Fruit Pest News

Volume 6, No. 5  April 19, 2005

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. Apple: Disease Control During Bloom and at Petal Fall

    3. Apple: Rust Diseases

    4. Peach: Disease Control

    5. Blackberry: Time to Watch for Rosette Disease

    6. Vegetables: Soybean Rust Control

    7. Tree Fruits: Caterpillar Defoliators

    8. Tree Fruits: Pheromone Trap Catches and Biofixes

1. Current Conditions

The weather has been dry for the last week, which is good news for spring disease control.  Strawberries are in peak bloom, so a dry spell at this time will help keep down Botrytis problems. There is a chance of frost coming up Saturday night. This spring has been strange in that the weather has been cool enough to cause a "late" spring, yet there has been no frost activity since mid-March. Dews have generally been light around here, which should help reduce fire blight infections of the blossoms. (SB)

2. Apple: Disease Control During Bloom and at Petal Fall

The sterol inhibitors (SI's) are important fungicides for the control of apple scab, powdery mildew, and rust diseases. Examples of SI's are Nova, Rubigan, and Procure. Some areas of the country are beginning to experience loss of control of scab due to the development of strains resistant to the SI's. As far as I know, this has not happened in Tennessee. (If you think it is happening in your orchard, please let me know.) Let's try to prevent resistance from developing by always tank mixing our SI's with a protectant fungicide such as mancozeb, captan, ziram, etc., and using SI's only when necessary.

Bloom. If your bloom-time spray is applied only 6 or 7 days after the pink tip spray, it may not be necessary to use fungicides with lengthy kick-back activity (i.e. the SI's). A contact material such as mancozeb or ziram may be sufficient at that time, and these two materials would also provide rust control. However, these materials are not suitable for powdery mildew control. For mildew-susceptible varieties such as Jonathan, Ginger Gold, Rome Beauty, Stayman Winesap, Idared, Paulared, and Granny Smith, mildewcides such as the SI's, Topsin M, or sulfur should be used in each spray until terminal growth stops. Early season sprays (tight cluster to petal fall) are essential if mildew is to be managed successfully.

Petal fall. Petal fall through first cover is a peak risk period for powdery mildew, cedar-apple rust, and fruit infection by scab. Use an SI with a contact fungicide at each of these two growth stages. Note: I recommend that the strobilurin materials (Flint, Sovran) be reserved for use during the summer, when their characteristics are more fully utilized. (SB)

3. Apple: Rust Diseases

We are entering a period of peak vulnerability of apple trees to rust. This would be a good time for a review of the rust diseases of apple. The following is modified from an article written by Dr. David Rosenberger, Cornell University, for the Scaffolds newsletter.

Three different rust diseases caused by Gymnosporangium species occur on apples in this area. Quince rust (G. clavipes) infects fruit (Fig.1) but does not cause leaf lesions. Cedar apple rust (CAR), caused by G. juniperi-virginianae, infects both leaves (Fig.2) and fruit of susceptible cultivars, but leaf infections are far more common than fruit infections. Hawthorn rust caused by G. globosum only infects leaves and is generally less damaging than CAR and quince rust. Hawthorn rust affects apple, pear, and hawthorn plants. On infected leaves, the early symptoms of CAR and hawthorn rust are so similar that the two species cannot be easily differentiated. By mid-August, hawthorn rust and CAR can be differentiated based on the appearance of the fungal fruiting structures (aecia) that form on the bottom sides of infected leaves.

All three of the apple rust diseases require red cedar trees as an alternate host. For both CAR and hawthorn rust, the spores that infect apples are produced on the orange, jelly-like telial horns that are generated by cedar galls during wet spring weather (Fig.2). Quince rust does not produce a spherical gall on cedars. Instead, the cylindrical gall produced by quince rust on cedar twigs might be referred to as a swollen canker. The cankers can be easily located only when they are wet and are producing short, knobby, orange-red telial horns during spring (Fig.3). Unlike CAR, where individual galls produce spores for only one season, quince rust infections can survive and produce spores on cedars for many years.

