Although many new fungicides have been developed in the past decade, Kentucky's tobacco growers will have essentially the same foliar fungicide options for the 2004 season they had in 2003 as no new fungicides have been labeled for field use on tobacco. The number of available options is low, especially when compared with other high value crops. Many chemical manufactures report that labeling pesticides on tobacco is not economical, and the crop does not qualify for the labeling assistance provided under IR-4 Minor Use Pesticide Program. For social reasons, others have no desire to label their material for use on tobacco.
Foliar applied products can be important tools for controlling tobacco diseases, especially blue mold and bacterial leaf spots, in the tobacco field when used correctly. However, we still do not have available effective fungicides for some other important foliar diseases of tobacco, especially target spot and frogeye. Some of the blue mold materials will significantly reduce frogeye disease but residue issues prevent sufficient post-topping applications that are need to provide acceptable control of frogeye.
Using the correct chemical, the proper rate, the appropriate application method, and at the correct timing are important to successful use of foliar-applied fungicides. All those currently labeled on tobacco will perform best when used prior to infection (in a preventive role) rather than waiting until the disease is damaging the crop, yet certain of these chemicals also have some rescue potential. For most foliar applications, thorough coverage is critical to success, especially under strong disease pressure. Consequently, a good sprayer specially equipped to deliver foliar protectant-type fungicides in a tall, dense, row-crop is needed. In fact, the failure to adopt proper spray equipment is the leading reason for lack of success with foliar fungicides in tobacco.
The Kentucky Blue Mold Warning System should be a excellent tool to assist growers in the need and timing of foliar fungicides in tobacco. Although this website mainly provides information on blue mold, advice is also provided on other tobacco diseases. That website is located at: http://www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm
The chemical options listed below have proved effective in our experiments and demonstration trials and were labeled for the uses mentioned as of April 20, 2004. There may be others that are labeled for tobacco, but are not included here, because they have not proven to be effective under Kentucky's disease conditions, or in valid efficacy tests conducted by pathologists in other major tobacco production areas. Should any fungicide receive a tobacco label during the growing season, special updates will be provided in this newletter, plus it will be posted on the above website.
Not included below are chemicals which are reportedly being used and may even have proven efficacy, but that are not labeled for field-tobacco-use in Kentucky, including: Aliette, Bayleton, Benlate, Bleach, Captan, Flint, Nova, Quadris, Rovral, and Tilt. In addition to unlabeled uses being prohibited by state and federal pesticide laws, tobacco marketing laws also directly prohibit the marketing of tobacco treated with unlabeled chemicals. Therefore, the use of these unlabeled materials should be discouraged at all levels of the tobacco industry.
ACTIGARD 50WG has a federal label supporting use in blue mold control on both burley and dark tobaccos as a broadcast, foliar spray at 0.5 oz/acre, using 20-30 gallons of water per acre. The pattern of use in burley and dark tobaccos is very different from that labeled in flue cured tobacco, so read the label carefully. The preharvest interval is 21 days and the re-entry interval is 12 hours. Application cannot begin in burley and dark tobacco until after the plants reach a height of 18" (stalk length from bud to the soil line) due to phytotoxicity problems. A second application can be made 10 days later. Our studies have demonstrated that Actigard is a valuable product in improving the plants resistance to blue mold when applied correctly, but has serious. limitations as a stand-alone control for blue mold under prolonged or high disease pressure.
