kentucky pest news, july 16, 2013

7/28/2019 Kentucky Pest News, July 16, 2013

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Online at:www.uky.edu/KPN

Number 1348 July 16, 2013

TOBACCO- Severe Spotting and Scorch

of Burley Tobacco Leaves

FRUIT CROPS

- Spotted Wing Drosophila Widespreadand Active in KY

ORNAMENTALS-Aerial Blight Infections on Vinca and Herbaceous

Annuals

FUNGICIDES- Some Principles of Fungicide Resistance VI:

Application Rate and Fungicide Resistance

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

TOBACCO

Severe Spotting and Scorch of Burley Tobacco

Leavesby Bob Pearce, Kenny Seebold, and Julie Beale

Massive amounts of rain fell through much of theburley production area of Kentucky over the 4th of

July weekend. This has led to a number ofproblems such as drowning, leaf scald, and black

shank, as we would expect. We have also begun

to see rapid development of spotting on lowerleaves, weather flecking and in many cases severe

scorching of bottom leaves (see images below).Before the rains came, we were already seeingfoliar symptoms of deficiencies of nutrients likenitrogen, potassium and phosphorus, which wesuspected were directly related to poor root

development resulting from generally wet soilconditions that had prevailed during the earlyseason. The presence of symptoms before therains and the sudden development of severespotting after the heavy rains have raised concerns

that a new and explosive leaf disease is occurring.However, even though some of the symptomologyis similar to what we would see with angular leafspot (which, in fact, is present in some areas); wehave examined numerous samples and are sure

that this problem is not caused by a pathogen.Instead, what we are seeing is the result of aninteraction between stressed tobacco and theenvironment.

So why did these symptoms appear so suddenly

and across a wide area of the burley region? Theshort answer is that we dont know for sure. The

problem may be related to one specific factor, or acombination of factors. Weather flecking mayhave a lot to do with what we are seeing, and it is

possible that we are seeing worst-case examples ofweather fleck. Some of the spotting seems to be

actual physical or mechanical injury from raindrops driving into the leaves. The symptoms of

severe scorching between the veins of lower

leaves and nutrient deficiency symptoms (likepotassium and phosphorus) have also been

common. One possibility that would explain thissudden onset of symptoms is nutrient imbalance in

the affected plants. Plants with impaired rootsystems would not have been able to take upnutrients at a sufficient rate to supply the growing

points, and would have re-mobilized these fromthe lower leaves. More than one nutrient could be

involved, but we dont really know with certainty.We are in the process of having leaves analyzedfor nutrient content to try and pinpoint what might

be deficient.

The scorching has a passing resemblance toSpartan injury, which can occur when excessrainfall washes herbicide into the root zone.

However, these symptoms are showing up in fieldsthat were not treated with Spartan as well asSpartan-treated fields, so our feeling is that we arenot dealing with herbicide injury in most cases.

Lexington, KY 40546
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPN


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The biggest question of all is what to do in fields

where this syndrome is occurring. The difficultyin making a recommendation right now is that we

really dont know the exact cause (or causes) ofthe problem. Until we get a better handle on the

situation, the following are some points ofdiscussion to share with producers.

- Although theres not a pathogenassociated with what we are seeing, we areconcerned that extensive damage to thefoliage will make it more susceptible totarget spot and possibly brown spot.

Because of this, and because theres quitea bit of active target spot right now, an

application of Quadris is recommendedfor growers who have not applied it

already. The standard 8 fl oz./A rateshould be sufficient for protection, andgrowers who are seeing disease alreadyshould consider a rate of 10 to 12 fl oz./A.

- The nutritional problems that were seeingright now are not generally associatedwith deficiencies in the soil, but insteadare a result of the inability of roots toreach nutrients that are already there.

- Side-dressing would be of potential valueif nutrients can be placed into the rootzone without creating additional damage.

For tobacco that is waist-high orbigger, do not apply more than 25

lb. of actual N per acre.

For tobacco that is smaller thanwaist-high, use no more than 50lb. of actual N.

Ammonium nitrate would be theideal N source, but liquid N(UAN) would be an acceptable

alternative. For potash, 100 lb. /A of sulfate of

potash (0-0-50) should be

sufficient.

- Foliar nutrient applications historicallyhave not resulted in yield increases.However, under current conditions a foliar

application may be effective to deliver aquick dose of nutrients to the crop.

The most likely benefit fromfoliar application of fertilizerwould be correction of

micronutrient deficiencies. It will be less likely to see benefits

from N, P, and K with a foliar

application.

Be aware that foliar fertilizers cancause leaf burn; do not apply

excessive amounts in any onetreatment.

