Category Archives: Disease

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

December Row Crop Disease Update

A few things to think about with regards to disease and nematode management in preparation for the 2017 field season.

La Nina:  Our UGA Extension climatologist Pam Knox has good information available on our current conditions, but here are my thoughts:

We are currently in a “weak” La Nina situation, “weak” because the equatorial waters of the cost of Ecuador are more than a half degree COOLER than normal.  As best I can tell, the waters have been about 7/10 of a degree cooler which barely qualifies as a La Nina (as opposed to last year where we had a robust and sure-enough El Nino).  So what does this mean? During La Nina years, the Southeast tends to (“tends to” means more often than not, but not always..) experience warmer and drier winters. Because we have a weak La Nina, this forecast could change.

Pigweed seedhead in broccoli before Thanksgiving. We are yet to have frost to knock back pigweed growth.

Pigweed seedhead in broccoli before Thanksgiving. We are yet to have frost to knock back pigweed growth.

How does our current “La Nina” impact our recommendations?

  1.  Drier is not a good thing as it may mean we don’t fill up irrigation ponds for next year.  It my mean we have a lot of trouble establishing cover crops this fall.
  2.  Warmer temperatures may mean that kudzu, volunteer peanuts, corn, cotton-regrowth, etc. pathogens (like those that cause soybean rust and southern corn rust) may survive and increase longer than they would with an earlier “killing” frost.  Also, as long as the crops and volunteers are active in the field, nematode populations can continue to increase and build.  This will lead to larger populations for next season. Once the plants are killed, the nematodes can no longer feed. Once soil temps drop below 65F, the activity of the todes drops off as well.
  3.  We may get some very cold weather soon, so we may not need to worry that much; however the general prediction is that we will have a warmer winter.
  4.  The weather this winter will have some effect on TSWV and insects for next year.  It remains to be seen what and how… but it will impact them.

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

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

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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

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Filed under Cotton, Disease, Peanuts, Soybeans

Peanuts: Terminating Fungicide Sprays

We are starting to dig some peanuts this week in the county. Profiles are showing high percentage of mature, gradable peanuts. This week, it seems as profiles have slowed and not much change. One of the most difficult decisions is terminating our fungicide sprays. Some fields still show hits of white mold. Remember that if we get 60-70% control of soilborne disease, this is considered good – especially fields prone to WM.

peanuthullscrape-001

Here is an update from UGA Extension Pathologist Dr. Bob Kemerait on cutting off fungicide sprays based on our profile charts:

  1. Grower is 4 or more weeks from harvest and DOES NOT currently have disease problems in the field:
    • Suggestion – I recommend the grower apply at least one more fungicide for atleast leaf spot control.
    • Suggestion – Gen 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 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 (Toppsin M) or cyproconazole (Alto) with chlorothalonil. Others may consider applying Priaxor, if they have not already applied it twice this season.
    • If white mold – Grower should continue with fungicide applications for management of WM. If they have completed their regular WM program, they should extens the program, perhaps with a tebuconazole/chlorothalonil mix.
    • If 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 increase disease management.
  3. Grower is 3 weeks or less from harvest and DOES NOT current 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.
  4. Grower is 3 weeks or less from harvest and DOES have a problem with disease.
    • If leaf spot – A last leaf spot fungicide application may be beneficial. If leaf spot if very severe, a last application will not help.
    • If white mold – It is likely beneficial to apply a final white mold fungicide. If harvest is 2 weeks away or less, then it is unlikely that a fungicide will be any benefit.
    • NOTE: If harvest is likely delayed by threat from a hurricane or tropical storm, then the grower may reconsider recommendation for end-of-season fungicide applications.

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Filed under Disease, Peanuts

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

 

 

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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

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Filed under Cotton, Disease