Nearly all apple cultivars are susceptible to quince rust, although the degree of susceptibility varies. Many apple cultivars are resistant to either cedar apple rust or hawthorn rust, but very few are resistant to both CAR and hawthorn rust. An interesting side note: Rust-resistant cultivars can develop a leaf spot that resembles frogeye leaf spot (Fig.4). This results when rust spores germinate and kill a few leaf cells before fungal growth is interrupted by the incompatible host reaction of the resistant cultivar. The killed leaf cells are then invaded by other secondary pathogens such as Alternaria, Botryosphaeria, or Phomopsis.

Infection is promoted by frequent showers interspersed with cloudy weather. Intermittent wetting promotes production and dissemination of rust spores, allowing time for spores to be blown into orchards from the alternate red cedar hosts. Also, light rains are less effective than heavy rains for washing spores out of the air. The period of peak susceptibility for rust infections on fruit occurs between pink and first cover. Infection of apple leaves continues until the telial horns on cedar are depleted, usually around second cover.

The EBDC fungicides (mancozeb, Polyram) and the SI fungicides (Rubigan, Nova, Procure, Bayleton) are all effective for controlling rust diseases on apples. The SI fungicides provide at least 96 hr of post-infection activity against rust infections on leaves. The EBDC fungicides do not provide any post-infection activity, although they may arrest the infection process when applied during the first 12—18 hr after rains begin. Captan and Topsin M are ineffective against rust diseases.

The strobilurin fungicides (Sovran, Flint) have provided good control of rust diseases in some trials and moderate levels of control in other trials. The inconsistent performance of strobilurins against rust diseases may be attributable to differences in spray timing. Several tests at the Hudson Valley (New York) Lab have shown that strobilurins controlled rust diseases as well as 3 lb/A of mancozeb if the sprays were applied before the infection period. However, the strobilurins have much less post-infection activity than the SI fungicides. In a 2001 trial where control plots had 69% of Jerseymac fruit with quince rust, Nova provided 98% control of quince rust when it was applied at either 3 days or 7 days after the infection period, whereas Flint provided only 23% control at 3 days post-infection and no control after 7 days.

Eliminating red cedars near orchards has long been recommended as one approach for reducing the incidence of rust diseases on apples. The number of spores reaching an orchard declines rapidly as the distance to the nearest cedar trees is increased. However, eliminating nearby cedars rarely provides complete control of rust diseases in areas where cedar trees are common, because small numbers of spores can be blown to apples from distant cedars. Where all cedars are eliminated within several hundred yards of an orchard, outbreaks of apple rust diseases are likely only in years when light rains cause extended intermittent wetting periods.

4. Peach Disease Control

Many peach cultivars are now at the shuck split stage. Fungicide applications for control of peach scab should begin at the shuck split to shuck fall stage, about one week after petal fall. Do not wait until all the shucks have fallen to make this application. Scab pressure is greatest from shuck split through 2nd or 3rd cover because scab spore counts are high during this time and the cool, wet weather that occurs during this time favors infection. Continue on 10-day intervals until 40 days before harvest. Bravo cannot be used after the shuck fall stage. Captan, sulfur, Pristine, Flint, Scala, and Abound are other peach scab products. Pristine, Flint, and Abound are strobilurin materials and should be rotated with non-strobilurin products that have scab activity, such as captan or sulfur.

Shuck split is also the time to begin bacterial spot sprays on susceptible varieties. Mycoshield should be applied every 10 days until 3 weeks before harvest. (SB)

5. Time for Blackberry Growers to Watch for Rosette Disease

The key to managing rosette is to remove the infected blossom clusters before the blossoms open. That is because all of the spores that cause new infections come from infected blossoms. The infected blossom clusters should now be apparent. They are recognized as bunchy growths consisting of multiple shoots, rather than the normal single shoot. Such growths are known as rosettes or witch's brooms. The sepals (the green, leaf-like structures that enclose blossoms) are abnormally long and pointed. When the blossoms open, they will be pinkish and ruffled.