The active ingredient (acibenzolar-S-methyl or benzothiadiazole) is not directly toxic to the target pathogens. Instead, it is a plant defense activator that induces (triggers) a series of natural chemical reactions in the treated plant that activate the plant's own resistance mechanisms - called the SAR (systemic activated resistance, also called systemic acquired resistance). Consequently, disease control is normally not obtained until four or five days after the application is made and there may be other desirable and undesirable physiological changes that occur under certain conditions in the treated plant. The rate needs to be calculated carefully, as high rates can be very phytotoxic and lower rates greatly reduce efficacy. Yellowing of the foliage occurs during the time defense chemicals are present, but this yellowing and the control dissipate with time. It is important to control blue mold prior to the plants reaching the stage that Actigard can be used, as well as, in late-maturing varieties, by using additional fungicides when blue mold favorable periods exist. Follow directions carefully, in order to achieve the desired disease control without causing crop damage. Application rate and timing are critical to achieving control while minimizing the phytotoxicity. The label clearly states these "do nots" and I urge growers to follow label warnings:
ACROBAT MZ is labeled under a state label (24c) in Kentucky that expires Decemeber 31, 2004. This state label was renewed because the national label for Acrobat 50 WP was not made available in the Kentucky market. The state label can be found at http://www.cdms.net/ldat/ld751003.pdf. Acrobat MZ contains two fungicidal chemicals - the systemic dimethomorph and the protectant mancozeb. Acrobat MZ is labeled only as a foliar spray to be applied at 2.5 lbs/100 gallons/acre (volume adjusted for stage of growth). It is highly effective when applied well and at close intervals, even under aggressive disease pressure, but of limited value when applied poorly or the intervals are not maintained. Application can be made on a 5-7 day spray schedule, once advisories have been issued, but applications should be discontinued when and if the threat of blue mold subsides. Sprays should be applied in a preventive manner by ground-operated, high-pressure sprayers equipped with hollow-coned nozzles on drops, or with mist blowers or other air-blast equipment. Up to 8 applications can be made per crop, but the limit is 10.0 lbs/field/season, and with no more than 2.5 lbs/acre per application. The preharvest- interval is 30 days between last application and harvest. When being used in a weekly spray schedule, this fungicide will also provide some control of frogeye leaf spot, brown spot and ragged leaf spot, but it is not specifically labeled for these. However, the greatest pressure for these diseases is after topping, so in reality, Acrobat MZ protection against these late season leaf spots depends on when they develop in the crop. Also, it has not proven effective in the control of target spot in the field.
DITHANE DF RAINSHIELD is labeled under a state label, 24-c for use in the field, that expires December 31, 2004. A copy of that label can be found at http://www.cdms.net/ldat/ld4EA004.pdf. This special state label for the field was needed mainly to have a mixing partner for use with other foliar fungicides. Dithane DF applications need to be made as with Acrobat MZ but the rate is 1.5-2.0 lbs/100 gallons of water in weekly foliar sprays for blue mold prevention. To be effective, the fungicide mixture must be applied to achieve complete coverage of the plant's foliage. Sprays should be discontinued when the threat of blue mold no longer exists. This spray program will also assist in early season control of frogeye, brown spot and ragged leaf spot, but not target spot. The preharvest interval between last application and harvest is 30 days.
STREPTOMYCIN 17-21% [sold as Agri-Mycin 17, Agri- Strep 21, and others] @ 0.5 to 1.0 lbs/ 100 gallons of water is labeled for control of angular leaf spot and wildfire under a national label. Rarely is this material needed in the field, but if serious levels of angular leaf spot persist, then control can be achieved in most cases with streptomycin, if it is applied with a good sprayer. It has some systemic activity, but good coverage of at least one side of the leaf is important. If the disease is active at the time of the application, make the first spray at 1.0 lbs/ 100 gallons (200 ppm) then shift to lower rates until control has been achieved. These sprays may be repeated at 5 to 7 day intervals. For best results, make these applications late in the day or at night. Streptomycin is also labeled for control of blue mold, but we have had limited success in the lab and field against current isolates of blue mold using Streptomycin. Some isolates are streptomycin-sensitive, however. Because bacterial diseases normally develop under very wet conditions in rapidly growing tobacco, having soil conditions to support spray equipment is often the limiting factor unless sod drive- strips are present.
For the latest blue mold status and other tobacco disease information, check the KY Blue Mold Warning System online.
For more information about tobacco pests, visit "Insect Management Recommendations".
For information about corn pests, visit
"Insect Management Recommendations".
As of 4/26/04, alfalfa weevil degree-day totals range from 528 at Princeton to in northern Kentucky. Consequently, weevil development ranges from nearly complete to just hitting maximum feeding. Check fields closely for tip feeding and the presence of the small light green weevil larvae in plant tips. Early harvest or application of an insecticide should be considered if 25% or more of the tips are being eaten and there are 2 or more live larvae per stem.
Early harvest can be an excellent option if alfalfa is in the 30% bud stage or greater. If this technique is used, then the field should be examined for damage to re-growth by lingering larvae or adults.
Insecticide applications usually fit best when weevil numbers are high and harvest is several days away. These situations call for a quick knock down without need for long residual protection. Many insecticides have a range of rates and harvest intervals that allow selection of an optimum combination. Also, pyrethroid insecticides (permethrin, cyfluthrin, z-cypermethrin, and l-cyhalothrin) generally perform better than organophosphate insecticides when temperatures are cooler than normal.
