June 26
Crop, Soil, & Pest Management Field School, UK Spindletop Farm, Lexington, KY.
4 General hours: Categories 1 (Ag Applicator), 10 (Demo and Research), 12 (Retail Pesticide Sales Agent).
Contact: Dr. J. D. Green (859) 257-4898.
Blue mold has been confirmed in southeast Kentucky, with
the advisories and watches remaining, with warnings for
Estill and Perry counties. The first confirmed cases of blue
mold in Kentucky for this crop season were confirmed on June
23 from Perry and Estill counties. Each find involved a single
farm and the level of activity was low with little new
sporulation.
This general area had been under a blue mold watch for several weeks, but the activity in Estill County was located a few miles north of the watch area. Both local lesions and systemic infections were found in the region - indications that the disease probably has been present for several weeks. But, the level of activity found was very low and the lesion quality was very poor. These are indications the blue mold pathogen has had difficulty dealing with the extensive wet weather experienced in southeast Kentucky during the past several weeks. Nearby in the Appalachian region, low levels of blue mold have also been reported from Green and Claiborne counties of east Tennessee and Lee County in extreme western Virginia.
In Robertson County of middle Tennessee at least two outbreaks of much stronger and more immediately threatening blue mold were reported last week. Movement of inoculum from these outbreaks into south central Kentucky may have occurred last week, as predicted by the North American Plant Disease Forecast System at NC State. Typical lesions resulting from this inoculum should be present by mid- to late- week on rapidly growing tobacco. However, if the disease has been present in middle Tennessee longer than estimated, we likely have blue activity established further west, so field and bed scouting is important in the west, too. Blue mold development in the southern flue cured production continues to increase in southern Georgia and South Carolina, which could also continue to threaten us under certain weather events.
It is difficult to predict where blue mold might be, thus aggressive scouting efforts are recommended to locate the distribution pattern. I suspect blue mold may be present at a low level over a wide area in southeastern Kentucky and may have spread into central Kentucky. We will not expand the watch area until more threatening activity is confirmed, however, as the entire state remains under an advisory. Most can appreciate that the host (tobacco plant) has had difficulty growing under the stressful weather experienced recently, with much of the crop in the watch area growing poorly, but some excellent crops are scattered about. Keep in mind that the blue mold pathogen (being an obligate parasite) prefers a rapidly growing otherwise healthy host, so when its host is unthrifty, expect the pathogen’s development to be slowed, too. Moreover, we found evidence in the Perry County case that secondary invading organisms probably had damaged the blue mold infection/colonization sites making them poor or unacceptable hosts for the blue mold pathogen to grow and sporulate aggressively. If this is typical of current blue mold development, it helps explains why blue mold has developed much more slowly than anticipated in southern Kentucky.
As growing conditions improve, the tobacco plant will become a better host for blue mold, so a key question is whether inoculum is established in the field, even if conditions are not favorable for long range transport. Under such conditions, expect sporulation to begin and more typical activity to be established if the weather cycles between good tobacco growing conditions and moisture events, especially when nights remain cool.
Growers are advised to maintain aggressive fungicide programs in all transplant production and holding situations, and to avoid setting infected plants. Be especially watchful for systemic blue mold development. Fields should be scouted at least twice weekly for blue mold, checking stunted plants carefully for systemic blue mold. Systemic blue mold can take on many appearance, but it usually includes discoloration of the vascular system (especially the phloem and cambial tissues) of stem, buds, leaves or roots - along with any of the following symptoms: general yellowing, stunting, plant distortion, narrowed leaves, mottled leaves, and darkened roots.
In the field, should blue mold be found within a county, weekly fungicide spray programs with Acrobat MZ should be immediately put in place, followed by activation of the plant with Actigard 50W once the plants are 18 inches tall and able to tolerate the treatment. Additional sprays of Acrobat MZ may also be needed later in the season after the second application of Actigard if strong blue mold pressure is present, especially for late-maturing varieties.
