Fruit Pest News

Volume 4, No. 8   May 5, 2003

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. Blackberry Anthracnose

    4. Blackberry: Orange Rust

    5. Apples: Secondary Blooms and Fire Blight

    6. Grapes: Intrepid 2F Registered

    7. Apples: Aphid Control

    8. Tree Fruit: Pheromone Trap Catches and Biofixes 

1. Current Conditions

As the days pass, the crop damage caused by the violent and tragic storms that began Sunday night will become apparent. Hail, high wind, and flooding will leave their prints on this year's crops. I hope you were not affected too severely. Storms may continue for a few more days, with the chances decreasing toward the end of the week. When you are able to enter your planting to apply pesticides, remember the rule of thumb: If you received 2 or more inches of rain, reapply as soon as you can; 1 to 2 inches -- reduce the number of days until the next spray by 1/2; less than 1 inch -- spray on regular schedule. (SB)

2. Strawberry Diseases

Fruit anthracnose has been confirmed in three cases in Tennessee. For information on a spray program for anthracnose, refer to last week's issue of Fruit Pest News. The problem now is inability to get into fields, with the deluge of rain we just received, with more in the forecast. A case of yeast spot of fruit was reported. This time last year, we saw some wilting plants that turned out to be Botrytis stem rot. It was not a major problem. Don't panic if you see scattered, wilting plants -- it's not necessarily Phytophthora or anthracnose. If light hail has affected your field, your berries may be more subject to fruit rots due to the injuries. Botrytis, Rhizopus, and miscellaneous secondary fungi may seize the opportunity to invade the fruit. In such cases, an application of a broad-spectrum fungicide such as captan, thiram, Topsin M, Quadris, or Switch (heed plantback restrictions) may prevent some infections. (SB)

3. Blackberry Anthracnose

Probably no blackberry disease was impacted more by the loss of Benlate than anthracnose. Suitable alternatives were available for rosette and Botrytis. The only registered fungicides with any activity against anthracnose were copper and lime-sulfur, neither of which provides sufficient control against anthracnose. Recent registrations have given us Cabrio and captan, which should improve our anthracnose-control capabilities (although there is a scarcity of research data supporting this).

I have found in my research trials with Benlate that control of blackberry anthracnose was best when applications were made at early bloom and at two-week intervals for two additional applications. In plantings with a history of anthracnose, this protectant schedule is recommended, using Cabrio and captan. More frequent applications may be needed in excessively rainy weather. Do not apply Cabrio more than twice consecutively before switching to captan. After harvest, floricanes should be removed and destroyed, to reduce the amount of carryover inoculum.

Anthracnose is characterized by dull brown, scabby, flattened, cracked drupelets on blackberry fruit. On ripe berries, recently-infected drupelets show a light purple discoloration. Leaf lesions are small, purple spots with white to tan centers. Spores produced by these spots can splash to the berries and produce the scabby berry condition. The fungus overwinters on leaf and berry debris and on canes. (SB)

 4. Watch for Orange Rust in Blackberries

Orange rust can be very destructive to blackberries and black raspberries. Most of the blackberry varieties that we grow in Tennessee are moderately to highly resistant to orange rust. However, some varieties, such as Navaho, are quite susceptible.

The fungus causes plants to be so stunted and weakened that they produce little or no fruit. The fungus is systemic in the plant, and is perennial inside the below-ground parts. Once a plant is systemically infected by orange rust, it is infected for life. It is for this reason that removal of infected plants is recommended, to prevent spread of the fungus to other plants.

The time to control orange rust is in the spring. Your queue to take action is the appearance of weak, spindly new shoots with pale green to yellowish leaves. Such plants should be removed before they begin to produce the orange-colored, blister-like pustules on the lower leaf surface. The orange pustules contain spores that spread to other plants and cause new infections that may not become apparent until the following spring.