See Insect Recommendations
for more alfalfa pest recommendations.
On April 16, 2004 EPA granted Kentucky's section 18 request to allow the use of Folicur 3.6F on wheat to suppress Fusarium Head Blight (FHB) and Deoxynivalenol (DON) accumulation in harvested grain. Folicur use was approved for the period April 20 to May 20, 2004. In any given field, applications may be made over an approximately 7-day period beginning at full head emergence (Feeke's stage 10.5) through and including early bloom (Feekes's stage 10.51).
I gave many specific details on the proper use of Folicur in last week's issue of Kentucky Pest News (http://www.uky.edu/Agriculture/kpn/kpn_04/current.htm ). Presently, we are watching and waiting. Some wheat in southern Kentucky is now in bloom. The rest of the wheat in the state will follow over the next 15 days or so. I have been following the Head Blight Prediction Center's (http://www.wheatscab.psu.edu/) FHB forecast for different parts of Kentucky since April 14. Overall, we have had periods of time in various parts of the state that would have been favorable for FHB if wheat had been in flower. I suspect that those conditions have also been favorable for spore production by the causal fungus, Fusarium graminearum. Thus, we appear to be set up for a serious epidemic, state-wide, if temperature and moisture conditions are above average over the next 10 to 15 days. In almost every year some fields are severely damaged by FHB. I would encourage you to monitor the above web site daily during this period to determine the FHB risk for your area. If the risk is moderate to high, you may consider spraying with Folicur as a disease suppression tool. The use of Folicur represents your last line of defense against FHB and DON until crop harvest.
See "Insect Management Recommendations" for more wheat pest information.
Achieving good weed control in grain sorghum is a challenge, and the outcome is often dependant on decisions made early in the season.
Avoid Problem Fields
Avoid weedy fields, particularly those with johnsongrass, shattercane, or perennial broadleaf weeds. Troublesome weeds are especially difficult to control in grain sorghum; therefore, work on the problem fields while in rotation with soybeans or corn before going to grain sorghum.
Preplant Burndown Control
Herbicides commonly used for burndown weed control in grain sorghum include Gramoxone Max or products containing glyphosate. Banvel and Clarity are examples of dicamba products that must be applied at least 15 days prior to planting grain sorghum for burndown control of broadleaf weeds, especially clovers or certain perennials.
Preemergence Broadleaf Weed Control
Atrazine is commonly used in preemergence applications for controlling a broad spectrum of annual broadleaf weeds in grain sorghum. The rate of atrazine is dependant on a number of factors and should not exceed 2 lb ai/A. Although crop injury can occur from atrazine, it is rarely a problem in Kentucky. Situations that may enhance the risk of injury due to atrazine include high rates, high soil pH, sandy soil, or shallow planting. Follow label restrictions concerning setbacks and atrazine rates to help protect ground and surface water.
Preemergence Grass Control
Products approved for preemergence annual grass control in grain sorghum are included in the following list with their active ingredients:
|Single Ingredient Products||Premixes|
Dual II Magnum (S-metolachlor)
Micro-Tech or Intrro (alachlor)
|Bullet (alachlor + atrazine)
Bicep II Magnum (S-metolachlor + atrazine)
Bullet (alachlor + atrazine)
Cinch ATZ (S-metolachlor + atrazine)
Guardsman Max (dimethanamid-P + atrazine)
In order to use these herbicides in grain sorghum, the crop seed must be coated with a protectant or safener by the seed company. Concep III (fluxofenim) is an example of a safener commonly used. Sever crop injury will likely occur if these herbicides are applied to fields where grain sorghum seeds were not properly treated with the protectant. The protectant enhances the sorghum's ability to metabolize the herbicide during seed germination and seedling emergence.
Using these herbicides at reduced rates is not a good practice for controlling annual grasses, particularly where fields are heavily infested or have fall panicum. There are no postemergence grass herbicides that can be used as a "back up" where preemergence herbicides fail; therefore, it is important to use the rate recommended for your situation.
Prowl or Prowl H2O (pendimethalin) in combination with atrazine is approved as an early postemergence treatment only after grain sorghum has reached the 2 - leaf stage and before weeds exceed 1 inch in height. Do not apply Prowl or Prowl H2O preplant incorporated or preemergence in grain sorghum as severe crop injury can occur. In order to minimize the risk of crop injury, the seedbed should be firm and free of clods and there should be adequate tillage to provide good seed coverage. Grain sorghum seed should be planted at least 1½ inches deep. Weed control may be less than optimum if rainfall does not occur within 7 days after application.
