Month: August 2017

Corn Leaf Disease beginning to show in numerous hybrids.

Del Voight – Penn State Extension

Corn Leaf Diseases – Adapted from Purdue University Plan Pathology.

Corn Leaf Diseases – Adapted from Purdue University Plan Pathology.

Many of my colleagues are reported that they viewed numerous hybrids exhibiting gray leaf spot infections.     However it is wise to determine the hybrids performance in resisting plant diseases.  The major rule in managing leaf diseases is similar to wheat in that one strives to keep the leaf that feeds the ear clean of disease.  Infections below that point typically have less of an impact on corn yields.  Most if not all recommendations particularly for no till corn will stem in hybrid selection to manage diseases.  Applications during tasseling are also an option.   Data from across the east and Midwest is variable and the key to determine the need to treat is related to specific field conditions.  In some studies completed with industry and Extension involvement it appears that fields that have observable disease infecting the lower leaves, fields with hybrids that are prone to disease infection, and reduced tilled fields that are showing signs of infection are fields that may prove to return a profit.

LEAF DISEASES
CORN

Disease Name: Gray Leaf Spot

Pathogen: Fungus. Cercospora zeae-maydis

Symptoms: Initial lesions appear as greenish black water soaked circular areas with chlorotic halos, expanding into oval and then the diagnostic parallel sided rectangular brownish gray lesions.

Conditions: Infection is favored by extended warm, wet, humid weather.

Inoculum Survival: Infected crop residue (leaves and leaf sheaths).

Inoculum Dispersal: Airborne spores.

Management: Select hybrids with resistance (tolerance based on risk), two year crop rotation, cleanly plow under infected residue.
Click on an image to display it in larger detail.
CORN

Disease Name: Anthracnose Leaf Blight

Pathogen: Fungus. Colletotrichum graminicola

Symptoms: Small, oval to elongated water-soaked lesions enlarge to become brown, spindle shaped spots with yellow to reddish-brown borders. Lesions may coalesce and blight entire leaves. Older lesions will turn gray in the center with small black specks (acervuli with sterile black hairs). Leaf blight may be followed by top kill and stalk rot. Leaf blight rarely causes large yield losses. Stalk rot phase is most important (see Anthracnose Stalk Rot).

Conditions: Favored by cool to warm, wet, humid weather, continuous corn with reduced tillage.

Inoculum Survival: Infected crop residue (leaves, leaf sheaths and stalks), seed (endosperm).

Inoculum Dispersal: Airborne spores.

Management: Resistant hybrids, rotate corn with nongrass crops. Cleanly plow under infected residue.
Click on an image to display it in larger detail.
CORN

Disease Name: Common Corn Rust

Pathogen: Fungus. Puccinia sorghi

Symptoms: Initial symptoms are chlorotic flecks on leaf surfaces. Flecks develop into oval to elongate reddish brown powdery pustules on upper and lower leaf surfaces. Reddish brown spores break through the leaf epidermis. Pustules become brownish-black as they mature. Usually not a serious disease in hybrids.

Conditions: Disease favored by cool (66 F optimum) humid weather.

Inoculum Survival: Spores blown into the Midwest from the South. Does not survive winter in Indiana, except possibly in rare years along the Ohio River.

Inoculum Dispersal: Airborne spores.

Management: Resistant hybrids. Foliar fungicides may be useful in seed production fields.
Click on an image to display it in larger detail
CORN

Disease Name: Southern Corn Rust

Pathogen: Fungus. Puccinia polysora

Symptoms: Similar to common rust except pustules occur almost exclusively on the upper leaf surface, rarely on lower. Pustules are more orange than brick-red and slower to break through epidermis of leaf than common rust pustules.

Conditions: Favored by high humidity and temperatures around 80 F.

Inoculum Survival: Spores blown into the Midwest from the South. Does not survive winter in Indiana, except possibly in rare years along the Ohio River.

Inoculum Dispersal: Airborne spores.

Management: Resistant hybrids. Foliar fungicides may be useful in seed production fields.
Click on an image to display it in larger detail.
CORN

Disease Name: Northern Corn Leaf Blight

Pathogen: Fungus. Exserohilum turcicum

Symptoms: Long cigar-shaped gray-green or tan lesions.