The fungicides Nova and Cabrio can now be used for control of orange rust. These fungicides help prevent leaf infections. They will not cure a systemically-infected plant. Begin applications soon (the orange pustules should mature and release their spores sometime in the month of May) and continue every 10 to 14 days until mid-summer. For Nova, the maximum amount is 10 oz per acre per year, and the rate per application is 1.25 to 2.5 oz per acre. Cabrio is labeled at 14 oz per acre, with a maximum of 4 applications per year. (SB)

5. Fire Blight: Secondary Blooms

Most apple varieties have finished blooming, with the exception of secondary (tag-on) blooms. The MaryBlyt program ceases to predict fire blight infection periods and the need for streptomycin sprays after all blooms are gone. We do not recommend the use of streptomycin after bloom because of its ineffectiveness against shoot blight infections, and because such use increases the risk of resistance developing. Beware, however, of tag-on blooms. Streptomycin sprays may be needed as long as they are present. In such warm weather, tag-on blooms can easily become infected and negate all your hard work in preventing infections during the bloom period! If only a few secondary blooms are present, it would be worth your while to remove them by hand, because they potentially represent the beginning of a fire blight epidemic!

6. Intrepid 2F for Grapes

The Intrepid 2F label was revised as of 3-10-03. It now can be used on grapes for control of grape berry moth, grape leaf roller, omnivorous leafroller, obliquebanded leafroller, orange tortrix, and redbanded leafroller. The grape berry moth is our most important pest and the insecticide should be applied at the 4-8 fl oz/acre rate at the initiation of egg hatch for each generation. Reapply within 10-18 days to ensure complete coverage of rapidly expanding fruits or foliage. The other pests mentioned should be treated at the 10-16 fl oz/acre rate. There is a 30 day pre-harvest interval.

Intrepid is in the diacylhydrazine class of insecticides and mimics the molting hormone of the lepidopterous larvae. This causes a lethal premature molt. Feeding typically ceases within hours of ingestion although it may take several days for the larvae to die. This insecticide has vertually no effect on any other insects or arthropods so your bees and other beneficials are safe.

Tests performed by Ohio State University entomologist Dr. Roger Williams at the Ohio Agricultural Research and Development Center have shown this insecticide to provide excellent control of grape berry moth. According to Dr. Williams, "Last year was the worse year on record for the damage caused by grape berry moth" in Ohio, Michigan, Pennsylvania and New York. This is an important addition to the grape growers' arsenal.

7. Aphids in Apples

Rosy Apple Aphids

These rosy brown aphids have a powdery covering which gives them a pinkish cast. Starting at petal fall, their feeding causes leaves to twist and curl. Their most significant damage is to the fruit. When they feed on leaves around fruit clusters, the cause bunching, stunting and malformation of the developing fruit. These fruit will not be salable. Like other aphids, they can also produce copious amounts of honeydew on which sooty mold will grow. Sooty mold can affect the finish of the apple. Something in their saliva works like a "stop drop" to prevent fruit abscission at normal harvest.

Early detection of this pest is important for control. It is best to control this pest at pink, petal fall or hopefully by first cover. Treat again at petal fall if control was poor at pink. Recommended insecticides at pink include Actara 25 WDG, Thiodan 3EC, Phaser 3EC, Diazinon, 50W, Dimethoate 4EC/400, Danitol 2.4 EC, Ambush 2E or 25WP, or Asanal XL. At petal fall and first cover this pest can be controlled using Diazinon 50 WP, Dimethoate 4EC/400, Provado 1.6F, Danitol 2.4EC, or Actara 25WP.

Green Apple Aphids and Spirea Aphids

These aphids can be a problem starting about second cover. There is a threshold for green apple aphids of 50% infested terminals. Control is most important in young trees and in dwarf plantings. On mature trees, a higher threshold is tolerable. (FH)

8. Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2003

* Biofix for RBLR in Davidson County estimated as occurring on March 8

Bradley County Pheromone Trap Catches

*Biofix for redbanded leafroller in Bradley County estimated as occurring on March 8
**Biofix for codling moth in Bradley County was April 5 (2 caught)

Putnam County Pheromone Trap Catches

*Biofix for Putnam County estimated as occurring on March 8

Obion County Pheromone Trap Catches

*Biofix for RBLR occurred prior to trap placement, estimated as occurring on March 8
(FH)

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