Kentucky Pest News, June 11, 2013

7/28/2019 Kentucky Pest News, June 11, 2013

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Online at:www.uky.edu/KPN

Number 1343 June 11, 2013

TOBACCO- Disease Update for the Week of June 10

WHEAT-Wheat Fusarium Head Blight Active in

Parts of Kentucky

VEGETABLES

-Late Blight of Tomato Reported in Western

Tennessee

FRUIT CROPS-Update on Spotted Wing Drosophila

-Cherry Fruit Fly

FUNGICIDES- Some Principles of Fungicide Resistance II:

Increased Crop Disease Pressure Increase

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

TOBACCO

Disease Update for the Week of June 10Kenny Seebold, Extension Plant Pathologist

Current situation

Very high temperatures back at the end of Maycaused a few problems on newly-set tobacco in

some areas. A problem that seems to be commonat the moment is sun scald on the stems oftransplants. When tobacco seedlings are

transplanted in very hot weather, they tend to wiltin the heat of the day and can be damaged by

intense sunlight. Wilting is most likely to occurwith tender plants, plants with poor rootdevelopment, plants with active Pythium root rot,

or plants set into very dry soil. In most cases, ascalded area will appear on the side of the stem

that is exposed to the sun and injured plants willrecover. We do see situations in which plants are

killed or stems are girdled above the soil line.With the latter, its possible to see regrowth belowthe girdled zone. Ive also seen a little chemical

injury from materials that were used in the setterwater; the symptoms are yellowing or mottling oflower leaves. In all cases, plants have recoveredand have begun to grow after getting a little rain.

Blue Mold

As of June 10, no blue mold has been reported inthe tobacco-growing areas of the United States.

WHEAT

Wheat Fusarium Head Blight Active in Parts ofKentuckyBy Don Hershman, Extension Plant Pathologist

There is a considerable amount of Fusarium headblight (FHB) showing up in many wheat fields inthe central and northeastern parts of the state. Withsome exceptions, west and southern KY are in

pretty good shape, overall.

The field shot (Figure 1), taken by David Harrison,Larue County ANR Agent, is from a farm in Larue

County in the heart of the state. I have receivedother reports of significant FHB from the same

part of the state. This development is not a surprise

based on the output of the FHB risk prediction toolfor the period May 10-12 (see Figure 2). I suspectmany wheat fields east of I-65 (especially in themore northern areas) were flowering during this

period, which is about a week later than when

most wheat fields flowered in the western half of

Lexington, KY 40546
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the state. Flowering is the time when FHB takeshold in a crop if weather conditions are favorable.

FHB Symptoms begin to show up in force about 3weeks following infection.

Figure 1. Field in Larue County, Kentucky, showing severe

Fusarium head blight.

Figure 2. Screen shot of FHB Prediction Tool website

(www.wheatscab.psu.edu/) on May 11, 2013. Red indicates

high FHB risk areas; yellow indicates moderate risk areas;

green indicates low FHB risk.)

I have selected the Elizabethtown, Hardin County,weather station (Figure 3) as an example of whatthe FHB models were showing during the critical

infection window. As you can see, the FHB riskwas very high for this weather station and

surrounding area.

Figure 3. Screen shot of FHB Prediction Tool website

(www.wheatscab.psu.edu/) on May 11, 2013 for

Elizabethtown, Hardin County, Kentucky.

It is my understanding that the field shown in the

above photo was sprayed with a fungicide, but stillhas what looks to be about 50-60% incidence ofdisease. It is possible that the application wasmade too early or too late or that there was someother factor that limited efficacy. On the other

hand, the grower might have actually gottenreasonable control from the application, in that 40-45% control of FHB and DON is about all one canexpect from a FHB fungicide when the FHB riskis high and the variety is susceptible. In fact, it is

common to have 80-90 percent incidence ofdiseased heads in a FHB-susceptible variety whenthe risk is high and a fungicide IS NOTdeployed. Thus, 50-60% incidence may actually

represent reasonable disease control. This is allspeculation for this specific field since I do notknow the variety or the details of fungicide

application. But my statements are in line withyears of research data and past experience.

