kentucky pest news, june 25, 2013
TRANSCRIPT
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Online at:www.uky.edu/KPN
Number 1345 June 25, 2013
CORN-Recognizing Gosss Wilt on Corn
- Efficacy Ratings for Corn Fungicides, 2013
Version
TOBACCO
Disease Update for the Week of June 24
VEGETABLES
-Tomato Spotted Wilt on the Increase
-Late Blight of Tomato Found in Kentucky
DIAGNOSTIC LAB HIGHLIGHTS
INSECT TRAP COUNTS
CORN
Recognizing Gosss Wilt of Corn
By Paul Vincelli, Extension Plant Pathologist
Gosss Wilt is an emerging bacterial disease
of corn (dent corn, popcorn, sweet corn) in the
Midwest. For decades, this disease has causedproblems in several Plains states, especially in
Nebraska, Colorado and Wyoming. In thepast few years, the disease has also been foundin scattered fields in Indiana and Illinois,
causing losses as high as 60 bu/acre.
Although Kentucky may be too far south for
serious outbreaks, it is worth keeping a watchout for this disease.
SymptomsInfection of corn by the Gosss wilt bacterium
(Clavibacter michiganensis subsp.
nebraskensis) produces death of leaf tissue.The disease results in long, tan spots of deadtissue anywhere on leaves. Infected leaves
usually become blighted.
Figure 1. Goss's wilt of corn (photo by Alison Robertson,
Iowa State University).
These symptoms can be confused with otherdiseases and disorders, such as Stewarts wilt
or northern leaf blight. However, there are a
few distinctive features to look for. The main
symptom that distinguishes Gosss wilt fromother problems is the presence of dark green,
water-soaked flecks or freckles.
Lexington, KY 40546
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Figure 2. Goss's wilt of corn, showing dark green flecks and
"freckles." (photo by Carl Bradley, University of Illinois).
Figure 3. Goss's wild of corn, showing dark green flecks and
"freckles." (Photo by Alison Robertson, Iowa State
University).
Also, when leaves are wet, one might be able
to observe a cloudy bacterial exudate ondiseased tissues. When these exudates dry,
they leave a faint shiny cast on lesions that canbe seen with reflected light.
Infections can also occur in the stalk. Vascular
infection often results in symptoms of leafdesiccation and premature plant death.
Figure 4. Stalk and leaf symptoms of systemic Goss's wilt.
(Photo by Howard F. Schwartz, Colorado State University,
Bugwood.org).
Suspect cases can be diagnosed through the
University of Kentucky Plant Diagnostic
Laboratories. Contact your county Extensionagent for more information about sampling
and testing.
Figure 5. Stalk symptoms of systemic Goss's wilt. (Photo by
Howard F. Schwartz, Colorado State University,
Bugwood.org).
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Management Notes
The bacterium that causes Gosss wilt
survives between seasons in infested cornresidue. Therefore, the risk of disease is
higher under conservation-tillage and/or
continuous corn. Rotation of even one yearaway from corn reduces disease pressure
substantially. Hybrids of yellow dent corn
with resistance to Gosss wilt are available.
The bacterium also is seed-transmitted. Seedproducers may be required to obtain
phytosanitary certificates for corn seed export.
The bacterium is not insect-transmitted.
Fungicides do not provide protection against a
bacterial disease like Gosss wilt. Crops other
than corn are not affected by this disease.
Efficacy Ratings for Corn Fungicides, 2013
VersionBy Paul Vincelli, Extension Plant Pathologist
The Corn Disease Working Group has
prepared an updated table of efficacy ratingsforcorn fungicides, available at
http://bit.ly/126i8ty. This table only provides
efficacy ratings for diseases. It does not rankfungicides for physiological plant health
effects.
Diseases of primary concern to us in Kentuckywould include gray leaf spot and, sometimes
.northern leaf blight. In selected fields in
some years, southern rust may justify afungicide application under Kentucky
conditions, but in most fields, levels of
southern rust are so low that routine fungicide
application is difficult to justify. It would bevery uncommon for the other diseases listed to
pose yield-impacting threats under Kentucky
conditions.
This table is a work in progress, so efficacy
ratings are subject to change, should ongoingresearch indicate that changes are justifiable.
In the meantime, these ratings may be useful
to corn producers.