Should blue mold be found, immediately get sample material to one of our two Plant Disease Diagnostic Labs for confirmation and testing. This is required for the first outbreak in each Kentucky county.
Application guidelines for the fungicides labeled for blue mold control in transplant production systems and in the field in Kentucky have been presented in recent issues of Kentucky Pest News:
Transplant fungicides in the March 24, 2003 issue number 978 at web address- http://www.uky.edu/Agriculture/kpn/kpn_03/pi030324.htm
Field fungicides in the April 28, 2003 issue number 983 at
web address -
http://www.uky.edu/Agriculture/kpn/kpn_03/pi030428.htm
For the latest blue mold status and other tobacco disease information, check the KY Blue Mold Warning System online.
http://www.uky.edu/Agriculture/kpn/kyblue/kyblue.htm
For more information about tobacco pests, visit "Insect Management Recommendations".
The pattern of emergence of giant ragweed (also known as
horseweed) may vary depending on biotype. Research in the
Midwest indicated that plants from Iowa emerged in a short
span of time compared with some of the biotypes collected in
Illinois and Ohio. The fact that research in Illinois during the
1970's indicated that giant ragweed emergence pattern was
relatively short, leads some scientists to speculate that this
weed may be adapting to survive control programs in grain
crops.
In Kentucky, giant ragweed usually begins emerging in March and may continue into late June or early July. This prolonged emergence makes it difficult to achieve season- long control of this problem in soybeans.
A study in Lexington last season indicated that timing of application of certain postemergence herbicides as well as crop row spacing impacts giant ragweed control in soybeans. Results showed that delaying applications of Roundup Ultra Max in Roundup Ready soybeans until giant ragweed was 12 inches tall, provided better control than when weeds were 4 or 8 inches tall. The earlier applications appeared to control giant ragweed present at the time of application but did not control plants that emerged after treatments were applied.
Soybeans that were planted in 7- inch row spacing providedfaster shading from the crop canopy and improved control of giant ragweed compared with soybeans in 30-inch row spacing. However, the level of giant ragweed control did not exceed 80% for the early applications in 30-inch or 7 inch wide rows.
Giant ragweed control with FirstRate was good regardless of timing of application or row spacing. FirstRate has soil- residual activity that contributed to the control of late- emerging weeds following applications.
Table 1. Timing of Postemergence Applications for Giant Ragweed Control in Soybeans (Lexington, KY 2002)
| Giant Ragweed Control (%) | |||||||
| 30" Wide rows Giant Ragweed Size |
7" Wide rows Giant Ragweed Size |
||||||
| Herbicide | Rate | 4" | 8" | 12" | 4" | 8" | 12" |
| Roundup UltraMax1+AMS¹ | 26 oz/A10 lb/100 gal | 33 | 47 | 92 | 63 | 78 | 98 |
| FirstRate + Surfactant + Liquid N |
0.3 oz/A 0.25% 2.5 % |
96 | 97 | 98 | 96 | 98 | 98 |
Table 2 lists postemeregence herbicides used in soybeans and maximum size of giant ragweed. While glyhphosate and FirstRate/Amplify are capable of controlling large giant ragweed relative to other postemergence herbicides, there are limits to how consistent they will perform across a wide variety of environmental conditions. It is also worthy to note that although ALS-resistant giant ragweed has not been confirmed in Kentucky, such biotypes have been observed in Ohio, Indiana, and Illinois.