Aside from the obvious yield and grain qualityproblems associated with FHB, the mycotoxin,

deoxynivalenol (DON), is most certainly going tobe a factor in grain, silage, hay or straw harvested

from fields with significant levels of FHB. DONaffects both marketability and, potentially, enduse. For example, grain destined for human

consumption cannot have greater than 2 parts permillion (ppm) DON. Grain with greater than 2

ppm will be docked at the point of sale. Very highlevels may be a cause for rejection at the


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elevator. For grain, silage, hay, or straw destinedfor animal feed/bedding, the allowable levels of

DON are greater than 2 ppm, but maximumallowable/safe levels vary according to the animal

species in question. Check with your county ANRagent for more information on DON risk and

standards relative to specific animal species.

My main role is to alert you that where FHB

symptoms are widespread and severe, high DONlevels are most certainly going to be encounteredin grain and miscellaneous harvested spike tissues.For fields harvested for grain, turning up the air onthe combine and blowing light-weight scabby

kernels out the back of the combine has beenshown to limit DON in harvested grain. Fields

destined for silage and hay should be harvested assoon as possible since DON levels will continue to

increase while the crop is still in the field. Keepingtrack of grain from specific fields may be a goodidea since it is probable that DON levels will varyfrom field to field, depending on when the cropflowered and the weather conditions at flowering,among other factors.

Grain elevators and mills will test grain for DONlevels using ELISA test kits. There are alsovarious test kits that you may purchase and test forDON yourself(www.gipsa.usda.gov/fgis/tech-servsup/metheqp/testkits.pdf). Kits tend to not be

as accurate as more specific tests often used bymycotoxin testing laboratories; nonetheless, testkits often provide the general information neededto make appropriate decisions. You may also sendsamples off to a laboratory that has the capabilityof testing for DON. If you need DON analysis for

complex feeds, such as hay, it would be wise tocall the laboratory before sending samples todetermine if they only test for DON in grain (suchis the case with the UK Regulatory ServicesTesting Laboratory) or are set up to test for DON

testing in complex feeds (such is the case for the

UK Veterinary Diagnostic Laboratory).

VEGETABLES

Late Blight of Tomato Reported in Western

TennesseeBy Kenny Seebold, Extension Plant Pathologist

Back in 2009, a massive epidemic of late blightcaused severe losses to tomato and potato growersin 16 eastern and midwestern states (includingKentucky). The summer of 2009 was unusually

cool and wet, setting the stage for the large-scaleepidemic of late that was initiated by infected

tomato transplants sold at garden centers. Theweather in Kentucky this season has been similarto what we saw back in 2009; however (and

fortunately), there are no indications that tomatotransplants are a source of the late blight pathogen

this year. That being said, late blight was recently

reported on tomatoes in a home garden located inDickson County, Tennessee. This location is due

south of Hopkinsville, Kentucky and the weatherpatterns over the past couple of days had potentialto move the late blight pathogen into Kentucky.Potatoes and tomatoes in southeastern Kentuckyare at risk in particular and all tomato and potato

growers in the state need to be on the lookout forlate blight. Prevention should be a priority at thisstage, meaning that growers (gardeners andcommercial producers alike) need to put out a

protectant fungicide application as soon as

possible. Information and treatment guidelines forlate blight are listed below. Refer also to factsheet PPFS-VG-13, Late Blight of Tomato(http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-VG-13.pdf). Visithttp://www.uky.edu/Ag/kpn/kyblue/Galleries/TLBKY/index.htmlfor images of symptoms on

tomato.

The Disease. Late blight is caused byPhytophthora infestans, a fungus-like organism,and is a fast-moving and highly destructive disease

of tomatoes and potatoes under cool and wetconditions. Late blight epidemics in the late1840s were responsible for the Irish potatofamine and subsequent migration of millions of

people to the United States. All plant parts are

affected, including fruit and tubers. Total lossesare common in gardens and fields if controlmeasures are not put in place. Late blight caneasily enter greenhouses and high tunnels as well.
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Symptoms. Early symptoms of late blight are

large water-soaked blotches on foliage that willenlarge and form green-to-brown lesions.

