June 4, 2002 Supplemental Report
Wind patterns have changed during the past 24 hours, such that blue mold spores could be arriving from the southeast into southern Kentucky. The following statement was released on June 3 by the Blue Mold Forecast Center at NC State University. “ Trajectory events from southern GA and northern FL will impact growing regions in the TN and OH river valleys. There is Moderate Risk for eastern TN, southeast KY, and extreme southwest VA.” Blue mold activity continues to build in the southeast. If this event materializes, we could expect to see first symptoms during the weekend or early next week.
June 3, 2002 Report
Blue mold continues to spread northward in flue cured production areas, with activity being reported now from northern Florida, through Georgia and the Carolinas into southern Virginia. The disease is also active at low levels in seed beds in southern Pennsylvania's production. That region of Pennsylvania was directly in the spore-path several times during May while we were west of the predicted routes of travel. I am aware of no blue mold activity occurring in any burley production area of the USA, even in burley production located closest to flue cured fielkds which have had more potential exposures. There has been some rumored activity, but samples submitted from the rumored events have involved other diseases or disorders, rather than blue mold.
The current blue mold outbreaks in the eastern and southern USA are a threat to our region under two conditions. One, we import plants from those areas or plants from communities where spores from those outbreaks are blowing into transplants coming into burley or dark production. Or two, there is a change to easterly or southeasterly winds. Also, if the activity builds to a higher level in Pennsylvania, we will need to be concerned about winds from the northeast - especially producers in the northeastern burley production of West Virginia, northeastern Kentucky, and southeastern Ohio. Michigan transplant producers, if they are still growing plants at this late date, will also need to remain alert to the Pennsylvania situation.
Transplanting to the field in our region remains behind the five-year average, but considerable acreage was planted last week. Some agents reported that availability of transplants has become a concern in some communities following the cold weather of late May. Regular fungicide spray schedules should be maintained in all transplant production and transplant-holding systems - See issue 943 of Kentucky Pest News (March 18, 2002) for more specifics on chemical options. However, fungicide sprays in the field are not warranted at this time for blue mold control, based on the information available to us, unless a southern transplant connection exists with the crop. However, crops should be scouted twice weekly for evidence of bacterial and fungal diseases. If sprays are needed, see issue 948 of Kentucky Pest News (April 22, 2002) for the foliar fungicide options labeled in Kentucky for use in the field. Should blue mold be found, please take immediate action to get it under control plus promptly report the activity through county extension offices to me so all growers can be alerted to the risks involved. The warning system is just as valuable during season with little or no blue mold as it is in seasons with strong or early activity, because accurate and timely reports can greatly reduce the need for fungicide use - especially with the fungicide options now available.
With the reduced potential for blue mold, it is easy to drop the guard in other areas of disease control. In the field, growers will need to remain focused on black shank control, and not under estimate the need for post-transplant applications of mefenoxam-containing fungicides (Ridomil Gold or Ultra Flourish). The potential for black shank has been greatly reduced with the major increase in crop rotation that is occurring with the sharp decline in planted acres. Some farms still have high potential for black shank due to either lack of rotation, re-contamination during flooding events, or use of infested transplants.
For the latest blue mold status and other tobacco disease information, check the KY Blue Mold Warning System.
http://www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm
The tobacco budworm is a potential problem in the earliest set fields, especially in south central and western Kentucky. Budworms feed in the bud region of
tobacco plants, chewing rounded holes in the developing leaves. As the leaves expand, the familiar large rounded holes are appear. At this point it is
usually too late to do anything that is effective. Tobacco plants usually can compensate for this damage without yield or quality loses. Feeding by this
insect can kill the bud, resulting in the development of suckers. Budworms also can tunnel into the plant, causing the stalk to break.
The trick to reducing budworm damage is to catch infestations early by carefully inspecting plant buds at least weekly. Feeding by small budworms can be detected early and the black pepper grain-like droppings are also a good diagnostic clue. Treat if you find 5 or more budworms (1/2" to 3/4~' long) per 50 plants any time prior to button stage. Budworms rarely cause damage after the button stage of development.
Tobacco hornworms can be found on tobacco in June and again in August and September. Hornworms can completely devour all of the foliage on small
plants so begin to watch for them regularly starting about 4 weeks after transplant.
