Kentucky Pest News Newsletter

HIGHLIGHTS IN THIS ISSUE

Number 925__________ July 16, 2001

TOBACCO
CORN
WHEAT
FRUIT
LAWN AND TURF
SHADE TREES AND ORNAMENTALS
ANNOUNCEMENTS
DIAGNOSTIC LAB HIGHLIGHTS
IPM TRAP COUNTS


ANNOUNCEMENTS




NEW INSECTICIDES FOR ARMYWORM CONTROL IN PASTURES
By Lee Townsend

(Frankfort) The U.S. Environmental Protection Agency has granted special registration for two insecticides to combat armyworms in pastures and hayfields in Kentucky, the Ky Department of Agriculture has announced.

The insecticides are Pounce 3.2 EC (FMC Corp.) and Confirm 2F (Rhom and Haas Co.). Both are Restricted Use pesticides. Cattle can be present during application, if necessary, when Pounce is applied and they may graze fields after treatment. However, pastures sprayed with Pounce cannot be cut for hay during the remainder of the season. Pastures sprayed with Confirm 2F can be harvested for hay after a14-day wait.

Applicators must have a copy of the appropriate state (24-c) label for Pounce or the Crisis Exemption label (Section 18) for Confirm. These are available from the pesticide dealer when the products are purchased.

 

 


Ky Blue Mold

 

 

TOBACCO


 


CURRENT BLUE MOLD STATUS
By William Nesmith

For the latest blue mold status and other tobacco disease information, check the KY Blue Mold Warning System.
Blue Moldhttp://www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm

 

 


Corn




CORN



DISEASES OF CONCERN IN CONTINUOUS CORN
By Paul Vincelli

Corn Although current agricultural statistics do not suggest a trend towards large acreages of continuous corn, individual producers are often interested in planting corn following corn. In these situations, one of their main concerns is increased pressure from diseases, and rightfully so. Crop rotation is one of the most fundamental disease control practices available. Rotating to other crops deprives pathogens (disease-causing microorganisms) of a food source and exposes them to starvation. Furthermore, as infested crop residues decompose, pathogens are exposed to antagonism by native soil microbes. These mechanisms have the effect of naturally eradicating many pathogens from the soil.

Numerous diseases can be more active under continuous corn, particularly those caused by pathogens that survive in crop residue or in the soil. Three are important enough under Kentucky conditions that they deserve specific management attention.

Gray Leaf Spot
This disease is a significant threat wherever corn is grown after corn. The fungus survives between growing seasons in residues of corn leaf blades and sheaths. From there, it is spread by wind and rain to leaves of the new corn crop. Tillage practices can reduce levels of inoculum (spores or other pathogen structures that initiate disease), but rotation is a key management practice, as well. Thus, in the absence of crop rotation, susceptibility to gray leaf spot should be carefully considered when selecting a hybrid.

Hybrids exhibit differing levels of to gray leaf spot. Partial resistance is the most common type of disease resistance in field crops. Varieties with partial resistance are those that, under uniform conditions, exhibit less disease than some standard cultivar or host line. Gray leaf spot will still develop on a partially resistant hybrid, but it typically is slower to develop and less severe. For example, compared to a fully susceptible hybrid, a hybrid with partial resistance will usually have fewer lesions for a given spore load, and those lesions will be smaller. This reduces the impact of the disease on crop development and yield.

When growing continuous corn, always select hybrids with as high a level of resistance as you can against gray leaf spot. This is particularly important in fields under conservation tillage, in which corn residues provide high amounts of inoculum.

Susceptible hybrids growing in a no-till, continuous corn situation will sometimes benefit from application of a fungicide. For a susceptible hybrid, a single application sometime between the V10 (about head height) and V14 stage will often be beneficial, if scouting indicates the disease is present at least halfway up the plant. Specialty corns susceptible to gray leaf spot are especially likely to benefit from a fungicide application in a no-till, continuous corn situation, because of their inherently higher crop value. Although products containing mancozeb (Dithane, for example) are labeled for gray leaf spot, best results can be expected with Quadris (azoxystrobin) or Tilt (propiconazole). Expect best results from a fungicide when applied using a ground rig fitted with a single nozzle over the row and two drop nozzles straddling each row.