Fungicidal control also has a place if you do not currently have rosette, but are growing a susceptible variety. Shawnee is particularly susceptible. Cherokee, Comanche, Triple Crown, and Black Satin are also quite susceptible. Chester, Hull, Lock Ness, Arapaho, and Navaho have good tolerance. (SB)

6. Soybean Rust Control for Vegetables

Asian soybean rust is expected to make its way into the United States this year. Some of the vegetable crops could be vulnerable to attack by Asian soybean rust, particularly snap beans.  Southern pea is relatively resistant, and the other types probably fall somewhere in between.  Here is a rundown of products currently labeled for use on legume vegetables that should be effective for control of soybean rust (resistance management group number in parentheses):

Commercial

•       Snap bean, succulent – Quadris (11), Headline (11), Nova (3), Endura (7), chlorothalonil (M)

•       Dry beans (Navy, Pinto, Kidney, Lima, Southern, etc.) – Quadris (11), Quadris Opti (11, M), Headline (11), Endura (7), chlorothalonil (M)

•       Lima bean, succulent – Quadris (11), Endura (7)

•       English pea, succulent – Headline (11), Quadris (11)

•       Southern pea, succulent – Quadris (11), Endura (7)

Organic commercial

•       all legume vegetables – sulfur, Sonata (biological)

Home garden

•       all legume vegetables – sulfur

•       snap beans – chlorothalonil

Additional product labels have been applied for that would provide more options for control of rust in commercial fields.  I will let you know when they are granted. (SB)

7. Caterpillar Defoliators

Eastern tent caterpillars have hatched from their egg masses. The activity of the small caterpillars is evident as small silken nests of wild cherry. It can also be found in plum, peach, apple, crabapple and at least nine other ornamental landscape trees. Individual nests can be removed by hand or with a rake and destroyed.

Spring cankerworms are inchworms that feed on elm, maple, ash, hickory, beech, basswood, oak and apple. The female moth crawls up the trunk of the tree in the early spring and lays her eggs. The tiny looping caterpillars are active now. They hang down on silken threads and can land on your clothing when working in the orchard. Populations can be high and much of the leaf feeding damage seen now and for the next few weeks can be from these caterpillars. Unsprayed landscape trees can be defoliated some years but Petal Fall sprays should control this pest in apple orchards. (FH)

8. Pheromone Trap Catches and Biofixes

In Nashville at the Ellington Center, pheromone traps were put out on April 18 for American plum borer, armyworm, fall armyworm, beet armyworm, cabbage looper, diamondback moth, squash vine borer and a turf pest, sod webworm.

Nashville (Davidson County) Pheromone Trap Catches for 2005
Oriental fruit moth (OFM), redbanded leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry moth (GBM), variegated leafroller (VLR), black cutworm (BCW)

* Biofix for RBLR in Davidson County estimated as occurring on March 12.
**Biofix for GBM in Davidson County is April 4.
***Biofix of BCW in Davidson County on April 12.
****Biofix for OFM in Davidson County on April 12.

Bradley County Pheromone Trap Catches for 2005

*Biofix for RBLR in Bradley County on March 12.
**Biofix for OFM in Bradley County on March 25.
***Biofix for CM in Bradley County on April 16.


Putnam County Pheromone trap Catches for 2005

*Biofix for RBLR in Putnam County on March 21.
**Biofix for OFM in Putnam County on April 6.

Obion County Pheromone Trap Catches for 2005

*Biofix for RBLR in Obion County estimated to be on March 12 (trap not out early enough).
**Biofix for OBLR in Obion County on April 4 (waiting for confirmation).
***Biofix for CM in Obion County on April 4 (waiting for confirmation).
****Biofix for OFM in Obion County on April 11.

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

Copyright 2005 The University of Tennessee. All rights reserved. This document may be reproduced and distributed for nonprofit educational purposes provided that credit is given to University of Tennessee Extension.

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