Fruit Pest News

Volume 5, No. 10  May 18, 2004

A weekly, online newsletter whose goal is to update Extension agents and growers of commercial tree fruit and small fruit crops

on diseases and insects in Tennessee.

Text appearing in blue or red can be clicked to link to other web sites. Be aware that much of the linked information is produced in other states and may not be applicable to Tennessee.

In This Issue:

    1. Current Conditions

    2. Fruit Spray Guides: Update

    3. Grape: Spray Program Strategies for Black Rot

    4. Grape: Florescence Galls

    5. Grape Cane Gallmaker

    6. Apples: Summer Rots Can Start Now

    7. Apples: How to Deal With Fire Blight Now

    8. Apple IPM: Sooty Blotch and Flyspeck

    9. Tree Fruit: Pheromone Trap Catches

1. Current Conditions

Thunderstorms were a daily occurrence the past week, causing frustration in pest control efforts. Rainfall totals ranged from 0.02 to 4.22 inches. First reports for the year during the past week: cedar-apple rust -- May 12, Davidson County. Other notes: Cedar-apple rust teliospores should be depleted and no further rust sprays should be needed. Those white patches on your peach fruit are powdery mildew. If present, using sulfur in lieu of captan for the peach scab sprays would help prevent additional spread of powdery mildew. (SB)

2. Fruit Spray Guides: Update

I am repeating this information, with a URL that was missing when I first published this article.

• 2004 Commercial Vegetable Disease, Insect and Weed Control (University of Tennessee PB 1282). Printed, bound copies are available at county Extension offices. It is also available for downloading from our web site at http://www.utextension.utk.edu/publications/pbfiles/PB1282.pdf

• 2004 Commercial Small Fruit Spray Schedules (University of Tennessee PB1197). Printed, bound copies are available at county Extension offices. It is also available for downloading from our web site at http://www.utextension.utk.edu/publications/pbfiles/PB1197.pdf

• 2004 Integrated Orchard Management Guide for Commercial Apples in the Southeast (regional publication). Printed, bound copies are available at county Extension offices. It is also available for downloading from http://ipm.ncsu.edu/apple/orchardguide/contents.html

• 2004 Southeastern Peach, Nectarine and Plum Pest Management and Culture Guide (regional publication). Printed, bound copies are available at county Extension offices. It is also available for downloading from http://entomology.ent.uga.edu/peach/peach_guide/title.htm (SB)

3. Spray Program Strategies for Black Rot of Grape

Black rot is the most destructive disease affecting grapes in Tennessee. In some of the literature and on some fungicide labels, you will see two types of strategies for applying fungicides for black rot control. One is referred to as protective or preventive. It involves spraying on a set schedule such as every 7 to 14 days. The spray interval chosen by the grower would be determined by the amount of rain: More frequent sprays would be needed in rainy weather, because most disease organisms are favored by wet conditions, and because rainfall can remove some of the fungicide residue.

The other strategy for applying black rot fungicides is referred to as a postinfection or eradicative schedule. With this method, certain systemic fungicides such as Bayleton or Nova are applied within 72 hours after the beginning of an infection period. An infection period occurs when moisture is present long enough at a certain temperature for the fungus spores to germinate and enter the plant tissue. The table below shows how long the tissue must remain wet at each of several temperatures for infection to take place.

The idea behind the postinfection method is to attempt to reduce the number of fungicide applications and to make the applications only when they are truly needed. Research is currently being conducted to determine whether the number of fungicide applications can actually be reduced when using this method in the South, where frequent heavy dews can cause numerous infection periods. The research also hopes to determine what impact such a program would have on other grape diseases.

