Lowndes – Echols Ag News

Downy Mildew Disease

Published on 06/04/19

Georgia vegetable growers need to apply fungicides to stay ahead of downy mildew disease.

By Clint Thompson for CAES News

Georgia vegetable farmers should be on alert as downy mildew disease has been spotted in at least three southern Georgia counties this spring. Additional counties could follow as weather conditions remain favorable for the disease into early June, according to University of Georgia Cooperative Extension plant pathologist Bhabesh Dutta.

Cucurbit crops — like cucumbers, melons, squashes and pumpkins — are susceptible to the disease. Dutta ranks downy mildew among the top diseases in cucurbit crops, along with Fusarium wilt and Phytophthora fruit rot.

Downy mildew disease can destroy plant foliage and cause the leaves to curl and die. Without healthy leaves and vines, a plant is vulnerable to blisters and sunscald during hot days, conditions most of Georgia has experienced since early May.

Much of the state has not experienced a substantial rainfall event since the weekend of May 11, and many growers have had no relief from temperatures that reached or eclipsed 100 degrees Fahrenheit.

“We really need some balanced days, not full-blown sunshine with 100 degrees Fahrenheit every day like we’ve experienced here recently, and also not heavy dew nights,” Dutta said. “We need some cloudy days, but most importantly, we need some rain.”

High temperatures during the day, followed by dew at night and in the early morning hours for the past three weeks, have led to the disease developing in cucurbit fields in Crisp, Decatur and Lowndes counties.

“Most of our growers are doing preventative sprays for downy mildew. We do have fairly effective fungicides that can manage downy mildew. I think growers are diligently following UGA recommendations and they should continue to do so,” Dutta said.

Growers need to be aware of what downy mildew symptoms look like and the damage it can inflict on vegetable crops. The pathogen thrives in wet, humid conditions and needs moisture on the surface of the plant for successful spore germination and further infection.

The pathogen that causes downy mildew can’t survive a hard frost, so it overwinters in frost-free regions like southern Florida. During May and early June, wind currents blow the spores into Georgia.

For up-to-date information about potential diseases impacting Georgia’s vegetable production, see https://site.caes.uga.edu/vegpath.

Clint Thompson is a news editor with the University of Georgia College of Agricultural and Environmental Sciences based in Tifton.

Cabbage Crops Signs of Disease

Published on 05/08/19

Farmers must watch cabbage crops closely for signs of disease

By Bryce Ethridge for CAES News

As temperatures increase this spring, Georgia cabbage farmers should scout their crops regularly to ensure that disease pressure is not too high, says University of Georgia Cooperative Extension vegetable specialist Andre da Silva.

If farmers are proactive and maintain proper pest management programs during the growing season, diseases like black rot and Alternaria leaf blight can be controlled, da Silva added.

Symptoms of these disease are easy to identify in the field, but once identified, yield may have already been compromised. The increase in temperatures and rainfall can create perfect conditions for disease, and da Silva and Bhabesh Dutta, UGA Extension vegetable disease specialist, are currently tracking the emergence of the two diseases throughout south Georgia.

“As we get to the summer — or later in the spring — the warmer temperatures increase the chance of these diseases,” he said. “If growers don’t pay attention and keep a proper pest management program, we might suffer a high loss.”

According to the UGA Center for Agribusiness and Economic Development, the farm gate value for cabbage in Georgia in 2017 was $53.6 million.

Alternaria leaf blight can cause spots on some brassica crops and render them unmarketable. Symptoms first appear on older leaves as small, dark spots that gradually enlarge with concentric rings. As the disease gets worse, younger leaves become infected. Infection becomes more problematic in humid and wet conditions.

Black rot causes v-shaped lesions on leaf edges which can lead to the plant’s death.

Lack of proper irrigation scheduling could also lead to the appearance of these diseases, particularly due to the application of high volumes of water.

“Since we’re starting to have warmer conditions with frequent rain showers, soil might have plenty of moisture to supply crop demand,” da Silva said. “There is no need to overirrigate, and if growers are irrigating their cabbage in those conditions, it’d create the perfect conditions for disease. That’s what we don’t want.”

