois at Urbana-Champaign.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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Fusarium ear rot<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fusarium Ear Rot\u00a0is the most common fungal disease on corn ears. It is caused by several species of\u00a0Fusarium<\/em>.<\/p>

Symptoms<\/strong><\/h3>

Symptoms of Fusarium ear rots are a white to pink- or salmon-colored mold, beginning anywhere on the ear or scattered throughout. Often the decay begins with insect-damaged kernels. Usually, it does not involve the whole ear. Infected kernels are often tan or brown, or have white streaks. These fungi can produce mycotoxins.<\/p>

Biology of Fusarium ssp.<\/em> on Corn<\/h3>

The most common ear diseases in the Midwest are caused by\u00a0Fusarium spp.<\/em>\u00a0fungi.\u00a0\u201cFusarium ear rot\u201d or \u201cFusarium kernel rot\u201d<\/u>\u00a0refer to the disease caused by\u00a0Fusarium verticillioides, F. proliferatum and F. subglutinans<\/em>. Symptoms of Fusarium ear rots are a white to pink or salmon-colored mold, beginning anywhere on the ear or scattered throughout. Often the decay begins with insect-damaged kernels, but most of the ear can be affected. Infected kernels are often tan or brown-colored, or have white streaks. Fusarium species also cause corn stalk rots. The fungi survive on corn residue and the residue of other plants, especially grasses. Fusarium spores are spread by wind and splashing rain to the silks, which are most susceptible as they are senescent and turn brown. Infection of kernels can also occur through the stalk, but this mode of kernel infection is less common. Insect damaged kernels are very susceptible, and spores carried on the insects can infect the damaged kernels.<\/p>

Gibberella ear rot<\/u>\u00a0of corn is caused by the fungus\u00a0Gibberella zeae<\/em>, also known as\u00a0Fusarium graminearum<\/em>.<\/p>

Maisfusarium1 1It can be identified most readily by the red or pink color of the mold. It almost always begins at the tip of the ear. In some cases, the color is too pale to bee seen readily, so the mold appears white. In this case, it may not always be possible to distinguish\u00a0Gibberella<\/em>\u00a0ear rot from Fusarium ear rot without microscopic examination.<\/p>

This fungus also causes corn stalk rot and Head Scab of wheat; it survives in corn and small grain residue.<\/p>

The spores of this fungus infect through silks; stalk infections are not believed to lead to Gibberella ear rot. Spores reach the silks by splashing water or they may be carried by insects. Infections may originate at insect wounds rather than at the ear tip.<\/p>

Gibberella ear rot\u00a0infections occur more commonly when the\u00a0weather is cool and wet<\/u>\u00a0during the first five days after silking. Continued development of the mold also depends on\u00a0subsequent cool, wet weather. Optimum temperatures for disease development are 19\u00b0C \u2013 24\u00b0C.<\/u><\/p>

Corn Fusarium Infection Model<\/h3>

Corn and Wheat is susceptible for fusarium infections in BBCH stage 61 to 75. After stage 75 the model is only used in case of heavy infestations of the European Corn Borer.<\/p>

The fungal agents belonging to the Fusarium Head Blight complex on corn are known to be favored by\u00a0warm temperatures of 20 \u00b0C to 30 \u00b0C<\/u>\u00a0and\u00a0long humid periods<\/u>. Several day long leaf wetness periods will lead to early visible symptoms. But Symptoms can be seen after a longer latency period if the infection is followed by and leaf wetness period of 18 hours or even shorter. Symptoms can be found after artificial inoculation at temperatures of 15\u00b0C too. Summarizing all different temperatures and moisture combination, which we found in literature we decided to point out\u00a0Fusarium Head blight Infections\u00a0if\u00a0temperature and leaf wetness period or periods with more than 85% relative humidity<\/u>\u00a0are exceeding the values visualised in the following graph.<\/p>

Infections are started when the air temperature is between 2 and 32\u00b0C and rain sum by 2 mm or more or rel. humidity of more than 85%. Infection increases when rel. humidity stays equal or more than 85% (when no leaf wetness occurs). But if rel. humidity decreases lower as 85%r.h. the infection progress stops.<\/u><\/p>

Fusarium Head Blight Infection can be assumed if the infection progress value reaches 100%. The calculation of this progress value follows the relation in between the duration of moist conditions and the temperature displayed in the graph above.<\/p>

This model is used to visualize the infection days and the climate conditions. The grower\u2019s knowledge about the development stage of the different wheat varieties he grows, which gives him the possibility to access if he should apply a curative spray immediately after infection.<\/p>

References:<\/em><\/p>