A need for the eradicative technique is obvious at times, and weather monitoring equipment is not needed. Extended rainy weather, causing infections and preventing spray applications, would create an obvious need for a postinfection application of a fungicide, regardless of the type of program the grower is on. Use a fungicide with good eradicative activity, such as Nova, Elite, or Bayleton, if black rot infection is expected to have occurred. These fungicides are locally systemic, i.e. they are absorbed into the tissue onto which they are applied. Significant infection should not occur within 7-10 days of the last application of one of these systemic materials, because of their rainfastness. However, if only a protectant (mancozeb, ferbam, ziram, captan) was used, the residue can be completely removed after two inches of rain. As you can see, systemic fungicides have benefits both prior to and after rainy periods.

A word about the strobilurins (Abound, Flint, Sovran, and Pristine): These broad-spectrum fungicides are locally systemic, just as Nova, Elite, and Bayleton are. However, the strobilurins do not have as good eradicative activity as Nova, Elite, and Bayleton, and should be used primarily as protectants -- rainfast protectants, but protectants nonetheless. (SB)

4. Florescence Galls on Grape

Gall midges lay their eggs in plant tissue, which causes the plant to produce strange looking growth. Recently, Marion and Blount County samples had reddish globose galls forming in the inflorescence, leaves and tendrils of grape. The pink larvae can be found inside the protective galls. Once the gall formation is initiated there is nothing that can be done to stop it. Preventative insecticide sprays would have to be made prebloom (3rd new shoot spray). Usually, galls are not a major problem. Later generations of the insect will not be as damaging since they will attack leaves and tendrils and not the florescence. (FH)

5. Grape Cane Gallmaker

This small brown weevil (1/8 inch) moves to grapes in April from wooded or brushy areas, where it overwinters. The females chews holes lengthwise on the new shoots (beginning when shoots are 10-20 inches long) just above the node. An egg is placed in the hole next to the node. A shoot splits and a brownish swelling forms around the split which is 3/4 to 1 inch long. The weevils probably continue laying eggs into May. When the larvae are mature, they pupate within the gall and adults emerge by August. They seek overwintering sites by late summer and there is only one generation per year. Since most of the galls are formed beyond the grape clusters, yield loss is minor. The canes with galls can produce a crop next year. If pruning is desired, remove the canes with galls prior to mid-July to remove the immature weevils before they can become adults and move to their overwintering sites. (FH)

6. Apples: Summer Rots Can Start Now

The various summer rots are always a problem in the South. Some of these rots get started around this time of year, although the infections may not become apparent until mid- to late-summer. The recent deluges and humid weather can be expected to increase our problems with the summer rots if we don't keep our guard up.

White rot, in particular, is a fruit rot that can have a delayed effect. While lesions usually don't appear on the fruit until mid-summer or later, they can be the result of infections that occurred in May, and remained dormant until the sugar levels began to increase in the ripening fruit. The white rot fungus lives within the tree in dead wood. It can either invade already-dead wood such as fire blight strikes, or it can infect healthy wood through lenticels in the bark. In stressed trees, the latter type of infection can expand and produce cankers capable of killing branches. Spores of the fungus are spread to the fruit by rain.

Where problems with white rot are expected, captan plus Topsin M should be included in the cover sprays. The strobilurin fungicides Flint and Sovran also provide good control. (SB)

7. How to Deal With Fire Blight Now

Remember, do not use streptomycin to prevent shoot blight. It is ineffective and the unnecessary use of it can lead to resistance developing in the fire blight bacterium. An exception can be made by using it after a hail storm.

Should you cut out infected shoots? This has been debated for some time because of inconsistent results. The operation should be conducted as soon as possible after the fire blight strikes appear. If it is not possible to complete this task within a couple of days, it is probably best to let nature take its course. Remember that the job will need to be repeated as new symptoms appear.

