kentucky pest news, july 16, 2013
TRANSCRIPT
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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
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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.