Diplodia Ear Rot
Although most corn fields do not experience notable amounts of this disease, Diplodia ear rot can occasionally cause severe epidemics, causing rot on as many as 50-75% of the ears in a field. The fungus that causes the disease only attacks corn, and it survives between seasons in residue of corn stalks, cobs, and fallen kernels. Thus, continuous corn production especially under conservation tillage-- allows the pathogen to build up to potentially destructive levels.

It is a good practice to scout fields for Diplodia ear rot as the crop matures, especially if under conservation tillage. Pull back the husks of 50-100 plants selected at random as you walk the field. Look for white, cottony mold growth between the kernels, which usually progresses upwards from the base of the ear. Suspect samples can be confirmed through your county Extension agent. Producers growing no-till corn who find more than 2-3% of ears with Stenocarpella ear rot should consider implementing some management practice, such as rotation to another crop, tillage, or both.

Whenever corn is planted following corn, check with your seed supplier to determine if the seed company specifically breeds hybrids with partial resistance to Diplodia ear rot; some companies do, but not all. Also, avoid hybrids that have experienced serious outbreaks of Diplodia ear rot, since this may indicate unusually high susceptibility to the disease.

Pythium Seedling Diseases
Pythium microbes commonly present in agricultural soils can cause a variety of symptoms on corn seed and seedlings. Seed decay, pre-emergence damping off, and postemergence damping off are the more striking problems caused by Pythium. However, Pythium can also infect root hairs and young rootlets, causing reduced vigor of developing plants, which can ultimately affect yields. Studies with a variety of monocot crops, including corn and sorghum, have shown that Pythium diseases can significantly reduce stand, vigor, and yield in continuous cropping situations. These studies have shown a significant advantage to using seed treated with metalaxyl fungicide, which specifically targets Pythium. Metalaxyl is found in several products, including Allegiance and Apron. Given the relatively low cost of seed treatment fungicides and the apparent enhanced Pythium risk when monocots are cropped without rotation, sowing seed treated with metalaxyl would make sense where corn follows corn.

Other Diseases
Diseases caused by the anthracnose fungus, including top dieback (a rot of the upper stalk during grain fill), can be enhanced in continuous corn. This is because corn is the only important host of this pathogen. Attention should be paid to hybrid susceptibility to anthracnose when growing continuous corn. Substantial levels of resistance would be especially important in areas with a history of top-dieback or other anthracnose diseases.

Southern leaf blight generally occurs at low levels in Kentucky, because past breeding efforts have led to high levels of resistance in most of the hybrids currently available. Yield-limiting levels of northern leaf blight are also uncommon, because of our generally warm summer conditions as well as sound breeding for resistance. Be aware, however, that the risk of both diseases is higher under continuous corn because, like the gray leaf spot pathogen, the fungi that cause these diseases pathogens survive in corn residue. Thus, it may be wise to consider hybrid reaction to these diseases when growing continuous corn.

Concern is sometimes expressed that stalk rots might be worse in a continuous corn situation. In reality, studies to date indicate that rotation has little to no impact on the severity of stalk rots. Stalk rot incidence is influenced by high plant populations, excessive nitrogen, leaf diseases, and other factors.

Additional Information The following publications provide more information on several of these subjects. They can be accessed on the web at www.ca.uky.edu/agcollege/plantpathology/PPAExten/pppublin.htm#CornandSorghum.

Ear Rot of Corn Caused by Stenocarpella maydis (=Diplodia maydis), UK Extension Publication PPA-43.

Gray Leaf Spot of Corn, UK Extension Publication PPA-35.




Wheat

WHEAT


 


WHEAT FUNGICIDE LABEL UPDATES
By Don Hershman

Wheat Very recently, the Bayer Corporation received approval from EPA for the removal of a very significant use restriction on their newly-labeled product, Stratego. This foliar fungicide is actually a mixture of two active ingredients. One, trifloxystrobin, is in a rather new class of fungicides and is similar to the active ingredient in Syngenta's Quadris. The other is propiconazole, the active ingredient in Tilt.