As part of his research on the UGA Tifton campus, da Silva is looking for cabbage varieties that are more disease tolerant or disease resistant.

Until disease-resistant varieties are discovered, growers should keep these tips in mind when managing diseases in cabbage:

  • Maintain a proper pest management program.
  • Rotate chemical products to avoid disease resistance to a particular product.
  • Change up irrigation schedules to apply water only when necessary.
  • Frequently survey crops for symptoms.

To learn how to identify rot, contact da Silva at 229386-3806 or adasilva@uga.edu. For more information on the Department of Horticulture at UGA-Tifton, visit http://tifton.caes.uga.edu/departments/horticulture.htm

Fungicide resistance spells trouble for Georgia, Virginia vegetable farmers

Published on 03/06/19
By Clint Thompson for CAES News

Popular vegetables like broccoli and kale are among the crops that could be in danger from Alternaria leaf blight — a disease that can cause spots on some brassica crops and render them unmarketable — which has developed resistance to a once-dependable fungicide that Georgia farmers rely on, according to Bhabesh Dutta, University of Georgia Cooperative Extension plant pathologist.

Dutta recommends producers stop using Quadris on brassica crops, which include cabbage, collards, kale, mustard greens and broccoli. The fungicide is the main one farmers currently use when treating for the disease. Although further research is required to confirm his hypothesis, Dutta believes a new species of Alternaria may be responsible for the outbreak of disease. The species normally associated with Alternaria leaf blight differs from the disease that has recently been observed in Georgia’s brassica fields.

Tift County, Georgia, vegetable farmer Bill Brim is among the brassica farmers concerned about the development.

“Alternaria has become resistant to Quadris, so it’s not as good as it once was,” said Brim, co-owner of Lewis Taylor Farms in Tifton, Georgia, which includes about 1,500 acres of brassica crops. “We’ve got a little bit left in our arsenal to use for Alternaria. We just need to get something back in there we can use.”

Dutta is conducting a research trial evaluating different varieties of Alternaria leaf blight, along with different fungicide programs against this disease, at the Blackshank Farm on the UGA Tifton campus.

Dutta, an assistant professor of plant pathology in UGA’s College of Agricultural and Environmental Sciences, emphasizes the need to develop an integrated pest management (IPM) program to fight Alternaria leaf blight, especially in broccoli and leafy brassicas.

“We do have some other groups of fungicides that we’ll need to rotate, but considering how effective Quadris has been for our vegetable farmers, this resistance is a huge hit on our growers,” Dutta said.

Alternaria leaf blight first became a problem in Georgia in 2016, but has gotten significantly worse over the past two years.

“Alternaria is a foliar pathogen. Symptoms first appear on older leaves as small, dark spots that gradually enlarge with concentric rings. As the disease progresses, younger leaves can also become infected. In severe cases, infection can occur that results in rot on heads. Infection is exacerbated by humidity and extended periods of leaf wetness from overhead irrigation or frequent rainfall,” Dutta said.

Farmers can employ alternative methods to help prevent the disease from becoming more widespread in their fields. Since the pathogen can survive in crop debris, Dutta recommends farmers bury their crop debris when their spring and fall crops are harvested.

Because the disease propagates and spreads through overhead irrigation, growers should use drip irrigation or a form of subsurface irrigation to help reduce the splashing effect of the pathogen, Dutta said.

Excessive rainfall Georgia in January and February led to outbreaks of the disease this year.

“We have to try to manage this issue with good resistance-management techniques, such as rotating different modes of action in order to preserve the chemistries that we have,” said Jeremy Kichler, Colquitt County Extension coordinator. “Hopefully, if we implement good resistance-management strategies, then we can effectively manage this disease.”

According to the UGA Center for Agribusiness and Economic Development, cabbage production in Colquitt County accounted for more than $42 million in farm gate value in 2017. Colquitt County, which produces approximately 6,500 acres of cabbage in the fall and spring, has experienced severe disease outbreaks.