Several insecticides are registered for budworm and hornworm control but proper timing is essential to get the best results. Spray coverage must target
the bud area of the plant so that the insecticide comes in contact with the budworms or they feed on leaves that have a residue of the insecticide.
Hornworms are not protected within the bud area and are easier to kill with an insecticide application.
Tips for improving budworm control -
-Good coverage of the bud area with 30 gallons or more of finished spray per acre. This will help to get the product to the pest.
-Use hollow cone nozzles placed directly over the row. Additional nozzles on 6" drops and angled in from the side will improve coverage, as well.
-Be sure the bud leaves are open when the field is sprayed. Bud leaves will close over to protect the bud during very hot periods.
Bud closure will keep the treatment from reaching the target.
-Check back in about 48 hours to evaluate the degree of control achieved. Anything over 70% should be considered good. Research trials have shown
Orthene (Acephate) and Tracer to be effective in properly timed sprays with good coverage. Thiodan (Golden Leaf Tobacco Spray) have not been as
effective against this insect.
Budworm checks now also will allow a look at the build up of tobacco aphids. These insects generally begin to build at about 4 weeks after transplant.
Soybean drills are now moving at a furious pace. Lots of beans will be up and out of the ground in a very short period of time. So, it is the time of the
season to be on guard for the bean leaf beetle.
This beetle is generally an important pest of very young soybean plants. The most dangerous time is during the cotyledon stage (seed leaves) but is also important during the unifoliate stage. Generally speaking, if the growing season is good, by the time the soybean plants put out their first trifoliate leaves, they are growing so rapidly that they will out grow any beetle damage.
It is very important to prevent damage to the cotyledons. These plant parts provide nutrition required for the plant to get started growing. If the seed leaves are damaged the plants will be less thrifty and more susceptible to all forms of pest activity. If the seed leaves are completely destroyed before the unifoliate leaves emerge the plant may die.
BLBs are abut 1/8" to 1/4" long. The body is slightly convex and the beetle is longer than wide. Color is variable, ranging from light brown to dark red, spots
and or stripes may be present or absent. However, all beetles will have a black triangle pointing backward behind the head. BLBs feed on cotyledons,
leaves and pods. Leaf feeding consists of very distinctive almost circular holes. Feeding on cotyledons and pods usually appears as scooped-out
holes in the surface.
When scouting look for areas of stand reduction or heavily damaged cotyledons. If stand is reduced on average 30% or when feeding on leaves if the defoliation level reaches 30% then treatment is warranted. A more precise scouting method and economic threshold calculation can be found in IPM-3, KY ICM Manual for Field Crops 'Soybean'. You may view or obtain this manual from the IPM web page at: http://www.uky.edu/Agriculture/IPM/ipm.htm
If insecticidal controls are warranted you may find products labeled for control in ENT-13, In your County Extension office or on our Insect Management web
site at: http://www.uky.edu/Agriculture/PAT/recs/rechome.htm
The Fusarium head blight (head scab) situation in
Kentucky this year does not approach the level of
damage we saw in 1991. However, there is a
significant amount of head blight affecting wheat in
Kentucky this spring, but the disease is highly
variable from field to field. This variation seems
mainly to do with the time of the flowering period of
each individual crop. I believe that cool temperatures
during flowering was probably the main factor that
limited infection in many fields. There are also some
varieties planted (Patton for example) which have
"Type II" resistance to head blight. This is resistance
to spread of the head blight fungi within the head
following infection. The net effect of this type of
resistance is to limit the extent (i.e., severity) of blight
in any given head. This type of resistance, which is the
only commercially available form of head blight
resistance at this time, may fail entirely if heads are
overwhelmed with numerous infection points. Most
wheat varieties grown in Kentucky are highly
susceptible to Fusarium head blight.
About two-thirds of the fields I have walked recently have a head blight incidence of 2-4 percent. However, some fields apparently flowered when conditions were highly favorable for head blight. Many of these fields have an incidence of 20-40%, and an overall field severity of 10-15%. Field severity, which is an average severity of head blight across the field, is a pretty good estimate of potential yield loss. Of course, another aspect of damage, vomitoxin and subsequent dockage or rejection of loads at the elevator, is likely for some harvested grain. We will not know the full extent of the wheat quality situation until harvest and beyond. At this point, I would encourage all farmers to get out and look at their wheat crops while (if) there is still some green in the heads. Once the heads have matured, it is much more difficult to assess the damage caused by head blight. If significant head blight damage is evident, I would encourage farmers to develop a plan on how to deal most effectively with damaged fields. This includes everything from proper combine adjustment to possible blending of grain prior to sale.
