kentucky pest news may 3, 2011

8/7/2019 Kentucky Pest News May 3, 2011

1/12

Online at:www.uky.edu/KPN

Number 1266 May 3, 2011

WATCH FOR

-ArmywormOutbreak Averted?

ALFALFA-Soggy Soils Will Favor Root Rots in Alfalfa

CORN

-Wet Conditions Create Weed Management

Challenges in Corn-Does a High Application Rate Prevent

Fungicide Resistance?

-Late Planted Corn and Insect Management

WATCH FOR

ArmywormOutbreak Averted?By Doug Johnson and Patty Lucas

Capture of armyworm moths in the UK-IPM

traps has decreased this past week. Though we

lost some data from the Princeton location lastweek it appears that the moth flight is in decline.

Because of the missing data point, it is not

possible to say with certainty that the population

will not be of outbreak size this year, though thatcertainly appears to be the case. Just remember

there is never a zero risk with this insect. If you

look hard enough you will find them in all small

grain and most pasture fields every year.

Nonetheless, generally their numbers are notlarge enough to be of economic importance.

Additionally, it is difficult to know how theextremely stormy & rainy weather we have

experienced, is affecting our trap captures. Also,

cool spring weather seems to favor this insect.

So, keep a watch on your fields over the next

several weeks. If we use April 22 as our biofix,

and apply our degree-day model we find that the

peak of caterpillar populations should be about

TOBACCO

-Watch for Insect Problems in Float Systems

-Be on the Look out For Bacterial Soft Rot in

Transplants

-Tray Drench and/or Transplant Water

Insecticides for Tobacco

SHADE TREES & ORNAMENTALS

-Emerald Ash Borer Update

-Managing Flowering Crabapple Rust, and

Powdery Mildew

DIAGNOSTIC LAB HIGHLIGHTS

INSECT TRAP COUNTS

May 11-12, 2011. Remember there will be

caterpillars before and after this date; and this

date is a prediction based on 2011 data throughtoday (5/2/11) and historic data thereafter.

ALFALFA

Soggy Soils Will Favor Root Rots in AlfalfaBy Paul Vincelli

With all the wet weather over the past fourweeks or so, new seedings of alfalfa have been

exposed to stressful conditions in the root zone.

Saturated soils favor three important diseases of

alfalfa: Aphanomyces root rot, Pythium root rot,

and Phytophthora root rot. All three diseases arecaused by water molds that produce

swimming spores in soggy soils. It wont besurprising if we diagnose cases of these diseases

in the next few months.

In new seedings, plants affected by

Aphanomyces appear stunted. Leaves are

yellow, especially the cotyledons or older leaves

(Figure 1). Leaves may curl up and fall off,sometimes turning red before doing so.

Lexington, KY 40546
http://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPNhttp://www.uky.edu/KPN


2/12

Belowground, the small feeder roots appear

rotted, often light or dark brown in color and/or

with little structural integrity (Figure 2). This

can result in poor stand establishment (Figure 3).

Aphanomyces can cause disease of matureplants as well as seedlings. However, in mature

plants, Aphanomyces infections are confined tothe feeder roots (Figure 4), so established plants

rarely die from these infections; they simply are

stunted, especially in dry weather. Pythium actssimilarly: It can kill seedlings, but only causes

feeder root rot on established plants.

Phytophthora root rot can kill alfalfa seedlings

(Figure 5). However, it can also cause a

destructive taproot rot that can kill mature

plants.

All three diseases are common in Kentuckysoils. Because of this, I recommend substantial

levels of resistance to Aphanomyces and

Phytophthora root rots for all spring seedings of

alfalfa. By "substantial", I mean levels of R

(resistance) or HR (high resistance). Resistance

to Pythium is not available commercially,

although seed treatments help to reduce that

disease. Sowing alfalfa in well-drained soils

with minimal compaction also helps reduce the

risk of all three diseases.

As a reminder, the levels ofsusceptibility/resistance to diseases in alfalfa

are:0-5% resistance Susceptible (S)

6-14% Low resistance (LR)

14-30% Moderate resistance

(MR)

31-50% Resistance (R)51+% High resistance (HR)

Figure 1. Stunted discolored alfalfa seedlings affected by

Aphanomyces root rot. Note healthy seedling laying on its

side, for comparison.