You may recall that when Tilt received a label in late 1987, the label had a serious restriction which prohibited farmers from planting doublecrop soybean (or any crop) following a Tilt-treated wheat crop in the same season. Ciba-Geigy (the company name at that time) was able to have that restriction removed from the Tilt label after the company presented sufficient data and a sound argument that planting other crops in the same season in which Tilt was applied would pose no heath hazard. That change was made and, consequently, Tilt has been used for many years on Kentucky wheat crops.

Recently, when Novartis was in the process of merging with Zeneca to create Syngenta, they sold the Stratego rights to Bayer. Soon after this acquisition, Bayer was successful in receiving a Federal label for Stratego. A result was that Stratego was generally available for use by Kentucky wheat farmers in 2001. However, very little Stratego was used this spring. The reason was that the initial Stratego label carried the same rotational restriction that originally was on the Tilt label as discussed above. Don't forget that Stratego and Tilt have a common active ingredient - propiconazole.

We have been recently informed by Bayer that this rotational (e.g., soybean doublecrop) restriction has now been lifted for Stratego. Consequently, expect a full-fledged marketing campaign from Bayer this next winter and spring anywhere farmers are apt to apply wheat foliar fungicides. There are slight differences in the performance of Tilt, Stratego, and another recently-labelled wheat fungicide Quadris, but nothing major; they are all excellent products if applied according to label instructions and in the presence of sufficient disease pressure. The big clincher, as far as farmer use goes, will be price and availability. Marketing programs which often include incentives of various types are likely to also come into play. In any event, the foliar fungicide story this winter and early spring should be interesting.

One final note on Stratego. Unfortunately, like Tilt, Stratego must be applied to wheat before a crop's flag leaf has completely emerged. Quadris, on the other hand, may be applied much later, up to, but not including crop flowering. Quadris is a great product and will fill a significant mid- to late-season void in foliar disease management programs if the price comes down significantly.

One other update I would like to tell you about is related to the recent karnal bunt issue in Texas. I was informed that Syngenta has issued a Section 2(ee) Recommendation for three of their wheat seed treatment fungicides: Dividend, Dividend XL RTA, and Maxim 4FS. The 2(ee) is for the "partial control of karnal bunt on wheat". For your information, 2(ee) recommendations are the equivalent to a pesticide manufacturer saying that their product will control a particular pest and that they are will to accept some liability as to performance of their product. If you are concerned that you may be vulnerable to planting karnal bunt-infected wheat seed you might consider applying one of these seed treatment fungicides, or others that specifically state on the label that karnal bunt is a target pest.


  Blackberries

FRUIT



GREEN JUNE BEETLES
By Lee Townsend

Green june beetle Green June beetles with their dull velvety green and tan wing covers and iridescent green undersides are a common summer sight in Kentucky. They make what may be considered a threatening buzzing sound as they fly about crashing into objects and people but they are harmless in these encounters.

Green June beetles do have a fondness for very ripe fruit and large numbers of the beetles can accumulate on damaged or rotting fruit or the tips of sweet corn ears. In general, Sevin (7 day harvest interval) or malathion (1 day harvest interval) can be used for reducing beetle numbers of crops. Be sure the crop is on the label and follow the appropriate harvest period. Pyrenone Crop Spray (Aventis), containing 6% pyrethrins, can be used on a wide variety of fruits up to and including the day of harvest. Pyrenone contains natural pyrethrins and is not a synthetic pyrethroid insecticide. This insecticide has a quick knockdown effect and degrades very quickly so it provides no residual protection. It is a good choice for "cleaning up" beetles.

Regardless of the insecticide used, the odors from overripe fruit will continue to draw beetles even after applications are made. This means that beetle pressure will remain high in areas where the insect is abundant, creating a frustrating problem for growers. Removal and destruction of overripe or crushed fruit will help to make sites less attractive to green June beetles. Sanitation is an important part of beetle management.



  Lawn and Turf

LAWN & TURF



WHAT WAS THAT BIG YELLOW, ORANGE & BLACK THING?!?
By Mike Potter

Cicada killer Cicada killers are now flying, prompting many calls from homeowners. Despite their menacing appearance (up to 2 inches long with rusty red head/thorax, amber-yellow wings, and black and yellow striped abdomen), the wasps seldom sting unless handled or otherwise molested.