Conditions: Favored by extended wet, cool, humid weather, minimum tillage, continuous corn. Usually occurs during or after pollination.

Inoculum Survival: Infected crop residue (leaves, husks, stalks).

Inoculum Dispersal: Airborne spores.

Management: Resistant hybrids. Foliar fungicides may be useful in seed production fields. Cleanly plow under infected residue.
Click on an image to display it in larger detail.
CORN

Disease Name: Northern Leaf Spot

Pathogen: Fungus. Helminthosporium carbonum (Race 3)

Symptoms: Narrow, small, linear to oval shaped leaf lesions. Lesion type may vary with the genotype of host and isolate. Lesions are grayish tan and surrounded by a light to darkly pigmented (usually purple) border. Chain-like leaf lesions are often produced.

Conditions: Favored by moderate temperatures and high relative humidity, minimum tillage, continuous corn.

Inoculum Survival: Infected crop residue (leaves, husks, stalks, seed).

Inoculum Dispersal: Airborne spores.

Management: Resistant hybrids. Disease is primarily a problem in seed production fields with certain highly susceptible inbreds. Foliar fungicides may be useful in seed production fields. Cleanly plow under infected residue.
Delbert G. Voight, Jr. -M.S, CCA Penn State Extension – Crop Management Team
2120 Cornwall Road
Lebanon, Pa 17042
7178210699

Brown Stem Rot- Case Study

Del Voight Penn State Extension

Street View of problem area

 

Visible Leaf Disease narrowing diagnosis down to Brown Stem and or Sudden Death
Initial Walk in view of problem area

 

Root area to pull infected plants and begin to cut stems in two to differentiate between BSR and SDS

 

 

 

Cut Stems with the initial browning of the stem will check field in a week to see if more distinct stem browning occurs. No presence of the bluish fruiting bodies of SDS at this point leaning to BSR however that there are distinct differences in the internal stem browning that you would look for between the two diseases, even if you never see any blue mycelium.  With BSR, the pith (very center of stem) becomes brown (image below).  With SDS, the cortex (the tissue surrounding the pith) becomes discolored.  So, that pic is not really leaning toward BSR, but there can be a few other things that cause cortex discoloration, so it is not definitive yet.

 

Update Checked field 2 weeks after initial call and found fruiting bodies on roots and the stem remained water soaked in appearance.  This now confirms SDS and management for future soybean crops should consider this disease.

 

Note the bluish fruiting bodies

 

Note the absence of brown stem more water soaked appearance with SDS.

For more detailed information and to walk through distinguishing between SDS and BSR as well as several other maladies navigate to https://crop-protection-network.s3.amazonaws.com/publications/cpn-1011-sudden-death-syndrome.pdf

 

White mold in Soybeans Lebanon Case Study

Early morning call to look at bean field.  Here we go another day of more diseases popping up. Here is  a case study.Drive by picture of suspect field.

Video looking into the field

Walking into white mold field

Inspect area with dead plants and see cottony growth on the plant stem.

Diagnose- White mold

What to do now?  Nothing infection occurred during  flowering

Combine infected field last and clean combine after field to prevent movement.

In two years what is that  years plan?

Select a highly resistant variety
Utilize wide rows, consider Cobra early to mushroom phase of disease on soil surface. Another option is the use of biologicals such as Trichoderma,  Ulocladium, and others still to be identified to decrease the presence of the organism.  There needs to be more work on this approach as to timing in soybeans but is an option.

Consider fungicides active on this disease(Aproach, Domark etc) might require two applications. The PA On Farm Soybean network looked at this disease and with applications of Aproach three out of 4 locations had a significant response to controlling the disease and yields ranged from 4.8 to 16 bu/acre due to treatment.

How long does this field require management for white mold?

The hardened cases termed sclerotia can last for a few years suggesting that a management plan for at least three rotations in soybeans or going 5 years continuous corn might be in order.  Be mindful that alfalfa is also a host so that is not an option.

More info?

http://extension.psu.edu/plants/crops/news/2014/09/so-youve-got-white-mold-in-soybeans