Category Archives: Disease

Bermudagrass Leaf Rust

aliciabermuda-leafrust-010

It’s not unusual for us to be dry in October. But it is unusual to go into October already dry. Many folks have not seen one measurable rain in the month of October. As we walked through this Alicia hay field, our boots were covered in rust spores. Clouds of rust were seen with each step. Leaf rust this time of year is pretty typical in Alicia. We may not see it exactly this bad with Coastal.

Identification

Will rust, you will see red to orange lesions on the leaf and stem. Look for a raised area or blister which is the rust postules like we see in wheat and corn. Rubbing your finger over the leaf will leave a rusty color.

Leaf Rust

Leaf Rust

Leaf Rust

Postules of rust are raised

Management

We cannot use fungicides on our hay fields, so management is strictly avoidance. Coastal, Tift 44, and Tift 85 have some level of resistance while Alicia is extremely susceptible. But even less susceptible varieties are infected with leaf spot when POTASSIUM is low. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from bermuda hay fields in about a 4-1-3 ratio of N, P2O5, and K2O with harvest. We need 75 percent as much potash as nitrogen  applied each season. Split applications of K are better in sandy soils. In these cases, nearing the end of the season, we need to go out with another shot of straight potassium.

Visit Leafspot Diagnosis and Management in Bermudagrass Forages for more information.

Leaf rust on boots

Leaf rust on boots

Leave a comment

Filed under Disease, Fertility, Forages

Peanut Harvest & Row Crop Disease Update

Boston Peanut

Boston Peanut

Golden Peanut in Meigs

Golden Peanut in Meigs

After afternoon showers and rain last week, we are really getting back to picking this week. Growers are also wide open on defoliating cotton. I saw some cotton being picked yesterday.

I visited our buying points this week and looked at grades and other issues. Thankfully, we are not having many Seg 2 burrower bug hits as last year and the year before. Between both buying points, I only know of one known burrowing bug Seg 2. In every other Seg 2 case, they’ve turned around and cleaned them and they were fine.

Grades are probably a little down this year compared to last, but are definitely not bad. Many good grades overall and low percentage of our sound splits and other kernels (pops). We could be pulling the trigger early on the some of the fields. Almost all growers are checking maturity twice in fields before digging, and many have checked more than two times. We’ve not seen maturity develop at a normal pace with our dryland peanuts which has made digging decisions tough. With more peanuts in the ground, growers are having to dig when they have help, or wagons are available, or weather permits. Vine condition is also a factor in our decision at this time. Overall, we’ve had good harvest conditions this week. Even with afternoon storms or showers, sunny days have been able to dry peanuts quickly.

Collecting grading samples at Boston Peanut

Collecting grading samples at Boston Peanut

UGA Extension Pathologist Dr. Bob Kemerait has this information on current disease issues:

Peanuts

Harvest is well under way by this time, but disease issues still affect peanuts that won’t be harvested for another three weeks or more. I have seen some fields where harvest is approaching and where white mold (stem rot) is still active, and I have recommended growers late in the season apply a mixture of tebuconazole and chlorothalonil to finish the season (both products have a 14-day preharvest interval). Other white mold products could also be applied (check preharvest interval first), but with time running out in the season, the value of tebuconazole is certainly a consideration.

Late Leafspot

Late Leaf Spot

I have also observed where leaf spot, especially late leaf spot, is aggressive late in the season, primarily on a susceptible variety like ‘Georgia-13M’. If less than two weeks to go before digging, it is doubtful anything should be applied (or legally can be applied). If peanuts are 30 days or more away from harvest, then the grower can mix a pint of chlorothalonil with 5.5 fl oz/A of Alto. If harvest is more than 14 days away from harvest, the grower can mix 5-10 fl oz/A Topsin with a pint of chlorothalonil. Fields where defoliation from leaf spot diseases has reached 50% or more and have not yet reached the optimal digging date should be considered for an early digging.

