Fruit Pest News

Volume 5, No. 4  April 6, 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. Strawberry Diseases

    3. Methyl Bromide Use Extension

    4. Grape: Early-Season Disease Control

    5. Blueberry: Twig Blight

    6. Apple: MaryBlyt Update

    7. Apple: Spring and Fall Cankerworms

    8. Tree Fruit: Pheromone Trap Catches and Biofixes

1. Current Conditions

The weather has been generally cool lately, and plant development has been slow. Apples have begun bloom, peaches are at petal fall, most strawberries and blueberries are blooming, and blackberries have two-inch shoots. The cool weather is beneficial to the apple growers as the trees enter the bloom period, because temperatures below 65° reduce the fire blight inoculum potential. The weather for the next week is supposed to be seasonal, with highs in the 60's and lows in the 40's, with a chance for showers. We have been spared major frosts and no problems have been reported. (SB)

2. Strawberry Diseases

It has been much too cool for anthracnose to begin its year, so your spray program does not yet need to aim at this disease. Any captan or thiram used in a bloom spray will provide any needed anthracnose control until the weather gets warmer. Phytophthora crown rot, however, is a different story. If this disease is present in your field, you need to get ahead of it by applying Ridomil to the soil. This organism becomes active at much cooler temperatures than anthracnose. Botrytis is always a threat during bloom, but needs moisture on the blossoms or very high humidity to gain entry. The weather has actually been quite dry.  Fungicide sprays every 7 to 10 days should do a good job in these conditions. (SB)

3. Methyl Bromide Use Extension

Methyl bromide use in developed nations was scheduled to be phased out completely by January 1, 2005. The 181-nation Montreal Protocol met in March to determine the fate of the applications for extensions on the use of methyl bromide in critical use situations. Details are still sketchy, but the Montreal Protocol acknowledged that suitable alternatives to methyl bromide are not available for many applications. An allotment equal to 35% of the 1991 level used as a baseline was granted to the U.S. for 2005. The source of this allotment will include existing methyl bromide stocks (5%) and new production (30%). By comparison, the production level for 2004 is 30% of 1991 levels. Additional details will be provided as they become available. (SB)

4. Early-Season Grape Disease Control

Grapes have begun growth and many are at the 1-inch bud stage (and growing rapidly) at which the first black rot spray is recommended. Other diseases such as Phomopsis cane and leaf spot and powdery mildew can also begin activity at this stage of growth. Choose a fungicide(s) based on the history of disease problems in the vineyard, using an efficacy table such as the one on page 26 in the small fruit spray guide, PB1197. Sterol inhibitor fungicides can be used in the early sprays, but keep in mind that they do not provide control of Phomopsis or downy mildew. The multi-site inhibitors (e.g. captan, mancozeb, maneb, ziram) are better choices for control of Phomopsis and black rot. The sterol inhibitors can be tank mixed with the multi-site inhibitors to provide control of powdery mildew and systemic control of black rot. Strobilurins have the broadest spectrum of activity, but are more expensive and are limited to 4 applications per year.

Considering the arsenal of fungicides available to the grape grower, it is a good idea to become familiar with the classification of the products, as listed on page 50 of the spray guide. (SB)

5. Twig Blight of Blueberry

Blueberry growers should look for twig blight, caused by Phomopsis vaccinii, beginning in early spring, since the symptoms can begin to show shortly after budswell. Control measures can then be initiated.

Individual buds turn brown and die, followed by browning of the bark around the bud as the fungus moves from the blighted bud into the twig. The infection usually advances inside the twig until most or all of the flower buds on a twig are killed. Click here http://www.ces.ncsu.edu/depts/pp/notes/Fruit/fdin010/fdin010.htm to see images of these symptoms. Click the images to enlarge them. The dieback does not progress into the older wood, making twig blight easy to distinguish from stem blight, caused by Botryosphaeria dothidea. Frost injury can also resemble twig blight. Twig blight lesions usually continue to enlarge and may be centered around a bud.