TOBACCO
Disease Update for the Week of June 24
By Kenny Seebold,
Extension Plant Pathologist
Current situation
Summertime temperatures have settled inacross Kentucky, and rainfall levels have been
a little higher than normal in many areas. As a
result, conditions have been pretty favorablefor diseases and black shank, target spot, and
frogeye leaf spot are becoming fairly active
around the state. For black shank, post-
transplanting applications of Ridomil Gold,Ultra Flourish, or MetaStar can be helpful so
long as the tobacco variety that was planted
has at least a moderate level of resistance to
both races of the black shank pathogen. Makesure these products are applied to soil and
incorporated by cultivation or irrigation (alsorainfall), and that soil moisture levels are
adequate before treating. The last time,
according to product labels, to apply
fungicides for black shank control is layby(last cultivation).
Seeing target spot and frogeye this early intothe growing season can mean that well have
problems later if rainfall continues to beplentiful. Quadris fungicide, applied at 8 floz/A, has been shown to give reasonably good
control of target spot if applied at least once at
beginning around layby. A second application
may be needed at topping to help with thisdisease if needed, and to suppress late-season
frogeye leaf spot should that disease be active.
http://www.uky.edu/Ag/GrainCrops/Briefs/CDWGCornFungicideEfficacy_Table_2013_FINAL.pdfhttp://www.uky.edu/Ag/GrainCrops/Briefs/CDWGCornFungicideEfficacy_Table_2013_FINAL.pdfhttp://www.uky.edu/Ag/GrainCrops/Briefs/CDWGCornFungicideEfficacy_Table_2013_FINAL.pdfhttp://bit.ly/126i8tyhttp://bit.ly/126i8tyhttp://bit.ly/126i8tyhttp://www.uky.edu/Ag/GrainCrops/Briefs/CDWGCornFungicideEfficacy_Table_2013_FINAL.pdf -
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When it comes to frogeye, anecdotal evidence
indicates that a rate of 10-12 fl oz/A would be
more appropriate for control. Timing theQuadris applications for frogeye control
should follow what were recommending for
target spot unless disease pressure is heavybefore layby. In these cases, treat with
Quadris as soon as possible. A follow-up
treatment may be necessary later in the season
if disease is active, particularly around toppingtime. If multiple applications of Quadris are
needed, the label requires alternation with a
fungicide which has a different mode of actionthan Quadris. For frogeye and target spot,
our only options would be Manzate Pro-Stick,
Dithane DF, or Penncozeb (mancozeb
fungicides). So a grower applying Quadris atlayby could come back with mancozeb 2-3
weeks later, and then treat with Quadris either
before or after layby to stay compliant withthe label. Quadris should never be tank-mixed
with any pesticide formulated as an
emulsifiable concentrate; also avoid foliarfertilizers, surfactants and (later in the season)
sucker control materials. With regard to
Orthene, we have had some reports of injuryin Kentucky when this insecticide is tank-
mixed with Quadris; however, many have
applied this combination with no ill effects.To play it safe, it may be best to not use
Orthene and Quadris together during the hot,
dry spell that were under right now. Quadris
can cause weather flecking if applied by itselfin hot weather, and would be more likely to
burn if tank-mixed with Orthene under these
conditions.
Blue Mold
As of June 24, no blue mold has been reportedin the tobacco-growing areas of the United
States.
VEGETABLES
Tomato Spotted Wilt on the Increase
By Kenny Seebold,Extension Plant Pathologist
Tomato spotted wilt (TSW) is being reportedaround the state on tobacco and tomatoes.
The incidence of symptomatic plants in
affected fields is fairly low (less than 1%) in
most cases, but at least one tobacco growerhas reported 10% incidence in some fields.
Losses to TSW are generally negligible in
Kentucky although decreased yield andquality of tobacco can occur on individual
farms if incidence exceeds 10%. With
tomatoes (and also peppers), yield losses canoccur at lower incidence, especially if
infection takes place early in the growing
season.
The causal agent of TSW is the Tomato
spotted wilt virus (TSWV) and is transmitted
to susceptible host plants by several species ofthrips, including the western flower thrips
(Frankliniella occidentalis) and the tobacco
thrips (F. fusca). Larval and adult thrips
transmit the virus during feeding, but the viruscan be acquired by larvae only. Following
acquisition of TSWV, thrips carry the virusfor life. It is believed that roughly 10% of the
thrips population in an area with endemic
TSW actually carries TSWV. Thrips feed on
a number of plant species, and TSWV hasmany hosts in nature (including tomato,
pepper, and many ornamental plants). Thus
there are numerous reservoirs for both thevirus and vector in areas where tobacco is
grown.
Tobacco and susceptible vegetables can be
infected by TSWV at any stage of growth. It
is believed that plants are most susceptible
when young and actively growing, andsymptoms tend to be severe on young plants
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Figure 1. Severe symptom of TSW on a young burley
tobacco plant
Severe stunting or death is likely if tobacco
becomes infected with TSWV prior to layby.