The ugly stub method. The late Dr. Paul Steiner claimed that the old method of making a cut 10 to 12 inches below the symptom was useless, because the bacterium is usually systemic much further down the limb than that. It does no harm there, because of the natural resistance of the tree. Making a cut, however, breaches this natural defense, and a small canker almost inevitably forms around the cut. By making two cuts, the canker and its associated bacteria can be eliminated. The first cut is in 2-year-old wood, 2 to 4 inches above the supporting limb. A canker may form around the cut surface of the stub, but the second cut removes the stub at the supporting limb. This is done during the dormant season, when the bacteria are not active (paint or flag the stubs to make them easier to find).

Alternatively, you could wait until the dormant season and make one cut, and save a lot of work. But the ugly stub method allows those who wish to prune out fire blight during the growing season a method of doing so without leaving cankers around the cuts. (SB)

8. Apple IPM: Sooty Blotch and Flyspeck

One of the goals of this newsletter is to teach IPM techniques. Disease control is included in IPM, just as insect control is. We may be able to reduce the number of fungicide sprays by timing them well, with the help of predictive models that use information from weather-monitoring equipment.

Sooty blotch and flyspeck is a disease complex for which we have such a model. The only parameter it uses is hours of leaf wetness, caused by rain or dew. This disease is different from most, in that the speed at which infections develop is determined by wetness, not temperature. Using this model, you can eliminate two to four fungicide applications per year. Since the model does not apply to the summer rots, I don't recommend that you reduce your number of fungicide applications where these diseases are a problem. However, even in these locations, you can reduce the number of applications of Topsin M, Flint, or Sovran, since these materials are used primarily for control of sooty blotch and flyspeck.

Using a leaf wetness recorder, accumulated wetting hours (AWH) can be used to determine when a fungicide with post-infection activity (Topsin M, Flint, or Sovran) should be used to arrest the development of infections. Research in North Carolina showed that symptoms appear at 275-300 AWH and the workers suggested that a fungicide should be applied at about 3/4 of that time (225 AWH). Researchers in New York have suggested that the time for the fungicide application should be at about 1/3 of the incubation period. In Kentucky, 175 AWH was suggested.

Regardless, wetting periods of less than four hours are not included in the total. The count is begun at 10 days after petal fall. In New York, the 100 hours of leaf wetting are not begun until 21 days after the last scab spray, which is typically first or second cover. The New York system makes sense, because of the protection against sooty blotch and flyspeck provided by the last scab spray.

I am operating a leaf wetness sensor at Brentwood, in Williamson County. I am considering the biofix of 10 days after petal fall to be May 1. In the first 17 days of May, wetting periods of 4 hours or more have amounted to 96 hours. (SB)

9. Pheromone Trap Catches

Nashville (Davidson County) Pheromone Trap Catches for 2004

* The three RBLR caught in trap left over from last year. New RBLR trap put out 3-4-04. Biofix for RBLR in Davidson County estimated as occurring on February 29.
**Biofix for OFM estimated to have occurred on March 26.
***Biofix for grape berry moth (GBM) estimated as occurring on 3-30.
****Biofix for obliquebanded leafroller.

Bradley County Pheromone Trap Catches

*Four RBLR moths caught in trap from last year. Biofix for redbanded leafroller in Bradley County estimated as occurring on February 29.
**OFM biofix on March 19.
*** CM biofix on April 23.
**** TABM biofix on April 23.

Putnam County Pheromone Trap Catches

*Biofix for RBLR in Putnam County estimated as occurring on February 29.
**Biofix for OFM estimated as occurring on April 7.
*** Biofix for OBLR on April 16 (waiting for confirmation).
****Biofix for CM.


Smith County Pheromone Trap Catches (Two orchards, a set of traps at each site))

* Biofix for RBLR estimated as occurring on February 29.
** Biofix for OFM estimated as occurring on April 9.
*** Biofix for CM on April 21(waiting for confirmation)
**** Biofix for OBLR on April 28 (waiting for conformation)

The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm

Contacts:

Steve Bost, Professor and Extension Plant Pathologist

scbost@utk.edu

Frank Hale, Professor and Extension Entomologist

fahale@utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211