It is helpful to prune out and destroy the infected twigs, but this should be done prior to the bloom period, for maximum benefit. Many spores are released from infected twigs beginning shortly after bud break. Those that land in opening buds germinate and invade the twig. However, all is not lost if you have not done this. Removing infected twigs between this time of year and August is helpful in that it reduces twig blight in next year's crop. That is because dead twigs continue to produce spores, which land on and infect buds that become next year's flowers.

Preventive fungicide applications may be needed in plantings in which twig blight has been a problem in the past. Captan, ziram, Cabrio, and Pristine are the most effective fungicides for twig blight.

The highbush varieties Murphy and Harrison are highly susceptible to twig blight and will surely need a control program. Croatan is moderately susceptible, while Reveille, Cape Fear, Bluechip, and Wolcott are relatively resistant. Some rabbiteye varieties are susceptible, especially Delite. (SB)

6. MaryBlyt Update

The MaryBlyt program for fire blight prediction indicates infection when 4 conditions occur: (i) any blooms are open; (ii) rain or dew occurs; (iii) the average temp for the day is 60 or above; and (iv) there have been enough accumulated heat units to allow colonization of the blossoms by the bacteria. The risk of infection is rated as "low," "medium," "high," or "infection." These ratings correspond to any one, two, three, or four of the previously-mentioned conditions, respectively. All the program needs from the operator is the high and low temperature for each day beginning at green tip, and rainfall or dew for each day beginning at first open bloom.

MaryBlyt guides your streptomycin spraying decision-making with this rule: You should spray if the risk of an infection is high and an infection is predicted for the next day. You use the weather forecast with the prediction function of MaryBlyt to determine whether an infection is predicted for the next day.

The Golden Delicious trees at the Plant and Pest Diagnostic Center began blooming April 2. The cool weather lately has helped us by reducing the bacterial inoculum load. Two years ago, a cold period around the beginning of apple bloom saved us from disaster. There was unusually hot weather for a week during bloom, usually a recipe for fire blight havoc. Cold weather prevents the fourth condition listed above from being positive. However, it does not require much warm weather to allow the population to build and spread to the open blossoms. (SB)

7. Spring and Fall Cankerworms

The unsprayed apple trees at the Ellington Agricultural Center in Nashville has revealed feeding by small spring and fall cankerworms. These caterpillars bow or loop when they crawl like an inchworm or looper. They have fewer of the fleshy prolegs (2 or 3)on the abdomen than most lepidopterous caterpillars (codling moth, Oriental fruit moth, redbanded leafroller, etc.) that have 5 pair of prolegs. These cankerworms are 3/16 inch long or less and are either grayish brown or light green. They will drop down on a silken thread if disturbed. The cankerworm moths do not fly but instead climb up the tree trunk to lay their eggs in masses on the twigs in the late fall (November - December) for the fall cankerworm and in by late February and early to mid-March for the spring cankerworm. A delayed dormant oil spray by mid-March will control the eggs of spring and fall cankerworms before they hatch.

The feeding damage on some leaves appears as tiny holes. Many of the small leaves around the flower cluster were fed on as they were unfolding and expanding, causing them to become puckered, crinkled and misshapen. There are also holes in the flower petals and feeding along the blossom stems which may cause some of these blossoms to drop. These caterpillars have the potential to defoliate unsprayed fruit or shade trees as they grow to an inch or so in length at maturity. At present, the peach foliage does not have much if any feeding damage. (FH)

8. Pheromone Trap Catches and Biofixes

The 80 degree temperatures of March 27 and 28 were followed by much cooler temperatures. In Nashville, only one Oriental fruit moth (OFM) has been caught (April 5) since the first ones were caught on March 22 (1 moth) and March 29 (25 moths). The RBLR flight continues but the cool weather slowed the catch from the peak on March 29.

The first grape berry moths were caught on April 1 (caught 6). None have been caught since (FH)


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.

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.

Putnam County Pheromone Trap Catches

*Biofix for RBLR in Putnam County estimated as occurring on February 29.


Smith County Pheromone Trap Catches

* Biofix for RBLR estimated as occurring on February 29.

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, Associate Professor and Extension Entomologist

fahale@ext1.ag.utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211