Sporulation may be evident on the undersides oflesions under moist conditions; this sporulation

will be gray to white in color. Necrotic leaf tissuewill blacken and shrivel, giving affected plants a

blighted appearance. The pathogen will also

attack petioles and stems, killing the plant in somecases. Tomato fruit affected by late blight developas darkened spots that enlarge over time, andfungal growth may be seen in rotted tissue.Infected fruit are invaded by secondary organisms

and develop soft rot. Potato tubers can becomeinfected from spores washed from leaves into the

soil and will decay.

Control Commercial Growers. Preventiveapplication of fungicides is necessary to preventlosses to late blight. Protectant fungicides such aschlorothalonil (Bravo and generics), mancozeb(Dithane, Koverall, Penncozeb, or Manzate), andfixed coppers can help when disease pressure is

low; however, when inoculum levels increase or ifdisease is found in fields, stronger products arerecommended. Late-blight-specific fungicides aresummarized below (as published by Dr. MegMcGrath, Cornell University):

Curzate 60DF (Group 27). 3.2-5 oz/A (3.2 oz forpotatoes). 5 oz on 5-day interval when late blightpresent. 30 oz/A seasonal max. 3 d PHI.EPA RegNo. 352-592. Active ingredient is Cymoxanil. 12

h REI. Must be tank-mixed with a protectantfungicide.

Forum (Group 40). 6 fl oz. 30 fl oz/A seasonalmax. 2 consecutive spray max. 4 d PHI. EPA Reg

No. 241-427. Dimethomorph. 12 h REI. Must beapplied with another fungicide.

Gavel (Group 22). 1.5-2 lb/A. 16 lb or 8application seasonal max. 5 d PHI tomato; 3 d PHIfor potato (14 d in some states). Latron surfactantrecommended. EPA Reg No. 62719-441.

Zoxamide + mancozeb. 48 h REI.

Omega 500F (Group 29). 5.5 fl oz/A for potatoesonly. 3.5 pts/A seasonal max. 14 d PHI. EPA Reg

No. 71512-1-100. Fluazinam. 48 h REI.

Presidio (Group 43). 3-4 fl oz/A for tomatoesonly. 12 fl oz/A seasonal max. 2 consecutivespray max. EPA Reg No. 59639-140.

Flupicolide. 12 h REI. 2 d PHI

Previcur Flex (Group 28). 0.7-1.5 pt/A (1.2 ptmax for potatoes). 7.5 pt/A seasonal max fortomatoes; 6 pt/A for potatoes. 5 d PHI for tomato;

14 d PHI for potato. EPA Reg No. 264-678.Propamocarb hydrochloride. 12 h REI.

Ranman (Group 21). 1.42.75 fl oz/A (2.1-2.75for tomato). 16.5 fl oz or 6 application seasonal

max for tomatoes; 27.5 fl oz or 10 applications forpotatoes. 0 d PHI for tomatoes; 7 d for potatoes.EPA Reg No. 71512-3-279. Cyazofamid. 12 hREI.

Revus (Group 40). 5.5 to 8 fl oz. 2 consecutivesprays max. 32 fl oz/A seasonal max. 1 d PHI fortomato; 14 d PHI for potato. EPA Reg No. 100-1254. Mandipropamid. 12 h REI.

Zampro (Groups 45 & 40). 11 to 14 fl oz/A (14 floz for tomato). 2 consecutive sprays max. 42 floz/A seasonal max. 4 day PHI. EPA Reg No.7969-302. Ametoctradin plus dimethomorph. 12h REI.

Strobilurins, such as azoxystrobin (Quadris),pyraclostrobin (Cabrio/Headline), and fenamidone(Reason) have not performed as well as the

products listed above in university trials. Ridomil

Gold Bravo and Ridomil Gold Copper are notrecommended due to widespread resistance in

pathogen populations to Ridomil. Consult ID-36(KY Production Guide for CommercialVegetables) for specific use rates. Keep in mind

that some of these products may be difficult tofind in local dealerships and may have to be

special-ordered. Of the materials listed above,

Ranman, Revus, Forum, Curzate, or Gavel may bethe easiest to obtain in Kentucky, and are effectiveagainst late blight when used as directed.