The production of brassica crops is a profitable industry for Georgia farmers. According to the UGA Center for Agribusiness and Economic Development, the state farm gate value for cabbage was $53.6 million in 2017.

Georgia is not the only state experiencing problems with Alternaria leaf blight. As early as 2015, broccoli growers in Virginia’s Northern Neck region reported severe Alternaria head rot in fields where Quadris was the primary fungicide used. During 2015 and 2016, some growers experienced complete crop failures from this pathogen.

Virginia Tech researchers led by Steve Rideout, director and vegetable plant pathologist at Virginia Tech’s Eastern Shore Agricultural Research and Extension Center in Painter, Virginia, have determined isolates of Alternaria that possess resistance to Quadris.

To learn more about vegetable production in Georgia, see http://extension.uga.edu/topic-areas/lawn-garden-landscapes/fruits-vegetables.html.

Row Crop Disease Update Before Hurricane

By Dr. Bob Kemerait  Like they say, “no rest for the weary.”  It looked like we were going to be able to get out of this with fairly dry weather and then here comes the potential for a tropical storm.  If the path of the storm continues, it should hit sometime late on Wednesday and affect us through Thursday with wind and rain and, depending on how much rain we get, could keep growers out of the field for some period of a day or so to longer.

There is the obvious damage that wind and rain will bring, especially to the cotton crop- lodging cotton and putting lint on the ground.  For cotton not yet ready to pick, the weather could increase boll rot, though there is really nothing we can do about that.

For peanuts, the question is timing of digging.  It is my opinion that if the vines and pegs are healthy and not too much defoliation from leaf spot or damage from white mold is present, then it is better to leave the peanuts in the ground and to dig them after the storm passes.

If the peanuts are severely affected by leaf spot disease (significant defoliation) or disease (white mold) and the potential for yield loss is severe if they must stay in the ground into next week, then I would consider digging them.

If the crop is already behind in being dug (past harvest maturity) or the soil is “heavy” and digging may be delayed considerably, then I would also think about digging them.

Where peanuts are two or more weeks away from projected digging date, growers should consider whether a final fungicide application for management of leaf spot is needed.