Table 2. Maximum Size or Growth Stage of Giant Ragweed for Selected Soybean Herbicides.
| Herbicide | Size/Growth Stage | Herbicide | Size/Growth Stage |
| Amplify 0.3 oz/A | 10" | Raptor 5 oz/A | 5" |
| Basagran 2 pt/A | 3" | Reflex 1.5 pt/A | 4 Lf |
| Classic 0.75 oz/A | 6" | Roundup WeatherMax¹ 116 oz/A 22 oz/A |
6" 12" |
| Cobra 12.5 oz/A | 6 Lf | Stellar 5 oz/A 7 oz/A |
2 Lf 4 Lf |
| Extreme | 9" | Storm | 6" |
| Flexstar 1 pt/A 1.5 pt/A |
4 Lf 8 Lf |
Synchrony 0.5 oz/A | 4" |
| Front Row 0.42 oz/A | 10" | Touchdown IQ 1 32 oz/A 48 oz/A |
6" 12" |
| Pursuit 1.44 oz/A | 3" | Ultra Blazer 1.5 pt/A | 3" |
Peach bacterial spot, caused by Xanthomonas campestris pv pruni, may appear on some cultivars in years with stormy, rainy weather. The disease is sporadic, but potentially devastating to peaches and other stone fruits in Kentucky. Entire crops can be lost in years with warm, wet weather.
Symptoms. Leaf lesions start out small, angular, gray, and water-soaked, appearing on the leaf undersides, especially along the mid-vein, tip or margins. Lesions become brown to black and generally angular in outline. Often the centers of spots fall out, and margins have a reddish coloration; severely infected leaves turn yellow and drop. Infected fruit becomes pitted and cracked. Elliptical cankers develop on current-year or 1-year-old twigs and branches.
Disease development. The bacterial spot pathogen overwinters on twigs and in buds, sometimes with canker symptoms, sometimes not. In the spring, bacterial populations multiply, and primary infection occurs during wet conditions. Water congestion (water soaking of leaf intercellular spaces due to rain being driven into the stomata) of plant tissue is important for disease development, and outbreaks are especially severe following storms with wind- driven rain. Abrasion by wind-borne sand injures tissue and leads to further infection. Warm, rainy weather throughout the season is conducive to secondary infections.
Disease management. Diseases caused by bacteria are nearly impossible to manage when conditions favor bacterial growth and bacterial spot of stone fruits is no exception. The following are important to disease management.
Empty Bin Treatments
For use in the treatment of empty bins, our
recommendations have not changed. We still recommend
the use of Tempo SC Ultra (cyfluthrin). Reldan may also
be used. However, if you use Reldan on your grain as a
protectant, then you should use a different product on your
empty bins.
We do NOT recommend the use of malathion. Most malathion products have lost their stored grain labels. Insect control with this product is not sufficient and overuse of malathion, because of the lack of control, is producing unacceptable pesticide residue on some grain.
Grain Protectants
A new product has entered the market. Storcide is a
mixture of chlorpyrifos-methyl (which you know as Reldan)
and cyfluthrin (which you know as Tempo). This product
is expected to provide good control of both "bran bugs"
(flour beetles, flat grain beetle, rusty grain beetle, etc) which
are secondary feeders, and our most important beetle pest,
the lesser grain borer, which is a primary feeder.
Users are advised to notice the following warning that is on the label of this product. It states, "Cyfluthrin, a component in STORCIDE does not have CODEX MRLs. Please check with your grain handler before exporting." Codex MRLs are values of pesticide residue on the grain that are used by many countries to regulate exposure to pesticide. If your grain is not going out of the country then this is not important. If, however, it is destined for international trade it might be good to let your buyer know ahead of time that you intend to use this product.
Reldan , as of this time, is still labeled for use as a protectant on stored grain. How long this will last is anybody's guess. However, of more importance, is whether or not it will be available. My guess is that it will be replaced in the market with Storcide .
Insecticides are not your only tool for protecting grain. In fact, they may not even be the best tools. Your best management tools remain to store:
As always, the base line is: store clean, dry grain in clean, dry bins.
For more information about crop and livestock pests, visit "Insect Management Recommendations".
Apart from the annoyance, the blood-feeding habits of adult
mosquitoes can occasionally result in life-threatening
diseases. Malaria and yellow fever used to be common in the
United States, but they have been successfully eliminated
through widespread public health efforts. Currently, viral
encephalitides are the most common mosquito-borne
illnesses transmitted to people. "Encephalitis" simply means
an inflammation of the brain and can be caused by a variety
of pathogens in addition to those transmitted by mosquitoes.
Mosquito-borne strains of viral encephalitis include Eastern Equine, Western Equine, St. Louis, LaCrosse and (most notably), West Nile. Birds and small mammals are important natural hosts for these viruses, which are transmitted to humans and horses through the bite of an infected mosquito. Symptoms of viral encephalitis in humans range from mild to severe and may include high fever, vomiting, drowsiness, and convulsions. Mortality rates vary with the strain of virus involved, e.g., up to a 50 percent risk of mortality with Eastern Equine encephalitis compared to less than a 1 percent mortality rate for West Nile.
--West Nile Virus
West Nile virus (WNV) was first isolated in 1937 in the West
Nile province of Uganda, and is common in Africa, eastern
Europe, western Asia, and the Middle East. The disease first
became apparent in the United States in the summer of 1999,
when an outbreak occurred in New York City. In
subsequent years it quickly spread from coast to coast,
infecting birds, horses and humans. By the end of 2002, West
Nile virus activity had been documented in 90% of Kentucky
counties in either birds, horses, humans or samples of
mosquitoes.
Mosquitoes become infected after biting infected wild birds, which are the primary host for the virus. The virus multiplies within the mosquito's body, and is transmitted to animals while taking a blood meal. Other than birds, WNV is most likely to cause illness in horses and humans. Dogs and cats appear to have a much lower risk of infection. Unlike such illnesses as influenza, WNV cannot be transmitted from person-to-person by sneezing, coughing, touching or kissing.
Most people infected with WNV experience few if any symptoms. A small percentage develop fever, headache, body aches, swollen lymph glands or skin rash. Less than one percent of infected people experience more severe symptoms, which may include headache, high fever, neck stiffness, disorientation, convulsions, paralysis, and sometimes death. Elderly persons are most at risk of suffering severe symptoms.
In 2002, there were about 4200 confirmed cases of WNV in the U.S. and 277 deaths. Seventy- five cases and five confirmed deaths occurred here in Kentucky. While the virus is clearly a public health concern, about 41,000 people die each year from motor vehicle accidents, 64,000 from pneumonia/influenza, and 430,000 from smoking-related illnesses. Although some people are indeed bitten by disease-carrying mosquitoes, the risk of serious infection is extremely low compared to other risks we encounter each day.
Serious health effects can be further reduced by promptly seeing your physician if symptoms arise, and following the mosquito prevention tips mentioned in earlier (e.g., 5/19, 6/16) newsletters.
Diseases of the root, stem, foliage, and fruit caused by Phytophthora capsici and other Phytophthora spp. have become increasingly common in Kentucky during the past few years. Moreover, for the past decade, these diseases have been causing serious losses in several major vegetable production areas of the US. We have diagnosed seriously damaging outbreaks in the following crops in Kentucky: peppers, pumpkins, summer squash, winter squash, tomato, watermelon, eggplants and tobacco.
The wet weather and field flooding experienced this year is likely to result in a more rapid increase of Phytophthora blights as this pathogen is a water mold. Furthermore, all the rain may cause growers to mistake the problem as just related to wet soils because there is considerable physiological injury due to wet soils (as described last week), plus the centers of Phytophthora outbreaks are often in those same wet sites within the field. Particularly at this stage of the season in Kentucky, Phytophthora capsici is mainly operating as a root rot, which often produces no striking above ground symptoms. Infected plants just appear stunted with poor color, especially those in the low wet areas of the field making it easily ignored as flood damage or "wet feet", unless you examine the roots. In some crops, the disease progresses to wilting and death of the plant, while in others, it moves into the stem, and in most it causes a fruit rots in closed wet canopies later in the season.
Kentucky's tobacco-vegetable growers, extension agents, and dealers are probably very familiar with black shank, caused by a close relative of this vegetable pathogen, so use that experience with black shank to help you know where to suspect Phytophthora blights in vegetables. We have noticed in our surveys and farm visits that field sites with a history of black shank are often the first sites to experience Phytophthora blights in vegetables. There are several reasons for this, but the main one is habitat. The wet habitat needed for black shank is the same wet habitat needed for diseases caused by other Phytophthora spp. Thus, just like with black shank, initial disease development within fields often follows drainage patterns. BUT, because P. capsici has highly detachable sporangia and is much more windblown in thunderstorms, P. capsici can rapidly spread across an entire field from the centers of disease that get started in the wet areas.
This vegetable disease resembles many aspects of black shank, but normally does not cause the extensive yellowing seen in burley tobacco with black shank. Some infected plants often have brown to black discolored roots, crowns, and stems. The disease is more easily seen on infected fruit, initially as dark, water-soaked lesions, which may develop a distinctive white layer or crust of spores on the surface of the fruit, as well as stems and leaves. Fruit infection is especially troublesome because the infection may occur days before the symptoms become visible and thus show up in post harvest markets. Produce buyers will likely be very alert to this, which can impact their interest in our produce - at least it should. In fact, the extensive wet weather in many of the leading vegetable growing areas this year has resulted in considerable Phytophthora blight developing in the produce available to the consumer- especially on slicing cucumbers, summer squash and peppers ready for display. Just this past week, I visited several super markets and vegetable stands, and found it on sliced cucumbers, summer squash, and watermelon in nearly every market visited that had out-of-state produce for sale, including finding it on two salad bars- yes on the serving line!
Phytophthora capsici can rapidly spread throughout a field during warm (80 F being ideal for the pathogen), wet conditions. The fungus produces sporangia on the surface of roots, crowns and fruit of infected plants and can be dispersed short range by rain splash, irrigation, and windblown rain. After arriving at the infection site, the sporangia may directly germinate and cause infection, or if in water, stop and produce swimming zoospores (indirect germination) which greatly increases the pathogen's ability to locate host cells and be spread. One zoospore is all that is needed to infect a plant. This disease, like black shank, is polycyclic, meaning the cycle of infection and spore production can be repeated many times during the same growing season. This polycyclic nature making this a very explosive disease in wet weather. Thus, low levels of infection early in the season may result in an epidemic by harvest, if the disease is not controlled.
Just like with the black shank pathogen, Phytophthora capsici produces a thick-walled, long-surviving resting spore. But, there is a big difference! The black shank pathogen's resting spore is an asexual spore, while that in the vegetable pathogen is the product of sexual reproduction and is called an oospore. Since oospores are the product of sexual reproduction (creating a unique blend of genes), this vegetable pathogen has considerable ability to quickly adapt to its environment, including development of resistance to the fungicides used to control it. Two mating types (A1 and A2) are required of Phytophthora capsici to make oospores, and both mating types appear to be common in Kentucky as we regularly find oospores. In Michigan, researchers report that both A1 and A2 mating types have occurred in every field sampled and oospores have been found in diseased cucumber and squash fruits. Recent research suggests that oospores survive in soil at least five years while others report they can remain there much longer.
Phytophthora capsici has become resistant to mefenoxam, the active ingredient in commonly used fungicides, in several states. We have not confirmed resistance here in Kentucky, but resistance is probably operating here, too.
Control of this pathogen is difficult, just like with black shank control requires an integrated approach that relies on a combination of cultural practices, crop rotation, and judicious use of fungicides. No single chemical will resolve this problem!
Moisture management is critically important because that controls the habitat for this pathogen. Create the habitat and expect Phytophthora to dominate, but limit the habitat and you will be able to control it! The more time the site is wet and the mores places that are wet, the greater the probability for this pathogen to cycle. Good drainage is important in managing this disease. Susceptible crops should be planted on well-drained sites and in raised beds. However, even plants growing on well-drained fields on raised beds may have severe disease if rainfall is heavy. Thus, preventive cultural practices that help reduce excess soil moisture will be very important in controlling this disease. You will have to learn how to manage irrigation to have adequate moisture to the plant while avoiding excess moisture. Thus attention should be given to site/field preparation, waterways, raised beds, depressions within beds, hardpans, back-furrows, transplant production, and water-holding capacities of media associated with transplants. For example, on one farm last year, I noticed they had formed there raised beds but had formed a low area in the center of the bed during the leveling stage. Beds need to be high in the center such that water drains away from the plant. Cover crops and stubbles that help reduce rain splash probably also have a place in controlling this disease.
Crop rotation is critical to reducing the volume of pathogen spores in the field. A key problem is the wide host range of Phytophthora capsici among the high valued cash crops you grow. We know that in Kentucky pathogenic isolates have been recovered from all of the following crops: peppers, cucumbers, pumpkins, summer squash (yellow and zucchini), winter squash, gourds, watermelon, tomato, eggplant, tobacco, and several weeds in the nightshade family - including common black nightshade. A minimum of 3 years crop rotation to hosts other than those known as host is recommended to avoid build-up of Phytophthora capsici spores. However, longer rotations may be needed in planting into a field with a history of a severe outbreak of this disease, especially if the site is wet-natured.
Fungicides are most effective when used with appropriate cultural practices to reduce the disease potential, and when fungicides are rotated. Growers should avoid relying on a single fungicide, to delay development of fungicide resistance with Phytophthora capsici. Mefenoxam-containing fungicides are the most helpful in reducing the soilborne aspects of the disease, but be sure to rely on other fungicides in the rotation for the above ground phases of this disease. See ID-36 for the available fungicides by crop.
Development of host resistance is underway in several
vegetable crops, so remain alert to the performance of
resistant varieties.
Plant bugs and lacebugs use their sucking mouthparts to
feed on plant sap. Damage ranges from many small white
spots on the leaves to distortion or destruction of plant
tissue, depending on the pest and host plant. Some feed on
many different types of plants while others feed only on a
narrow range or single species.
Adults fly readily and are often gone before symptoms appear. Their injury is often light to moderate and widely distributed. In contrast, the immature or nymphal stages are wingless and can move only by walking. Injury builds slowly but can become very intense as the insects near maturity. In addition to the feeding damage, white cast skins and tarry waste specks may be seen when nymphs have been present for a long time. The adult and nymphal stages of the same species can look very different, which can confuse identification.
Fourlined plant bugs feed on mint, as well as many herbaceous and woody ornamentals including currant, rose, forsythia, sumac, and viburnum. The nymphs are bright red or yellow, adults is yellow to yellowgreen. Both stages have four distinct black lines running the length of the body, hence their name.
This plant bug can be very destructive, especially to herbs and mint. It feeds first on the upper, tender foliage leaving distinct redbrown spots. These spots, the plant's reaction to enzymes injected into the leaf by the insect, can range from white to almost black depending on the host. Feeding by large numbers of plant bugs can produce large brown blotches and/or leaf distortion.
Females cut slits into the host plant and lay six to eight eggs inside. There is one generation a year. It occurs during a six- week period from late May through June.
Control is difficult because the adults fly readily when disturbed. Both the nymphs and wingless adults drop to the ground if the foliage is disturbed. Insecticidal Soap can be used for control but requires direct contact with the insect. A plant covering may be used to exclude these insects from herbs.
On all grasses, affected patches are often somewhat circular
and can range from several inches to two or more feet in
size. On tall fescue and Kentucky bluegrass, leaves exhibit
tan, irregular lesions with a thin, brown border. On
creeping bentgrass and perennial ryegrass, a ring of olive-
green leaf blades appears on the outside margin of the patch;
these blighted leaf blades dry to a tan color. On humid
mornings, the mycelium of the fungus often appears as a
sparse, very light tan webbing in the lower canopy. This can
be best seen with a hand lens. In some cases, mycelium can
be quite dense, cottony, and fluffy, and grow all over the leaf
blades. In this state, it can look quite a bit like Pythium
cottony blight. Since different fungicides are used against
Pythium cottony blight and Rhizoctonia brown patch,
knowing the identity of the disease can be quite important
from a management standpoint. Laboratory diagnosis is
one option; another is the use of Alert Plant Disease
Detection Kits from Neogen, which have worked well in my
evaluations (
MANAGEMENT
During the next eight weeks or so, be careful with
postemergence herbicides, some of which have been shown
to increase brown patch activity on cool-season turfgrasses.
Perennial ryegrass and creeping bentgrass. High- maintenance perennial ryegrass and creeping bentgrass swards should have preventive fungicide applications on at this point, and putting greens should continue to receive preventive applications for brown patch control through August (and possibly later, depending on weather). There is a wide selection of fungicides with very good activity for brown patch control. These include products with the following active ingredients: azoxystrobin, chlorothalonil, fludioxonil, flutolanil, iprodione, mancozeb, and trifloxystrobin.
--Tall fescue. Recent seedings of tall fescue often can suffer severe outbreaks of the disease during summer months. These should be monitored carefully and treated if necessary. Once these swards make it through their first summer and are well-established, they often do not need fungicide treatment to maintain sward density, although fungicides do improve overall greenness during summer. Be aware that products containing chlorothalonil and iprodione are no longer labeled for use on home lawns.
--Kentucky bluegrass. Although brown patch was active last week in adapted varieties of Kentucky bluegrass, I believe that this was simply the result of the unusually long string of rainy days since mid-April. Although some foliar damage may be evident now, I don't expect brown patch to continue developing aggressively enough on this host to justify fungicide treatment.
Dobsonflies are large, prehistoric looking insects. They have
soft bodies with clear wings, are usually found near water,
and have fluttery flight. The male has long, slender
mouthparts that could give a pinch if he is handled but they
are not aggressive and do not feed on anything. Females
have the same body shape but very small mouthparts.
The adult females lay eggs on overhanging branches or undersides of bridges over streams, or on stones. The eggs hatch at night after 5-6 days and drop into the water. The larvae called "hellgrammites" usually occur under stone in streams where they feed on insects that live in the water. The larvae live for several years in the water and are used as bait by fishermen. The adults only mate, lay eggs and die.
Over the past two or three weeks, the Plant Disease Diagnostic Laboratories, both in Lexington and Princeton have received a number of white pine samples showing a distinct tip burn on the new needles. Some of these trees also show stunting of the new needles in addition to the tip burn, but others have normal, even vigorous, needle and shoot growth. In affected trees, symptoms are reported to occur all over the tree not one-sided as we might see with a salt injury. Also affected trees can be adjacent to white pines with no symptoms.
Close examination of the needles reveals an interesting pattern: while the basal portion of the needle is green, there is a band of dark, reddish tissue around the mid-point of the needle and from this band to the tip, the needle is brown (or reddish-brown) and desiccated. Under the dissecting microscope, we see the "band" on the needle is a narrow area of sunken tissue that constricts the needle. Since many needle blight or needle cast diseases will produce a band on the needle at the point of infection, it is helpful to contrast this symptom with those of our common needle diseases. First, most diseases affect trees in a scattered or random pattern, i.e., some needles are affected, and others on the same tree are not. In addition, the two major needle diseases we see in this area, brown spot needle blight and Naemacyclus needle cast, are much more common on Scots and Austrian pines, although they can occur on white pine. These diseases both produce a spot or band on the needle, followed by needle browning and drop. However, the infections of both of these fungal diseases are occurring now (spring and early summer) on current-year needles, and the symptoms will not be visible until late summer or fall; often they are not noticed until the following spring. We do not see the Sphaeropsis tip blight disease which blights the entire growing shoot on white pine. Obviously, the symptom patterns of these diseases differ from this recent white pine problem, and of course, infectious diseases are confirmed by finding the microbial pathogen on affected needles, not only looking at the symptoms.
A number of possible causes for the symptoms exist. The most likely scenario is that new needles were injured by late frosts as they were expanding this spring. Temperatures reached the low 30's on the morning of April 23rd throughout the region, and this may have killed a band of the youngest (basal) needle tissue. Once this band of tissue was damaged, water supply to the tip was cut off, eventually resulting in the death of the needle beyond that point. Needles expand from the base, so healthy needle tissue continued to expand after the injury occurred.
Air pollutants, including ozone and sulfur dioxide, are also reported in some sources to produce this symptom, called "semi-mature tissue needle blight," but we do not have air pollution data to support this diagnosis, nor has recent weather been conducive to episodes of high ozone. Other environmental factors may also be contributing to the symptoms; we suspect that the stunting of needles in some trees may relate to cool, wet spring conditions in general. Individual trees will differ in their susceptibility to environmental stresses, as well as air pollutants, so it is not that unusual for certain trees to have no symptoms. Affected trees may not be at their most attractive this year, but the overall health of the tree should not be impacted long-term.
Also consider the differences between these symptoms and
those of white pine decline that we so often see in Kentucky
landscapes. This abiotic disorder starts out with a general
yellowing and thinning of the entire canopy of a tree over a
period of several years. Tip burn can occur on old and new
needles as well as premature drop of needles from the
previous season, reduction in annual shoot growth,
shriveling of the bark and eventual decline and death. This
disorder is related to our soil conditions, which are generally
not appropriate for eastern white pine. Dr. Bill Fountain,
Extension Horticulturist, reminds us that white pines
evolved in areas with deep, well-drained loamy or sandy
soils with a low pH (below 6.5). Our higher pH clay soils
and compacted landscape sites hardly provide good
growing conditions for these trees, hence their tendency to
decline after twelve to fifteen years in our area.
Field crop samples from the past week included diagnoses of Lepto leaf spot, Phytophthora root rot and spring black stem on alfalfa; manganese deficiency on soybean; Septoria glume blotch (S. nodorum) and leaf spot (S. tritici) on wheat; and black root rot, black shank, soreshin, Pythium root rot, target spot, alfalfa mosaic virus, tomato spoted wilt virus, poty virus complex, and manganese toxicity on tobacco.
On fruit and vegetable samples, we diagnosed Mycosphaerella leaf spot and Botrytis fruit rot on strawberry; black rot and anthracnose on grape; cedar-apple rust and Phytophthora collar rot on apple; brown rot on peach; black knot on plum; Rhizoctonia stem and root rot on bean; and Septoria leaf spot, Pythium root rot, magnesium deficiency, chemical injuries and wet feet on tomato, and phytophthora fruit rot on pepper, squash, cucumber, and watermelon..
On ornamentals and turf, we saw leaf streak on daylily; Botrytis blossom blight, Cladosporium leaf blotch and low fertility problems on peony; black root rot, Rhizoctonia stem rot, and Botrytis blight on petunia; Pythium root rot on vinca; brown patch on fescue and zoysia; anthracnose on bentgrass; rust and anthracnose on bluegrass; anthracnose (Discula) and powdery mildew on dogwood; cedar-quince rust on hawthorn; anthracnose and Phyllosticta leaf spot on maple; frost injury and ozone injury on white pine; and transplant shock symptoms on many landscape shrubs and trees.
UKREC-Princeton, KY, June 13 - 20| Black cutworm
| 3
| True armyworm
| 56
| European corn borer
| 0
| Southwestern corn borer
| 2
| Corn earworm
| 13
| | |
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