Control Homeowners. The generalmanagement practices listed above apply also to

the homeowner. Regular scouting of plantings,and prompt removal of infected plants is animportant consideration. The bulk of cases


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reported thus far have come from home gardens,where regular application of fungicides is less

common than in commercial fields. Fewfungicides are available to home gardeners;

however, products containing chlorothalonil,maneb/mancozeb, or fixed copper are the tools of

choice. These should be applied regularly, and theuser should refer to the product label for rates,PHI, and safety precautions. These products, as

mentioned earlier, will not function well ifpressure is high or if disease is present beforespray programs are started.

Control Organic Producers. Control measures

for organic producers are similar to thoserecommended for home gardeners. OMRI-

approved fungicides such as fixed-copper(depends on the product) can be used in a

preventive program. Other OMRI-approvedproducts include: Sporatec, Sonata, SerenadeMax, Oxidate, and Companion. As with the

protectants recommended for home gardeners,these products do not perform well under highdisease pressure or if disease is present prior to

treatment. Consult product labels for rates, PHI,and safety precautions.

All Producers. Scout plantings regularly for lateblight and other diseases. Preventive fungicide

applications are recommended at this point for

all Kentucky tomato and potato growers to helpcombat late blight, and also early blight andSeptoria (tomato). Growers should not wait to seesymptoms of late blight before treating. A good

protectant program aimed at late-blight preventionwill also aid against other foliar fungal diseases.During favorable conditions, sprays need to bemade every 5-7 days, and every 7-10 days duringdrier weather.

If late blight is found, growers should immediatelydestroy plants in the affected area plus bordering

plants (as these are likely infected). Plants can besprayed with an herbicide, or removed and diskedunder. Do not handle plants when they are wet, asthis may spread disease; perform this operation

when conditions are sunny and dry if possible. Atthe end of the season, promptly destroy crop

residues. Do not leave cull piles out in the open,as the pathogen can spread or potentially survivein this residue. Bury this material if at all possible.

FRUIT CROPS

Update on Spotted Wing DrosophilaRic Bessin and Patty Lucas, Entomologist andExtension Entomologist

Patty and I have been working with county agentsand producers of small fruit crops in strategiclocations across Kentucky to trap for spotted wingdrosophila (SWD). In these locations we have

been using apple cider-baited traps that have beenplaced in fields of small fruits as the initial fruitsbegin to turn color and soften. The good news isthat with each of the locations, with the exceptionof one, we have captured a number of drosophila

fruit flies but no spotted wing drosophila. In theseearly summer locations we have been trapping instrawberries and blueberries. As the summer

progresses we will trap in other small fruit cropsas they progress toward harvest. So far, this is very

good news for our small fruit producers.

Figure 4. A spotted wing drosophila male on a sticky card.

In one location Patty Lucas did find one femalefruit fly that is a SWD suspect. That suspect wasfrom Warren County and at the same farm where

we did confirm SWD last year. This week I willlook at the suspect to see if it is our first SWD onthe year.

While searching a cherry tree in Fayette County

for SWD damage this spring, I came across a largenumber of brown lesions on the fruit and found

brown marmorated stink bugs on the foliage. Thedamage was consistent with BMSB.


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Cherry Fruit FlyRic Bessin, Entomologist

The have been a number of reports of cherry fruit

fly this summer and people begin to harvestcherries from their backyard trees. Some of the

fruit that was sent to me revealed plum curculiolarvae rather than cherry fruit fly. We do have

both of these pests that need to be managed on

sour and sweet cherries in Kentucky, but how wemanage them can be different.

It is helpful to distinguish between plum curculioand cherry fruit fly in order to better manage them

in subsequent years. Cherry fruit fly is a maggotwithout a distinct head capsule and without legs.

Some people refer to this as a headless larvawhich isnt correct, it is just that the head is not

easy to distinguish from the rest of the body. Thefruit fly larva has a whitish body that taperstoward the head. The plum curculio larva is also

legless, but has a distinct brown head capsule. Thebody is widest in the middle tapering at both ends.

Plum curculio females lays their eggs singly aftershuck fall and creates a crescent wound and laysan egg in the flap. This egg laying wound resultsin a small visible scar at harvest. Plum curculiosprays are usually most effective at shuck fall and

the following two cover-spray periods. Cherry

fruit fly sprays begin about 10 days after the shuckfall stage with the first cover spray and rarereapplied at 10 day intervals. For homeowners,Sevin can be a good spray for cherry fruit fly but

this can thin the fruit when used within 30 days ofpetal fall.

