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Bacterial blight has been reported within the past week on cotton in Georgia and Mississippi. So, far this disease has not been reported in Alabama but probably will make an appearance in the next week or two. In Geogia, bacterial blight has been found in DP 1747 and to a lesser extent DP 1646 along with one or two additional varieties.
In past years, I've seen bacterial blight at or shortly after pinhead square on susceptible varieties like DP 1558 and DP 1747, so it's not too early for this disease to make an appearance. Current wet weather patterns are quite favorable for onset, spread, and development of bacterial blight. As a result, I would expect to see a this disease show up over the next few weeks in susceptible cotton varieties.
So far, there are no post plant controls for bacterial blight in cotton. I do have a study from Syngenta being conducted in Fairhope looking at foliar treatments to control or suppress bacterial blight. Cotton varieties do differ in their susceptibility to bacterial blight. As noted above, the root knot resistant variety DP 1747 is highly susceptible to bacterial blight. Please refer to this URL for information relating to variety sensitivity to bacterial blight https://lubbock.tamu.edu/files/2018/01/2017-Bacterial-blight-trial-results.pdf. Looks like a lot of the newer variety releases from Phytogen, Deltapine, Stoneville, and some other seed companies are partially or highly resistant to the dominant strain of the causal bacterium (#18) in U.S. cotton, while many of the susceptible varieties are gone. Given favorable weather pattens, however, bacterial blight may damage even varieties reported to be 'resistant'.
Grasshoppers have been a sporadic pest of seedling cotton for 10 or more years. This problem emerged as a result of the conservation movement to reduced tillage. Certain seasons seem to be worse than others and 2018 has resulted in greater concern than more recent years. Growers reported observing high numbers of adult grasshoppers during harvest season in fall 2017. Overwintering populations are influenced by environmental conditions. Rainfall is likely more important than temperatures. Dry winters are favorable for grasshopper population since they overwinter as eggs in the soil. Grasshopper problems are sporadic and almost always associated with reduced tillage fields.
The primary grasshopper that damages cotton is the differential species which also overwinters as eggs in the soil. Eggs hatch from late March throughout April, May and June as soil temperatures rise and spring rains occur. The first nymph to leave the egg pod makes a tunnel from the pod to the soil surface through which the succeeding nymphs emerge. Nymphs feed and grow for 35 to 50 days before becoming adults which can then fly. The nymphs or immatures can only jump. Their development proceeds most rapidly when the weather is warm but not too wet. Mature grasshoppers mate and continue feeding on plants About 2 weeks later, females begin to deposit clusters of eggs in the soil. Soil particles are glued together around the eggs to form a protective pod Each pod may have 25-150 eggs. Most grasshopper species only complete one generation per year.
In fields with historical grasshopper problems, growers may want to take a more preventative approach by adding a grasshopper insecticide to their burn down herbicide. Since not all grasshoppers emerge from the egg stage at the same time, a long residual IGR (insect growth regulator) insecticide could also be utilized. Dimlin has proven to be a good management tool for grasshoppers. It has extended residual that provides good control of immature grasshoppers but will not control adults.
There are no established thresholds for grasshoppers in cotton and will likely never be since their feeding habits are so unpredictable. Some fields and some years may have grasshopper damage while other fields and years have the same level of grasshoppers but no damage. Preventative insecticide applications for grasshoppers are a judgment call. When grasshoppers are observed, and cotton is in the susceptible stage, treatments can be based on the risk level that an individual grower is willing to take.
Grasshopper problems are greater in lighter soils or soils with higher sand content. Damage often occurs in the same fields or farms from year to year. Grasshopper damage as stated is unpredictable but can potentially threaten a stand. Grasshoppers may feed on foliage, but most economic damage occurs when grasshoppers feed on the mainstem of emerging (in the crook or cracking stage) seedlings. In some cases, grasshoppers may completely sever the stem, but more often they will chew partially through the stem weakening the plant which will fall over at the feeding site.
Most all cotton insecticides will control immature grasshoppers when applied at a low labelled rate. Later into the spring, adult grasshoppers are very difficult to control with any insecticide, even at a high labelled rate. Acephate (Orthene) at 0.6 lb. active per acre has proven to be the most effective grower treatment for adult grasshoppers.
