Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Posts Tagged ‘Plant pathology’

Target Spot in Cotton

Posted by romeethredge on July 31, 2015

We’re seeing a little Target spot, aka Corynespora in cotton. This is the leafspot that we sometimes spray for, it’s about the only one that responds to fungicide sprays.

I saw it in a lush field that is waist deep with thick foliage and well watered.

In talking with crop consultant Wes Briggs, he says he’s seen it at low levels in several fields, nothing bad.  Here are some photos I took of this disease.

Thomas County Agent, Andrew Sawyer has an excellent post concerning cotton spots at this link: Cotton Leaf Spots

IMG_7765-001target3Here’s what it looks like under my microscope. target

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Cotton Angular leaf Spot

Posted by romeethredge on July 23, 2015

 COTTON ANGULAR LEAF SPOT (aka bacterial blight):   Angular leaf spot is a bacterial disease caused by the pathogen now known as Xanthomonas axonopodis pv. malvacearum.  We have not seen a major outbreak in many years but are seeing it more frequently this year.   I have seen it in a couple of fields here in Seminole county, and I’ve had reports of it from consultants in Decatur county.

Here’s advice from Dr. Bob Kemerait, UGA Extension Plant Pathology. 

A.  The disease is caused “angular leaf spot”  because the water-soaked lesions are typically defined by the veins of the cotton leaf and take on an angular appearance.

B.  As the lesion develops, it can take on an appearance more like target spot  ( like in second photo below)  but is typically differentiated from target spot because of a yellow halo around the spot and because the initial water-soaked lesion is still discernable in the larger lesion.

C.  Angular leaf spot CAN NOT be managed with a fungicide or anything else applied to the leaf.

D.  While the bacteria can be spread through moisture and splash from irrigation and rain, reducing irrigation is likely to cause more harm to the crop during hot weather than it will help manage the disease.

E.  Angular  leaf spot may produce rapid defoliation of the cotton crop in severe cases.  However, yield losses are not reported to be catastrophic and in a worst-case-scenario may approach 10% (note:  worst-case-scenario).

F. The angular leaf spot found thus far in Georgia has been south of Tift County and west of I-75; it is currently relatively confined.

 

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Peanut Impostor

Posted by romeethredge on July 10, 2015

When I came across this white stuff yesterday in a peanut field, it was startling. I thought I’d found some white mold aka southern stem rot (sclerotium rolfsii) disease.

But on closer inspection you can see that it’s the harmless, False White Mold (Phanerochaete). You can scrape this mold off and the stem underneath is not harmed. It also looks “toothy” and sometimes yellowed.

 

Conditions are right for white mold, however so preventative measures need to be taken now in our peanuts.

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Southern Rust in Seminole

Posted by romeethredge on July 2, 2015

Here is some Southern Corn Rust I saw this week here in Seminole County. I have been pleasantly surprised at how slowly southern rust has spread. In other words, it has not exploded this year as it has in some years. Even in this field it was spotty around, not a lot anywhere.  Part of the reason may be that most everyone protected their crop from the disease pretty well.

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Corn – Southern Rust in the Area 2015

Posted by romeethredge on June 8, 2015

There has been some southern rust found in Mitchell county Georgia by County Agent Andy Shirley. It’s now also been found inTerrell County, by Agent Nick McGhee.

Here’s a photo from last year when we had a bad problem with it in our corn fields.

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Here are comments from Dr. Bob Kemerait, UGA Plant Pathologist.  “Corn growers in south Georgia should be very much aware NOW that rust is here. 

Current weather patterns increase the risk. 

I believe that any irrigated field corn with good yield expectations and that is at tassel or beyond is a good candidate for treating with a fungicide.

 Corn approaching tassel is also certainly at risk.”

Here are some comments from Dr. Dewey Lee, UGA Grains Scientist.

“Even though this southern rust infection is earlier than usual, most of our corn crop is a little head of schedule.  While this might not be much comfort, it does mean we might have saved at least one spraying.  Last year, it was extremely difficult to stay a head of southern rust because the infectious time was longer than normal due to favorable conditions for infection.  Some corn in the southern areas of the state is as far along as the R3/R4 stage.  This makes it easier to control rust and reduce the impact since it is much closer to maturity.  Much of the corn crop though, is silking to early ear development (R2/R3) which adds roughly 2 to 3 weeks of time to our potential spraying.

If you have good yield potential (and most irrigated growers do), I would consider spraying a combination of fungicides to provide both a curative and preventative type of action.  There are great choices today from lots of sources.  You may not have a current infection taking place, but spores are active and an application of a combination of fungicides will be great insurance and likely prevent yield loss.  As long as southern rust is active, I would consider staying on a 14 day spray schedule or shorter.  This disease can certainly undermine all your efforts this year and significantly reduce corn yields.”

Link to Dewey’s Blog.

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Chlorothalonil Short, What do we do?

Posted by romeethredge on May 28, 2015

 Peanuts and the short supply of Bravo/cholothalonil:  What to do?? Here’s what Dr. Bob Kemerait, UGA Plant Pathologist says will be good. 