FUNGICIDES

Some Principles of Fungicide Resistance II:

Increased Crop Disease Pressure IncreasesRiskBy Paul Vincelli, Extension Plant Pathologist

This is the second in a series of articles on

fungicide resistance.

The title summarizes the present article perfectly:higher disease pressure means higher risk offungicide resistance. Figures 1-2 help inunderstanding why this is so. Field 1 (represented

by Figure 5) has approximately twice the sporenumbers as Field 2. Clearly, Field 1 has higher

disease pressure. You can also see that Field 1has two resistant spores, rather than one.

Figure 5. Initial step in fungicide resistance development:

Occurrence of mutant spores with resistance to the

fungicide (filled circles). Note that there are two resistant

spores in this imaginary crop field.

Figure 6. Imagine that this a second crop field, where the

population of infectious spores is about half that of Figure

1. Only one mutant spore with resistance has occurred,

instead of the two mutants that emerged in Field 1. See

text for explanation.

If you count them up, you will find that thepercentage of spores with resistance is slightlyover 1% in both fields. That is to say, the

mutation rate is the same in both fields, which iswhat we expect to find in nature. However,

because of the higher disease pressure, Field 1 has

approximately twice the overall spore populationas Field 2. Thus, no matter what the mutation rate

is, twice as many resistant spores will show up in


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Field 1 than in Field 2, because the overall sporepopulation is twice as high.

So does this really matter? After all, resistant

spores emerged in both fields. The answer is,Yes, it matters, because resistance development

is a matter of risk. Not all mutant spores that showup in a field will go on to cause disease. Some fallto the ground and never have a chance to infect a

plant. Others may land on a plant but not beexposed to enough wetness to infect. Still othersmay infect but fall victim to plant defenses. So thehigher number of resistant spores in Field 1 doesdefinitely represent a higher risk for the producer,

especially when one considers that billions offungal spores can easily present in an acre of crop.

So, what does this mean for a producer? It means

that, the more we depend on at-risk fungicides1 fordisease control, the more pressure we are puttingon the fungus to develop fungicide resistance. If it

is possible to use others practices to reduce diseasepressure, we reduce the overall risk of resistance.Anything that reduces disease pressure reduces the

size of the spore population. And as Figures 1-2show, reducing the spore population reduces the

chance that a resistant mutant will occur in ourfields.

This guideline applies to all practices that

contribute to disease control: Sanitation, croprotation, varieties with partial resistance, etc., etc.Anything we do to reduce disease pressure,reduces the risk.

Bottom line: The best way to protect the utility of

fungicides is by not over-relying on them.

DIAGNOSTIC LABORATORY HIGHLIGHTS

By Julie Beale and Brenda Kennedy

Agronomic samples diagnosed in the PDDL in thepast week have included stinkbug injury andmagnesium and phosphorus deficiencies on corn;

1If you missed last weeks article, the phrase at-risk

fungicide means that the fungicide has a moderate to

high risk of resistance development.

Pythium root rot on alfalfa; Fusarium head blighton wheat; Pythium root rot, growth regulator

injury and symptoms of transplant shock ontobacco.

On fruit and vegetable samples, we have

diagnosed angular leaf spot, common leaf spot andPhomopsis leaf blight on strawberry; crown borerinjury on blackberry; fire blight and powdery

mildew on apple; leaf curl on peach; black knot onplum; angular leaf spot on squash; timber rot(Sclerotinia), early blight, leaf mold (Fulvia),

bacterial pith necrosis, tobacco mosaic virus andtomato spotted wilt virus on tomato.

On ornamentals, we have seen Pythium root rot on

zinnia; Ascochyta leaf spot on clematis; Kabatinatwig blight on juniper; blight on contorted filbert

(Ansiogramma); rose rosette and rose mosaicvirus on rose; bacterial leaf spot and bacterialcanker on ornamental cherry; and anthracnose onmaple.

2013 INSECT TRAP COUNTS

May 31 June 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.

Location Princeton,

KY

Lexington,

KY

Black cutworm 11 0

Armyworm 13 56European cornborer

0 2

Corn earworm 6 16

Southwesterncorn borer

11 0

Fall armyworm 0 31
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, June 11, 2013

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