Figure 1. Weather flecking.

Figure 2. Interveinal scorching and weather flecking.


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Figure 3. Severe scorching between veins.

Figure 4. Weather flecking and spotting between veins.

Figure 5. Severe scorching on lower leaves.

FRUIT CROPS

Spotted Wing Drosophila Widespread and

Active in KYBy Ric Bessin, Entomologist

We have been working with producers in a

number of KY counties to monitor spotted wingDrosophila (SWD) this summer. The first traps

positive for SWD were in Breathitt and BourbonCounties, but since the start of July, trappinglocations in seven addition counties have been

positive for SWD. SWD is a serious threat to smallfruit production, the adults lay eggs under the skin

of otherwise sound fruit. This can result in smallmaggots in the fruit at harvest or just after harvest.

Blueberries, blackberries and raspberries are verysusceptible to this new invasive pest. In addition to

damaging a large percentage of a crop, this pestalso has the potential to upset customers and ruinmarkets.

Figure 6. The end of the female SWD abdomen with the

enlarged, toothed ovipositor.

So far we have recorded SWD in Breathitt,

Bourbon, Larue, Warren, Daviess, Caldwell,Crittenden, McCracken, and Meade counties. So it

isnt restricted to one region of the state, it is in thewestern, central, and eastern parts of the state.This past year we have recorded SWD only from

Warren and Daviess Counties. We are finding itagain in these two counties as well as theadditional new counties.

In other states were SWD has become established,

producers that have detected SWD often need to


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spray periodically during the harvest period toreduce losses. Because of this, producers need to

coordinate their harvests and spray timing in orderto comply with pre-harvest intervals (PHIs) with

the respective insecticides. As the small fruit cropsare harvested several times a week, this limits the

types of materials that can be used. Insecticidetrials at Michigan State have indicated that someinsecticides in the organophosphate, pyrethroid,

and spinosyn classes have good activity againstSWD. The neonicotinoids have not been effective.

Several states have developed extensionrecommendations and have factsheets available on

line. I would recommend the following ofblueberry and blackberry/raspberry producers.

They list monitoring methods (that we have beenusing) and available insecticides.

SWD Management Recommendations for

Michigan Blueberry Growers

http://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdf

Spotted Wing Drosophila Management

Recommendations for Michigan Raspberry and

Blackberry Growers

http://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdf

There are several cultural controls that may behelpful. The first is timely and clean harvests. Thisincludes removal of overripe and damaged berries.Burial of infested fruit has not been effective asthe SWD can still emerge. Placing fruit in clear

bags that are sealed and left in the sun will kill anySWD that emerge. Removal of wild hosts(brambles, poke, honeysuckle, wild grape) nearcommercial plantings may help.

When SWD has been detected on a farm, growers

may need to begin insecticidal control. Butinsecticides need to be applied correctly in order to

be effective. They need to be in place prior tooviposition (egg laying), coverage needs to be

thorough as the adults often hide in the denseportions of the canopy. So, higher pressure andhigher spray volume will be needed to reach thesedifficult to reach spots. Even the best of theinsecticides will not consistently last more than 7

days, so at minimum, weekly applications will beneeded. With heavy rains, sprays may need to be

reapplied. Producers should also rotate amonginsecticides with different modes of action to

prevent/delay resistance. A general rule of thumbis to switch modes of action with each new pest

generation, which would mean switching to a newIRAC insecticide group. Since this pest cancomplete a generation in less than two weeks, we

need to have multiple types of insecticidesavailable.

ORNAMENTALS

Aerial Blight Infections on Vinca and

Herbaceous AnnualsBy Nicole Ward Gauthier, Extension Plant

Pathologist

Aerial blight (also referred to as shoot blight) hasbeen popping up in landscapes and garden centers.Typically, two different organisms can cause

aerial blight symptoms Rhizoctonia solani (atrue fungus) andPhytophthora parasitica (a watermold). Recent outbreaks of aerial blight inKentucky have been reported on vinca (Figures 7-9), calibrachoa (Figure 10), and petunia, each

caused by the Phytophthorapathogen. Thus, thefollowing information will be specific toPhytophthora aerial blight.

Phytophthora species are water mold pathogens.

Briefly, that means that they must have free waterto complete their life cycles (produce spores,infect, and cause disease). During wet weather(frequent rains) or under excessive water orhumidity (greenhouse conditions or heavy

irrigation), water mold pathogens proliferate.Clearly, this years rainy conditions are favorable

for disease.