Last week, Miravis (a.i. adepidyn), a FRAC Group 7 carboxamide fungicide, was registered for the control of foliar diseases in peanut. Other Group 7 carboxamide fungicides labeled for use on peanut include Elatus, Priaxor, and Fontelis. Unlike Elatus and Priaxor, Miravis contains just the a single a.i. adepidyn. As a result, following resistance management practices will be critical to maintaining the long term efficacy of all of the above Group 7 carboximide fungicides.
The efficacy of Miravis against early and late leaf spot is superior to all fungicides currently recommended for early and late leaf spot control in peanut. Performance of Miravis against late leaf spot under heavy disease pressure with nearly daily rain showers in 2017 at GCREC was impressive. Miravis does not control white mold in peanut nor does it have activity against peanut rust. To obtain white mold control, Miravis will need to be tank mixed with 7.3 or 9.5 oz/A Elatus or another fungicide with good activity against white mold. Other peanut diseases controlled or suppressed by Miravis include pepper spot, web blotch, and Sclerotinia blight. While web blotch causes some defoliation on late planted peanuts, pepper spot and Sclerotinia blight are not issues in Alabama peanuts.
In recent Alabama field studies, the recommended rate of 3.4 fl oz/A Miravis, when included in a five application fungicide program with 7.3 or 9.5 oz Elatus, provided superior early and particularly late leaf spot control than other registered fungicides. According to the label, Miravis applications can be scheduled at 21- to 28-day intervals as apposed to the standard 14-day application schedule recommended for nearly all other leaf spot fungicides. For meet resistance managment criteria, applications of the above FRAC Group 7 fungicides should be limited to no more than half of the total number of fungicide applications. While recommended Miravis-based fungicide programs have yet to be finalized, a possible five application program would include alternating applications of a chlorothalonil fungicide with Alto or similar product and 3.4 fl oz/A Miravis + either 7.3 or 9.5 oz/A Elatus or other white mold fungicide.
Miravis is a premium early and late leaf spot fungicide that may be available in 2018 in limited quantities. Additional field trials designed to evaluate the efficacy of Miravis against foliar diseases will continue through the summer, 2018 with the results being available by early 2019.
Australian scientists have confirmed hybridization of two of the world's major pest species into what they say could be a new mega-pest. The 2 pests are: Helicoverpa armigera, referred to as the "old world bollworm;" and Helicoverpa zea, known in the U.S. as the corn earworm or cotton bollworm.
H. armigera was confirmed in Brazil in 2012 and 2013, where they settled into an area already populated by H. zea. This mating has now led to hybridization. Previously, these 2 species had been separated geographically by continents for about 1.5 million years.
H. armigera, the old world bollworm, is widespread in Africa, Asia, Australia, and Europe and causes damage to over 100 crops including corn, cotton, and soybean. This species has developed resistance to most every pesticide used against it. The U.S. corn earworm or cotton bollworm has limited resistance potential and host range.
H. armigera was detected in south Florida in 2015, but no additional finds have been reported. Alabama Extension entomologists Drs. Tim Reed, Ron Smith, and Alana Jacobson utilized pheromone baited traps at Fairhope, Brewton, and Headland AL in both 2016 and 2017 but no H. armigera were captured. These sites will be monitored again in 2018, along with those in several other southeastern states.
Researchers have confirmed hybridization between the two species in Brazil as reported in the Proceeding of the National Academy of Sciences of the USA. These hybrids could be hard to ID at borders and could go undetected once it enters another country.
In Brazil, scientists reported that among the caterpillars studied, every individual was a hybrid. The findings among the hybrids was that 51% of the H. zea (corn earworm, bollworm) larvae carried a known resistance gene from the H. armigeraspecies.
Leading researchers believe that the hybrid study has wide-ranging implications for the agricultural community here in the U.S. Is it estimated that 65% of the U.S. agricultural output is at risk of being affected by this hybridization between H. armigera and our H. zea species.
Shown below are two H. armigera "old world bollworms" attacking a cotton boll in Australia and an H. armigera moth. Picture was taken by Ron Smith while on a cotton education tour of New South Wales and Queensland Australia in Feb. of 1999. This pest was causing major economic damage to non-genetic varieties at that time.