Figure 2. Rot of alfalfa feeder roots caused by

Aphanomyces.

Figure 3. Alfalfa varieties susceptible (left) and

resistant (right) to Aphanomyces.

Figure 4. Feeder root infections by

Aphanomyces on mature alfalfa.


3/12

CORN

Wet Conditions Create Weed Management

Challenges in CornBy Jim Martin and J.D. Green

The prolonged wet conditions this spring have

created additional challenges in regards to weed

control. The following are possible scenarios

that corn farmers may encounter and factors to

consider as we progress through the next severaldays.

1. Corn Not Planted And Herbicide WasNot Applied:Growers will have flexibility in the

choice of burndown options; however,

weeds may be larger than typically

observed when corn is planted earlier in

the spring. Glyphosate may be the best

choice for control of larger emerged

weeds, but higher rates may be required.

Whereas, paraquat may be preferredover glyphosate in cases where rapidburndown control of weedy vegetation

is needed for a more favorable

environment for corn to emerge. Some

disadvantages with paraquat are: a) it

may be more expensive, b) usually

requires a greater spray volume for best

results, and c) is limited in its ability to

control large plants relative to

glyphosate. The addition of dicamba

(eg. Clarity, etc.) or 2,4-D with

glyphosate or paraquat may be

warranted to aid in control of larger

broadleaf weeds. A soil-residualherbicide treatment will extend control

during the early part of the season and

will limit the need for multiple

postemergence herbicide treatments.

However, warm-season weeds are likely

to emerge quickly and grow rapidly as

temperatures increase; therefore,

growers should monitor fields regularly

and be timely with postemergence

herbicide treatments when needed for

managing weed escapes.

2. Corn Not Planted But PreplantHerbicide Was Applied:A significant portion of soil-residual

herbicides applied earlier in the spring

have probably dissipated from the soil

surface due to the large volume and

intensity of rains that occurred since the

treatments were sprayed. The need to

spray an additional herbicide treatment

will depend on specific field situations.

If fields are currently weed-free and do

not have a history of weed problems,growers may prefer to go ahead and

plant the field, and then monitor fields

closely and apply additional herbicide

treatments as needed in a timely manner.However, if weeds are emerging, then it

would be prudent to apply a burndown

treatment that also includes a soil-

residual herbicide. The maximum

cumulative rate of the soil-residualherbicide (i.e. amount initially applied

plus what will be applied) can determine

the rate and specific herbicide to apply.For example, if the previous amount ofatrazine applied was 1.5 lb ai/A, then an

additional amount of 1.0 lb ai/A can be

applied in order to comply with the

maximum total of 2.5 lb ai/A of atrazine

allowed per season. When usingpremixed products, consider the

cumulative level of all active ingredients

Figure 5. Phytophthora root rot causing death

of alfalfa seedlings.


4/12

for determining the rate of a specific

product.

In cases where growers plan to switch

from corn to soybeans, they need toconsider the risk of soybean injury from

corn herbicides applied earlier in thespring. Soil-applied herbicides

containing atrazine are a primary

concern when switching from corn tosoybeans. For additional information

on this matter consult Corn & Soybean

News April 2007, Vol 7 Issue 5

http://www.uky.edu/Ag/CornSoy/cor

nsoy7_5.htm#3

3. Corn Emerged But No Herbicide WasApplied:

Growers who planted Roundup Ready(RR) corn hybrids will have theopportunity to use glyphosate for

managing emerged weeds after corn has

also emerged. It may be more difficult

to salvage fields where corn does nothave the RR herbicide tolerant trait.

Several cool-season weeds are

beginning to mature and dieback and

should not pose a problem; whereas,

such weeds as Italian ryegrass,marestail, ragweeds will be a challenge

to control, particularly if nitrogen wasapplied preplant. Applying a soil-

residual herbicide is a good strategy for

extending weed control during the early

part of the season. Many soil-residual

herbicides can be tank mixed with

postemergence glyphosate applications

in RR-corn. Consult the labels of soil-

residual herbicides for timing relative to

maximum size or growth stage of corn.

