kentucky pest news july 13, 2010

8/9/2019 Kentucky Pest News July 13, 2010

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Online at:www.uky.edu/KPN

Number 1238 July 13, 2010

CORN-More on Foliar Fungicides in Corn

CUCURBITS-Plant It, and They Will Come: Cucurbit Pests

Emerge in the Central Bluegrass Region

TOBACCO-Disease Update

FRUIT CROPS

-Grape Root Borer Active

CORN

More on Foliar Fungicides in CornBy Paul Vincelli

In recent years, the use of foliar fungicides in

corn production has received a lot of attention.Last week, plant pathologists from Iowa StateUniversity (Drs. Daren Mueller and AlisonRobertson) published a summary of theindependent research done in Iowa on cornfungicides for 2007-2009. (For the full article,seehttp://www.extension.iastate.edu/CropNews/2010/0706muellerandrobertson.htm.)

Here is a summary of the research, in their ownwords:

Data from corn fungicide small plot trialsconducted by Iowa State University faculty andstaff, and on-farm trials conducted by the IowaSoybean Association On-Farm Network, theISU Corn and Soybean Initiative and the ISUNorthwest On-Farm research program wererecently collated and summarized:

SHADE TREES & ORNAMENTALS-Crown Rot in the Landscape

-Mimosa Webworm on Mimosa andHoneylocust

-Dogwood Sawfly

BUGS OF SUMMER-Jurassic Park Escapee?

PESTICIDE NEWS-High Temperature and Pyrethroid Insecticides

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

For the total 574 observations, theoverall mean yield response was 4.04bu/A.

Yield response of small plot trials (173observations) was 4.39 bu/A, comparedwith 3.89 bu/A for on-farm strip trials

(401 observations). The mean yield response in all years

was similar: 3.42 bu/A (2007), 3.83bu/A (2008) and 3.72 bu/A (2009).

The mean yield response was higher incorn-following corn trials comparedwith corn-following soybean trials (4.54bu/A vs 3.96 bu/A).

Applications at VT, R1 or R2 resulted inthe highest mean yield response (4.12bu/A, 4.21 bu/A and 4.17 bu/A,respectively).

Greater yield responses occurred withfungicides that contained a strobilurinalone (4.57 bu/A) compared withfungicides that contained a premix of astrobilurin and a triazole (2.85 bu/A).(Side comment: It will be interesting tosee if the trend continues, since thenewer premixes contain roughly

Lexington, KY 40546
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equivalent amounts of strobilurin activeas the strobilurin alone fungicides.)

Mean yield response was greatest whendisease severity in a field at R5 washigh. If disease severity on the ear leafat R5 was 5 percent, the mean yield responsewas 9.46 bu/A.

Based on the price of corn of $3.72 and$24 product + application, thebreakeven yield response is 6.45 bu/A.

Consistent with the university research inKentucky and throughout the Corn Belt, thereseems to be no justification for widespread useof fungicides in corn. If one is planning to use a

fungicide, it makes sense to allocate theapplication to fields with the highest diseaserisk. I know I must sound like a brokenrecord, since I have repeated this theme somany times in the past year or two. However,the growing mountain of research continues topoint to this basic conclusion, and it is soimportant that it is worth repeating over andover.

Bottom line: Indiscriminate use of fungicides on

corn is not likely to lead to increased yield and

profitability. In fact, it likely will reduce theprofitability of the average corn field.

