As we are approaching tassel emergence in some early-planted corn fields in the western part of the state, fall armyworm is beginning to be detected infesting whorl stage corn. Although these infestations were far below economic thresholds for treatment, producers should begin to monitor for this pest. Fall armyworm can be one of the more difficult insect pests to control in field corn. Late planted fields and later maturing hybrids are more likely to become infested.
Fall armyworm causes serious leaf feeding damage, as well as direct injury to the ear. While fall armyworms can damage corn plants in nearly all stages of development, they will concentrate on later plantings that have not yet silked. Like European corn borer, fall armyworm can only be effectively controlled while the larvae are small. So early detection and proper timing of an insecticide application are critical.
Fall armyworms vary from light tan to black with three light yellow stripes down the back. There is a wider, dark stripe and a wavy yellow-red blotched stripe on each side. Four dark spots, arranged in a square, can be seen on the top of the eighth abdominal segment.
Fall armyworms resemble both the armyworm and the corn earworm, but the fall armyworm has a white inverted "Y" mark on the front of the dark head. The corn earworm has a orange-brown head, while the armyworm has a brown head with dark honeycombed markings.
Larger fall armyworm larvae consume a lot of leaf tissue, resulting in a ragged appearance to the leaves similar to grasshopper damage. Larger larvae are usually found deep in the whorl often below a "plug" of yellowish brown frass. Beneath this plug, larvae are protected somewhat from insecticide applications. Plants often recover from whorl damage without any reduction in yield. However, larvae will also move to the ear as plants begin to tassel and young ears become available. The ear may be partly or totally destroyed. Damage to the ear may be much more important than leaf damage.
For more IPM information, see ENTFACT 110,
Fall Armyworm.
See ENT-16, Insecticide recommendations
for Field Corn for control recommendations.
European corn borer levels are highly variable among fields. Some producers in the western part of the state have reported early-planted fields with treatable infestations. However, the worst infestations have been reported in sweet corn. Because European corn borer is so highly variable among fields, producers are advised to monitor each field in order to make corn borer management decisions.
Producers also should begin to monitor for first generation southwestern corn borer. Strong moth flights last week in some western Kentucky counties indicate that they should be about two to three weeks behind European corn borers. For more information, see ENTFACT 108, Southwestern Corn Borer.
When postemergence herbicide applications are used as part of a weed management program the type and size of weeds present, crop growth stage, interactions of the herbicide with the environment, and several other factors, need to be considered. Some of the most important ones are highlighted below. 1) Timing of the herbicide application. Applying the herbicide treatment at the right time is just as important as picking the right herbicide or combination of herbicides to use. Scout the field to determine the type and size of weeds that are present. Look for the density and distribution of the weeds present. In general, optimum weed control is obtained with postemergence herbicides when weeds are small and actively growing. Larger weeds can be much more difficult to control.
2) Choosing the herbicide. The most effective herbicide product(s) to use will depend on the type and size of weeds present. Also, the size or stage of crop growth may limit the use of some herbicide products.
3) Tank mixtures. When tank mixing two or more herbicides together to make one application, make certain that the herbicides are compatible within the spray tank or they do not cause antagonism. Antagonism between herbicide products can reduce the effectiveness of one or more of the herbicides applied. In some cases, such as for the control of both grasses and broadleaf weeds in a field, a sequential application 7 to 10 days apart often provide the best results. Risk of crop injury may also be increased when certain herbicides are applied as a tank mixture.
4) Application Rate. The application rate for the herbicides used also depends on the type and size of weeds present, the tank mixture used, and/or the stage of crop growth. The spray volume (or gallons per acre) may need to altered depending on the herbicide products used.
5) Use of additives. Additives such as a non-ionic surfactant or crop oil are often used with many postemergence herbicide products to improve their penetration through the leaf surface and/or to serve as a spreader. A liquid nitrogen fertilizer solution is sometimes recommended in addition to surfactant or crop oil to improve the activity for certain weeds such as velvetleaf. Choosing the right additive for the spray tank can sometimes create a lot of confusion. Consult the herbicide label to select the right additive for the herbicide or herbicide combination to be used.
6) Environmental conditions. Weeds that are stressed due to hot/dry weather can be harder to kill. Also, crops under stress have a greater potential for herbicide injury with some products. Other extremes in environmental conditions, such as wet field conditions can prevent applications from being made on a timely basis. Expected rainfall soon after application can wash the herbicide off the plant; thus, reducing its effectiveness. The rain free period suggested for many products range from 1 to 8 hours, depending on the herbicide.