Do not use liquid fertilizer as a carrier

for applying herbicide treatments after

corn has emerged. If initial corn standsare poor, consider a burndown program

that will control surviving plants and

then replant. For options to manage

unwanted corn to replant see UK

Extension bulletin AGR-6 (page 23)

http://www.ca.uky.edu/agc/pubs/agr/

agr6/02.pdf

4. Corn Emerged and Herbicide WasApplied:Many comments in scenario 2 may alsobe applicable for this situation. An

additional soil-residual herbicide that isregistered to be applied over-the-top of

emerged corn may be warranted in order

to extend early -season weed control.Corn plants stressed due to saturated soil

conditions may be prone to herbicide

injury compared with corn growing in

normal soil conditions. If corn stands

are not acceptable, consider a burndown

program that will control the unwanted

corn and provide soil-residual control of

weeds.

5. Corn Emerged But Field HasScattered Flooded Low Lying Areas

With No Corn:Assuming that corn stands in the

majority of the field is acceptable;

growers may replant the low lying areas.

Keep in mind corn growth in the

replanted areas will be delayed relative

to the remainder of the field. This may

impact how the areas are managed in

regards to weed control particularly in

regards to applying post-emergenceherbicides.

Does a High Application Rate Prevent

Fungicide Resistance?By Paul Vincelli

In the January 25, 2011 issue ofKentucky Pest

News, I wrote about the risk of fungicideresistance in corn pathogens. In that article, I

gave reasons why I thought it seems likely to

develop in corn sooner or later. You can read

that article at

http://www.ca.uky.edu/agcollege/plantpathology

/extension/KPN%20Site%20Files/pdf/kpn1256.

pdf.
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5/12

In this short follow-up, I want to address one

particular aspect of this issue: fungicide

application rate. Some agricultural professionals

believe that using the high-labeled rate of a

fungicide will basically prevent the occurrenceof fungicide resistance. On the surface, it seems

logical: Use the high labeled dose, and let nospores survive, and that will prevent the

development of resistance.

The flaw in this thinking is this: Mutant spores

that are highly resistant to a fungicide will

survive the high-labeled rate.

There are two kinds of fungicide resistance:

quantitative and qualitative.

In quantitative resistance, resistant spores are

less sensitive than the wild-type spores, but theystill can be poisoned by the fungicide at high

doses. In these cases, higher doses do indeed

slow down the buildup of resistance populations.

In qualitative resistance, resistant spores are

insensitive to normal field rates of the fungicide.

In fact, sometimes these resistant spores can

actually causemore disease when the fungicide

is applied (a phenomenon called hormesis). In

cases of qualitative resistance, full-labeled rates

of fungicide do nothing to slow the buildup of

fungicide resistance, and in fact, they actuallymay speed it up somewhat.

The fungicide products used on corn in

Kentucky all are based on strobilurin fungicides

(also called QoI fungicides). This family of

fungicides includes Headline, Quadris, and

Evito, as well as premixes that contain a

strobilurin, such as Quilt, Stratego, Avaris,

and Headline AMP. Resistance to strobilurin

fungicides almost always falls into the category

of qualitative resistance. What this means is that

producers cannot slow down the development ofresistance by using high labeled application

rates.

Late Planted Corn and Insect ManagementBy Ric Bessin

Many growers are finding themselves sin a late

planting or replanting situation with corn due to

the prolonged rain patterns over a substantial

portion of the state. While delayed planting does

affect corn production in many ways, it does

affect the risk to attack by some insect pests.

Several above ground pests will pose a greaterrisk to late planted corn as the corn will likely be

in vulnerable stages when high pest populations

are present. This includes resident pests like

European corn borer and southwestern corn

borer, and migratory mid-season pests like corn

earworm and fall armyworm.

Fortunately most corn planted in Kentucky has

some protection to insect pests with common Bt

traits. The most common Bt traits will provide

protection against both corn borer pests, theEuropean and southwestern. Corn planted afterMay 5th in western Kentucky is a greater risk to

economic losses by corn borers, and as planting

dates fall closer to June 1st

the yield advantageof Bt corn may approach 20 bushels per acre in

the western areas of the state.

Figure 6. Corn earworm feeding on field corn.