Gray mold, caused by the fungus Botrytis cinerea is a
serious disease of strawberry. During wet growing
seasons, gray mold can decay a high proportion of fruit in
the strawberry bed, causing direct yield losses.
Management of gray mold requires good cultural practices
and timely fungicide applications.
Good cultural practices can reduce disease pressure. If disease pressure is decreased, then the need for fungicide decreases and the effectiveness of the fungicides that are used increases. Some of the non-fungicidal alternatives for gray mold management, include the following:
After taking measures to reduce disease pressure, fungicides should be considered. Benlate (benomyl) and Topsin-M (thiophanate methyl), can be very effective against Botrytis, as long as the Botrytis fungus isn't resistant to them. Elevate (fenhexamide) and Switch (cyprodinil + fludioxonil) are also highly effective against gray mold. Protectant fungicides such as captan and thiram and strobilurin fungicides such as Cabrio (pyraclostrobin), Pristine (pyraclostrobin + boscalid), and Quadris (azoxystrobin) are moderately effective and where good cultural practices have been used will manage gray mold quite well.
Gray mold infections usually occur during bloom, so sprays need to be applied now, while strawberries are in flower. Two or three fungicide applications at bloom time (early bloom, mid-bloom, late bloom) are more effective in stopping gray mold than fungicide applications made after fruit begins to form and ripen. Commercial growers should consult U.K. Cooperative Extension Publication ID- 94, Midwest Commercial Small Fruit and Grape Spray Guide 2004 for disease management details.
Early in the season it is important to get the seedlings and vegetable transplants off to a good start. Cool weather after transplanting or seedling emergence can cause young plants to remain vulnerable for longer periods of time. Scouting, use of economic thresholds, and rescue treatments are the primary strategies for managing most of these pests in the early season. There are a few early season insects that need to be managed to ensure healthy stands.
Cole crops (Cabbage, Broccoli, Cauliflower)
Striped flea beetles, imported cabbageworm and diamondback moth larvae are the pests that attack the spring crop. With flea beetles on seedling plants, less than 4 to 5 true leaves, use a threshold of an average of two beetles per plant when deciding whether or not to spray. A threshold of 15 percent infested plants can be used with worms until either head-fill or crown formation, then the threshold drops to 5 percent infested plants. While the type of mixture of worms it is not important when deciding if to spray, the types of worms will determine which insecticides are used.
Corn flea beetles and cutworms are the two primary pests that will attack seedling corn. Use 3 percent cut plants with cutworms actively feeding as the guideline for treating cutworms. Flea beetles can transmit the bacterium that causes Stewart's Wilt, so wilt resistant cultivars may be needed in years following mild winters. If corn flea beetle is common, use a 50 percent of the plants with leaf scars and some leaves turning white as the threshold for spray decisions.
Tomatoes and Peppers
Tobacco and potato flea beetles will attack both tomato and pepper plants. Usually, the plants will quickly outgrow moderate damage. Occasionally, serious damage can occur to plants less than six inches. Use 4 or more beetles per plant and plants less than 6 inches as the guideline for treatment. Colorado potato beetle can also do serious damage to tomato plants less than 8 inches. Use 10 beetles per 20 plants as the guideline for treatment when the plants are less than 8 inches.
Eggplant and Potato
As with tomato, flea beetles and Colorado potato beetle are serious early season pests of potato and eggplant. Use the same threshold for tomatoes above. Resistance to insecticides continues to be a serious problem for Colorado potato beetle. Because of this, producers should not use insecticides with the same mode of action for consecutive generations of this insect. Often local populations of this insect may be resistant to one group of insecticides, and in other areas they may be resistant to others. For this reason, what works well in one county may not work at all in another. ID-36 lists the insecticides for Colorado potato beetle control and the chemical classes they belong to.
