Night 3 – “Corn Disease Update”
Dr. Pierce Paul, Chair and Professor
Department of Plant Pathology
As harvest approaches, its time to check our corn plants for stalk integrity. Time spent tin the field now, may pay huge dividends later this fall. As stalk tissue becomes compromised below the main ear the stalk may become brittle or weak and be prone to lodging.
There are a number of plant pathogens that can cause stalk rot including, Anthracnose, Bacteria, Charcoal, Diplodia, Fusarium, Gibberella, and Pythium. Some of these stalk rots have very characteristic symptoms that can help identify the specific problem, while others may require laboratory diagnosis (Table 1). The Purdue Extension Publication Corn Diseases: Stalk Rot has good images to help identify the major stalk rot diseases. (https://www.extension.purdue.edu/extmedia/BP/BP-89-W.pdf ).
Check field by using the Push or Pinch Test by evaluating 20 plants in at least five random areas in a field.
Threshold: 10% or more of the stalks fail then consider field for early harvesting to avoid risk for lodging.
What can you do in the future – management options will depend on the specific disease (see table 1). Production practices that promote good plant health including balanced fertilization, appropriate plant populations, and good water management can reduce stresses that might predispose corn to stalk rot. In addition, these key management tools can help mitigate future stalk rot issues.
Corn
Most of the corn that I have seen this week is in either the R4 (Dough) or the R5 growth stage.
R5 – Dent
Scouting
I have heard a wide range for projected corn yields this year. The Yield Component Method is the most widely used procedure for estimating corn yield. While you are out checking potential corn yields, also keep an eye out for:
Soybeans are continuing to mature. Last week I highlighted the R6 growth stage the next stage is R7 the last growth stage prior to maturity.
R7 – Begining Maturity
Scouting
Estimating soybean yields
It is much more difficult to accurately predict soybean yield. The process to estimate soybean yields can be found here.
They are here! Palmer Amaranth and Waterhemp are prevalent in MANY Knox County fields. One female plant can produce 1,000,000 seeds. If you find Palmer Amaranth or Waterhemp you should do whatever you can to prevent these devastating weeds from going to seed, including removing the entire plant from the field.
Continue to remain vigilant!
Click here for tips on identifying pigweed, palmer and waterhemp.
Most of the corn that I have seen this week is in either the R3 (Milk) or the R4 (Dough) growth stage. Some of our early maturing hybrids have reached the R5 dent stage.
Disease pressure throughout the county continues to be very low. Continue to scout for:
Most of the corn that I have seen this week is in the R6 (Full Seed) growth stage. Some of the early maturity beans are entering the R7 (Beginning Maturity) stage soon.
Scouting
Disease pressure throughout the county continues to be very low. As you continue to scout your bean fields, look for:
Last week I highlighted the R3 (milk) growth stage. R4 is the next stage, occurring approximately 26 days after silking.
R4 – Dough
Scouting
Disease pressure throughout the county continues to be very low. Continue to scout for:
Soybeans are continuing to mature. Recent rains will help with seed fill. Last week I highlighted the R5 (Beginning Seed) growth stage. R6 is the next stage, occurring approximately 10 days after R4.
R6 – Full Seed
Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf
Scouting
As you continue to scout your bean fields, look for
Click here for tips on identifying pigweed, palmer and waterhemp.
Red crown rot (RCR) is a soybean disease caused by the soilborne fungus Calonectria ilicicola that is spreading to parts of the Midwest. There have been no confirmed reports of RCR in Ohio, but it has been detected in Kentucky and Illinois. RCR can be easily confused with other soybean diseases that cause similar foliar symptoms.
RCR can be misidentified as sudden death syndrome (SDS) or brown stem rot (BSR) as all three diseases can cause yellowing between the leaf veins or interveinal leaf chlorosis (Figure 1.)
Proper diagnosis will require digging up the plant, scraping the soil off, and inspecting for red discoloration on the outer stem (Figure 2). Also look for small, brick red perithecia (fungal sexual structure) on the lower stem or root crown area. These perithecia will be smaller than the tip of a pencil and more likely to be observed following wet weather.
In general, concentrate scouting efforts for RCR in low-lying, saturated areas of the field between the R3 (beginning pod) and R5 (beginning seed) growth stages. Keep an eye out for scattered patches of plants dying off early.
If you have questionable areas in your beans and suspect RCR or sudden death let me know. I can collect plant samples and send them to our lab for diagnosis.
Corn development continues to vary throughout the county. Last week I highlighted the R2 (Blister) growth stage. R3 is the next stage, occurring approximately 20 days after silking.
R3 – Milk Stage
Disease pressure throughout the county continues to be very low. At this stage of growth, with little to no disease pressure, and new crop corn under $5 can we justify at least $25 per acre for a fungicide application?
Read more on disease scouting here.
Like corn, soybean development continues to vary throughout the county. Beans are looking much better than they were a few weeks ago. Last week I highlighted the R4 (Full Pod) growth stage. R5 (Beginning Seed) is the next stage, occurring approximately 10 days after R4.
Scouting
All of the bean fields that I have seen this week look very similar to this one. I am seeing very little (if any) disease pressure. Current and projected weather conditions may change this. As you continue to scout your bean fields, look for Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot.
It’s that time of year when weeds are beginning to show their ugly heads above the soybean canopy in many fields. During your scouting, if you find Palmer Amaranth or Waterhemp you should do whatever you can to prevent these devastating weeds from going to seed, including removing the entire plant from the field.
Click here for tips on identifying pigweed, palmer and waterhemp.
Source: Horacio Lopez-Nicora
Now is the time to scout for mid-season soybean diseases. Though, disease levels across Ohio are low to moderate, current weather conditions are turning things around, and more fields are developing disease symptoms.
Sudden Death Syndrome (SDS)
We are finding fields in Ohio affected by sudden death syndrome (SDS). These symptoms are showing up earlier than normal. SDS is caused by the fungal pathogen Fusarium virguliforme. This species is the most prevalent in the region, however, other Fusarium species can cause SDS. SDS above-ground symptoms can be confused with those produced by a different fungus (Cadophora gregata) that causes brown stem rot (BSR). To distinguish SDS from BSR, symptomatic plants should be dug out and stem cut open longitudinally. SDS-infected plants have white, healthy-looking pith, while BSR-infected plants present brown discoloration of the pith. Moreover, fields with severe SDS symptoms can also have high levels of soybean cyst nematode (SCN).
If you are seeing SDS symptoms, we encourage you to submit a sample to the Soybean Pathology and Nematology Laboratory in the Department of Plant Pathology at The Ohio State University in Columbus (read more HERE). We will confirm if it is SDS or BSR; additionally, if it is SDS, we want to determine what Fusarium species is the causal agent. To submit samples, dig out three to five symptomatic plants (including roots), placed them in a plastic bag, complete the SDS submission form, and submit them to our lab. Do not hesitate to contact your extension educator or us if you have any questions.
White Mold, and Phytophthora Root and Stem Rot
Weather conditions are favorable for development of white mold, a fungal disease caused by Sclerotinia sclerotiorum. To scout for this disease, we recommend walking soybean fields and looking in-between rows. A white fluffy mass of fungal mycelia will be observed in infected plants (Fig. 4). Black round sclerotia will be present amidst the white mycelia. Visit here for more information about scouting for white mold of soybean.
We continue to receive samples with plants affected by Phytophthora root and stem rot. Commonly, these samples come from fields with poor drainage. Phytophthora root and stem rot can sometimes be confused with stem canker and white mold. You are welcome to submit samples to the Soybean Pathology and Nematology Lab for diagnosis. Visit here for more information about scouting for Phytophthora root and stem rot in soybean.
Frogeye Leaf Spot
We are finding frogeye leaf spot in our fungicide trials in northern and southern Ohio. Frogeye leaf spot is caused by a fungal pathogen (Cercospora sojina) which can reduce yield if plants are severely affected between R3 to R5 soybean growth stages. This year, symptoms in Ohio are visible at R2/R3 growth stage. We encourage growers to submit samples with frogeye leaf spot lesions to our lab. The fungus can develop resistance to fungicide, and we want to determine if these populations are present in Ohio. Best way to submit frogeye leaf spot samples to our lab is by placing symptomatic leaves in a plastic Ziploc bag and mail it to our lab as soon as possible. Keep samples in cool conditions and avoid exposure to sunlight and heat. Visit here for more information on frogeye leaf spot.
We can help diagnose soybean diseases with you!
You are welcome to submit your samples to the address below. Contact us if you have any questions. Send your samples to:
Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu
Source: Horacio Lopez-Nicora
We are finding fields in Ohio affected by sudden death syndrome (SDS). These symptoms are showing up earlier than normal. SDS is caused by the fungal pathogen Fusarium virguliforme. This species is the most prevalent in the region, however, other Fusarium species can cause SDS.
With support and funding from Ohio Soybean Council, we will process soybean plants with SDS symptoms from fields in Ohio to: 1) Determine the species and genetic diversity of Fusarium associated with SDS in Ohio, and 2) Determine the fungicide sensitivity of isolates in the culture collection. To successfully achieve these goals, we need your help.
If you are seeing SDS symptoms, we encourage you to submit a sample to the Soybean Pathology and Nematology Laboratory in the Department of Plant Pathology at The Ohio State University in Columbus (read more HERE). If it is SDS, we want to determine what Fusarium species is the causal agent. To submit samples, dig out three to five symptomatic plants (including roots), placed them in a plastic bag, complete the SDS submission form, and submit them to our lab. Do not hesitate to contact your extension educator or us if you have any questions. Read more about SDS and other mid-season diseases of soybean HERE.
Mail your samples to:
OSU Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu
Corn development continues to vary throughout the county. Last week I highlighted the R1 (Silking) growth stage. R2 is the next stage, occurring approximately 10 days after silking.
R2 – Blister
Disease pressure throughout the county is very low. SO … Do I spray or not? This is literally the same decision that we had to make with our wheat crop this year. Read more on disease scouting here.
Like corn, soybean development continues to vary throughout the county. Beans are looking much better than they were a few weeks ago. Last week I highlighted the R3 (Beginning Pod) growth stage. R4 (Full Pod) is the next stage, occurring approximately 10 days after R3.
R4 – Full Pod
Scouting
All of the bean fields that I have seen this week look very similar to this one. I am seeing very little (if any) disease pressure. Current and projected weather conditions may change this. As you continue to scout your bean fields, look for Sudden Death Syndrome, White Mold, and Frogeye Leaf Spot. More information on scouting for these problems next week.