Dr. Alana Jacobson, research entomologist at Auburn University is using a DNA-based test to identify moths captured in both H. armigera and H. zea traps at the three trap sites in Alabama. This real-time assay is able to differentiate H. armigeraand the F1 hybrids of H. armigera and H. zea from the non-hybridized moths. Funding for these efforts is provided by the Alabama Cotton Commission and Alabama Soybean Producers Committee.
May 11, 2018 - Gramoxone (paraquat) is a commonly used herbicide in peanut for weed control. It can be tank mixed with Storm, Basagran, Ultra Blazer, 2,4-DB and other residual herbicides to apply over the top of small peanuts. Tank mixing herbicides with Gramoxone increase weed control spectrum and efficacy, however, peanut injury has always been a concern for some growers who plan to use Gramoxone. Currently, we do not have enough information regarding the tolerance of newer peanut varieties to Gramoxone-based tank mixes in dryland. Therefore, research trials were conducted in 2016 and 2017 at Shorter, Fairhope and Headland, AL, to evaluate the tolerance of four common peanut variety to Gramoxone-based treatments. At each location, GA-06G, GA-14N, GA-12Y and TUF-511were planted in May to early June and sprayed with different treatments at 21-28 days after planting with backpack sprayers. Non-ionic surfactant at 0.25% v/v was used with all these treatments. Experimental design was RCBD with 4 replications. All trials were maintained weed free during the season. Peanut height, width and final yield were measured at each location. Data was analyzed in SAS 9.4.
Table 1: Peanut yield responses to Gramoxone-based treatments. Data was averaged across three locations in Alabama (Headland, Shorter and Fairhope)
Table 2: Peanut yield responses to Gramoxone based treatments. Data was averaged across three locations in Alabama (Headland, Shorter and Fairhope). Peanut yield was not different between treatments as compared to non-treated check.
Results of this study show that peanut width was more sensitive than peanut height. No peanut variety showed greater sensitivity to Gramoxone-based treatments than the other varieties. Gramoxone + 24DB + Dual Magnum or Warrant produced most of the visual injury as compared to other treatments. Adding Storm or Basagran with Gramoxone reduced peanut injury by 10-15%. However, final yield was not affect by any of these Gramoxone-based treatments except for Gramoxone 24 oz/A at Fairhope and Headland in 2016 (this rate is over the label rate and included for research purpose only). The use rates of each herbicide for the 2017 trial was the highest label rate and I would not recommend growers using these much of products. These highest label rates were used only to test crop tolerance. At the end of season, all four varieties showed similar tolerance to these treatments and no yield loss was found after statistical analysis at p=0.05 level. This means all the Gramoxone-based treatments produced statistically equivalent amount of yield compared to non-treated check.
Peanut varieties evaluated showed very good tolerance to Gramoxone tank mixes. Temporary leaf burn should be expected but peanut will soon recover from injury under normal growing conditions. Considering the dry weather we have been having this spring, Gramoxone based treatments are good options if residual herbicides applied behind the planter were not properly activated due to lack of rain in dryland fields. Dual Magnum, Zidua, Warrant or Outlook should be tank mixed with Gramoxone to provide extended residual weed control and this is important to ensure a successful season long weed control.
Extension Weed Scientist, Crop, Soil and Environmental Sciences
Weather patterns have gotten much warmer and drier over the past three weeks since the last report. As a result, overall weather patterns have not been very favorable to disease development in wheat but have favored high wheat yields statewide.
Fusarium scab has not been a major issue in Alabama wheat. This disease has developed in fungicide and cultivar screening trials at the Gulf Coast Research and Extension Center but has not been an issue at other research locations despite rains occuring at flowering. Leaf rust did appear late in some field wheat at GCREC but that disease has not appeared in cultivar or breeding line screening trials at other AAES outlying research units. In addition, strip rust, which is an occasional problem in the Tennessee Valley, also has not been observed in 2018.
Septoria leaf spot and Septoria leaf spot was observed at several location but damage, except at GCREC, was limited to the lower leaves. As a result, the impact of this disease on yield and test weights should also be low. Powdery mildew pressure was also low statewide.