Soybeans

Soybean producers in southern Georgia have experienced losses to Asian soybean rust this year; however it appears that most have successfully protected their crop with judicious fungicide applications. MORE IMPORTANTLY, I have observed a SIGNIFICANT amount of frogeye leaf spot (Cercpospora sojina) disease in a number of fields this year; something I have not seen in many years. I am not sure why this is so; however it is something we will need to watch again next season as well. Additionally, I am seeing pre-mature defoliation to Cercospora blight (Cercospora kikuchii) in a number of fields; this disease often results in purple stain of the soybean seed. Cercospora blight is diagnosed, in part, by the prominent loss of leaves in the top of the plant leaving only the petioles, reaching like bony fingers to the sky.

Cotton

Bacterial blight (Xanthomonas citrii pv malvacearum) continues to cause concern to many growers in the state. From your reports, reports from our consultants, and from my own observations, it is clear that bacterial blight can be found in a number of fields across the Coastal Plain. Classic symptoms or bacterial blight on leaves, bracts, bolls, stems and petioles are fairly easy to diagnose; still symptoms of other diseases may inadvertently be diagnosed as “bacterial blight”. 

It is my belief, based upon my observations and discussions with a number of experienced individuals, that losses to this disease are likely to be small and even negligible in many fields. Finding a little bit of disease in a field is an important contribution to understanding the occurrence of bacterial blight in 2016; but incidence alone does not mean significant yield loss.

Certainly there are some fields, especially in extreme SW Georgia, were boll rots appear to be closely associated with bacterial blight and losses are likely to occur. Effective management of bacterial blight by a grower revolves around variety selection (we are composing such a list for Georgia cotton producers now) and management of crop debris/residue as the pathogen can overwinter in such. Crop rotation and burying of crop debris can help to minimize the development and spread of the disease in upcoming seasons.

Bacterial Blight

Bacterial Blight

Leave a comment

Filed under Cotton, Disease, Peanuts, Soybeans

Ultra-Late Soybeans Look Good

BrandonBarnes-Soybean-Pioneer95Y70 002

Here is a look at some of Brandon Barnes’s ultra-late soybeans that are looking very good. This is Pioneer 95Y70s, planted behind sweet corn on June 20th. Ultra-late soybeans can  be risky, but something to consider for income and our environment.

Planting date is probably biggest issue.Traditional research has shown that we lose 0.75 bushel/acre when planting mid June to July. UGA Agronomist Dr. Jared Whitaker says initial work in the ultra-late system is losses planting goes into August, the best educational guess as to cutoff date is first week of August.

Dr. Whitaker also likes narrow rows. This row spacing is set at 20 inches. We need to also have 175K – 200K seed population. Brandon planted at 200K seed population. A little nitrogen in this system doesn’t hurt either. Though soybeans don’t need supplemental nitrogen if properly inoculated, the window for growth in this system likely takes away ability to produce enough N.

We definitely need irrigation in this system. Brandon is now putting out close to 2 inches of water per week as soybeans are entering the reproductive growth stage. Once flowering occurs, we are in reproductive growth stage. The plant will go from R1 to R8. Below is a chart on growth stages. These are important when we look at pests.

SoybeanReproductiveGrowthStages-UGAHandbook-2015

SoybeanReproductiveGrowthStages

Disease

Asian soybean rust has been found in the county on Kudzu. They’ve already treated with fungicide on this field. We are not considered safe from ASR until we get to R6 growth stage (seeds are touching in the pod).

Insect

BrandonBarnes-Soybean-Pioneer95Y70 007

Once we hit reproductive growth, our insect thresholds change. They’ve treated for caterpillars already, but we noticed lots of leaf damage still. We can have 30% defoliation before bloom. After bloom our threshold is down to 15%. We also want to check caterpillars since soybean loopers have pyrethroid resistance. Brandon and I found some soybean loopers, but no green cloverworms or velvetbean caterpillars. UGA Entomologist Dr. Phillip Roberts says green cloverworms are rarely at high enough levels to treat. They usually appear early and serve as host for insect parasites and predators.

We can terminate our insecticide applications when we hit R7 (leaves turning yellow.)