 

A.  Replace 1.5 pt/A chlorothalonil with 15 fl oz/A Elast

B.  Replace 1.5 pt/A chlorothalonil with 10 fl oz/A Topsin/thiophanate methyl, but ONLY one time!

C.  Replace 1.5 pt/A chlorothanil with 7.0 fl oz/A Stratego (concern about resistance management…)

D.  Replace 1.5 pt/A chlorothalonil with 3.5 fl oz/A Absolute (concern about resistance management…)

E.  Replace 1.5 pt/A chlorothalonil with 5.5 fl oz/A Alto (better to mix 1.0 pt/A chlorothalonil with 5.5 fl oz/A Alto, or at least SOME chlorothalonil with the Alto!)

F.  Replace 1.5 pt/A chlorothalonil with 5.5 fl oz/A Alto + 5 fl oz/A Topsin/thiophanate methyl

G.  Extend chlorothalonil with 1.0 pt/A chlorothalonil with 1.0 pt/A Kocide

H.  Extend chlorothalonil with 1.0 pt/A chlorothalonil with 5.0 fl oz/A Topsin/thiophanate methyl

I.  Extend chlorothalonil with 1.0 pt/A chlorothalonil with 2.0 fl oz/A propiconazole.

Posted in Peanuts, Plant Pathology | Tagged: , | Leave a Comment »

Bacterial Stalk Rot in Corn

Posted by romeethredge on May 23, 2015

I’ve not seen this Bacterial Stalk Rot before but crop consultant, Jim Griffin, brought me some diseased plants from far eastern Decatur county yesterday. We confirmed it with Dr. Bob Kemerait, UGA plant pathology, by photos and discussion.

We scouted the fields and found it in the areas irrigated from a pond. In areas not irrigated by that pond, we didn’t see it. It is in low amounts maybe half of one percent of plants, more in some areas, but it is startling to see. Fortunately, it is reported not to usually spread within the field. The bacterium causes a type of meltdown and you can sometimes smell it before you see it. It really stinks, especially if you cut into the stems. Univ of Nebraska has a good writeup about it. Here’s an excerpt…

“The initial symptom is discoloration of the leaf sheath and stalk at a node. As the disease progresses, lesions develop on the leaves and sheath. Disease then develops in the stalk and rapidly spreads up the stalk and into the leaves. As the decay progresses, a foul odor can be detected and the top of the plant can be very easily removedfrom the rest of the plant. The stalk rots completely and the top collapses. Bacterial stalk rot can affect the plant at any node from the soil surface up to the ear leaves and tassels. Infections that occur high on the plant may impair normal tasseling and affect subsequent pollination. Although it may spread along the plant to infect additional nodes, the bacteria do not usually spread to neighboring plants unless vectored by an insect. Splitting the stalk reveals internal discoloration and soft slimy rot mostly initiating at the nodes. Because the bacteria usually do not spread from plant to plant, diseased plants are quite often found scattered throughout the field. However, there are reports of plant-to-plant transmission by certain insect vectors.

Bacterial stalk and top rot is favored by high temperatures and high relative humidity. It can be a problem in areas of heavy rainfall or where overhead irrigation is used and the water is pumped from a lake, pond, or slow-moving stream.”

 

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NCLB 2015

Posted by romeethredge on May 14, 2015

We are finding some Northern Corn leaf Blight (NCLB) in field corn now at low levels. I had not found any until today, myself but crop consultant, Jim Griffin sent me some this photo yesterday of some he found in Baker county. Some of the lesions we are seeing may be Northern Corn Leaf spot which isn’t a big problem, but there is some NCLB at low levels in some fields.

He said it was in tall corn with a close rotation, every other year corn, not quite to tassel stage.

I found some at low levels in tasseling corn in Seminole county today.  I also saw some stinkbugs in corn at low levels. There are more of them near small grains fields that are drying down.

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Wheat Harvest 2015

Posted by romeethredge on May 13, 2015

We have begun wheat harvest in deep south Georgia. Moisture is running about 10% in some fields, depending on the variety as well.  I’ve heard some 60 to 70 bushel estimated yields. Some test weights are low, but some at 60 or so reported. We are seeing shriveled kernels from disease problems, mainly Fusarium head blight.  Look for the pink on them and it’s likely fusarium. This can cause deductions so if you are seeing pink on shriveled kernels then make sure to turn up the fans to blow most of that out.  I have photos of some below.

UGA Grains Scientist, Dewey Lee, has more observations at his Georgia Grain Crops.

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Fusarium Head blighted kernels on right side, notice pinkish appearance.

 

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Posted in Plant Pathology, Wheat | Tagged: , | 1 Comment »

Fusarium Head Scab….again

Posted by romeethredge on April 22, 2015

I didn’t think we’d see it 2 years in a row like this. But I’m seeing some wheat Fusarium head scab today here in Seminole county and it concerns me.  I don’t think at this point that we are seeing this disease at the level we saw last year and it will differ field by field. We just released a new publication concerning this disease at this post Fusarium Head Blight (Scab) of Wheat in Georgia.

It was bad last year and not at all bad before that. I would see it in low levels if at all. I started worrying about it when we started getting so much rain. Not much we can do about it. We may need to look at variety selection next year, and a few other things you can read about in the publication.

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Posted in Plant Pathology, Wheat | Tagged: , | 1 Comment »

 
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