Category Archives: Disease

Terminating Fungicide Sprays In Peanuts

Our peanuts are once again taking 140 – 150 days to mature. We’re digging in the 130’s only if peanuts are turning loose in the hull. This is a good crop, and we want to get all the weight and grades we can. UGA Extension Pathologist Dr. Bob Kemerait helps us out each yeah with an update on terminating fungicide sprays:

  1. Grower is 4 or more weeks away from harvest and currently has excellent disease control.
    • Suggestion – I recommend the grower apply at least one more fungicide at least for leaf spot control.
    • Suggestion – Given the low cost of tebuconazole, the grower may consider applying a tank-mix of tebuconazole  + chlorothalonil for added insurance of white mold and leaf spot.
    • NOTE: If white mold is not an issue, then the grower should stick with a leaf spot spray only.
  2. Grower is 4 or more weeks away from harvest and has disease problems in the field.
    • If the problem is with leaf spot – Grower should insure that any fungicide applied has systemic/curative activity. If a grower wants to use chlorothalonil, then they would mix a product like thiophanate methyl (Topsin M) or cyproconazole (Alto), with the chlorothalonil. Others may consider applying Priaxor, if they have not already applied Priaxor twice earlier in the season.
    • If the problem is white mold – Grower should continue with fungicide applications for management of white mold. If they have completed their regular white mold program, then they should extend the program, perhaps with a tebuconazole/chlorothalonil mix.  If the grower is unhappy with the level of control from their fungicide program, then we can offer alternative fungicides to apply.
    • If the problem is underground white mold – Underground white mold is difficult to control.  Applying a white mold fungicide ahead of irrigation or rain, or applying at night, can help to increase management of this disease.
  1. Grower is 3 or less weeks away from projected harvest and does not currently have a disease issue. Good news! This grower should be good-to-go for the remainder of the season and no more fungicides are required.  SEE NOTE BELOW ABOUT HURRICANES.
  2. Grower is 3 or less weeks away from harvest and has a problem with disease.
    • If leaf spot is a problem and 2-3 weeks away from harvest, a last leaf spot fungicide application may be beneficial. If leaf spot is too severe, then a last application will not help.  Tank mixing chlorothalonil with a systemic fungicide, like thiophanate methyl or other appropriate systemic fungicide, could be beneficial.
    • If white mold is a problem and harvest is 3 weeks away, then it is likely beneficial to apply a final white mold fungicide. If harvest is 2 weeks or less away, then it is unlikely that a fungicide will be of any benefit.

NOTE:  If harvest is likely to be delayed by threat from a hurricane or tropical storm, then the grower may reconsider recommendations for end-of-season fungicide applications.

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Row Crop Disease Update

In cotton this week checking whiteflies, we are reaching treatable thresholds by the way… I am also seeing some target spot in RANK cotton. Also, it is very low on the plant and is not moving up. Cotton I’ve looked at is 4th and 5th week of bloom. Below is a current disease update from UGA Extension Pathologist Dr. Bob Kemerait:

Cotton

The current weather is very favorable for development of target spot and also spread of bacterial blight.  To date, bacterial blight is only a problem in susceptible varieties…The season is not over yet, and things could change.

Target Spot seen in ‘rank’, irrigated cotton, but on the very lower leaves.

TARGET SPOT:  In some, but not all, of your trials  target spot is a significant issue. From your trials, some varieties are CLEARLY for susceptible. Conditions we have now are perfect for it.  Should every grower spray every field for target spot?  NO!  But growers SHOULD BE AWARE. In one field, target spot was becoming established, and I told him I would likely treat the field with a fungicide. In another field, no target spot was found and I told him I would not treat that field.

Peanuts

We are at a critical point in the peanut season. Reports of white mold in fields are coming in every day and I am receiving some reports of leaf spot. I don’t know of any fields where leaf spot is “out of control” and only one field where white mold is “breaking loose”.  However, both diseases can be explosive given the right environment and time to become established. Growers should stay on an appropriate fungicide program for these diseases and also Rhizoctonia limb rot. Timeliness and coverage are CRITICAL.

Soybeans

Asian soybean rust has been puzzling this year. We found it in kudzu very early in the season, yet to date it remains confined to kudzu in our southern tier of counties. I still expect soybean rust to “break out” as southern corn rust has done, but I can’t understand what it is doing now. Fortunately, our Sentinel Plots are being monitored, so we can keep you up-to-date. Even though the disease has been slow to develop, I still believe that there is merit, especially in southern Georgia, to protect the soybeans during late-bloom/early pod set, especially when applying something like dimilin and boron. There are other diseases, such as frogeye leaf spot, which can be problematic and that can be managed with the same fungicides at the same time.