Foliage Feeder Thresholds Soybeans

 

 

Leave a comment

Filed under Disease, Entomology, Soybeans

Bacterial Blight In Cotton

BacterialBlight-PHY444 012

We are seeing bacterial or angular blight again in cotton. I have a dryland variety trial I looked at this morning and it is showing up in different varieties. Unfortunately, we cannot do anything we can spray. We can irrigate during the night to reduce leaf wetness. Our trail was planted in late May, so we are being everything else. Cotton is not yet too rank. I’m not seeing but a few leaves here and there, but every leaf I find has already dropped from the plant. It is too early to know how much this will impact us. Here is more information from UGA Extension Pathologist Dr. Bob Kemerait:

Once again, we are finding bacterial blight, caused by Xanthomonas citri pv malvacearum, in cotton in Georgia.  The disease can be diagnosed by presence of water-soaked-to-necrotic spots on the leaves that are delimited by the veins of the leaf. This gives the spots a particular “angular” appearance.  The disease can also spread in the veins and gives a “lightning bolt” streak on the leaf.  Crater-like, water soaked lesions can form on bolls.

There is nothing that can be done to manage this disease.  Managing growth of the crop and irrigating at night to reduce leaf wetness periods can help a little. 

Photo by Jeremy Kichler

Photo by Jeremy Kichler

Leave a comment

Filed under Cotton, Disease

Dollar Spot In Bermuda Pasture

Tift85-Hay

Last week, I mentioned seeing leaf spot in the pasture. UGA Extension Pathologist Dr. Alfredo Martinez wanted to confirm what appeared to be fungal structures on the leaves as well. The last few years, we’ve looked at leaf spot pathogens in hay fields. Usually, it is leaf blight (Helminthosporium) or leaf rust. What we looked at a few weeks ago appeared to be more damaging to the lower leaves. The lesions of dollar spot are white to straw colored surrounded by a brown border. This was affecting the lower leaves bad. This is the first time I’ve seen dollar spot in pasture. It is maintained the same as helminthosporium and/or leaf rust. Keep in mind, this pasture was burned off last season.

Dollar Spot

Dollar Spot

Looking at the pasture, Tim Flanders noticed these odd structures on the leaves. They almost looked like a fertilizer granular. Dr. Martinez plated them out and did find them to be fungal related. There were basically some saprophytic fungi that ARE NOT associated with the dollar spot.

Dollar Spot lesions

Dollar Spot lesions

Management

Management is strictly avoidance. Coastal, Tift 44, and Tift 85 have some level of resistance (to leafspot pathogens) while Alicia is extremely susceptible. But even less susceptible varieties are infected with leaf spot when potassium is low. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from bermuda hay fields in about a 4-1-3 ratio of N, P2O5, and K2O with harvest. We need 75 percent as much potash as nitrogen  applied each season. Split applications of K are better in sandy soils. It is also advised to remove inoculum that exists in thatch. In addition to tying up nutrients, thatch holds water and reduces air circulation. This is a conducive environment for inoculum. The only practical way to reduce thatch is burning in spring before green-up.

Visit Leafspot Diagnosis and Management in Bermudagrass Forages for more information.

Leave a comment

Filed under Disease, Forages

Peanut Pest Update

Our peanuts have been lapping for a few weeks now. They are looking good so far. We are more or less 60 days old now. Seeds are developing inside pods, and growers are starting another round of fungicides. Here is some information from specialists concerning insects and disease:

Peanuts-Lapping-Insects 019

Peanuts-Lapping-Insects 020Insects

Here is an update from UGA Extension Entomologist Dr. Mark Abney:

There continues to be lesser cornstalk borers (LCB) in Georgia peanut fields, and I do not see any reason that should change over the next few weeks. Interestingly, most of the heavy pressure has not been in the Southwest but in the middle and eastern portions of South GA. I expect that some of the infestations we were seeing in irrigated fields prior to the vines covering the row middles will be diminishing as irrigation water is applied with greater frequency.