CUCURBITS

Plant It, and They Will Come: Cucurbit Pests

Emerge in the Central Bluegrass RegionBy Logan Minter and Ric Bessin

Kentucky growers face a number of challenges

in producing cucurbit crops including intensepressure from competition with insect pests.Several insects cause damage by direct feeding,such as the squash beetle and the squash vineborer. We have been closely monitoring the firstemergence of cucurbit pests this summer usingsentinel plants and pheromone traps in FayetteCounty. We have noted several squash beetles,which look like large brown lady beetles and

create holes in the foliage, feeding in Zucchiniplantings on a farm in Boyle County on June17th. This date also marked the first day wedetected squash vine borer moths withpheromone traps in the Lexington area as well asobserving them around fields in Boyle and Scott

Counties. These colorful moths are activeduring the daytime and are mimics of paperwasps. Eggs are laid on the stems of plants andhatch in seven to ten days. The caterpillarsimmediately bore into the stems, making timelycontrol imperative. Sprays need to penetrate thecanopy to cover the vines to be effective. Homegardeners may have some success withdeworming the vines by slitting the vineslengthwise near where the damage is found,removing the borers, and immediately coveringthe vines with soil.

Other insects transmit plant diseases in additionto direct feeding damage to leaves, flowers andfruit. Striped and spotted cucumber beetlestransmit organisms which cause bacterial wilt,while squash bugs vector the bacteriaresponsible for yellow vine decline. We haveobserved cucumber beetle activity in the fieldsince the first week of May and squash bugssince late May. Clusters of the gleaming goldeneggs of squash bugs on squash leaves havebecome common over the past month and are

continuing to hatch in the Lexington area.Searching out and destroying these egg clustersmay be helpful on smaller scale or home gardenplantings. These insects are most susceptible tochemical control just following hatching; beforethey develop waxy coverings. We have beenobserving late stage nymphs for the past fewdays, indicating that the second generation ofadults is just around the corner. Multiple foliarsprays may be needed for extended periods ofcontrol in many cases. Keep in mind that insectpollination is critical for cucurbit crops so

measures should be taken to minimize negativeeffects on these beneficial insects. One methodto avoid injuring pollinators during bloom is tospray in the early evening after pollinators havequit for the day. The squash and pumpkinflowers that are open will be closed the next dayand new blooms, free of insecticide on the innersurface, will open in their place.


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Photos by Logan Minter.

TOBACCO

Disease UpdateBy Kenny Seebold

Blue mold continues to be an issue in CT, NC,and PA as of July 12, with new reports comingin from western NC during this past week.Current forecasts from North Carolina StateUniversity indicate a low threat to KY andsurrounding areas from the known sources ofdisease. This information can be accessed athttp://www.ces.ncsu.edu/depts/pp/bluemold/andthen selecting Current Forecast. It seems that

blue mold is beginning to creep westward, andmay eventually reach the Commonwealth.Growers should scout crops regularly, eventhough we face little risk from blue mold at themoment, and be prepared to act if the disease isfound.

For recommendations on the control of tobaccodiseases, please consult past issues of theKentucky Pest News, or the Kentucky-Tennessee Tobacco Production Guide (ID-160),available athttp://www.ca.uky.edu/agc/pubs/id/id160/id160.

pdf.

FRUIT CROPS

Grape Root Borer ActiveBy Ric Bessin

Grape root borer adult moths are now active andshould be monitored by vineyard managers.

Grape root borer is potentially the mostdestructive insect attacking grapes in Kentucky.Larvae tunnel into the larger roots and crown ofvines below the soil surface. Symptoms includepoor vine growth and fruit set, even loss of somevines. Because damage is restricted to belowground, problems often go unnoticed until vinedecline is observed.

Injury by grape root borer is often most severe inlow, poorly drained areas of the vineyard. In

mid-summer, growers should examine aroundthe bases of vines out to a distance of 18 inchesfor empty pupal skins of grape root borer. InKentucky, a control action is recommended ifmore than 5 percent of the vines are found tohave grape root borer pupal cases emerging fromthe soil. If an insecticide is to be used, then it isbest to apply the insecticide just as the adults are

Figures 1 & 2. Cucurbit pests.

Figure 3. Male and Female grape root borer moths.
http://www.ces.ncsu.edu/depts/pp/bluemold/http://www.ces.ncsu.edu/depts/pp/bluemold/http://www.ca.uky.edu/agc/pubs/id/id160/id160.pdfhttp://www.ca.uky.edu/agc/pubs/id/id160/id160.pdfhttp://www.ca.uky.edu/agc/pubs/id/id160/id160.pdfhttp://www.ca.uky.edu/agc/pubs/id/id160/id160.pdfhttp://www.ca.uky.edu/agc/pubs/id/id160/id160.pdfhttp://www.ces.ncsu.edu/depts/pp/bluemold/


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beginning to emerge, but the preharvest intervalmay make it necessary to spray after harvest.The insecticide should be applied as a coarsespray to a 15 square foot area surrounding thevine. Treat with an insecticide only if necessary.If grape root borer is not a problem, there is no

reason to risk destroying the natural controlprocesses and increasing production costs.

SHADE TREES & ORNAMENTALS

Crown Rot in the LandscapeBy John Hartman

Herbaceous perennials and annuals are popular

in Kentucky landscapes because the plantsprovide a variety of colors and forms and aregenerally easy to grow. During prolongedperiods of hot, humid summer weather,however, crown rot disease, or southern stemblight caused by the fungus Sclerotium rolfsii,can be devastating to a variety of garden plants.Recent hot weather has promoted crown rot oflandscape flowers, ground covers, andvegetables.

Symptoms and signs of disease. The first

indication of trouble is when lower leaves beginto turn yellow and young shoots begin to wilt.This is commonly followed by the death anddrying up of the entire plant. Roots and lowerstems of affected plants are black or dark brownand rotted. Sometimes, as with hosta plants,leaves easily come loose from the plant due to asoft, brown, mushy decay at the base of thepetiole. Often-times, a coating of white fungalthreads or fungal mycelium (Figure 4) is presenton the rotted stems or petioles or on the groundat the base of the diseased plant. Tiny spherical

sclerotia (Figures 4-6), about the size of mustardseeds, are sometimes attached to the fungalthreads or are scattered or in clusters on theground under the plant. Sclerotia may be white,tan, orange, or reddish brown, and are thestructures that allow the fungus to survive forlong periods in the soil. For diagnosis,observation of fungal sclerotia and mycelium arepositive indicators for this disease.

The life ofS. rolfsii. Sclerotia of the fungusgerminate during warm, humid weather andfungal mycelium grows along the ground until itencounters a susceptible plant nearby. Thefungus attacks the lower stems with plant tissue-

degrading enzymes and toxins, causing thestems to decay. Fungal sclerotia live in the soilfor many years waiting for an opportunity toattack new plants. The fungus can be spread inthe garden when sclerotia are carried on tools,on shoes, and in soil; the fungus can be movedlong distances on transplants and nursery stock.

In Kentucky gardens S. rolfsii is likely to attack: Herbaceous perennials such as ajuga

(Figure 5), anemone, aster, bleedingheart, caladium, chrysanthemum,

columbine, coreopsis, daffodil, dahlia,daylily, delphinium, dianthus, foxglove,hibiscus, hosta, hydrangea, iris, lily, lily-of-the-valley, liriope, pansy, peony,periwinkle, phlox, tulip, and even wildviolets.

Annual flowers such as ageratum,begonia, cosmos, impatiens, marigold,nasturtium, petunia, and zinnia.

Garden vegetables such as beans,soybeans (Figure 4), peppers, andtomatoes.

Woody nursery seedlings of apple(Figure 6), arbor vitae, catalpa,dogwood, forsythia, prunus, rose, andwalnut.

Figure 4. For illustration purposes: stem blight of soybean showing

the white fungal mycelium and sclerotia on the infected stem (D.

Hershman photo). These fungal structures would look the same on

many herbaceous landscape plants and garden vegetables.


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Disease management. A combination of culturalpractices and selection of resistant or tolerantplants will aid in management of crown rot.

Purchase only healthy perennials,looking especially for causes ofyellowing or browning of lower leaves.

Avoid moving plants from contaminatedbeds to other parts of the garden.

Use effective garden sanitation practicessuch as digging up and destroying

diseased plants and surrounding soil andthoroughly washing contaminated soilfrom tools. Although drastic, carefullydigging and removing contaminatedgarden bed soil to a depth of 8 inchesand replacing it with non-contaminatedsoil can be effective.

Grow plants not known to be hosts ofS.rolfsii such as bluebells, coral bells,cranesbill geranium, English ivy, forget-me-not, hellebore, ladys mantle, lambsear, Pachysandra, poppy, primrose,Solomons seal, spiderwort, and

Trillium. Hosta cultivars differ in susceptibility to

crown rot caused by S. rolfsii. In a 2-year evaluation of selected cultivarsdone at Iowa State University: The five most tolerant

(susceptible, but least damaged)Hosta cultivars were Halcyon,Zounds, Honeybells, SnowMountain, and Tall Twister.

The five most susceptiblecultivars were Lemon Lime,

Munchkin, Nakaiana,Platinum Tiara, andTardiflora.

Intermediate susceptiblecultivars in decreasing order ofsusceptibility includedSerendipity, Pee DeeGoldflash, Floradora,Harmony, Pearl Lakes, VeraVerde, Gold Drop, andTokudama.

All of these 18 cultivars aresusceptible to some degree.Most Hosta cultivars have neverbeen tested for crown rotsusceptibility, but it is likelythat most of them are alsosusceptible.

Mimosa Webworm on Mimosa and

HoneylocustBy Lee Townsend

Brown, curledleaves on mimosaand honeylocustare the callingcards of themimosa webworm.From a distance,

Figure 5. Ajuga crown rot (southern stem blight)

with small spherical sclerotia the size of mustard

seeds.

Figure 6. Appleseedling with stem

blight infection

which has produced

sclerotia (C. Kaiser

photo).

Figure 7. Brown and rolled

honeylocust leaves. Nearby

leaves can be green and normal.


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signs of infestations can mimic a leaf disease orsome type of chemical injury. Closer inspectionwill help tomake the diagnosis.

Mimosa webworm caterpillars are gray to brown

larvae with 5 white stripes running the length ofthe body. The caterpillars feed within groups ofleaves that they mat together with silk. There are2 generations each year; most of the damagecomes from the second generation that is activein August.

Generalshade treeinsecticides(includingBt, neem,

spinosad, andpyrethroids)can be usedif damagefrom thesecondgeneration

appears to be heavy. Watch trees carefully thatshow damage from the first generation. Checkfor fresh feeding and small worms near webbingfrom the first generation.

Dogwood SawflyBy Lee Townsend

Sawfliesare curiousinsects;they looklike thelarvae ofbutterflies

or mothsbut willturn intowasps.Dogwoodsawflies can

cause considerable damage to several dogwoodspecies, particularly gray dogwood and changecolor as they grow.

Newly hatched larvae are light yellow. Thesecond larval instar has a powdery whiteappearance while the last stage (about 1 inchlong) again is yellow with a black head. Thisfinal stage does not feed but leaves the host to

find a spot to spend the winter. There is onegeneration each year.

BUGS OF SUMMER

Jurassic Park Escapee?By Lee Townsend

From their

strikingappearance to aprimitive jerkylook as theyflap throughthe air,dobsonflieslook like theymay have just

escaped from the set of a prehistoric movie.

Dobsonflies are usually found near moving

water - streams or rivers. The male has long,slender mouthparts that could give a pinch if heis handled but they are not aggressive and do notfeed. Females have the same body shape butvery small mouthparts.

The adult females lay eggs on overhangingbranches or undersides of bridges over streams,or on stones. The eggs hatch at night after 5-6days and drop into the water. The larvae, calledhellgrammites, live under stones in riffles wherethey feed on other aquatic insects. A sign of

good water quality, they feed and grow forseveral years before leaving the water to pupateand emerge as adults in mid-summer. They onlylive long enough to mate, lay eggs, and die.

Figure 8. A closer look reveals white

silk and small dark frass pellets from

the caterpillars.

Figure 9. Two forms of the dogwood

sawfly (K. Cowherd photo).

Figure 10. Male dobsonfly resting in

mortar joint, females lack the long,

pointed jaws.


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PESTICIDE NEWS

High Temperatures and Pyrethroid

InsecticidesBy Ric Bessin

Early July was unseasonally hot and Im certainthat we have more hot weather in store for usthis summer. Over the years, some people havecommented about the ability of pyrethroidinsecticides (IRAC Group 3 insecticides) tocontrol insect populations during the peak heatof the summer. Often during these same periodssome pest populations are peaking with insectdevelopment near its fastest pace. This can testthe ability of an insecticide to control pestsunder harsh conditions.

There is a large amount of literature on the effectof post-treatment temperature on the efficacy ofinsecticides. DDT has a well know negativetemperature coefficient, it is more toxic to pestsat lower temperatures than at high temperatures.The information on pyrethroid insecticides is notquite as clear as some pyrethroids with somepests may exhibit a positive relationship withpost-treatment temperature, but generally,prethroids share this same temperaturerelationship and their activity shows a negativerelationship with temperature and insect pests.

They are more effective at low temperatures andless at higher temperatures. However, theorganophosphate and carbamate insecticideshave demonstrated a positive relationship withpost-treatment temperature.

When it comes to field applications we also needto consider how the pest is affected by the highertemperatures as well. It is likely that many pestswill be more active and moving more at hightemperatures than at low temperatures, this mayincrease the likelihood that it will come in

contact with treated plant surfaces. Insectconsumption may also be higher during periodsof higher temperature resulting is larger dosesconsumed.

DIAGNOSTIC LAB HIGHLIGHTS

By Julie Beale and Paul Bachi

Recent agronomic samples in the PDDL have

included brown spot (Physoderma), gray leafspot, Diplodia leaf streak, common rust andnutritional disorders including potassium andphosphorus deficiencies on corn; black shank,soreshin, Fusarium wilt, frogeye leaf spot andangular leaf spot on tobacco.

On fruit, nut, herb and vegetable samples, wehave diagnosed anthracnose and black rot ongrape; Phytophthora root rot on blackberry;Phyllosticta leaf spot and fruit rot on blueberry;Rhizoctonia root rot on strawberry; scab on

pecan; downy mildew on basil; Rhizoctoniaroot/stem rot on bean; bacterial spot andsouthern blight on pepper; bacterial canker,bacterial spot/speck, early blight, southernblight, Septoria leaf spot and blossom end rot ontomato; gummy stem blight on muskmelon andwatermelon.

On ornamentals and turf, we have seen southernblight on phlox; Cercospora leaf spot oncenturea and hydrangea; Pythium root rot oncoreopsis; Pythium and Rhizoctonia root rots on

petunia; powdery mildew on gerbera;Phytophthora root/crown rot on juniper andforsythia; black root rot on holly; frogeye leafspot and Botryosphaeria canker on crabapple;chestnut blight on American chestnut;anthracnose and Tubakia leaf spot on oak;Rhizosphaera needlecast on spruce; take-allpatch, Pythium blight and root rot andanthracnose on bentgrass; and brown patch onfescue.


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INSECT TRAP COUNTS

July 2-9

Graphs of insect trap counts for the 2010 season areavailable on the IPM web site at -http://www.uky.edu/Ag/IPM/ipm.htm.View trap counts for Fulton County, Kentucky at -http://ces.ca.uky.edu/fulton/InsectTraps

Location Princeton,

KY

Lexington,

KYBlack cutworm 7 39

Armyworm 12 961

Corn earworm 25 21

European cornborer

1 0

Southwesterncorn borer

10 0

Fall armyworm 17 0

kentucky pest news july 13, 2010

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