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Weather & Disease Update

It’s hard to say we don’t want more rain, but more and more we’re saying just that. We’re having showers nearly every day or every other day, sometimes as much as an inch and a half. It’s starting to show up in the field where cotton is getting ‘wet feet.’ Some of our rain has come with strong winds. Our largest field of tobacco took a hit from these winds knocking plants to the ground in some places. The only hope is to stand it back up as best as possible. It is still causing issues with topping since the flowers on the ground began growing straight up.

We have a good crop of tobacco this year, but it was hit hard from strong winds and rain. Some areas completely blown to the ground.

Flowers turned from wind affects topping

From UGA weather station in Cairo, here are the rain numbers since the beginning of May.

Disease Update

Here is our latest disease update from UGA Extension Pathologist Dr. Bob Kemerait:

Southern Corn Rust: I was stunned when agents in our disease diagnosis class visiting a field in Morgan County found a very active spot of southern rust. Unbelievable because until yesterday, it had ONLY been found lightly in Seminole and Marion Counties. Obviously, as we expected, southern rust could be present anywhere in Georgia now.  Why it has not “exploded” yet is a mystery to me given the conditions we have had, but CLEARLY the spores have spread across the state.

The corn in that field as at hard-dough/early dent, so it does not need to be treated; however growers with later planted corn not yet at R6/dough stages should be aware there is at least some threat.

Target spot of Cotton: Perfect weather but I am NOT calling for an automatic fungicide application at first or at third bloom.  BUT I am saying that every cotton grower SHOULD be aware that these can be important and critical timings. As cotton approaches bloom, I hope growers can put some eyes and boots in the field and begin looking for it, lower leaves first. Weather is very favorable- growers with a history of disease in the field and those with high-input, strong yield potential should be the growers with the greatest chance for benefit. Target spot will not steal the entire crop, but it will take away a valuable portion of the crop.

Consider:  Growth stage (blooming yet?)  history of disease, reports from scouting, (have early symptoms been found?), what’s the weather like now and what is the forecast?  What is the value to the growing in a preemptive application “to be done with it”?

White mold and leaf spot in Peanut: We are seeing some of both.  Growers, don’t get behind!

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Pecan Fungicide ‘Rainfast’

 

With rain and humidity, we are having ideal conditions for scab. Some growers essentially continue to spray around the clock. A common question is, “How long does my fungicide need to dry before rain?” This is a question pathologists have worked on for some time, but there are many variables involved making it difficult to generate data. UGA Plant Pathologist Dr. Tim Brenneman recently offered the following suggestions based on his studies with pecan and also on similar studies he has conducted in peanut:

Highly systemic materials like phosphite must be absorbed into the plant. It may require as much as 1/2 a day for this process to take place so that the material can be highly effective. While DMIs and strobilurins or combination products like Absolute, Top Gard, Quadris Top, and Quilt have some systemic activity they are not as systemic as the phosphites. Still, they would need a little time to be effective, so several hours to half a day would be ideal. A surfactant (80/20 or other) would increase the uptake speed of these materials and would likely provide some benefit in the conditions we’ve had over the last week or so. However, do not include a surfactant with Phosphite.

While the DMIs and Strobis have some systemic activity they still function largely as protectants. Other materials like Dodine (ELast) or Tin are pure protectants. These materials (Dodine and Tin) would be the most prone to wash off when rain arrives shortly after spraying. Dodine does adhere tightly to the plant cuticle, which likely helps it. Rainfall that occurs less than one hour after spraying makes the fungicide pretty well ineffective. Any rainfall within 24 hrs after spraying with a pure protectant will likely reduce the effectiveness of control to some extent. For each additional hour between the spraying and rainfall you gain additional control.

Ideally, all fungicides should be applied prior to rain events. If circumstances prevent you from getting a spray on in time and you have to spray after a rain event, the DMI/Strobi combinations would be the best choice.

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Corn Disease To Scout

Some of our dryland corn is now tasseling. The rest of our corn is very, very close to tasseling, and many growers will put out a fungicide. And this is okay. Should we have sprayed before now? UGA Extension Pathologist Dr. Bob Kemerait has found that early fungicide applications (V5-V6) on early planted (Spring) corn has no  benefit to yield and disease, but can have “some” benefit on later planted corn. This is likely because corn planted behind corn will be affected earlier in the growth stage.