I have not received a call about two spotted spider mite on peanut in 2016, but I am betting it is coming soon. Mites have been hanging around on cotton now for several weeks, and with continued hot, dry conditions I think we will be seeing mites move into peanut fields. If this happens, it is going to create a lot of headaches for growers, Extension agents, and crop consultants. 

  1. We need to catch mite infestations early to have any chance of getting good control. 
  2. With the one miticide available for use in peanut (Comite), we need to use a minimum of 20 gallons of water per acre, and two applications may be needed because egg mortality is low.
  3. The yield potential of some of our non-irrigated peanut acres is rapidly deteriorating; knowing when to pull the plug on inputs in these fields is going to be difficult, and most growers will be reluctant to “give up” on the crop. When making treatment decisions, we need to be realistic about the crop we already have set and our potential to add harvestable pods to it.
  4. I say this a lot, but we need to be sure to avoid pyrethroid insecticides in fields where spider mites are present or in fields at high risk for mites (hot and dry) in areas where mites have been found in surrounding fields. There are a couple pyrethroids that will suppress mites, but “suppression followed by resurgence” is a better description of what usually happens.

Rain tends to be the best treatment for LCB and spider mites, but a single rainfall event will not eliminate either of these pests once they are established in a field.

I have not heard of damage from potato leaf hopper, but have seen threecorned alfalfa hopper. Here is a picture of their damage. Immatures girdle the stem, and sometimes adventitious roots will grow.

Three-cornered Alfalfa Leaf Hopper damage

Three-cornered Alfalfa Leaf Hopper damage

Disease

Tomato Spotted Wilt Virus

Tomato Spotted Wilt Virus

This week we saw some spotted wilt, and there are other reports of spotted wilt – especially early planted peanuts.We are having the right conditions for white mold with the heat and afternoon rain showers. Only timely fungicides will protect us during this time. Here is a link to the 2016-PeanutRxwithVariousFungicidePrograms for the companies that provide them (BASF, Bayer, DuPont, Nichino, & Syngenta). We watch for white mold outbreaks now.

Brooks County Ag Agent Stephanie Hollifield makes a good point, that “If you have missed the afternoon thunderstorms and are experiencing the other extreme of dry weather, keep in mind that white mold control can be more difficult during drought. This is due to the fact that, dry weather prevents the ease of movement of the fungicide product from leaves of peanut plant to our target application spot in the crown of plant. To ensure white mold control products get down to crown/ground; irrigate if possible or apply white mold control fungicides with presence of dew on peanut plant and/or while leaves are still closed up.”

I’ve also had questions of mixing other products now. We should use caution with tank mix applications, especially during extreme hot and dry weather. The likelihood of plant burn can increase with any product, with the increase in environmental temperatures and tank mix partners.

Leave a comment

Filed under Disease, Entomology, Peanuts

Peanuts: Fungicide Programs Begin

Peanuts-30DAP

The Tropical Storm Colin came from the Gulf of Mexico and traveled the most important peanut production areas of the state. We had between 3 and 7 inches reported around the county. The subsequent rain will have impact on diseases affecting peanuts (and other crops). This also coincides with the time when growers are beginning their fungicide program. Also, it is the time when the peanut plant is shifting from vegetative growth to reproductive growth (flowering).

UGA Extension Plant Pathologist Dr. Bob Kemerait has this information:

Within a month after planting, the peanut crop enters the window where a traditional disease management program begins. An important principle of disease management on any crop is to apply fungicides prior to disease onset.

Aspergillus Crown Rot

Aspergillus Crown Rot

The most important disease observed in 2016 has been Aspergillus crown rot, a fungal disease that is our most common seedling disease. It is often diagnosed by the abundant black/sooty sporulation on the crown of the plant, typically just below the soil surface. The disease is most common in very hot and dry soils where the tender taproot and shoot is scorched by the surrounding soil, thus creating injury that is exploited by the fungus. The disease is also found where lesser corn stalk borers are a problem. Fungicide seed treatments are effective in managing this disease but can suffer when conditions favor crown rot. In-furrow applications can also reduce outbreaks of Aspergillus crown rot. Foliar fungicide applications after disease is observed have not been especially helpful.