One final note related to the head blight situation. You have heard me say many times over the years that Fusarium head blight, in Kentucky, is not significantly affected by the tillage situation or previous crop. This flies in the face of what you may have heard from other sources, that head blight is significantly worse in no-till wheat planted behind corn. I have always agreed that head blight levels in no-till wheat (behind corn) may be slightly higher than its conventionally tilled counterpart. However, I have always said, and continue to believe, that the difference is minor and is not a reason to shy away from no-till wheat. Now, you might be saying those are some good words, but lets see the data to back them up. It just so happens that we did evaluate Fusarium head blight in three "farm-scale" research plots (ca. 20-acre plots) in south central Kentucky late last week. This research, funded by the Kentucky Small Grain Growers Association, is a joint effort between the University of Kentucky and two wheat consulting groups (Miles OptiCrop and Wheat Tech). In a nutshell, these plots compare tilled and no tilled wheat, behind corn, in a real world, farm scale situation. Fifty heads were randomly collected from each of four different areas from the tilled and the no-tilled plots from each of the three test sites. This method means we evaluated 200 heads per treatment (i.e., till vs no-till, with all other production factors being the same). The head blight incidence results are as follows; there was no difference in severity, so data are not reported:
| HEAD BLIGHT INCIDENCE | ||
|---|---|---|
| Field no | No-till | Till |
| 1 | 21.5 | 22.3 |
| 2 | 20.5 | 18.5 |
| 3 | 13.5 | 17.5 |
| AVERAGE | 18.5 | 19.4 |
In addition to these specific results we have also observed and compared no-till and conventional wheat this spring in variety test plots in Shelby County and Caldwell County and have not seen any difference in the levels of head blight. Furthermore, two years of survey results (1998 - 1999) across almost two hundred fields also indicated that tillage (or lack of tillage) was not a major player in determining the level of head blight which develops in a field.
The thing you must remember is that Kentucky (unlike most states in the midwest) is characterized as having a great number of small (ave. size about 33 acres), widely-scattered, corn fields. And, there is fairly good overlap between the parts of the state where both corn and wheat-for-grain are grown. Also, even where corn stubble is tilled prior to planting wheat, there remains a significant amount of corn stubble on the soil surface. Do not fall into the trap of thinking that tilled corn stubble means no stubble left on the soil surface. This is not the case. Depending on the yield of the previous corn crop, I have seen fields with as much or more corn residue remaining on the soil surface following "conventional" tillage than where the stubble was left on the soil surface (no-till).
With the above in mind, it is not difficult to imagine that there is always a large quantity of randomly- scattered corn residue around the state. This residue, in fact, is the prime source of infectious spores for Fusarium head blight. This fact is not in dispute. However, based on the wind-blown nature of ascospores of Fusarium spp, and the widespread, random occurrence of corn stubble in wheat-for-grain production areas of Kentucky, it is highly probable that all wheat acreage is within a short distance of spores of the head blight fungi when weather conditions favor spore production and infection. This is, in fact, what we see. When weather conditions favor head blight, all crops will take a hit as long as they are in a disease-susceptible stage (i.e., slightly before through slightly after flowering). "Conventional" tillage of corn stubble prior to planting wheat (which in Kentucky usually means multiple discings) will does not protect the subsequent wheat crop in any way from spores blowing in from neighboring which were not tilled.
In deference to my plant pathology colleagues in other states who may read this article, I am not saying that planting no-till wheat behind corn may not be a significant contributor to head blight in specific fields in your states. Large acreage fields and regionalized areas of wheat and/or corn production, as well as other local factors, such as rotational crops and periods, may result in more head blight in no-till wheat compared to where wheat is planted into a tilled seed bed. However, until I see data to convince me otherwise, I stand behind the statements I have made in this article.