Take-all root rot was diagnosted in wheat at the Tennessee Valley Research and Extension Center. This disease is an issue primarily in North Alabama where wheat follows wheat. As a result, the most effective control is rotation of wheat with other winter cover crops, particularly oats, legumes, or winter brassica's like tillage radish or turnips.
Blue disease, which is caused by the aphid transmitted virus cotton leafroll dwarf, was tenatively identified in cotton collected in Barbour and Henry Co in 2017. Cotton with similar symptoms was observed at very low levels at two locations in Southwest Georgia. Presence of this virus has not been detected in the Georgia cotton but was found in the initial but not subsequent Alabama samples. This virus may be unstable and may 'disappear' in host tissues over time. Blue disease is responsible for sizable yield losses in Brazil in susceptible cotton cultivars as well as countires across tropical Africa.
All cotton cultivars marketed in the Southeast are susceptible to blue disease. Symptoms do not appear existing leaves but new leaves are stunted and often cupped or crinkly with a leathery appearance and deep green to almost blue color. The veins on young leaves may also turn yellow. Once infected, plant growth essentially stops as does boll set and maturation. Symptoms can easily be confused with those of phenoxy herbicide injury with the notable exception that individual or several diseased virus-infected plants probably will be found as compared with widespread damaged plants more often associated with overspray or drift events.
At this point, disease incidence in Alabama cotton appears to be very low. Grower or their scouts, particularly those in Southeast AL, need to be on the lookout for symptomatic plants. If you observe diseased plants, contact your Regional Extension Agent, state specialist, or Auburn University Plant Diagnostic Laboratory for further information.
As noted above, all cotton cultivars are susceptible to blue disease. Single gene resistance is available in commercial cotton germplasm but time will be needed if the disease intensifies to deploy resistant cultivars adapated to the Southeast. Control of weed hosts may help slow the spread of blue disease. Malvacaea weeds such as pigweed and prickly sida are hosts of this virus, so control of these weeds in a field and around field borders may slow virus movement into production fields. One observer mentioned that diseased plants were clusted along the field border, so weed control may help with disease avoidence. The value of controlling the aphid vector with post-plant insecticides is questionable as overspraying could lead to outbreaks of other arthropod pests, particularly spider mites.
For more information, see:
May 10, 2018 - In recent weeks, most of the south Alabama was warm and dry, mostly dry. We have not had any rainfall for over two weeks in a row and this is taking a toll on row crops. Many people cannot plant their dryland fields and the crops planted are suffering drought stress. I have received several calls and texts regarding the concerns of soil herbicides sprayed behind the planter may not get activated. So, I am writing this timely information sheet to further discuss this issue.
1. No chance of rain in forecast for the next 10-14 days. Should I still spray soil herbicides behind planter after I plant my dryland field?
I am a big advocate of using soil herbicides for weed control. However, in this case, I would suggest only spraying Gramoxone or Liberty behind the planter to smoke the weeds and start clean. We all know a fact for soil herbicides: it does not matter if it does not rain. They will not do you much good if there is no rain to activate them.
2. If I did not spray soil herbicides behind the planter, what do I need to do next?
My first thought is I hope you sprayed a good residual herbicide treatment in your preplant burndown application, so you may still have some herbicide residues in soil. If you did not spray any soil herbicide behind the planter, I would do postemergence treatment very timely when you know you will have a high chance of rainfall. Weeds will not germinate or grow much in a very dry situation, so spraying a residual herbicide such as Warrant, Dual Magnum, or Outlook with Roundup, Liberty, Enlist Duo or One, or Roundup + Dicamba within 3 days before you get a rainfall is very important. In peanut, you can spray either Warrant, Dual Magnum, Outlook or Zidua with a postemergence herbicide such as Cadre, Blazer or Cobra. Weeds always make a flush after the rain if it has been dry for a while. Therefore, I suggest growers spray residual and foliar herbicide before the rain and hammer them hard with a follow up treatment 14-21 days later if escaped weeds start to grow fast after the rain.
3. What do I need to do when I burn off emerged weeds behind planter and it is dry?It is likely that these weeds are in a drought stress too, so they may not respond to herbicides super well. They also can grow thick leaf cuticle and wax layer so herbicide absorption will be lower than normal. I would suggest growers using crop oil concentrate or methylated seed oil instead of non-ionic surfactant (NIS) because oil-based surfactant may dissolve cuticle wax better and allow more herbicide to get into weed foliage. Adding liquid ammonium sulfate may increase control of certain weeds. If you happen to get a shower, although it may be a very small one, it can still help you burndown weeds better after a little bit of moisture, and I would take advantage of that before it gets very dry again.