Cicada killers do not live in communal nests like hornets or yellowjackets. They overwinter as larvae within cocoons, deep in the soil, emerging as adults during July. The females feed, mate, and excavate burrows in the ground about " inch in diameter, ending in a series of brood chambers. Excess soil is pushed out of the burrow, leaving a small, U- shaped mound of dirt at the entrance. Each female excavates numerous burrows and provisions them with adult cicadas which she ambushes, paralyzes with her venom, and stuffs into individual brood chambers. She then lays an egg on top, backs out, and seals the cell behind her. The egg hatches within a few days and the hungry larva devours the offering, eventually transforming into a pupa the following spring.

Management - Cicada killers seldom sting and the females normally do not defend their burrows. The males, while incapable of stinging, sometimes dive- bomb passers-by, or hover menacingly nearby. Insecticide treatment may be warranted where the soil burrows become unsightly. Individual burrows can be effectively dusted or sprayed with most yard insecticides (e.g., Sevin, diazinon, Bayer Advanced Lawn & Garden Multi-Insect Killer) or a wasp & hornet aerosol spray. Large numbers of nests may need to be treated with a broadcast application to the surface of the turf.


Shade tree





SHADE TREES AND ORNAMENTALS



DOGWOOD POWDERY MILDEW UPDATE
By John Hartman

Flowering dogwoods (Cornus florida) are showing symptoms and signs of powdery mildew. This disease, first noticed in the mid-1990's appears to be as noticeable and damaging in 2001. New for this year, however, are three new mildew-resistant flowering dogwood cultivars recently developed by the Tennessee Agricultural Experiment Station.

SYMPTOMS AND SIGNS. On susceptible dogwoods, powdery mildew symptoms are appearing now, in many cases accompanied by the white powdery mycelium and spores of the fungus (signs). Affected parts of leaves develop a mottled yellowing or turn light green or yellow and often develop brownish patches. Yellowed leaves may fall. In some cases, a very light coating of the causal fungus can just barely be seen and, occasionally, small patches of the fungus are fairly visible. Often the disease begins as barely distinguishable reddish brown or purplish irregular blotches on dogwood leaves which then develop into dark brown to tan dead patches. The combination of dead patches and leaf yellowing is most noticeable for homeowners.

The typical white powdery mildew mycelium and spores may develop abundantly on the new growth, distorting and curling these youngest leaves by season's end. Many of these curled leaves may also be scorched with brown leaf margins and interveinal dead patches. The disease increases progressively from early June to early September. Severely affected trees may appear wilted and browned by late summer. Landscape dogwoods exposed to sunlight and dry soil conditions may be especially scorched.

CAUSE. The fungal signs present during the summer are the asexual Oidium stage which produces chains of white conidia. On leaves late in the season and on fallen leaves in fall and winter, ascocarps (cleistothecia, the sexual stage) of both Microsphaera and Phyllactinia spp. have been found, so this disease may involve two fungi. Although wet leaves favor most landscape plant diseases, powdery mildew is an exception. Like other powdery mildews, dogwood powdery mildew is favored by relatively dry, but humid weather.

HOW POWDERY MILDEW MIGHT AFFECT DOGWOODS. Powdery mildew has affected flowering dogwoods in Kentucky landscapes for several years. Although it would appear to weaken trees, it does not appear to be lethal. We have observed that under high disease pressure, flower production is decreased the following year. Powdery mildew most likely reduces plant photosynthesis and increases leaf water loss through disruption of the cuticle and through the superficial fungal mycelium. In the long run, this could weaken trees making them more prone to dogwood borer or Botryosphaeria canker. In reality, the long-term effects of powdery mildew disease development on tree health are not known. Most landscape dogwoods are grown from seedling sources, so the mildew susceptibility of individual dogwood trees in landscapes varies greatly.

DISEASE MANAGEMENT. Powdery mildew can be confronted by using cultural practices, planting resistant dogwoods, and by using fungicides.

When using fungicides for powdery mildew management, be sure that dogwoods are listed on the label and carefully follow all label directions.


DAY LILY RUST FOUND IN KENTUCKY
By John Hartman

Day Lily rust disease was identified for the first time in Kentucky today. This disease is a real threat to this popular Kentucky garden plant grown by homeowners, nurserymen and others.

The specimen came from a Fayette County non- commercial daylily grower who buys plants from the south.

