Category Archives: Disease

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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Filed under Corn, Cotton, Disease, Peanuts, Tobacco, Weather

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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Filed under Disease, Pecans

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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Filed under Disease, Peanuts, Weed Science

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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Disease & Nematode Management Considerations For 2017 Peanut Planting

Peanut growers can use a different products at planting time for the management of diseases and nematodes. Decisions as too what product to use over another, or to use a product at all, can be very confusing. Fighting seedling disease used to be simple- all growers used a fungicide seed treatment, and if they wanted some “stand insurance” they could also spray Abound in-furrow. Today, in-furrow applications are important considerations for the management of tomato spotted wilt, seedling diseases, Cylindrocladium black rot, white mold, and nematodes, not to mention thrips! Below are management options for the growers put together by UGA Extension Pathologists Dr. Bob Kemerait, Dr. Tim Brenneman and Dr. Albert Culbreath:

Note: The rates provided here are on a “per/A” basis. Typically, the full rate can be placed in single rows; the rate is typically halved per twin row. For example, Abound, 6.0 fl oz/A in-furrow for single rows becomes Abound, 3.0 fl oz/A in each of the twin rows:

Management of Tomato Spotted Wilt

Tomato Spotted Wilt Virus

A number of products can be used to manage thrips on peanuts. However, only one product, Thimet (ai: phorate) is effective in reducing the risk to this disease. The reduction in risk to tomato spotted wilt is not related to the thrips control that it provides, rather is seems to be associated with the response of the plant to Thimet. Thimet likely activates defense-response genes in the peanut plant that help to protect the plant from the virus. Growers who want to plant early (before May 1), or who want to use cultivars with spotted wilt risk points greater than those of Georgia-06G, might especially want to consider to using Thimet for management of tomato spotted wilt.

Management of Seedling Diseases

Peanut seed and young seedlings are susceptible to attack from a number of fungal pathogens. The two most important fungal pathogens causing death of peanut seedings in Georgia are Rhizoctonia solani and Aspergillus niger. Fungicide seed treatments are a critical tool to manage seed rots and seedling diseases; currently nearly all seed is treated with Dynasty PD. Dynasy PD is composed of azoxystrobin, fludioxonil, and mefenoxam. However, growers can also protect the developing plants from seedling diseases with in-furrow fungicide applications of fungicides like Abound (5.7-11.4 fl oz/A), Proline (5.7 fl oz/A), and Evito (2.3-3.5 fl oz/A). These fungicides are typically used to compliment seed already treated with a fungicide seed treatment.

Aspergillus Crown Rot

The most effective in furrow spray for stand establishment has been Abound, although Proline also has activity on these pathogens and Evito is labeled for this use as well. The benefits of these products have not been as consistent in recent years, and research is underway to determine the factors involved.

Management of Cylindrocladium black rot (CBR) and early-season white mold

Proline (5.7 fl oz/A) applied in-furrow has been an important treatment for the management of CBR. Though this disease has been less widespread in recent years, an application of Proline in-furrow is still useful where there is a threat of CBR. When favorable conditions, such as very warm weather, occur early in the season, in-furrow applications of Proline also offer some protection from early-season white mold. The extent of the protection is likely less than that provided by banded applications of Proline 3-5 weeks after planting. Decisions to use Proline in-furrow should be made based upon a) risk to CBR, and b) risk to early-season white mold (although there are effective alternatives for white mold).

Mycelium and sclerotia (yellow bee bee’s) from white mold

Management of Nematodes

Nematode-resistant cultivars continue to hold up well against even high populations of root knot nematodes. However, growers electing to plant a susceptible cultivar like Georgia-06G in fields infested with the peanut root-knot nematode should consider the use of a nematicide. Popular nematicides for peanut production in Georgia include Telone II (4.5-6 gal/A), Velum Total (18 fl oz/A) and AgLogic 15G (7 lb/A). To prevent injury to seed and seedlings, fumigation with Telone II should occur 10-14 days prior to planting and when soil conditions are not too dry (powder) nor too wet (mud). Fumigation with Telone II can provide excellent control of nematodes but DOES NOT control thrips. Growers who use Telone II must still apply something for management of thrips.

Velum Total is a combination of fluopyram for management of nematodes and also imidicloprid for management of thrips. Growers who use Velum Total do not need to add any additional thrips control product in the open furrow. (Note that imidicloprid does not reduce the risk to tomato spotted wilt.) Also, use of Velum Total does provide additional early-season management of leaf spot diseases. The extent of this protection from leaf spot is such that growers should be able to skip the 30-day after planting fungicide application for leaf spot, unless they have planted a very susceptible cultivar like ‘Georgia-13M’ or TUFRunnerTM’511’.

A question that often arises is, “If I use Velum Total, do I get any protection against seedling diseases as well?” The “bottom line” to this question is that use of Velum Total should complement a seed treatment and be good “stand insurance” and we would not add anything else. The biggest factor by far to reduce the impact of seedling disease is the quality of the seed and putting that seed in the right soil conditions at the right time.

AgLogic 15G (7 lb/A) is for management of thrips and nematodes. AgLogic does not reduce the risk to tomato spotted wilt. The rate is lower than what was historically used for Temik 15G (10 lb/A). Additional research is needed to assess the efficacy of the 7 lb/A rate on management of nematodes. In high risk field it may be advisable to use a combination of these nematicide options.

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Implications Of Bacterial Boll Rot

At our Georgia Association of County Ag Agents (GACAA) meeting, we get to see presentations and posters of work done around the state. I wanted to share this poster done by Holly Anderson in Ben Hill County, EVEN THOUGH our conditions this year were as less conducive for boll rot as they have been in a long time.

We’re normally wet in our area and this is a concern of many growers. Dr. Kemerait always has points about boll rot, but it is unavoidable if cotton is subjected to prolonged periods of wetness and humidity late in the growing season. This project shows the progression of boll rot from infection to harvest and potential losses.

implicationsofbacterialbollrot-holly

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Filed under Cotton, Disease