Tomato spotted wilt is showing up more and more on young peanuts. It was my observation that feeding injury from thrips was severe on both cotton and peanuts this year; I am concerned that we may see more TSWV this year than we have in the recent past. While there is nothing to be done at this point, being able to diagnose the problem and to explain why the disease has occurred in a field is helpful.

TSWV 017

Tomato Spotted Wilt Virus

White mold: I have not seen white mold on peanuts thus far in 2016, but strong early-season growth of the peanut plants coupled with very warm soil temperatures can set the stage (as in 2015) for a “white mold year”. The 2016 year may also be problematic for white mold because A) many growers are on shorter rotations and B) because of the price of peanuts, growers may be reluctant to spend more money on “premium” products.

WhiteMold 003

White Mold

Growers can begin a white mold fungicide program earlier than the traditional “60 days after planting” in a number of different ways. Two popular ways include banding a white mold fungicide like Proline early in the season and also by mixing a fungicide like tebuconazole with early leaf spot fungicide applications.

Leave a comment

Filed under Disease, Peanuts

Southern Corn Rust In GA

Southern corn rust has been diagnosed thanks to Extension Agents Chase Hembree (Seminole County), Andy Shirley (Mitchell County) and consultant Rome Ethredge. Here is a photo below:

Raised postules of southern corn rust - Photo by Andy Shirley

Raised postules of southern corn rust – Photo by Andy Shirley

We’ve sprayed some of our corn in the county already as we are two weeks into tassel. Here are some comments from UGA Extension Pathologist Dr. Bob Kemerait:

  1. Southern corn rust is the most important disease affecting corn in Georgia.
  2.  Southern corn rust was found today in a very small amount in Seminole County on corn at the R2/blister stage (older than most corn in the state).
  3. The disease cab spread rapidly in storms and also with irrigation.  Conditions last week were favorable for development and spread.
  4.  I have recommended that growers hold off spraying until we find rust.  Now that we have found it, I have enough respect for the disease to say that growers in the southwestern part of the state whose corn has reached (or is about to reach) tassel growth stage an application of fungicide to protect the crop. Growers in other areas removed from extreme SW Georgia should consider to monitor the spread of the disease. Some may want to make fungicide application either as a 1) Safeguard or because 2) they are already making a trip across the field to spray something else.
  5. If northern corn leaf blight is not a problem in a field, then growers have many fungicide options, to include tebuconazole to manage rust. For longer protective windows or where NCLB is also a problem, growers should apply strobilurin or fungicides that include some combination of strobilurins, triazoles, and SDHI active ingredients.

ASIAN SOYBEAN RUST

As of today, Asian soybean rust has now been found in small amounts on KUDZU in the following counties: Miller, Baker, Grady. We can assume that soybean rust is present in low amounts throughout SW Georgia.

Leave a comment

Filed under Corn, Disease

Row Crop Disease Update – Corn & Soybeans

CornTasseling

We are starting to tassel (VT) and move into reproductive growth stage on corn (R1), when the silks emerge from the little ears and the pollen starts falling from the tassels. For Seminole Agent Rome Ethredge writes, “The greatest production of pollen from a field will occur over 4 days, with some pollen shedding for a week or more. Over 2 million pollen grains fall from each tassel.  Peak pollen shed is mid morning and then towards late afternoon more falls, but if it’s raining or a heavy dew the plant won’t shed pollen until it dries. Also, some research shows that when the temperature goes above 86 degrees there isn’t much shed. If it’s cloudy and slightly cool, pollen may fall most of the day. Extreme heat (100 degrees) can kill some of the pollen.”

CornEar-R1This is also a critical time in corn development where we don’t want stress on the plants. Stress during silking can reduce the number of kernel per ear. The number or rows will not be affected now as they were decided already. Disease is the main topic this week with corn, and here is an update from UGA Extension Pathologist Dr. Bob Kemerait on disease in CORN and SOYBEANS.