Figure 7. Fall armyworm and the frass plug it

produces while feeding in the whorl.


6/12

Recently registered Bt traits and stacked traitsincluding SmartStax, VT2 Pro, Intrasect, and

Agrisure Viptera also provide improved control

of additional secondary pests including corn

earworm and fall armyworm. These insects areprimarily pests of late planted corn, read that as

planted after May 15th. Corn planted before thisdate has relatively less risk to both these pests.

Studies have found that corn earworm can

reduce both grain yield and quality, yield by as

much as 6 to 9 bushels on late planted corn. Itcan also increase bird damage, sap beetle

damage, and be one of several contributing

factors with aflotoxin contamination. In the past

it has not been practical or economical to controlcorn earworm with insecticide applications, so

these new Bt technologies provide opportunities

to effectively control a pest that we havent

controlled in the past.

The past two years we have seen large

populations of both of these pests move into

Kentucky by midsummer, too late to attack most

corn except late-planted fields. Generally, large

populations in states to our south can be a

predictor of later problems for us in Kentucky. It

is still too early to predict what will happen in

Late June and July.

One positive outcome of late planting is that we

will be planting into warmer soils which canhelp to reduce stand losses to wireworms.

Wireworms can cause more damage to seeds and

seedlings growing slowly in cool soils. Late

plating promotes rapid growth and provides less

time for wireworm attack of small seedlings.

TOBACCO

Watch for Insect Problems in Float SystemsBy Lee Townsend

Frequent close inspections of float trays can help

to catch insect pest problems early and to

minimize seedling losses. Variegated cutworms

are the greatest concern and some damage has

been reported. Cutworms found during the week

of 25 April were in the 0.75 inch range, just big

enough to cause visible damage. Rounded holesin leaves lying on or near the media surface and

cut stems are signs of cutworm feeding. They

can totally consume very small seedlings.

Variegated cutworms generally hide in the

media when not feeding but may be caught up

on plants during periods of low light. Small

cutworms are light brown to black with a single

row of light spots along the center of the back.

As they grow, the caterpillars turn light gray and

the spots become less distinct.

Figure 8. Variegated cutworm damage on small

seedlings.

Figure 9. Small cutworm.


7/12

Variegated cutworms feed for about 3 weeks,reaching a length of just over 1-1/2 inches when

full-grown. Most of the feeding is done during

the last few days of their development and many

plants can be destroyed in infested trays.

Variegated cutworm moths begin to fly in Marchand lay clusters of about 60 eggs on small

plants. Consequently, cutworm damage usually

occurs in distinct hotspots and is often nearside curtains where moths can get enter.

Orthene, or other acephate products, can be used

for cutworm control in float systems. Spray

areas where damage is being seen and buffers

around them because the cutworms will spread

outward as they feed and grow.

Wet media and surface algal growth are major

factors that contribute to problems with fungusgnats and shore flies in greenhouses and float

systems. Adults are the noticeable stage but the

larvae can damage small plants by chewing on

leaves or damaging developing roots.

Its easy to overlook a few gnats that appear first

but with a short generation time, populations can

build quickly. Yellow sticky cards, available

through greenhouse suppliers, provide an early

detection system.

Orthene (acephate) sprays will kill adults andreduce their numbers but it is difficult to

eliminate the flies because the larvae are down

in the algae or under the protective cover of the

leaves. Preventive control is based on keeping

media from getting too wet and eliminating asmany standing ground puddles as possible.

Fungus gnats are small (1/8") black flies with

comparatively long legs and antennae, tiny

heads, and one pair of clear wings. Females lay

tiny ribbons of tiny yellowish white eggs in the

growing media that hatch within 4 days. The

clear larvae are legless and have black heads.

Larvae feed for about 14 days and pupate nearthe surface of the medium. Adults live only

about a week. Under greenhouse conditions,about 20-25 days are required to complete a

generation.

Shore flies also are small gnats with short

antennae, red eyes, and heavier, darker bodies. A

pair of smoky wings with several clear spots can

be seen when looking closely at the insect. They

are good fliers and can be seen resting on most

any surface in the greenhouse.

