kentucky pest news, june 25, 2013

7/28/2019 Kentucky Pest News, June 25, 2013

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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

kentucky pest news, june 25, 2013

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