4. How much rain do I need to activate my soil herbicides?Not a lot, 0.5 inch of rain can usually do it. For some soil herbicides, they can be activated with as little as 0.25 inch of rainfall. In a previous study, 0.5 inch of simulated rainfall was able to activate Brake, Reflex, Diuron, Cotoran and Warrant for pigweed control. However, with only 0.25 inch of rainfall, Brake + Reflex was the only treatment that provided over 90% pigweed control. Brake + Warrant provided 73% of control which is better than Brake (43%), Brake + Cotoran (32%) and Brake + Diuron (40%). See pictures below (pictures credit to SePro).
Palmer amaranth control after 0.25-inch total irrigation at 7 days after application:
The fist picture shows Brake 16 oz/A, while the second picture shows Brake 16 oz + Reflex 12 oz/A.
I probably have been asked this question a hundred times so far, so I decided to run a large study to evaluate persistence of common cotton and peanut residual herbicides on soil surface before they can see a rainfall. More results will be available later in the fall.
Dr. Steve Li
Extension Weed Scientist, Assistant Professor
Weather patterns over the past month have been cooler than the historical average with average to below average rainfall totals. As a result, disease activity in wheat statewide has been relatively low.
In Southwest AL, light leaf rust along with some Septoria glume blotch was observed in wheat plantings at the Gulf Coast Research and Extension Center, while no disease activity was seen in the wheat variety trial at the Brewton Agricultural Research Unit. In addition, little to no disease activity was observed in the wheat variety trial in Central AL in the wheat variety trial at the Prattville Agricultural Research Unit. Late last week, light Septoria leaf spot but no leaf or stripe rust was found in a an advanced breeding line study at the Tennessee Valley Research and Extension Center.
So far, scab has not been observed in wheat at any of the above locations. While some rain showers have occured when wheat was in bloom at several research units, it is unlikely the the duration of the rain showers, which were quickly followed by dry and cooler air, were sufficent for sustained infection of the heads. Wheat trials at GCREC and BARU will be checked for scab tomorrow.
The wheat scab risk for Baldwin and Mobile Counties is high
as compared with the low risk for scab development for the remainder of
Alabama. Kim Wilkins mentioned that she saw some scab in early Baldwin Co. wheat. Wheat is flowering across Southwest Alabama, so producers should
make (or already have made) a fungicide application before the next rain event
scheduled for this coming weekend. Prosaro at 6.5 to 8.2 fl oz/A or Caramba at 10 to 17 fl oz/A are registered for scab control in wheat. Proline @ 5.0 to 5.7 fl oz/A also is labeled for scab control. Currently, Prosaro is the most widely used fungicide for scab control in wheat. Strobilurin fungicides (i.e. azoxystrobin, floxastrobin, picoxystrobin, and pyraclostrobin) when applied to the seed head at flowering can significantly intensify scab in wheat.
A low level of rust activity along
with a low to moderate level of Septoria glume blotch was also noted in Baldwin
Co at the Gulf Coast Research and Extension Center. Disease activity was
negligible across the entire wheat variety study as well as in several tiers of
wheat at the Brewton Ag. Research Unit in Brewton.
Head extension should just be getting started in North
Alabama. With the exception of trace levels of powdery mildew and
Septoria leaf spot, disease activity at two North Alabama locations visited late last week was low on
wheat showing the flag leaf but no seed heads. Producers need to scout
fields to determine if there is sufficient Septoria glume blotch, leaf rust,
and powdery mildew in their wheat to justify a fungicide application to protect
the flag leaf. Fungicide applications to the seed head for scab control
are almost mandatory as grain elevators will not purchase scabby
wheat. Scab fungicide applications will also provide good protection from
Septoria diseases on the leaves and head, along with leaf rust, and powdery mildew.
Last Friday, some cold injury to the flag leaves from the Thursday morning freeze was also noted on some breeding lines and commercial varieties at the Tennessee Valley Research and Extension Center.
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