Numerous symptoms of TSW can beobserved: ringspots on leaves, stems, and
Figure 2. Ringspots on tomato foliage infected with TSWV
(D. Langston, University of Georgia).
fruit; necrotic spots on leaves; leaf distortion;
root/vascular necrosis; yellowing stunting; and
wilting.
Figure 3. Yellowing and stunting of burley due to infection
by TSWV.
In other areas where TSW is problematic,
planting at a time when thrips are less active
(late spring) has helped reduce losses to the
disease. Tobacco varieties with resistance toTSWV are not known at this time; however,
resistance is available in tomatoes andpeppers. Research in other parts of the
country has shown that losses to TSW can be
reduced to a degree by minimizing stress to
plants (drought, pest, and nutrient). Removalof symptomatic plants (rouging) can help
reduce secondary spread of disease later in the
season.
For more information regarding TSW and its
control on tobacco and vegetables, visit theTomato Spotted Wilt page maintained at the
University of Georgia
(http://www.tomatospottedwiltinfo.org/).
Another excellent source of information is:www.ces.ncsu.edu/robeson/agriculture/tomspo
twiltvirus.pdf.
http://www.tomatospottedwiltinfo.org/http://www.tomatospottedwiltinfo.org/http://www.tomatospottedwiltinfo.org/http://www.ces.ncsu.edu/robeson/agriculture/tomspotwiltvirus.pdfhttp://www.ces.ncsu.edu/robeson/agriculture/tomspotwiltvirus.pdfhttp://www.ces.ncsu.edu/robeson/agriculture/tomspotwiltvirus.pdfhttp://www.ces.ncsu.edu/robeson/agriculture/tomspotwiltvirus.pdfhttp://www.ces.ncsu.edu/robeson/agriculture/tomspotwiltvirus.pdfhttp://www.tomatospottedwiltinfo.org/ -
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Late Blight of Tomato Found in Kentucky
By Kenny Seebold,
Extension Plant Pathologist
Late blight was confirmed this past Friday
(June 21) on tomatoes in Wayne County.There are unconfirmed reports of this disease
from a neighboring county as well. The
weather conditions that we face for the next 7-
10 days, fortunately, do not favordevelopment and spread of late blight. Still,
its likely that the disease has become
established in some areas, and we need to beon guard to prevent serious losses if and when
conditions do favor late blight. Taking
preventive action is critical, and this means
being on a regular fungicide schedule. Asummary of control recommendations for
homeowners, conventional commercial
producers, and organic growers was publishedon June 11, 2013 in Kentucky Pest News No.
1343
(http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13
/pn_130611.html). Please contact me at
[email protected] you suspect or findlate blight on tomato or potato, or if you have
questions.
DIAGNOSTIC LABORATORY HIGHLIGHTS
By Julie Beale and Brenda Kennedy
Agronomic samples diagnosed in the PDDL inthe past week have included Lepto leaf spot
on alfalfa; magnesium deficiency and root
zone compaction on corn; brown spot onsoybean; black shank, Rhizoctonia stem rot,
Pythium root rot, bacterial blackleg, tomato
spotted wilt virus, temporary phosphorusdeficiency and symptoms of transplant shock
on tobacco.
On fruit and vegetable samples, we have
diagnosed cane blight on black raspberry;
black rot on grape; Fusicoccum stem cankeron blueberry; Phomopsis leaf blight on
strawberry; scab, frogeye leaf spot, fire blight
and cedar-apple rust on apple; brown rot oncherry; bacterial leaf spot on pepper; Septoria
leaf spot, early blight, Botrytis leaf blight, leaf
mold (Fulvia), southern blight and tomato
spotted wilt virus on tomato.
On ornamentals and turf, we have seen
bacterial leaf spot on hydrangea;Botryosphaeria canker on holly; rose rosette
and sawfly injury on rose; Phomopsis dieback
on crabapple; anthracnose on ash; Pythium
root rot on bentgrass; and red thread onbluegrass.
2013 INSECT TRAP COUNTS
June 14 - 21
Location Princeton,
KY
Lexington,
KY
Black cutworm 8 21
Armyworm 86 202
European cornborer 0 13
Corn earworm 8 5
Southwesterncorn borer
32 8
Fall armyworm 1 7
Graphs of insect trap counts for the 2013season 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.
http://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlmailto:[email protected]:[email protected]://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.http://www.uky.edu/Ag/IPM/ipm.htm.mailto:[email protected]://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.htmlhttp://www2.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_13/pn_130611.html