Squashes, Cucumbers and Melons
Striped and spotted cucumber beetles can attack cucurbit crops anytime after seedling or transplanting. Cucumber beetles also transmit the bacterium that causes bacterial wilt. For this reason, cucurbit crops must be treated for cucumber beetles as soon as they are planted. With bacterial wilt susceptible crops, cucumber beetles need to be effectively controlled through the start of flowering. Many growers are using preventive systemic insecticides for cucumber beetle and squash bug control in place of foliar treatments early in the season. Keep in mind that cucurbits are insect pollinated, so measures need to be taken to control the beetles and avoid hurting pollinators with foliar sprays. One method to avoid injuring pollinators during bloom is to spray in the early evening after pollinators have quit. Systemic treatments at transplanting should have little effect on pollinators. The flowers that are open will be closed the next day and new blooms free of insecticide on the inner surface will be open the following day. Squash bug is now known to persistently transmit the agent that causes yellow vine. Therefore, we need to preventively treat for squash bug as we do for cucumber beetles.
Few outdoor encounters are as disconcerting as finding an attached tick. Besides their repulsive appearance, ticks inflict bites that cause itching and irritation. A small percentage may also transmit diseases affecting people, pets and farm animals. This column will help you answer some of the more common questions about ticks and the diseases they may transmit.
Q: Where do ticks come from and how can I avoid them?
A: Ticks thrive in woods, uncut fields and brush. They climb onto lower portions of vegetation and attach to a suitable host passing by. To reduce tick encounters, follow these precautions:
1. Don't walk through uncut fields, brush, and overgrown areas, especially during April-July. Walk in the center of mowed trails to avoid brushing up against vegetation. When hiking or camping in tick-infested areas, wear light- colored clothing and long pants tucked into boots or socks, and consider using tick repellent.
2. Inspect family and pets after being in tick-prone areas. Ticks often attach at the waist, armpit, neck and scalp, but can attach virtually anywhere. Promptly remove any ticks, using the method discussed below.
3. Keep grass and shrubs trimmed, and clear overgrown vegetation from edges of your property. Ticks and their wild hosts will not normally infest areas that are well maintained. Treating the lawn with insecticides is of little benefit since mowed areas are not normally infested. If insecticides are used, treatment should be concentrated mainly along borders and fences, and between overgrown areas and the lawn. A good way to confirm if ticks are present is to drag a white flannel cloth or sheet through suspected areas. Ticks will attach and be visible against the white background.
Insecticide sprays containing pyrethroids (e.g., Bayer Advanced Home/GardenJ Multi-Insect Killer, Spectracide TriazicideJ, Ortho Home Defense SystemJ) or carbaryl (Sevin) are effective. Such products are sold at hardware/lawn and garden shops. For better wetting and coverage of vegetation, it's often best to purchase these products as concentrates, so that they can be diluted and applied with a hose end or pump up sprayer, etc. A single application during late-April/May, or when ticks are detected, is often all that's required.
4. Free-roaming pets are more likely to become infested than if confined. Ticks on pets can be controlled or prevented using sprays, spot-ons, and insecticide- impregnated collars. See your veterinarian for appropriate products.
Q: What's the best way to remove an attached tick?
A: Using a tweezers, grasp the tick as close to the skin as possible and pull it straight out with gentle even pressure. Petroleum jelly, hot matches and other "folk" methods of removal should be avoided. Wash the bite area, apply antiseptic and cover with a Band-Aid. Attached ticks should be removed promptly to reduce the chance of infection and disease transmission.
Q: Some clients use the terms "deer tick" or "turkey
mite" ... what are they referring to?
A: These terms are often used when referring to immature (larval) lone star ticks, a common tick throughout much of Kentucky. A person who walks through infested vegetation may find hundreds of the tiny ticks (about the size of the period at the end of this sentence) crawling on them. Unattached larvae can be removed by bathing or showering. However, once ticks are attached, removal is difficult, and their bite can be very irritating. The lone star tick is not considered to be a vector of Lyme disease, although it can transmit Rocky Mountain spotted fever.
Q: Should I be concerned about getting Lyme disease or
Rocky Mountain spotted fever?
A: Each year about 20 to 40 cases of Lyme disease/Rocky Mountain spotted fever are reported statewide. Some of these victims may have been infected while traveling out- of-state. In Kentucky, probably tens of thousands of people are bitten by ticks each year; so the likelihood of contracting a disease is very low. In most cases, a tick must be attached for at least 18 to 24 hours for infection to occur. One cannot become infected simply by having a tick crawl over their skin or clothing. Concerned callers should be informed of the early symptoms of tick-borne disease, so they will know whether to seek medical attention.
Q: What are the symptoms of Lyme disease?