Phytophthora aerial blight, like other water mold

pathogens, is no different. It thrives in soils ofheavily irrigated or otherwise wet landscapes and

in production greenhouses. Infections occur whensoilborne pathogens splash up onto stems andfoliage. Leaves become blighted (rapid collapse)(Figure 7) and then infection spreads to petioles
http://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendations-RaspberryBlackberrySep2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdfhttp://www.ipm.msu.edu/uploads/files/SWD/ManagementRecommendsBlueberry-May2012.pdf


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(Figure 8) and stems (Figure 9). Lesions on lowerstems cause girdling and entire branches then fail.

Once plants are infected, fungicides do not cure

disease. Affected plants should be destroyed assoon as possible to prevent diseased tissue (and the

pathogen) from building up in landscape soil andgreenhouse floors. Homeowners should considerimproving drainage, mulching to prevent splash,

and switching to drip irrigation. No fungicides arerecommended for residential or landscape use.Commercial growers, on the other hand, shouldemploy a preventative program for healthy plantsif nearby plants become infected. Phosphorus acid

fungicides (e.g. Aliette) are effective against watermold pathogens and are recommended for

protection against Phytophthora aerial blight.

More information for commercial greenhousegrowers can be found athttp://www2.ca.uky.edu/agcollege/plantpathology/

ext_files/PPFShtml/PPFS-GH-4.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdf

Landscape and homeowner information can be

found athttp://www2.ca.uky.edu/agc/pubs/id/id87/id87.pdf

Figure 7. Initial infections by the aerial blight pathogen

occur on leaves of vinca.

Figure 8. Infection spreads from leaves, down petioles, and

then to stems.

Figure 9. Progression of symptoms to stems.

Figure 10. Advanced symptoms of aerial blight on

calibrachoa (million bells).
http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id87/id87.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id87/id87.pdfhttp://www2.ca.uky.edu/agc/pubs/id/id87/id87.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-3.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-4.pdf


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FUNGICIDES

Some Principles of Fungicide Resistance VI:

Application Rate and Fungicide ResistanceBy Paul Vincelli, Extension Plant Pathologist

This sixth article in this series addresses severalpractical questions about application rate and thebuildup of fungicide resistance. First, it isimportant to understand the two broad ways that

fungicide resistance shows up in fields.

In quantitative resistance1, resistantspores are less sensitive than the wild-type2 spores, much like an undersized,

partially effective shield (compare Figures11 & 12). If quantitative resistance is

present, you may notice you arent gettingthe level of control you once did, but that

you can still achieve decent control at highrates and short spray intervals. Commonexamples of this would be cases of

resistance to DMI fungicides (=FRACCode 3, seeprevious articleon FRAC

Codes).

In qualitative resistance, resistant sporesare completely insensitive to normal fieldrates of the fungicide. It is as if a large

shield prevented all fungicide fromcontacting the spores (Figure 13). To the

producer, qualitative resistance looks like

a complete loss of disease control. In fact,sometimes these resistant spores canactually causemore disease when thefungicide is applied, a phenomenon called

hormesis. (See Table 1 for a real-worldexample of hormesis.)

1Quantitative resistance is sometimes referred to as

reduced sensitivity.2

Wild-type spores refers to the spore population

that predominates before the widespread use of a

fungicide. These spores would be predominantly

sensitive to the fungicide.

Figure 11. In a population of fungal spores (orange objects

at right), sensitive spores are killed by fungicide.

Figure 12. Quantitative resistance: Some spores are

partially resistant. It is as if a small, partially effective shield

protected some of the spores. Some of them will survive

the application, though many will also die. (Image of shield

from office.microsport.com)

Figure 13. Qualitative resistance: The large majority of

Surviving spores are completely resistant to fungicide. It is

as if a large shield prevented fungicide from contacting the

spores. (Image of shield from office.microsport.com)

Table 1. Disease enhancement following

application of a QoI fungicide on perennial

ryegrass infected with QoI-resistantPyricularia

oryzae

Treatment (formulation &

amt product/1000 sq ft

% of plot

affecteda

Water 53 bThiophanate-methyl +

chlorothalonil 90WDG, 8

oz.

2 c

Azoxystrobin 50WG, 0.2

oz.

66 a

aWaller-Duncan statistical test, k=100, P~0.05
http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201346.pdf


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With that background, here are two commonquestions relating to application rate and fungicide

resistance.

If disease pressure is very low, doesnt it make

sense to apply a fungicide at a half-rate?

Yes, in a sense, it does. Reducing the applicationrate of a pesticide benefits ones pocketbook, theenvironment, field workers, and consumers.

However, applying a fungicide at rates belowthose listed on the label does increase the risk offungicide resistance. This is especially so forcases of quantitative resistance, such as resistanceto DMI fungicides (=FRAC Code 3).