Tray Drench and/or Transplant Water

Insecticides for TobaccoBy Lee Townsend

The table below summarizes options for tobacco

insect pest control available as tray drench and

/or transplant water applications. The insecticide

common name, brand names, and insecticide

mode of action group number appear in the first

column.

Pest lists may vary on labels of different brands

containing the same active ingredient. Higher

rates may be needed for some pests. Tray

drench / transplant water applications provide an

efficient way of applying preventive controls for

key pests. Pest levels may be high enough in

some fields to cause damage even if preventivetreatments are used. Therefore, it is important to

check fields to see if supplemental control is

needed. Many products have a range of rates.

Normally, high rates provide better control

under heavy infestation pressure and for longerperiods of time.

For example, tray drench / transplant water

applications may not provide effective cutwormor wireworm control if pest pressure is high. The

insecticide is present in a small area around the

plant and the insect may cause significant

damage before there is an effect. Prospects for

Figure 10. Yellow sticky cards with

fungus gnats and shore flies.


8/12

cutworm damage are greatest in fields wherethere is a significant flush of weed growth in late

winter or early spring, especially if transplanting

is delayed by wet field conditions. Wireworm

injury can be anticipated in tobacco fields thathave had a significant bluegrass component for

several years prior to tobacco. In theseinstances, preplant incorporated insecticide

applications are likely to provide better

protection of transplants.

Tray drench and transplant water insecticide

options for tobacco.

Check the label for specific instructions andprecautions. Insecticides applied as drenches to

trays of transplants should be watered

immediately after treatment so the insecticide

does not dry on the foliage. The insecticidemust get into the root ball to be taken up by theplant. In general, flowable and dry formulations

require agitation to keep the formulation from

settling in the tank.

Tobacco flea beetles overwinter as adults in

protected places around tobacco fields.

Although the winter of 2010-11 was long and

cold, it is likely that the snow cover helped to

protect these insects. Flea beetles are active

early and will be most problematic on theearliest-set fields. A preventive flea beetle

treatment should be a very good investment for

these fields. Some products labeled for

preventive aphid and flea beetle control require ahigher use rate for aphids than for flea beetles.

Be on the Look out for Bacterial Soft Rot on

TransplantsBy Kenny Seebold

The tremendous amount of rain that has fallen

over much of Kentucky during the past month,

along with extended periods of cool and overcast

weather, is really starting to push outbreaks of

diseases in tobacco float beds. In fact, weve

gotten quite a few reports of target spot,

Sclerotinia collar rot, and Pythium root rot (see

previous issues ofKentucky Pest News for more

information). Our temperatures are bound to

increase over the next couple of weeks, and I am

beginning to worry about bacterial soft rot, or

blackleg, showing up on tobacco seedlings in the

coming weeks. Lets take a closer look at

blackleg, the conditions that drive this disease,

and steps to take for best control of the problem.

Insecticide

(Group #)

Flea

beetle

Aphid Wire

worm

Cut

worm

Budworm

Hornworm

Acephate

(1b)

(Orthene,etc)

X - - X -

Bifenthrin

(3)

(Brigade/C

apture)

Larva

e only

- X X -

Chlothianid

in (4a)

(Belay)

Imidaclopri

d

(Admire,

Widow,

etc.Thiometho

xam

(Platinum)

X X - - -

chlorantran

iliprole

(28)

Coragen

- - - - X

Figure 11. Flea beetle damage on

tobacco.


9/12

BACKGROUND. Warm, humid conditions in

the float bed are the ideal environment for

Erwinia carotovora subsp. carotovora and other

bacterial species that cause blackleg. Initially,

organic matter in trays, or wounded tissues, arecolonized by the blackleg pathogen. Debris and

leaf tissue infected byErwinia appear necroticand slimy (Figure 12). Systemic infections,

which arise whenErwinia moves from debris or

wounded tissues into healthy plants, result indarkening of the stem that tends to move up one

side of the seedling primarily, hence the name

blackleg (Figure 13). Affected areas of the

stem may also show splitting, and in advanced

stages, seedlings will collapse. Under favorable

conditions, blackleg will spread rapidly, causing

significant loss of useable transplants in as few

as 1-2 days (Figure 14).The bacteria that cause blackleg are essentially

parasites of wounded or stressed tissue, and are

plentiful in soil and on leaf surfaces. Because

the pathogens are always present, development

of disease is dependent on a favorable

environment and plentiful food (in the form of

plant debris or wounded/stressed tissue).