A: Lyme disease is difficult to diagnose clinically because early symptoms mimic the flu, e.g., fatigue, headache, fever, or swollen glands, pain or stiffness in the neck, muscles or joints. The most definitive early symptom is a gradually expanding, circular or oval-shaped red rash, often (but not always) at the site of the bite. This rash only develops in about 70% of infected individuals, however, and may be overlooked. Persons, who experience any of the above symptoms after being bitten by a tick, or after spending time in an area where ticks are abundant, should see a physician immediately. In the early stages, Lyme disease can be successfully treated with antibiotics.
The mechanism by which Lyme disease is transmitted in Kentucky is unclear. The primary tick vector, Ixodes scapularis, has rarely been found here, although several of the ticks were found recently while surveying deer herds in southeastern (McCreary Co.) Kentucky. More probably will be found in the future.
Q: What are the symptoms of Rocky Mountain spotted
A: Symptoms of RMSF are flu-like, accompanied by headaches and a very high fever (104-106 degrees F), two to 12 days after being bitten by a tick. The most characteristic sign of RMSF is a rash that appears on about the second to fifth day on wrists and ankles, later spreading to other parts of the body. When promptly diagnosed, RMSF can be successfully treated with antibiotics. In the absence of treatment, victims may die.
Q: I don't have a rash but still feel "crummy"-are there
other tick-borne diseases I should be concerned about?
A: Tick bites can result in diseases other than Lyme disease and Rocky Mountain spotted fever. Human ehrlichiosis is one important, emerging disease complex, believed to be transmitted by the species of ticks (e.g., lone star tick) common in Kentucky. Symptoms of ehrlichiosis in humans include fever, headache, chills, muscle aches, nausea, and vomiting. There is usually no rash. Early treatment with antibiotics is generally prescribed. Localized itching and irritation are rather common at the site of a tick bite. But when in doubt, it probably pays to see a physician. (For more information on this topic, see ENT-35, Ticks & Disease in Kentucky).
Q: How important is Rocky Mountain spotted fever?
A: Rocky Mountain spotted fever (RMSF) has not received the media attention of Lyme disease, but it is potentially more serious. Each year there are about 10 to 30 cases reported statewide. The primary vector of RMSF is the American dog tick, although lone star ticks can also transmit the disease pathogen.
Symptoms of RMSF are flu-like, accompanied by headaches and a very high fever (104-106 degrees F), two to 12 days after being bitten by a tick. The most characteristic sign of RMSF is a rash that appears on about the second to fifth day on wrists and ankles, later spreading to other parts of the body. When promptly diagnosed, RMSF can be successfully treated with antibiotics. In the absence of treatment, victims may die. In most cases, the tick must be attached for at least a day for infection to occur. (For further information, see ENT-35, Ticks & Disease In Kentucky).
There are a number of turf fungicides the activity of which is based on the phosphite (=phosphonate) ion (PO3-). Chipco Signature fungicide (active ingredient fosetyl-Al) is the most common, and has become a "keystone" product for disease control programs on many golf courses across the country. This is in part because of the general enhancement in quality on stressed turfgrass that has been reported in some studies, including selected tests at the University of Kentucky. The product is also known to provide control of Pythium cottony blight in many circumstances, particularly when sequential applications are made. Other phosphite fungicides marketed for turf include Magellan, Resyst, Alude, Prodigy Signature, and Vital.
These fungicides are unusual in that they control diseases in two very different ways. They do have some direct toxicity to the fungus, much like all conventional fungicides which somehow poison the target fungus. However, phosphite fungicides also enhance the plant's natural defense mechanisms, which is not true for conventional fungicides. Because these fungicides attack fungi on "multiple fronts", the general belief among plant pathologists has been that they are less subject to fungicide resistance than most other systemic fungicides. And in fact, field experience has been consistent with this. Cases of failure of disease control by phosphite fungicides due to fungicide resistance have been rare.
However, fungicide resistance is not an impossibility with this group of fungicides. This point was made clear in a recent paper on lettuce downy mildew (Plant Disease, Volume 88, pages 502-508). (Although lettuce downy mildew in California may seem to have no relevance to Pythium cottony blight of turf in Kentucky, there are significant biological similarities.)