Lets consider a fictional example, called Blight-

Be-Gone. Suppose Blight-Be-Gone is labeled tocontrol a disease at 3-6 oz./acre. However, disease

pressure is really low, so we may logically decidethat we probably dont need the fungicide.

Nevertheless, suppose I decide to include it with a

post-emergence herbicide spray, because I amalready in the field, and it gives me peace of mind.Since disease pressure is so low, I might spray it at

1.5 oz./acre (which is half the minimum labeledrate). It is seems like sensible plan. However, therisk in using the half-rate is that I am allowing thespores with partial resistance to build up overtime. And the more opportunity they have to

multiply, the greater the risk that even more

resistant spores will emerge.

In cases of qualitative resistance3, half-ratesprobably have little influence on the buildup ofresistance. This is because spores that exhibitqualitative resistance thrive even at the highest

labeled rate of the fungicide.

Cant I prevent fungicide resistance by using

the high, labeled rate of a fungicide?No, definitely not. If a fungus has the genetic

potential to develop resistance to the product we

are using, there is no way toprevent fungicideresistance, short of never using the at-riskfungicide. We canonly slow down the buildup of

3Examples of qualitative resistance would include

many cases of resistance to strobilurin/QoI fungicides

(=FRAC Code 11) or to benzimidazole fungicides (FRAC

Code 1).

resistance. See thefirst articlein this series formore on this.

So, can we slow down the development of

resistance using a high, labeled rate? Yes and no.Yes, if the resistance is quantitative, no if it is

qualitative.

If resistance in your field is quantitative (Figure

2), high doses can suppress many of the spores,even many of those that have partial resistance. Inthese cases, higher doses may indeed slow downthe buildup of resistant populations.

If resistance in your field is qualitative (Figure 3),high doses essentially have no effect on the

fungus. The mutant spores survive even thehighest doses, so typically no disease control

occurs following the application of even thehighest labeled rate.

Bottom lineFungicide resistance appears as a partial loss ofdisease control (quantitative resistance) or

complete loss of disease control (qualitativeresistance). In cases of quantitative resistance,

using less than labeled rates is inadvisable,because it may accelerate the buildup ofresistance. Use of labeled rates may slow down

(though not prevent) the development of

quantitative resistance. In cases of qualitativeresistance, even high rates dont suppressresistance buildup.

DIAGNOSTIC LABORATORY HIGHLIGHTS

By Julie Beale and Brenda Kennedy

Agronomic samples diagnosed in the PDDL in thepast week have included Pythium and Rhizoctonia

root rots on corn; Rhizoctonia root and crown rotsand Mycoleptodiscus crown rot on alfalfa; leafstreak on orchardgrass; Fusarium head blight on

wheat; angular leaf spot, environmental leafspotting and/or weather fleck (see Dr. Seeboldsarticle), black shank, soreshin and Rhizoctoniaroot rot, Fusarium wilt, alfalfa mosaic virus,tomato spotted wilt virus, manganese toxicity and

frenching on tobacco.
http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201342.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201342.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201342.pdfhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/pdf/KPN%201342.pdf


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On fruit and vegetable samples, we havediagnosed black rot and anthracnose on grape;

raspberry ringspot virus on black raspberry; cedar-apple rust on apple; scab on peach; black knot on

plum; bacterial spot and powdery mildew oncherry; Rhizoctonia root/stem rot on bean;

southern blight on potato; Septoria leaf spot, earlyblight and Botrytis leaf blight on tomato.

On ornamentals and turf, we have seen black rootrot on petunia; Fusarium root/stem rot onsunflower; rust on snapdragon; Phytophthoraaerial blight on annual vinca, petunia andcalibrachoa; Cercospora leaf spot on rose; fire

blight and cedar-quince rust on hawthorn; leafblight on honeysuckle; Fusarium wilt on mimosa;

Pythium root rot on annual bluegrass and ryegrass;and brown patch on fescue.

2013 INSECT TRAP COUNTS

July 5 12

Graphs of insect trap counts for the 2013

season are available on the IPM web site at -http://www.uky.edu/Ag/IPM/ipm.htm.

Note: Trade names are used to simplify the information

presented in this newsletter. No endorsement by the

Cooperative Extension Service is intended, nor is

criticism implied of similar products that are not

named.

Location Princeton,KY

Lexington,KY

Black cutworm 15 1

Armyworm 49 398

European corn

borer

0 0

Corn earworm 6 4Southwestern

corn borer

3 2

Fall armyworm 0 0
http://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.

kentucky pest news, july 16, 2013

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