Fruit Pest News

May 29, 2001

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 cllicked 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. General: Disease Alert

    2. Peach Scab

    3. Grape Fungicide Sprays

    4. Tree Fruit: Insect Update

1. GENERAL: DISEASE ALERT

Last week's cool (cold) weather is now moderating somewhat, but temperatures still remain below normal for this time of year. With scattered showers and fronts moving through, certain diseases may become active. Fruit diseases favored by cool, wet weather include common leaf spot (Ramularia leaf spot) of strawberry, apple scab, sooty blotch and flyspeck of apple, Phomopsis cane and leaf spot of grape, and powdery mildew of grape and apple. Other diseases are also favored by wet weather, but the previously-mentioned diseases are especially prolific under cool conditions. Following are some strategies for dealing with these diseases. Remember, disease-control products should be applied prior to a rain, so that they are in place, protecting the tissues during the wetting event, when infections take place.

Common leaf spot of strawberry - In matted row plantings, apply Nova at 2.5 oz/acre. Can be repeated at intervals of no less than 14 days. Captan plus either Benlate or Topsin M can also be used. Common leaf spot is usually not a problem in Chandler. Nova also provides good control of Phomopsis leaf blight, a hot-weather disease.
Scab, powdery mildew, sooty blotch and flyspeck of apple - Tighten up spray schedule to 10-day intervals until weather becomes hotter and drier. If primary scab was not well controlled, this would be an especially good time to use Flint or Sovran, as they are very effective against fruit scab, powdery mildew, and sooty blotch and flyspeck. Powdery mildew control efforts can end when terminal growth ceases.
Phomopsis cane and leaf spot and powdery mildew of grape - See article number 3, below. (SB)

2. PEACH SCAB

I have not yet seen peach scab symptoms, which usually begin appearing around this time.  Peach scab has a 40-day latent period, which means that symptoms do not appear for 40 days after infection. The shower activity that began May 23 may cause some scab infections. However, control is not needed on varieties that are within 40 days of harvest, since any infections that occur will not have time to develop before harvest. Be sure to begin your brown rot sprays within 3 weeks of harvest for each variety. (SB)

3. GRAPE FUNGICIDE SPRAYS

The recent cool weather and shower activity increases the risk for infection by Phomopsis. The disease is already present on canes and leaves. The danger now is for infection of the rachis (main stem inside a cluster) and fruit. The use of a top-rated Phomopsis fungicide such as captan or mancozeb during this weather pattern would be wise. These materials are also unsurpassed for prevention of downy mildew. Mancozeb and maneb cannot be used within 66 days of harvest.

We are still within the critical period for black rot and downy mildew. If you apply captan in vineyards with a history of black rot problems, add Nova or Elite (this would also control powdery mildew). The use of Abound alone would also provide excellent black rot, powdery mildew, and downy mildew control, with only a slight sacrifice in Phomopsis control. (SB)

4. TREE FRUIT: INSECT UPDATE

Obliquebanded leafroller flights have probably peaked in Davidson County and redbanded leafroller flights have picked up since the middle of the month. The leaf feeding damage is not as much of a concern as the fruit feeding. The following is some general information about these two leafrollers from the book, Common Tree Fruit Pests by Angus H. Howitt. The larvae of redbanded leafrollers feed on the skin of the apple and some of the tissue just under the skin. The wounded tissue corks over when done early to mid-season. Late in the season, feeding damage usually does not cork over. Various rots may occur at the feeding sites or the fruit may suffer moisture loss. Injured fruit may drop early and do not store well.

Obliquebanded leafrollers feed deeper into the fruit than redbanded leafroller. At harvest, the feeding damage appears as a deep depression with a rough, russetted surface. The edge of the damaged area is rounded. They overwinter as third instar larvae inside a small silken sac called a hibernaculum, found under bark, old bud scales and other rough areas on the tree. The larvae leave the hibernaculum in the spring to bore into buds that are opening. They roll leaves into tubular chambers. If they feed on new fruit, most of this damaged fruit will drop before harvest. The fruit that remains has deep, corked-over scars.

Dogwood borer larvae were found feeding beneath the bark of one of our apple trees. The damage was occurring near the graft union. The bark looked rough and the insect frass (excrement) was dark brown like wet coffee grinds. I dug into the frass and found a small dogwood borer larva just under the surface. Supplemental Labeling for the Lorsban-4E label allows for post-bloom application to apple tree trunk for borer control of pests such as dogwood borer, American plum borer, roundheaded appletree borer, flatheaded appletree borer and others (in states east of the Rockies). The insecticide should be mixed with water at the rate of 1.5 qt./100 gal of spray. Apple directly to trunk from a distance of no more than 4 ft. using low volume hand gun shielded spray equipment. Do not allow spray to contact foliage or fruit. Up to 2 applications may be made with a minimum spray interval of 14 days between applications. I am recommending the first application in late April and the second application in mid-July. If you have not made your first application do so now. Make the second application in mid-July. (FH)

                                                    Obion Co. (traps put out April 9)

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