Here are a couple of notes on the current disease situation:

  1. Our scouts have found Asian soybean rust on kudzu in Miller County today (May 17th). This is the earliest we have found it since 2005, and it likely means rust will be problematic for our soybean producers this year. Current conditions favor spread of the disease within kudzu.
  2. Corn in the earliest planted fields is approaching the tassel growth stage and growers are beginning to ask questions about spraying fungicides.  Here are my thoughts:
  • Tassel stage (or just prior to tassel) is an appropriate time to consider applying a protective fungicide.  This is especially true if a) southern corn rust has been detected in the area, b) northern corn leaf BLIGHT is problematic in a field (typically with a less-resistant hybrid), c) conditions have been favorable for disease (very wet), d) the corn was planted LATE or e) the grower is aggressive in a disease management program and wants to make sure the crop is protected.
  • As of today (May 17th), we have not found SOUTHERN CORN RUST in Georgia and conditions have not been especially favorable for southern rust.
  • As of today, we have had one report of common corn rust from Mitchell County. Common rust typically forms pustules on both sides of the leaf and does NOT need a fungicide application.
Common Rust, Photo by Andy Shirley, Mitchell County

Common Rust, Photo by Andy Shirley, Mitchell County

  • As of today, I have only had a report of northern corn leaf BLIGHT from Ty Torrance in Decatur County. Northern corn leaf blight can be an important problem that requires a fungicide treatment IF it is severe (e.g., a susceptible variety and favorable weather). The NCLB in Decatur County was confined to the bottom leaves and there were only a few lesions on about one plant out of 15. The grower is right to be aware of the problem but I do not think a fungicide is needed for NCLB in that particular field.
Northern Corn Leaf Blight, Photo by Ty Torrence, Decatur County

Northern Corn Leaf Blight, Photo by Ty Torrence, Decatur County

  • Northern corn leaf SPOT has been found in Mitchell County by Andy Shirley.  Typically we do not spray for this disease, except in severe cases. The northern corn leaf spot in this field was confined to the lower leaves and did not appear to be spreading.
Northern Corn Leaf Spot - Photo by Andy Shirley, Mitchell County

Northern Corn Leaf Spot – Photo by Andy Shirley, Mitchell County

CORN:  We have not detected southern corn rust in Georgia yet. Conditions over the next few days are more favorable for disease spread, but (overall) conditions have been unfavorable. I would not argue with a grower who wants to apply a fungicide at this time (to corn) as it reaches the tasseling growth stage; HOWEVER I think the grower is better advised to DELAY a fungicide application at this point and wait at least a week or so.

1 Comment

Filed under Corn, Disease, Soybeans

Downy Mildew In Georgia

SpaghettiSquash 008

This morning we looked a Spaghetti Squash in the southern part of the county that is showing symptoms of downy mildew. We were able to get back to the office and confirm both downy and powdery mildew. We usually see powdery on the upper side of the leaf and downy on the lower side. With downy, the yellowing will stay within the veins, and powdery will cross over the veins.

Upper leaf

Upper leaf

Underside of leaf

Underside of leaf

Dissecting microscope - PM (left) DM (right)

Microscope – PM (left) DM (right)

Here is some information from UGA Extension Pathologist Dr. Bhabesh Dutta:

These observations indicate that inoculum of downy mildew is currently in GA and under favorable conditions (cool and wet conditions) potential disease outbreak in cucurbit can occur. I would suggest our cucurbit growers to look for the downy mildew symptoms in their fields and start applying protective spray of below stated fungicides.

Watermelon: Rotation (foliar application)  with Orondis+Bravo/Manzate; 

                                                                                               Ranman+Bravo/Manzate; 

                                                                                               Previcur flex+Bravo/manzate

Please do not use bravo after fruit set

Other cucurbits: Ranman+Bravo; Previcur flex+Bravo

If Orondis was used as a soil application, please do not use it as foliar (use restriction according to label).

If Orondis was not used as a soil application, foliar application can be done for controlling downy mildew.

Leave a comment

Filed under Disease, Vegetables