We are in the process of notifying USDA officials (through our USDA APHIS Kentucky Nursery Inspectors housed here at U.K.) as to what, if anything, needs to be done about the diseased plants to keep the disease from spreading.

Some of you may recall reading about this in a recent Kentucky Pest News article (July 2). Excerpts from that article follow.

Daylily rust was found for the first time in North America last year in Florida. Since then, it has been spread (mainly on infected nursery plant material) to several other states including Alabama, California, Georgia, Kansas, Louisiana, Minnesota, Mississippi, South Carolina, Tennessee and Texas. (...and now Kentucky)

The causal agent is Puccinia hemerocallidis, a rust fungus. The disease is identified by bright yellow or orange colored spots with raised pustules on the foliage of affected plants and by orange colored spores which emerge from the pustules. As symptoms progress, leaves turn yellow and dry up. The following web site (http://www.ncf.ca/~ah748/rust.html) shows good pictures of this and other daylily diseases and disorders.

It is believed that the disease will become a serious pest of daylilies. The disease is easily spread in the nursery trade because viable spores may be carried long distances on plants and propagative material not showing symptoms.

If daylily rust is suspected, immediately remove all infected foliage and burn or bury the clippings except to save a leaf or two to send to the County Extension Office; the agent will get them to our plant disease diagnostic laboratory. Most County Extension Agents will recognize rust disease and would be able to tell the homeowner immediately whether daylily rust is present, or if it is suspected. Following diseased foliage removal, sterilize tools with 70% alcohol, 10 % bleach, or lysol to prevent spread. Wash hands, gloves, or clothes afterwards, if necessary, to prevent spread to the rest of the garden. New foliage can be protected as it emerges with fungicides such as propaconizole (Banner Maxx), azoxystrobin (Heritage), flutolonil (Contrast), or myclobutanil (Systhane, Eagle). Because this is a new disease, there is no specific label of daylily rust. Be sure that the label indicates that the fungicide product used can be used on daylilies or on ornamentals generally in the nursery or landscape. Resistant cultivars have not yet been identified.

Agents, homeowners and nurserymen are urged to be on the lookout for this potentially serious disease of daylily.


Microscope

DIAGNOSTIC LAB HIGHLIGHTS


DIAGNOSTIC LAB - HIGHLIGHTS
By Julie Beale and Paul Bachi

Samples of field crops diagnosed last week included corn with gray leaf spot; alfalfa with Rhizoctonia stem canker and boron deficiency; soybean with downy mildew, Rhizoctonia root/stem rot, environmental stress and chemical injury; and tobacco with black shank, blue mold, Fusarium stem rot, Rhizoctonia root/stem rot, Fusarium wilt, root knot nematode, frogeye leaf spot, tobacco streak virus, tomato spotted wilt virus, alfalfa mosaic virus, tobacco ringspot virus, manganese toxicity and ozone damage.

Fruit and vegetable samples included Phytophthora crown rot on blueberry; black root rot (Rhizoctonia) and leaf spot (Mycosphaerella) on strawberry; black rot on grape; fire blight, cedar-apple rust and frogeye leaf spot (Botyrosphaeria) on apple; anthracnose on bean; bacterial wilt on cantaloupe, pumpkin and squash; oedema on pea; and bacterial canker, bacterial speck, early blight, Septoria leaf spot, Fusarium stem rot, Fusarium wilt, walnut wilt, catfacing, and blossom end rot on tomato.

On ornamentals, we diagnosed Fusarium crown rot and bacterial soft rot on daylily; bacterial leaf spot on ivy; Pythium root rot on poinsettia; Phoma on vinca; bacterial leaf spot on rudbeckia and salvia; powdery mildew on dogwood; Verticillium wilt on maple and tuliptree; tar spot on tuliptree; and anthracnose on yellowwood.

 

 


Scout Cat

IPM TRAP COUNTS:

By Patty Lucas, University of Kentucky Research Center

 

 

Insect Trap Counts

UKREC-Princeton, KY, July 6 - 13, 2001
True Armyworm 5
Fall Armyworm 3
Beet Armyworm 0
Corn Earworm 2
European Corn Borer 0
Southwestern Corn Borer 131

To see recent moth trap counts, click here.


Lee Townsend
Extension Entomologist

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