Fruit Pest News

Volume 6, No. 18  August 9, 2005

An 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. Grape: What to Do at this Time if Pierce's Disease is Found

    2. Plum and Cherry: Black Knot

    3. Apple: Late-Season Fungicide Selection

    4. Clearwing Borers and Using the Correct Traps

    5. Pheromone Trap Catches

1. Grape: What to Do at this Time if Pierce's Disease is Found

When Pierce's disease (PD) is found in a vineyard, the affected canes should be removed so that the insect vectors will not spread the bacterium from them to healthy vines. How much of the vine should be removed is debatable. Certainly, all symptomatic tissue should go. On vines having multiple trunks, the trunk supporting the affected cane or cordon should be removed. Severely affected plants with chronic infections should be dug up or cut off even with the ground. This type of case would be a highly susceptible variety in the second year of infection (In vines infected the previous season, the basal part of the cane will show symptoms first). In California, the pruning recommendations are rather severe, even for moderately infected vines: "Pruning a few inches above the graft union of vines with moderate foliar symptoms (some canes on entire cordons without symptoms or no symptoms at the bases of most canes) may eliminate Pierce's disease and allow vigorous regrowth the following year, but symptoms will reappear in many (30-40%) or most of these severely pruned vines the second year." Texas recommendations are to remove all infected vines, regardless of severity. Pruning recommendations in California and Texas are influenced by the presence of the glassy-winged sharpshooter, which we do not have here in Tennessee. As you can see, the basic problem in determining where to make the cut is that the presence of the bacterium inside the vine does not always correspond with the symptoms. It is probably best to err on the side of caution, and remove some tissue that may appear healthy.

Alternate host control. These plants can harbor the PD bacterium and serve as a source of infection for the grapevines. Many types of plants are hosts for the PD bacterium, and it would be impossible to eliminate them from the vineyard area. Instead, keep the vineyard floor and surrounding area mowed and control weeds in the row. In choosing a site for a new vineyard, locate it so that it is not within 150 feet of woodlots and fence rows.

2. Black Knot of Plum and Cherry

Black knot, caused by the fungus Apiosporina morbosa, is a common and destructive disease of plum and cherry. Losses in commercial orchards are usually not extensive except where the disease has become established. Residential plantings of edible or ornamental plum or cherry are commonly plagued with black knot. When left uncontrolled, purple leaf plum trees sometimes have to be removed.

Black knot affects only woody parts of the tree, mostly twigs, and is characterized by elongated swellings. When first formed, knots are olive green and corky in texture, and may be covered by a mold. Later, they turn black and become hard and brittle.

The fungus, living in the knots, produces spores that are discharged to other twigs, where they germinate and produce new infections. Young growth is very susceptible to infection. However, older branches can also be infected, especially if the bark has been damaged. Most infections occur during bloom, petal fall, and shortly afterwards. Some additional infections occur throughout active shoot elongation. Swelling of the twigs does not occur until autumn or the following spring. The knots develop rapidly the second summer.

Prune out all knots, cutting the stem a few inches below the knot. All pruned material should be removed from the area and destroyed or buried. Chemical protection against black knot can be afforded with captan, chlorothalonil, or Topsin M. Chlorothalonil cannot be used after shuck split. A fungicide spray may be needed throughout active shoot elongation. During the critical periods mentioned above, an application may be needed every week.

Among the most susceptible varieties of plum are Damson, Stanley, Bluefree, and Shropshire. Moderately susceptible are Methley, Milton, Fellenberg, Bradshaw, and Early Italian. Less susceptible are Formosa, Shiro, and Santa Rosa. President is highly resistant. (SB)

3. Late-season Fungicide Selection in Apples

Keep in mind the preharvest intervals (PHI) of the fungicides needed for disease control near and during harvest. Although Flint and Sovran have good residual activity (around 21 days), the PHI of Sovran (30 days) precludes its use near harvest. The 14-day PHI of Flint reduces the time it provides protection after harvest begins. Spraying near and during harvest may leave visible residues on the fruit, but is necessary where fruit rots have become a problem. Captan, thiram, Pristine and Topsin M have 0-day PHI's, and would be the products of choice in such cases. Refer to the July 29 issue for a discussion of the newly registered Pristine. In choosing a late-season fungicide, also consider the restricted-entry interval if you have employees. (SB)

Late-Season Apple Fungicides

4. Clearwing Borers and Using the Correct Trap

I have been wondering why I did not catch any squash vine borer moths. I know that they usually come out in late spring to early summer. On July 21, I caught a brown clearwing moth and another on July 27. When checking the trap on August 8, I had a dozen or more clearwings. All but one moth was in bad shape, but I think that they are grape root borers. Somehow I got the incorrect blend of pheromone. Just small changes in the blend of chemicals can make a huge difference in which clearwing moth male that you catch. Just one more reason to be sure that you have good pictures of the moths that you are trying to catch with your pheromone traps. Proper identification is critical. Do not assume that you have the right moth just because you caught it in the trap. (FH)

5. Pheromone Trap Catches

Nashville (Davidson County)
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.
*****Biofix for OBLR in Davidson County on May 13.
"Biofix for VLR in Davidson County on July 12

Bradley County

*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

*Biofix for RBLR in Putnam County on March 21.
**Biofix for OFM in Putnam County on April 6.
***Biofix for OBLR in Putnam county on May 11.

Obion County

*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 since this was much earlier than other locations).
***Biofix for CM in Obion County on April 4 (waiting for confirmation).
****Biofix for OFM in Obion County on April 11.
*****Biofix for VLR in Obion County on May 3 (waiting for confirmation).

Other Pheromone Trap Catches for Davidson County
Diamondback Moth (DBM), American Plum Borer (APB), Cabbage Looper (CL), Armyworm (AW), Sod Webworm (SWW)

* Biofix of DBM in Davidson County probably earlier than April 20
**Biofix of APB in Davidson County probably earlier than April 20
***Biofix of CL in Davidson County on April 29
****Biofix of AW in Davidson County on May 2
*****Biofix of SWW in Davidson County on May 9

Knox County*
Tufted Apple Budmoth (TABM)

*The Knox County traps were put out by a first time cooperator still learning to identify. the moths. Correspondingly, the trap counts for May 2 remain suspect. We do know that the traps were put out too late to accurately determine a biofix for Oriental fruit moth (OFM) and redbanded leafroller (RBLR). The obliquebanded leafroller (OBLR), codling moth (CM), variegated leafroller (VLR) and tufted apple budmoth (TABM) catches are possible biofixes or at least early in their moth flights.

(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, 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.

Programs in agriculture and natural resources, 4-H youth development, family and consumer sciences, and resource development. University of Tennessee Institute of Agriculture, U.S. Department of Agriculture and county governments cooperating. UT Extension provides equal opportunities in programs and employment.