There are a couple of other points I need to make in regard to the health of the wheat crop at this time. Wet soil, due to all the rain this spring, has damaged portions of many fields. It is a very common sight this spring to see wheat prematurely "turning" in patches or streaks which coincide with the most poorly- drained areas of individual fields. Affected plants can be easily pulled up due to the damage of the plant's root systems. The overall effect can look very much like damage due to take-all disease. However, when take-all is a factor, affected plants will have a shiny- black lesion in the vicinity of the soil line. Plants prematurely killed by wet feet will not have this black lesion.
Dr Lloyd Murdock, an Extension Soils Specialist located at Princeton, indicated to me that he is seeing most "wet feet" damage in conventionally tilled wheat crops. Apparently the drainage of surface water in no- till crops is superior to that of conventionally-tilled crops in most situations. He said this is related to the larger cracks which exist in no-till wheat. These cracks allow surface water to drain more efficiently compared with the smaller, less connected cracks which tend to exist in conventionally-tilled wheat crops. It will be interesting to see how overall yields compare between tilled and no-tilled crops this spring.
The April 29 issue of Kentucky Pest News contained an article describing some early outbreaks of the disease and some practices fo managing it. Dollar spot has increased greatly on golf turfs in Central Kentucky during the past two weeks.
Several cases of the disease were on creeping bentgrass greens that had received applications of a DMI fungicide. DMI ("demethylation inhibitor") fungicides are those that inhibit a particular demethylation enzymatic step in the production of ergosterol by fungi. Thus, these fungicides are also sometimes referred to as "sterol inhibitor" (SI) fungicides or "ergosterol biosynthesis inhibitor" (EBI) fungicides. Included in the DMI group are the following active ingredients:
There are two general types of resistance to fungicides: quantitative and qualitative. With quantitative resistance, the "resistant" strain exhibits reduced sensitivity: it is still somewhat sensitive to the fungicide, but significantly less so than wild-type strains. In this case, the fungus can still be controlled, but higher rates are necessary (within label limits, of course) and the duration of control is usually reduced. With qualitative resistance, the resistant strain is completely insensitive to the fungicide at normal field rates. Trying to control this strain with the fungicide to which it is resistant is no different than trying to control it using tap water no control can be achieved. Resistance to DMI fungicides in dollar spot is of the quantitative type. Thus, if a turf manager is experiencing less control than s/he expects with DMI fungicides, resistance is a very good possibility. Laboratory tests are required to confirm that the strain is resistant.
If resistance to DMI fungicides is present on a site, expect this resistance to be against all of the DMI fungicides. This is because, at the biochemical level, the fungus perceives them all to be identical, regardless of their differing trade names, chemical structures, and manufacturers. This phenomenon is called cross-resistance.
Rotation among different fungicidal active ingredients is commonly and properly recommended as a way to delay the development of a fungicide-resistant subpopulation. However, be sure to select products from different fungicide groups for a fungicide rotation. Rotating among DMI fungicides is not actually a true fungicide rotation, for the reason discussed in the preceding paragraph. Information on fungicides and the groups they belong to is available in the University of Kentucky Extension publication PPA-1, "Chemical Control of Turfgrass Diseases", available from county Extension offices or on the web at http://www.ca.uky.edu/agcollege/plantpathology/PPAExten/pppublin.htm#Ornamental%20-%20Turfgrass.
We are receiving in the Plant Disease Diagnostic Laboratory many landscape tree samples with leaves turning brown, branches dying, and trees described as looking sickly. In this newsletter, we have described many diseases such as anthracnoses, blights, mildews, and wilts caused by fungi, blights and leaf scorches caused by bacteria, and wilts and diebacks caused by nematodes.
Although most homeowners don't often associate growing conditions with tree symptoms, County Extension Agents and landscape maintenance professionals know that the majority of landscape tree problems are not caused by fungi, bacteria, and nematodes. Furthermore, most of the time when leaves show yellowing or dead areas, or when branches die back, the problem is not in the leaves or branches, but in the soil, roots, or trunk of the tree. When homeowners bring tree problems to the County Extension Office, Agents should be prepared to ask the following questions:
Has the tree been transplanted within the past few years? Even the best prepared nursery stock normally suffers the shock of transplanting for several years after the event.