7) Drift and nearby susceptible plants. As a rule, avoid applications when wind speed exceeds 10 MPH or temperatures are above 85 F. Under these conditions the potential risk of herbicide injury to nearby susceptible plants is greatly increased due to volatility and/or drift from certain herbicides.
8) Sprayer cleanup. The spray equipment should be thoroughly rinsed and cleaned immediately following a herbicide application. This includes flushing the tank, hoses, screens, and nozzles with clean water. In some cases running a cleaning solution, such as household ammonia, through the system is needed. Many of the herbicide labels discuss proper sprayer cleanup after use of a product. Sprayer cleanup is critically important when applying a herbicide on one crop and using the same equipment to treat another crop.
In summary, postemergence herbicide applications can be an effective tool for managing some weed problems. Choosing the right time for the application is just as important as choosing the right herbicide or herbicide combination. Finally, be aware of environmental conditions before and after making a postemergence herbicide application.
This is a critical time to check for potato leafhoppers (PLH) in fall- or spring-seeded fields. A 15" diameter sweep net is needed to get an accurate picture of field infestations. You may be able to borrow one of these from your county extension agent for agriculture. Treatment guidelines are based on plant height and the average number of leafhoppers per sweep (or total per 100 sweeps). See ENT-17, Insecticide Recommendations for Alfalfa, Clover and Pastures- 1998.
A June 12 check of a Fayette county alfalfa field seeded in mid-May produced 55 PLH per 100 sweeps. This is right at the treatment threshold for PLH considering the 3.5" to 4" tall plants in the field. There was no sign of hopperburn or stunting but these are sure to develop if nothing is done because it is a long time until harvest.
All of the leafhoppers in the sweep samples were adults but nymphs will be present soon. Sap feeding by both nymphs and adults produces the wedge-shaped yellow tip on alfalfa leaves and can cause stunted plants.
The following table presents data from forage entomology research specialist John Parr's 1997 insecticide evaluation plots. The percent control figures in columns representing days after treatment are calculated based on the reduction in numbers of leafhopper per sweep in treated and control plots for that date.
Comparable performance would be expected from Pounce and Ambush (not in the trial). Warrior has been very good against PLH in previous trials but was not included in the 1997 test.
Percent Control | On Days | After Treating | ||
Product | Rate per Acre | |||
____________ | ____________ | ______________ | ____________ | ____________ |
Baythroid | ||||
Pounce | ||||
Pounce | ||||
Cygon |
Except for Cygon (dimethoate), all of these products reduced PLH numbers by more than 90%during the first 7 days of the test. Cygon may be used at up to 1 pt per acre and a higher rate would be expected to provide better control.
Potato leafhoppers on the second and third cuttings With the high initial leafhopper numbers in the state, regrowth following the first and second cuttings from established fields should be monitored. The critical time period for this is 10 to 14 days after harvest. If leafhoppers are at or above treatment guidelines at this point, a prompt treatment is needed. If an insecticide application is applied more than 14 days after harvest, it is unlikely to prevent a loss in hay quality because the damage has been done already.
Blue mold activity continues to increase in western, southern, and central Kentucky, with the level of activity being highly variable. It has been confirmed as far north as Henry Co., and east to Bath Co. County Extension Agents report greatest damage is to transplant production, especially damaging to traditional beds still under cover where little preventive fungicide has been used. They indicate that most damaging field outbreaks are traceable to setting of infected transplants. Weather conditions during the past 10 days have been highly favorable to support rapid spread and development and have greatly complicated spraying activities. By noon on June 15, county agents were indicating they could find evidence of newly developing activity in the field and beds of east central Kentucky. I suspect blue mold is now present statewide, even though not reported that widely yet!
Dr. Bill Maysymowicz, Extension UK Tobacco Specialist located at the Research and Education Center in Princeton, stated that blue mold is probably much more widespread and potentially damaging in western Kentucky than is being estimated. He said: " I do not want to be an alarmist about this, but too many (with both burley and dark) are underestimating the potential impact of what blue mold can do, now and later in the season, with it so strongly established this early in the season. Although a lot of direct damage may not have occurred yet, the disease's potential to damage is great. Furthermore, most are not appreciative of the importance this extra element of time brings. First, the contribution of systemic blue mold has been grossly underestimated. It is going systemic in dark and we have almost no experience with systemic blue mold in dark tobacco. Also, people want to stop worrying about blue mold when a day or two of hot, sunny weather appears rather than using that time to catch up and get everything sprayed well."