Factors that may lead to outbreaks of blackleginclude: high nitrogen levels (> 150 ppm),

warm temperatures (>75 F), high humidity,

long periods of leaf wetness, and plant injury

(stress and wounding). The latter occurs

routinely during clipping and can lead to rapidspread of bacterial soft rot if carried out when

plants are wet.

MANAGEMENT. Cultural practices are the

most important ways to prevent of bacterial

diseases. Provide adequate ventilation to

shorten the length of time that foliage stays wet

this may be the most important of all

management practices to reduce the incidence of

blackleg. Most outbreaks we see in Kentucky

are associated with warm temperatures and

excessive moisture on float plants. Avoid over-

fertilizing, a practice referred to as pushing

seedlings, as this leads to dense, lush growth thatis more susceptible to disease and takes longer

to dry. Clip and handle plants only after they

have been allowed to dry properly. Leaf debris

left behind after clipping can serve as a starting

point for the pathogens that cause blackleg and

should be removed promptly. Along with

maintaining good airflow in the float system,

Figure 12. Early symptoms of blackleg include soft-

rotting of lower leaves and leaf material; a foul odor

can often be detected even before symptoms can

been seen.

Figure 13. Blackened, water-soaked lesions on the lower

stems of affected plants are typical of later-stage

blackleg.

Figure 14. In severe cases of blackleg, large numbers of

plants can be lost in a matter of a few days.


10/12

keeping as much leaf debris out of the beds as

possible is a key to holding blackleg in check.

Chemical options for control of blackleg are

limited. Agricultural streptomycin can be usedin outdoor plant beds to suppress bacterial

diseases, but is not specifically labeled for use intransplant facilities. However, because the use

of agricultural streptomycin is not expressly

prohibited in transplant production, EPA rulesallow its use in the float system. Streptomycin

provides only moderate suppression of blackleg,

though, and growers who choose to apply the

material in the greenhouse must accept all

liability. Apply 3-5 gallons of a 100-200 ppm

solution of streptomycin to 1000 sq. feet of float

bed. This use rate translates to 0.5-1 lb per 100

gallons of water, or 1-2 teaspoons per gallon.

Apply streptomycin before symptoms appear forbest results, using the lowest rate. Use the 200-

ppm rate immediately after the appearance of

symptoms of blackleg. Some plant injury may

be observed when applying the higher rate.

Refer to the product label and the 2011-2012

Kentucky-Tennessee Tobacco Production

Guide (ID-160) for more information. The

guide can be found online at

www.uky.edu/Ag/TobaccoProd/pubs/id160.pdf.

SHADE TREES & ORNAMENTALS

Emerald Ash Borer UpdateBy Lee Townsend

The degree day model predicts the beginning of

EAB emergence next week (5 May) in central

Kentucky; it should reach its peak in about 2

weeks. Individual beetles live for about 3 weeks

so adults could be around from mid-May

through early July. Adults will feed on ashfoliage high in the crown for several days before

mating and laying eggs. Suspected infested ash

trees outside of the EAB quarantine area (atriangular are bounded by Lexington

Louisville Covington and the Body Greenup

county area should be reported to the Office of

the State Entomologist (859) 257-5838. Insects

suspected of being emerald ash borers can be

taken to your local cooperative extension service

office.

Severe storms over the past several days have

knocked down a number of the purple EAB

traps. The surveyors will be checking andrehanging downed traps so it is best to leavethem where they can found and re-set.

Managing Flowering Crabapple Rust, and

Powdery MildewBy John Hartman

Kentucky flowering crabapples are enjoyed fortheir profuse flowers and for their attractive

foliage and fruit. Experienced growers and

homeowners are well aware that springtime isalso the time of year that many of the important

diseases of flowering crabapple are most active.

Many flowering crabapples are made unsightly

or are severely injured by one or more of four

common diseasesapple scab and fire blight

(discussed in Kentucky Pest News earlier this

spring), cedar-apple/-quince rust, and powdery

mildew. Cedar rust symptoms appear later inspring and summer and despite being unsightly,

are generally not life-threatening crabapple

diseases. Powdery mildew is also unsightly and

could weaken a crabapple making it more

vulnerable to other diseases or environmental

stresses.

Managing cedar-apple rust (Figure 15) and

cedar-quince rust (Figure 16) caused by the

fungi Gymnosporangium juniperi-virginianae

and G. clavipes:

Eliminate eastern red cedar trees andsusceptible junipers within 1/4 mile ofsusceptible crabapples to provide almost

complete control. Maintaining a

distance of 500 feet between cedars and

crabapples can provide good control.

If cedar-tree or juniper removal is notpossible, remove galls from infected

cedar trees near crabapple plantings
http://www.uky.edu/Ag/TobaccoProd/pubs/id160.pdfhttp://www.uky.edu/Ag/TobaccoProd/pubs/id160.pdfhttp://www.uky.edu/Ag/TobaccoProd/pubs/id160.pdf


11/12

before the galls produce the orange

spore horns in early spring.

If necessary, apply fungicides tocrabapples three times at 10-day

intervals, starting about the time color

shows in the blossom buds. Effective

fungicides include chlorothalonil,fenarimol, myclobutanil, propiconazole,

triadimefon, or mancozeb.

Consider using resistant varieties infuture plantings if cedar-apple rust has

been a serious problem. Cedar rust-

resistant crabapples: Adams,M.

baccata Jackii, Beverly, Candied

Apple, Centurion, Dolgo, Hopa,

Indian Magic, Liset, Mary Potter,

Molton Lava, Professor Sprenger,

Red Baron, Red Jade, Red

Splendor, Robiinson, Royalty,Ruby Luster,M. sargentii, Selkirk,

Sentinel, Silver Moon,M.

tschonoskii, Velvet pillar, Winter

Gold,M. yunnanensis var vechii,M.

zumi Calocarpa. Trees resistant to

cedar-apple rust are not necessarily

resistant to cedar-quince rust.

Where the disease seldom occurs or fewleaves are infected, no control is

necessary.

Managing powdery mildew (Figure 17) causedby the fungus, Podosphaera leucotricha:

Crabapple powdery mildew is normallynot serious enough to warrant control

measures except on the most susceptible

cultivars.

Prune out diseased shoots during thenormal pruning period for flowering

crabapples.

Apply fungicides at weekly or biweeklyintervals beginning at bud break until

shoots have completed elongation.

Effective fungicides includemyclobutanil propiconazole,

thiophanate-methyl, and triadimefon.

Mildew-resistant varieties should beconsidered in moist, shaded locations.

Most cultivars are resistant or

moderately resistant. Susceptible

cultivars include Adams, Molton

Lava, andM. yunnanensis var. veichii.

Figure 15. Cedar apple rust causes orange-

colored spots on infected leaves. Here, the

underside of the leaf reveals the mid-

summer aecial structures which produce

spores to infect nearby cedars and junipers.

Figure 16. Cedar-quince rust can infect new crabapple

shoots in spring, resulting in a swollen and distorted

branch tip.

Figure 17. Powdery mildew

deforms and creates a whitish

cast on crabapple leaves.


12/12

DIAGNOSTIC LAB HIGHLIGHTSBy Julie Beale and Paul Bachi

Samples this week have included Pythium root

rot, target spot and nitrogen deficiency in

tobacco transplants; cane blight on blackberry;

anthracnose on grape; leaf curl on peach andnectarine; Botrytis blight and black root rot on

annual vinca, as well as black root rot on

petunia; and Sclerotinia leaf blight ongreenhouse tomato.

From landscapes, we have seen Botrytis twig

blight on arborvitae; Rhizoctonia root rot on

azalea; black root rot on holly; Phytophthoraroot rot on juniper and pine; Dothistroma needle

blight on pine; rose rosette and Botrytis blight

on rose; and winter drying/injury on various

landscape shrubs.

INSECT TRAP COUNTSApril 22-29

Graphs of insect trap counts for the 2011 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

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 23 0

Armyworm 96 479

Corn earworm 1 12European cornborer

0 0

Southwestern

corn borer

0 0

Fall armyworm 0 0

kentucky pest news may 3, 2011

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