Was the right species planted in this location? In neutral to alkaline soils, one should not expect white pines or pin oaks to maintain good health, even if they grow well at first. Don't expect hemlocks or beeches to do well in a dry site, or most trees to do well in very wet sites.
Was the tree planted properly? One of the most common problems we observe in declining ten- to fifteen-year old trees is the phenomenon of having been planted too deep years before. Unfortunately, some tree planters have not been paying attention to planting depth to make sure that the normal buttress roots would appear at the soil surface. A corollary to too-deep planting is the excessive use of mulch mounds piled around the trunks of young trees. Too much depth often induces tree root formation near the soil surface with the potential to eventually girdle and kill the tree. This is unfortunate because this kind of tree loss should have been preventable.
Is the tree in a new home development? Mature trees almost always suffer from "bulldozer blight" when construction occurs on a wooded lot. New trees are often placed in inhospitable and compacted subsoils in new developments.
Has a grade change been made recently? Mature trees of most species cannot tolerate the addition or removal of even a few inches of soil in the root zone of the tree. Where is the root zone? This area is well beyond the drip line and often extends out a distance equal to the height of the tree.
Has a drought year preceded the decline of the tree? In this summer, 2002, some trees are still showing or, in some cases only just now showing the effects of the drought of 1999. Even during recent weeks this year, some areas of Kentucky have received adequate rain whereas other regions have been hot and dry. Is it any wonder that these kinds of stressed trees are attractive to canker disease or borers that finish them off?
Is the tree faced with poor drainage or excess moisture? Even with good external drainage along a slope, poor internal drainage of the soil or excessive watering can drown the roots and cause tree decline.
Is the tree surrounded by pavements or buildings? Trees growing in urban areas are exposed to higher temperatures than their suburban counterparts and often do not get enough water to grow well. In addition, many suffer physical and physiological abuse such as mechanical injury and de-icing salt exposure.
Does the tree have girdling roots? The first symptoms include constriction of the buttress roots and the gradual decline of the tree. Planting too deep is often the cause of the problem.
Has there been a leak in the gas or water main? When either natural gas or water fills soil air spaces, it excludes oxygen which is needed for tree root survival.
Was the tree struck by lightning? Sudden death can result if trees are struck by lightning.
Is there a septic tank near the tree? Be aware that strong chemical agents sometimes used in tanks can escape into surrounding soil and injure the tree.
Has the tree been sprayed? Sometimes pesticides or surfactants, if misapplied, can cause tree injury.
Was the tree injured by herbicides or weedkillers? Herbicides that drift, or in some cases, that are taken up by roots, can cause leaf deformities. Some soil sterilant herbicides can kill leaves and branches of trees whose roots take up the chemical some distance from the tree.
Has the tree been injured by air pollution? Air stagnation during the hazy days of summer often elevates ozone and other chemicals to levels that cause stippling, needle tip dieback and scorch.
What else can go wrong with the tree? Clothesline wires or dog chains around the trunk. Tree support wires or burlap binding twine not removed. Non- biodegradable burlap. Girdling by rodents. Lawnmower injury. Soil compaction from parking, walking, or driving over root zone. Winter injury. Wood preservative fumes.
Most of these kinds of tree problems are best solved
by the tree owner rather than the diagnostic
laboratory. So, ask the questions; you may be
surprised at how the answers may solve the problems
of what's wrong with my tree?
Samples diagnosed during the past week have included brown stripe (Cercosporidium) on orchardgrass; cold injury, target spot and bacterial blackleg on tobacco; Mycosphaerella leaf spot on strawberry; fire blight on apple; Pythium root rot on cantaloupe; bacterial spot, Rhizoctonia root rot and potash deficiency on pepper; and bacterial spot on tomato.
On ornamentals, we have seen Cercospora leaf spot on geranium; Cladosporium leaf blotch on peony; Botyrosphaeria canker and dieback on rhododendron and contorted filbert; rosette disease on rose; spot anthracnose on dogwood; scab on crabapple; Phyllosticta leaf spot and verticillium wilt on maple; and anthracnose on redbud.
UKREC-Princeton, KY, May 24 - 31| Black Cutworm
| 2
| True Armyworm
| 5
| Corn Earworm
| 6
| European Corn Borer
| 6
| Southwestern Corn Borer
| 54
| | |
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.
Lee Townsend
Extension Entomologist