The least blue mold activity so far this season is in central, northern and eastern Kentucky, the three regions hit hardest the past three years with blue mold. Although this pattern is in part related to luck of weather and other circumstances, County Extension Agents report widespread and time use of fungicides in transplant operations in these regions than has normal. Growers have responded to control recommendations for local transplant production and regular fungicide programs in transplant systems. However, even in these regions, there is still a large number of growers doing nothing to prevent blue mold. By now, the volume of inoculum is great enough that their first notice could be loss of a bed.
Foliar fungicide use in the field is low statewide, according to County Agents. In part, this is due to wet field conditions, but in too many cases direct management decisions have been made to not start spraying fungicides in the field until other timely farming operations have been completed. In several cases, this delay will cost the growers half the yield potential, because blue mold is going systemic when some timely sprays could have prevented this loss. Several County Agents report considerable disappointment in trying to cope with advising growers about this situation. Most growers just do not believe there is a need to spray until the level of blue mold activity is high in the community. Several agents have indicated that growers have just not accepted the idea that foliar fungicides must be used preventively to control blue mold. Many growers feel this is a sales, gimmick, and are not convinced by research data. Others, indicated there is just too much hard work and cost to the foliar fungicide approach. Still others, claim they just cannot fit foliar spraying into the many other things they must get done at this time of year. The bottom line, is that routine fungicide application in fields is basically not occurring, except on a few individual farms.
Laboratory tests indicate the blue mold operating in Kentucky is resistant to the active ingredients in Ridomil and Ridomil Gold, but very sensitive to dimethomorph, a component in Acrobat MZ. Earlier, we had reported that the isolates from Estill Co. were metalaxyl sensitive, but with time, these isolates proved resistant to Ridomil. It just took the fungus about 12 days to develop on the treated material. However, in repeat tests with the spores collected from the metalaxyl-treated tissues, the Estill Co. isolates showed resistance to Ridomil within 6 days.
Foliar fungicide spray programs should be maintained at five-day intervals in all transplant production systems in the state. Field sprays should be started in all counties with active blue mold, as well as in neighboring counties. With the number of unknowns involved, spraying of newly set fields throughout the state, irrespective of how close they are to known sources, is reasonable and prudent at this stage of the season. Acrobat MZ @ 2.5 lbs/100 gallons and Dithane DF @ 1.5-2.0 lbs/100 gallons are the two fungicides labeled for field use in Kentucky. The volume should be adjusted for crop stage with Acrobat MZ. Good coverage of the entire plant's foliage, stem, and bud is critical with both fungicides. Excellent coverage is achievable with high-pressure sprayers equipped with hollow-cone nozzles on drops. However, while the tobacco is small, good coverage may be possible with less sophisticate spray equipment. Failure to apply these fungicides correctly will result in little control and high input costs. In contrast, a very high level of control is possible with proper application of Acrobat MZ and moderate control is possible with Dithane DF. However, economic benefit is not achievable with foliar fungicides in crops with low yield potential, because of the high input costs associated with frequent foliar fungicide applications.
BLUE MOLD WATCH EXISTS STATEWIDE AND
WARNING exists for
the following State Extension Areas:
Purchase, Pennyrile, Green
River, Mammoth Cave, Lake Cumberland, Lincoln Trail, and Fort
Harrod.
Blue mold has been confirmed in the following Extension
Areas/Counties:
PURCHASE AREA: Calloway and Graves.
PENNYRILE AREA: Caldwell, Christian, Muhlenberg and Todd.
GREEN RIVER AREA: Daviess, Hancock, Henderson, McLean, Ohio,
and Webster.
MAMMOTH CAVE AREA: Allen, Barren, Logan, Monroe, Simpson,
and Warren.
LAKE CUMBERLAND AREA: Casey, Clinton, Cumberland, Pulaski,
Taylor, and Wayne.
LINCOLN TRAIL AREA: Hardin and Washington.
FT. HARROD AREA: Jessamine and Lincoln.
BLUEGRASS AREA: Clark, Estill, and Fayette.
LOUISVILLE AREA: Henry
NORTHERN KY AREA: none
LICKING RIVER AREA: Bath
NORTHEAST KY AREA: none
QUICKSAND AREA: none
WILDERNESS TRAIL AREA: none
The URL address is:
http:
//www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm