It Is Near Time for Injecting Oaks for Bacterial Leaf Scorch
By John Hartman

Bacterial leaf scorch, caused by Xylella fastidiosa, affects many Kentucky landscape trees including oaks (pin, red, scarlet, shingle, and white) maples (Norway, red, silver, and sugar), planes (American sycamore and London plane) sweetgum, hackberry, elm and mulberry.  Oaks are widely planted in Kentucky and the disease is most common in them.  Leaves of infected trees typically show marginal necrosis (scorch) late in the summer (Figures 1 & 2) followed by premature defoliation.  Infected trees re-foliate normally in spring and the process of late summer scorch and premature defoliation is repeated.  The disease begins on one or a few branches and over several years gradually spreads throughout the tree.  After many years, dead twigs, then dead branches and limbs begin to appear in the tree and the condition continues to worsen over the years until the tree needs to be removed.  Bacterial leaf scorch is a very problematic plant disease in Kentucky.

In 2006, we were able to show in replicated pin oak plots that root flare injection of oxytetracycline antibiotic in late spring delayed the appearance of scorch symptoms by about 2-3 weeks.  In 2007, we determined that the best results were obtained when injections were made about 3 weeks after the first emerging leaves were fully expanded.  This year, in Lexington, most red oaks and pin oaks were observed to have their first leaves fully expanded sometime during the week of May 4.  Thus, arborists with clients who want their trees injected with antibiotic may wish to concentrate their efforts for sometime the week of May 25.

In our experiments we used Bacastat®, a commercial injectable form of oxytetracycline.  This antibiotic is used for management of bacterial diseases in agricultural crops and is active against gram negative bacteria such as Xylella.  Mycoject® is also an injectable formulation of oxytetracycline, but our results indicated that the more viscous formulation of this product was not as effective.

Although the time of appearance of scorch symptoms was delayed as a result of these treatments, none of the treatments prevented disease or cured trees with bacterial leaf scorch.  When bacterial leaf scorch symptoms are delayed with antibiotic treatments, it is not known if this will prolong the life or vitality of the treated trees, but it might.  Nevertheless, if clients are demanding a treatment, certified arborists trained in micro-injection techniques will want to make the injections in late May to provide the greatest effect.  It appears that the effect of antibiotic injection lasts only one year, so annual injections may be needed.  More research is needed to determine these long-term needs and effects.

Figure 1. Pin oak bacterial leaf scorch symptoms.

Figure 2. Red oak bacterial leaf scorch symptoms.

Quadris Receives a Special Local Need Label for Use on Greenhouse-Grown Tobacco
By Kenny Seebold

Over the past two weeks, we’ve seen an explosion of target spot on tobacco transplants around Kentucky.   Even with a few of days of good weather, target spot is plenty active right now although it’s likely that the pressure will subside as the days get warmer (and drier).

Our current recommendations for managing target spot include taking steps to maintain good ventilation, adequate fertility, and application of mancozeb fungicides (like Dithane, Manzate, or Penncozeb) on a 5-7 day schedule.  Mancozeb is not specifically labeled for target spot, but is fairly suppressive when applied in a preventive manner.  Earlier in May, though, disease pressure reached the point that mancozeb just couldn’t keep up.  What’s been missing from the tobacco grower’s toolbox is a fungicide that can be used legally in the greenhouse AND which has strong activity against target spot.

The fact is, a legal option has been in place for a while.  Quadris fungicide, labeled for target spot and other diseases like frogeye and blue mold, does not have specific restrictions on greenhouse use on its label.  However, there is not specific guidance on using the product on transplants, and neither the manufacturer nor I did not particularly want to see Quadris in the float system.  The main reasons were potential for resistance development (especially with blue mold), and the potential for crop injury.  The current crisis, though, dictated that we find something that could help stem the tide of target spot.  I really think that, had we not found a solution, we were looking at a train wreck for a bunch of growers.  Thanks to the hard work of folks at Syngenta and Kentucky Department of Agriculture, a Special Local Need [24 (c)] label for the use of Quadris on tobacco in the greenhouse was approved on May 13. 

Effective now through July 30, 2009, growers will be able to make ONE application of Quadris at a rate of 6 fl oz/A, which is the equivalent of 0.14 fl oz (4 ml) of product per thousand square feet of float bed (roughly 400 trays), applied in a recommended volume of 5 gallons – enough to get good leaf coverage.  Thus, a grower mixing 20 gallons of spray solution would add 16 ml of Quadris, or roughly 3 teaspoons of product.  After making the Quadris treatment, producers should switch back to mancozeb until plants are set in the field.  This is critical to stay in compliance with the label, and to minimize the risk of resistance developing. 

In cases where target spot is severe on float plants, a follow up application of Quadris may be needed at about 5-6 weeks after setting to suppress the disease in the field.  Quadris is most likely compatible with products like mancozeb or Orthene, but it would be advisable not to mix Quadris and agricultural streptomycin to avoid potential injury.  In terms of resistance to rain and weathering, we can expect Quadris to be fairly rainfast if it can dry for a couple of hours after treatment.

It’s important that growers who use Quadris in the greenhouse have a copy of the 24(c) label in their possession.  It is equally important to remember that the greenhouse application counts toward the seasonal limit (4-5 applications) allowed on tobacco.  As I mentioned earlier, this label will expire at the end of July, 2009.  It is not clear at this time if we’ll renew this for next year.

Weather conditions have improved greatly over the past 4-5 days, giving float beds a chance to dry out.  Warmer, drier conditions have also slowed epidemics of target spot and collar rot – both of which had exploded about 10-14 days ago.

At the moment, target spot is fairly widespread but starting to slow, as I mentioned earlier.  The same can be said for collar rot, although there are indications that blackleg may be on the increase.  This is a big concern because of the fast-moving nature of blackleg.  What’s more, we’ve got a lot of plants out there that have been injured by disease and environmental extremes, and these could be more susceptible to blackleg as a result.  The key to controlling these problems is managing fertility, keeping as much air moving on plants as possible, clipping properly, and preventive applications of fungicide.  We can use Quadris (see article in this issue of KPN) and mancozeb to help with target spot, and agricultural streptomycin to keep blackleg in check.  For the latter, apply 5 or more gallons of a 100 ppm solution (1 tsp. per gallon of spray mix) weekly until plants are set for prevention of blackleg, or use a 200 ppm solution where disease is active.

The previous week also saw an uptick in the number of cases of Pythium root rot – to be expected as we get towards the end of May.  If Pythium shows up on plants that will go to the field within 5 or so days, there may not be a need to apply Terramaster; however, if plants will be held for longer than a week, treatment at 1-1.4 fl oz/100 gallons of float water is advisable.  This is because Pythium can really get going once float water warms up, and serious levels of disease could further delay planting or even result in losses to disease once plants are set.  Keep in mind that Terramaster should not be used any later than 8 weeks after seeding tobacco in the float system.

It’s important to keep watch for these late-season disease issues as we get ready to go to the field.  As we’ve mentioned in previous articles, setting has been delayed for many producers because of weather and this means increased risk of diseases like Pythium root rot, blackleg, and target spot.
Refer to the “2009 Kentucky-Tennessee Tobacco Production Guide” (ID-160) for more information.  The guide can be found online at www.uky.edu/Ag/TobaccoProd/pubs/id160.pdf.

Any venture into low damp places with rank vegetation – berry patches, woodland edges, or along lakes and streams could invite encounters with chiggers; the painful consequences could easily linger for a week or more. Once on a person, chiggers will move to preferred feeding sites where clothing fits tightly against the skin, or where skin is thin, tender, or wrinkled. Tops of socks or along waist bands are common sites of itching but there are more. Their bites are the body’s reaction to the digestive enzymes that chiggers use to liquefy skin cells. They cause the rash, intense itching, and misery that begins a few hours after chiggers have fed.
Protection from chiggers involves the same tactics used against ticks:

• Avoid walking through unmowed fields, brush, and other overgrown areas

• Wear long pants that are tucked into boots or socks and long sleeve shirts. Clothing made of tightly woven fabrics will tend to keep chiggers from reaching the skin as easily.
• Apply an insect/ chigger/ tick repellent. Products containing diethyl toluamide (DEET) or permethrin (clothing treatment only) are effective. Be sure to read and follow directions for use on the container.
• Showering or bathing immediately after coming indoors effectively removes chiggers which have not yet attached. If that is not possible, thoroughly and briskly rubbing your skin with a dry towel may remove many chiggers before they are able to attach and feed.

While most common in wild overgrowth, chiggers may become established in yards, parks, camps, picnic sites, and recreation areas. Effective vegetation management can make these locations less suitable for chiggers and may greatly reduce infestations. Pruning of trees and bushes and closer mowing allows more sunlight into an area and lowers humidity. Removal of scrub brush piles and accumulated debris reduces protection for small mammals and other animals that are important hosts for chiggers. These environmental modifications produce conditions that are less suitable for chiggers and can provide a more long term solution.

Insecticide sprays may temporarily reduce chiggers but, used alone, are not a long term solution. They are most effective when directed into "hot spots" where chiggers and their animal hosts are known to be abundant. Pay particular attention to borders and fences between wooded or brush areas and the lawn, around ornamental plantings, beside foot paths, and the dog house. Products containing bifenthrin (Ortho Home Defense MAX), carbaryl (Sevin), cyhalothrin (Spectracide Bug Stop Indoor + Outdoor Insecticide), and permethrin (various brands) can be effective. A single application during late-April or May is often all that is required, although in severe infestations, treatment may need to be repeated in June. The ground and vegetation up to a height of about three feet should be thoroughly wetted with the insecticide and applied according to label instructions. Children and pets should be kept off treated areas until the vegetation is completely dry.