In the paper, the authors reported about recent failures of fosetyl-Al to control lettuce downy mildew in commercial fields in the Salinas and Santa Maria Valleys. They conducted a series of experiments that show evidence of resistance to normal field rates of the fungicide. The "resistant" isolates obtained showed varying degrees of resistance, ranging from some that were still partially sensitive to normal field rates of the fungicide, to other isolates that were essentially insensitive at normal field rates. Their data, as well as another research report I have seen, suggest that isolates resistant to phosphite fungicides may be ecologically "fit". This means that, once resistance occurs, the fungal population possibly will remain resistant even if fosetyl-Al and similar materials are not used for a period of time.
In the study, the authors noted two factors that may have been involved in the selection of resistance to phosphite fungicides.
1. Repeated use of fosteyl-Al (or similar fungicides) over
the past decade.
2. Regular applications of fertilizers which provided phosphorous in the form of phosphite rather than the more common phosphate. This may have speeded selection towards resistance by exposing the pathogen population to frequent, low doses of phosphite.
Significance to Turf
This report, and a few others in the scientific literature, indicate that field resistance to phosphite fungicides is a definite possibility. Such resistance may take a period of years to develop at any particular site. How many years? There is no way to accurately predict this, because there are so many complex and interacting factors that influence this. However, I see this report as a reminder to remain aware of the possibility when using these fungicides.
This report of resistance does complicate disease management on golf courses somewhat. It is a common practice during the summer on many courses to spray putting greens every two weeks with Chipco Signature, tank-mixed with one of a number of other fungicides (usually iprodione or chlorothalonil). Such a program generally provides very good control of a number of important diseases, such as brown patch, dollar spot, and Pythium. It also sometimes provides improved turf quality unrelated to these diseases when stressful conditions hit.
This research report serves as a yellow flag with respect to these spray programs. It would be wise for golf course superintendents to continue to find ways to rotate among fungicide products, and to not rely exclusively during summer on phosphite-based spray programs. Also, it may be wise to avoid frequent use of both phosphite-based fertilizers and phosphite-based fungicides on the same sites.
With prolonged rains last week, cedar trees (mostly Juniperus virginianae) were seen to be decorated with rust fungi in many locations statewide. Cedar-apple rust (Gymnosporangium juniperi-virginianae) was most visible while displaying large galls decorated with masses of bright orange gelatinous spore horns. Cedar-hawthorn rust (Gymnosporangium globosum) with smaller galls and orange spore horns could be found on many cedars. Less conspicuous, but omni-present, cedar-quince rust (Gymnosporangium clavipes) also decorated leaves and swollen twigs of cedar trees with smaller orange spore masses.
Expect symptoms of these cedar rust diseases to appear on leaves, twigs and fruit of their alternate hosts, apple, flowering crabapple, and hawthorn in the coming weeks.
Field size production of sunflowers is sometimes grown in Kentucky and broadleaf weed control options have been limited. The EPA has recently granted a registration for use of SPARTAN 4F herbicide on sunflowers. As a soil- applied herbicide Spartan can help provide control of broadleaf weeds such as Eastern black nightshade, common lambsquarters, annual morningglories, and smooth pigweed. Spartan may be tank mixed with other soil-applied herbicides labeled for use on sunflowers.
Spartan can be applied to the soil surface in the spring as an early preplant application prior to planting up to 3 days after planting (before sunflower seedlings have broken the soil surface). It may also be applied as a preplant incorporated treatment if shallowly incorporated in the soil no deeper than 2 inches. Use rates may vary from 4 to 6 fl.oz. per acre depending on soil texture, organic matter, and soil pH. Some adverse crop response may occur on course textured soils with low organic matter (less than 1.5%) and pH >7.0. Inadequate seed furrow closure or shallow planting may result in undesirable crop response. Consult other label requirements regarding future crop rotations and other use precautions.
Samples diagnosed recently included problems from soil compaction and fertilizer burn on wheat; heat injury and Pythium root rot on tobacco; iron toxicity on greenhouse geranium; impatiens necrotic spot virus, low fertility, and spider mite infestation on greenhouse impatiens; and growth regulator injury on tomato transplants. On landscape samples we have seen white pine decline (Eastern white pine), pine needle rust (Loblolly pine) and tip blight (Scots pine); Verticillium wilt on maple; and Pythium root rot on turfgrass.
|UKREC-Princeton, KY, April 16 - 23, 2004||Black Cutworm
||European Corn Borer
For information on trap counts in southern Illinois visit the Hines Report at - http://www.ipm.uiuc.edu/pubs/hines_report/index.html. The Hines Report is posted weekly by Ron Hines, Senior Research Specialist, at the University of Illinois Dixon Springs Agricultural Center
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.
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