Former Seminole County Agent, Rome Ethredge found northern corn leaf blight (NCLB) last week. In corn disease, we are mostly watching for southern corn rust and NCLB. We have sentinel plots in the county to help us watch for rust. Unlike NCLB, southern rust is reintroduced each year and spores essentially blow in and re-infect corn.

Lesions o NCLB appear as a cigar shape. Photo by Rome Ethredge.

Control of NCLB

Northern corn leaf blight is more prominent where we have corn behind corn, overwintering in the leaf litter as well as irrigated corn. We have less of both situations in Thomas County. In fields with a) susceptible varieties and b) favorable conditions, you can have some NCLB in the field and NOT need to spray. When do we pull the trigger on spraying NCLB?Dr. Kemerait says treat for NCLB when lesions get as high as 3rd leaf from the ear leaf.

 

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Peanuts Cracking

Dryland peanuts are coming up in the northwest part of the county. This is where we have had more rain. We’re talking about thrips, herbicides and some disease issues now. Below is a graph from UGA Extension Peanut Entomologist Dr. Mark Abney on latest thrips counts:

Thrips numbers on our traps have remained relatively steady for the last 3 weeks, though we did see a spike last week in Colquitt County. My first thrips trials are just now emerging from the ground, and I have not heard any reports of thrips control problems on early planted peanut as of today.

I have had questions this week about rates of imidacloprid for in-furrow applications. I recommend the upper end of the rate range for whichever formulation a grower is using….We should NOT be doubling the rate or cutting the rate in half. Be sure to check the label of the product you are using as rates vary by formulation.

Weed Control

We may not have as much Valor as preemerge out there since we are dry and concern of no activation. Where we have Valor on the ground with good activation (0.5 – 0.75″ within 7 days), it usually gets us through our “at cracking ” treatments until we use Cadre. If we don’t have Valor, we will need to be gearing up for our cracking spray 15 – 25 days after planting. But we only need to apply ‘cracking’ sprays if weeds have come up.

Disease Control

The only note to make is this week’s rainfall this week could help to cool soils, at least in the short term, and reduce risk to Aspergillus crown rot of peanut.

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Pecan Fungicides Begin

Young Trees

All of our pecan fungicides have begun at this point. We have lots of newer planted trees in the county, here are some being sprayed last week. UGA Extension Horticulturalist Dr. Lenny Wells says trees in the first few years need to be sprayed but not on a detailed spray program. For very young trees, a few fungicide applications in a season with some Tin is good. Once the trees approach production age, we need to add a few more sprays throughout the season and get closer to a full spray program.

Timing

In our area, we have been hit so hard with scab that we tend to get our fungicide sprays out real soon. Dr. Wells always says we can wait a little longer than we do. He was down last week looking at a fertilizer situation, and we looked at trees around that were leafing out at different times. He explained the issue with spraying early is not having enough leaf area for the fungicide to contact.

The most difficult part is managing orchards for more than one cultivar, which all are pretty much the same. If Desirables are in the orchard, we have to begin spray on their schedule since they are more susceptible for scab. If an orchard doesn’t have desirables and mostly Stuart, you can wait until those leaves come out. Here is a few pictures of optimum fungicide initiation Dr. Wells and I looked at in an orchard last week.

Left – This is time to spray Desirable
Right – This is too early for Desirable

Optimum time to initiate Stuart fungicide sprays

Fungicide Schedule

Below is an 8-spray fungicide schedule from UGA Extension Horticulturalist Dr. Lenny Wells provided as an example to use for pecan scab management in light of emerging scab insensitivity issues surrounding some fungicides. Since Tin is an integral part of our fungicide arsenal for pecans, and we do see some orchards with insensitivity to Tin, we are recommending saving any Tin sprays for the nut scab period since this material is better on nut scab than it is on leaf scab.

1. Absolute

2. Tebuconazole+Topsin M+Phosphite

3. Absolute+Phosphite

4. Elast/Tin

5. Absolute

6. Elast/Tin

7. Elast/Tin

8. Elast/Tin

If rainfall during the growing season is excessive, more than 8 sprays will be required for management of scab on susceptible cultivars. Therefore, the following program serves as an example of how to accommodate this need:

1. Absolute

2. Tebuconazole+Topsin M+Phosphite

3. Absolute+Phosphite

4. Elast/Tin

5. Absolute

6. Elast/Tin

7. Elast/Tin

8. Quadris Top

9. Elast/Tin

10. Elast/Tin

These examples serve only as two possible options for fungicide programs to manage scab. Many more could be developed. If an orchard has a documented high level of insensitivity to any of the fungicides listed above, the grower should contact one of the UGA Extension for specific recommendations.

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