Row Crop Disease Update August 27

Dr. Bob  Kemerait gives a row crop disease update

  1. Soybeans: Asian soybean rust is still lightly scattered from Decatur County to Appling County, but has only been found so far in KUDZU.  Soybean rust is certainly not a major problem at the moment; however it could become so.  Management options are to protect the crop with a fungicide sometime between the R1 (early bloom) and R3 (early pod set) stages.  Such timings may correspond well with other disease and insect control measures.  Some “Cercospora leaf blight” is being reported; this disease causes much of the upper foliage to take on a “bronzed” cast and then leaves drop prematurely leaving the “bony” petioles like skeleton fingers to the sky.  Cercospora leaf blight also causes purple seed stain.  Fungicide applications at pod set (R3) can help manage this disease.
  2. Late-planted corn: Southern corn rust is now commonly observed on older corn across the Coastal Plain, corn that is too late for it to matter.  However, southern corn rust does pose a threat to younger corn and preventative protection with a fungicide is something to consider, especially as the crop approaches the tassel growth stage.  Also, I am receiving numerous reports of young corn affected by northern corn leaf spot (Bipolaris zeicola) which produces numerous, small-to-medium sized red/brown spots, sometimes with appearance of concentric rings.  Typically, corn is most severely affected by northern corn leaf spot early in the season and then grows out of it; however I cannot be sure that this will always be the case.  I have no data on fungicides for management of northern corn leaf spot, but as it is closely related to northern and southern corn leaf blights, I am confident that mixed mode of action products we already use will be helpful for the “spot” disease.  If a grower does spray, applications as early as V6-V8 would be appropriate. But again, I just don’t know if it matters.
  3. Cotton: I hear you.  And I feel your frustration.  We have three diseases of significant importance in the field right now.    Boll rot.  The rain and heavy vegetative growth we have seen this year has created perfect conditions for fungal boll rot.  We are seeing a lot of it.  We are not seeing a lot of bacterial boll rot, though some is certainly there.  Fungal boll rot is most severe in lower bolls deep in the canopy or where insect damage also occurs.  Fungicides are not an effective treatment; only opening the canopy up to increase airflow and reduce humidity can help reduce boll rot.  2.  Areolate Mildew.  First, Andrew S. and others, I didn’t make the name up.  Second, I know that there is great concern and I have heard growers complaining that there fungicide applications did not stop the disease.  Here are some thoughts.  For the second year in a row, Areolate mildew is early and widespread.  Areolate mildew can cause significant premature defoliation.  I do know that fungicides like Headline and Quadris and certainly Priaxor can slow the spread of the disease, though not necessarily stop it, especially when it is well established in a field.  It is not clear how much yield is at risk or that can be protected; but it is believed that significant premature defoliation is not a good thing, unless one is trying to open the canopy up to slow boll rot.  Here are my recommendations, though they have not been proven with any hard data.  If a grower is within 4 weeks of defoliating the crop anyway, save the money and don’t spray.  If the grower is more than 4 weeks of defoliating and the areolate mildew is not too severe (i.e. already causing significant leaf drop) then there may be a benefit to treating with a fungicide.  This may not stop the disease but will slow its development.  3.  Target Spot.  Target spot has been severe and widespread in this rainy season.  I believe well-timed fungicides have been helpful this year.  I don’t believe there is any benefit to a fungicide application after the 6th week of bloom.  Either there is too much disease already to stop it or there is not enough time for disease to develop.  In this season, a second fungicide application 2-3 weeks after the first application is something to consider.
  4. PEANUTS: Getting lots of questions these days about late-season peanut disease problems.  Just a few thoughts.    Three weeks to go until you dig the peanuts and little-or-no disease in the field?  I wouldn’t put out any more fungicides unless there is threat of a hurricane or tropical storm.  If three of more weeks out and on your last spray and you are seeing some leaf spot develop, applying a pint of chlorothalonil tank-mixed with 7.2 fl oz of  tebuconazole or 5.5 fl oz of Alto or 5 fl oz of Topsin or 2.5 fl oz of Domark.  If time for your last spray and very little leaf spot is present, then 1.5 pints of chlorothalonil may be all you need.

If white mold is popping up in your field late in the season and is confined to individual plants scattered across the field, then you may want to mix tebuconazole with your last leaf spot spray.  If the disease is more severe, or you are really worried about it, then you might consider using 16  fl oz or Convoy rather than tebuconazole.

It is generally advisable to wait to dig the peanuts until they are “ready” based upon the hull-scrape test.  This is true even if there is significant tomato spotted wilt in the field or some white mold.  HOWEVER:  if there is significant defoliation from leaf spot or significant white mold in the field, it often best to dig the peanuts earlier than planned to avoid excessive digging losses.

Row Crop Disease Update August 10, 2018

Dr. Bob Kemerait gives row crop disease update:

DISEASES of PEANUT:  White mold and leaf spot aren’t breaking lose in every peanut field in Georgia, BUT hot temperatures, high humidity and frequent rains have created near-perfect conditions for the development, spread and, sometimes, explosion of these diseases.  Growers need to stay on a good fungicide program, tightening spray intervals where disease is becoming problematic and/or where there is concern if the crops have received enough drying time after a fungicide was applied.

FOUR COTTON DISEASES:  Target spot, areolate mildew, Stemphylium leaf spot, and bacterial blight.

What a season it has become when target spot and areolate mildew are causing greater angst than bacterial blight.

 

EASY STUFF:

 

  1.  Bacterial blight is present and is affecting yield in some fields.  Susceptible varieties will get this disease and losses may occur.  THERE IS NOTHING TO BE DONE ABOUT IT NOW. However, growers should note the varieties where they find it and determine at the end of the season if the disease became severe enough to avoid planting those varieties again.
  2. Stemphylium leaf spot is present as well.  Stemphylium leaf spot is caused by a deficiency in potassium in the plant.  Dr. Glen Harris is our soil fertility expert; I believe he would agree that excessive rains could have leached potassium this year.  Fungicides ARE NOT a solution for Stemphylium leaf spot; Dr. Harris has the best information about managing potassium.

 

HARD STUFF:

 

  1.  Target spot and areolate mildew are present in a number of fields this year.
  2. At times, target spot and areaolate mildew appear late enough in the season that the defoliation resulting from these diseases does not affect yield and use of fungicides is not needed.
  3. The question for both diseases is not, “Can we protect the cotton in this field with a fungicides?” but rather, “Should we protect the cotton in this field with a fungicide?”
  4. We have very very little data on areolate mildew, but from what I do have, I am confident that we can easily control this disease using strobilurin products like Headline or Quadris, or mixed products like Priaxor or Elatus.  Proline may work as well but I don’t have data.
  5. Though we can control areaolate mildew, does it make us any more yield than if we didn’t control it?  When conditions are favorable, areolate mildew can rapidly defoliate a cotton crop.  If a grower is withing 3-to-4 weeks of defoliating anyway, I would NOT use a fungicide.  If the crop still had 4 or more weeks to go, I would consider weather, yield potential, how much disease is in the field and then decide to spray or not.
  6. If areolate mildew, or target spot, is already well-established in the field (i.e. causing significant defoliation, then there is little hope that a fungicide will help.
  7. Target spot is a significant concern this year and is widespread.  Not every cotton grower in the state needed to spray a fungicide for target spot, but I encourage growers to carefully consider their options.
  8. Target spot is of particular concern this year because a) the wet and warm conditions are perfect for an explosion of the disease, b) the disease has been found early in many fields, and c) the price of cotton makes protection 100-250 lbs lint/acre attractive.
  9. I believe the best window of opportunity for managing target spot is from the first week of bloom to the sixth week of bloom.
  10. A little target spot in a crop (meaning scattered spots on lower leaves and no defoliation) during the first week of bloom and favorable weather IS a concern, as it would be at the third week as well.  A “little target spot” at the 4th-6th week of bloom is much less of a concern.
  11. When a fungicide program begins as early as the first week of bloom because of the disease situation; a second application may be beneficial two-to three weeks later.  I don’t envision an application, follow-up or otherwise, after the 6th week.
  12. It will be quite difficult to control (impossible?) target spot if there is already significant defoliation in the field before an application is made.  If 25-30% of the leaves are already gone, a fungicide likely won’t work.
  13. THE  THREE MOST IMPORTANT POINTS TO MANAGE TARGET SPOT, in order of importance, are 1.  TIMING  2.  COVERAGE  3.  SELECTION of FUNGICIDE.

Some relevant information on Powdery mildew of cucurbits

Powdery mildew is a common disease of cucurbits under field and greenhouse conditions in most areas of the United States.  Although all cucurbits are susceptible, symptoms are less common on cucumber and melon because many commercial cultivars have resistance. This disease can be a major production problem if not manage timely.

Podosphaera xanthii and Erysiphe cichoracearum are the two important fungal organisms that cause cucurbit powdery mildew. P. xanthii is a more aggressive pathogen than E. cichoracearum.  E. cichoracearum requires a lower temperature optimum and hence, this fungus is found mainly during cooler spring and early summer periods. In contrast, P. xanthii are more common during the warmer months.

The causal fungi are obligate parasites and therefore cannot survive in the absence of living host plants. Possible local sources of initial inoculum include conidia from greenhouse-grown cucurbits, and alternate hosts. Verbena, a common ornamental plant and also a common weed, could be an important source of inoculum.

Pathogenically distinct races of Podosphaera xanthii have been differentiated on muskmelon.  Races 1 and 2 have most common in the eastern United States recently.

Fungicides: Quintec, Proline, Torino (rotation in watermelon and cantaloupe)

Proline, Torino, Procure (rotation in other cucurbits)