Fruit Pest News
Volume 7, No. 11 May 24, 2006
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. Stone Fruit: Leucostoma Canker
2. Apple: Summer Rots Can Start Now
3. Cucurbits: Planning for Powdery Mildew Season
4. Brassica Leafy Greens: Bacterial Leaf Spot
5. Tree Fruit: Dogwood Borer, Woolly Apple Aphid, and Pheromone Trap Catches
1. Leucostoma Canker of Stone Fruit
Leucostoma canker, also called perennial canker, Cytospora canker, and Valsa canker, can be an important disease of stone fruit in the South. Affecting twigs, limbs, and trunks, the disease reduces fruiting surface and can shorten tree longevity. The causal fungus enters wood through wounds or infected twigs. Pruning wounds are the most common entry point, but winter injury, borer wounds, and southwest sunburn injury are other possibilities. Cankers are often elliptical in shape and may have a dry, blackened appearance.
In orchards in which Leucostoma canker is a problem, delay dormant pruning until a warm, dry period occurs in the spring. Host defenses will be active during such conditions and will resist infection or limit advancement of infections. Try to keep the tree actively growing with proper fertilization and, if needed, irrigation, but allow it to slow down in late summer. Follow recommended tree training practices to minimize narrow limb crotches and shaded, weak limbs that are susceptible to Leucostoma. To encourage rapid healing-over, cut branches just beyond the ridge of the thickened bark which connects them to larger limbs. Do not leave pruning stubs. Avoid large pruning cuts. It is helpful to surgically remove cankers from trunks or scaffold limbs. Remove in midsummer, then burn or bury cankers. Do not apply a wound dressing. (SB)
2. Apples: Summer Rots Can Start Now
The various summer rots are always a problem in the South. Some of these rots get started around this time of year, although the infections may not become apparent until mid- to late-summer. The recent deluges and humid weather can be expected to increase our problems with the summer rots if we don't keep our guard up.
White rot, in particular, is a fruit rot that can have a delayed effect. While lesions usually don't appear on the fruit until mid-summer or later, they can be the result of infections that occurred in May, and remained dormant until the sugar levels began to increase in the ripening fruit. The white rot fungus lives within the tree in dead wood. It can either invade already-dead wood such as fire blight strikes, or it can infect healthy wood through lenticels in the bark. In stressed trees, the latter type of infection can expand and produce cankers capable of killing branches. Spores of the fungus are spread to the fruit by rain.
Where problems with white rot are expected, captan plus Topsin M should be included in the cover sprays. The strobilurin fungicides Flint and Sovran also provide good control. (SB)
3. Planning for Cucurbit Powdery Mildew Season
Cucurbit powdery mildew typically does not begin until mid-summer, but it is not too early to plan your fungicide program and make sure the products you wish to use are available from the dealers. Don't forget about the occurrence of strobilurin-resistant powdery mildew. Resistant strains began appearing across the country in 2002, and now appear to cause a re-thinking of powdery mildew control plans. You will not know whether the powdery mildew you get in your field is resistant to the strobilurins (Quadris, Cabrio, Flint) until it is too late, when you fail to get good control. If that is too big a risk for you, use sulfur or a sterol inhibitor (Nova or Procure). The strobilurin fungicide Pristine has a second ingredient that offers some protection against powdery mildew. The zoxamide fungicide Quintec should receive a cucurbit registration in the near future; it is highly effective against powdery mildew.
In a pumpkin fungicide trial that I conducted last year, powdery mildew control by the sterol inhibitors was significantly reduced, although not as bad as that by the strobilurins. Loss of sensitivity to the SI's by the powdery mildew population resulted in only about 50% control. Since resistance to the sterol inhibitors is also a threat, you should rotate occasionally to sulfur.
The strobilurins provide control of other diseases such as microdochium blight and downy mildew and, because of this property, are usually applied alone. Sulfur and the sterol inhibitors are specific to powdery mildew and should be tank mixed with broad-spectrum fungicides such as chlorothalonil or mancozeb. Remember that sulfur is strictly a surface protectant and coverage of both sides of the leaves is needed for good control. (SB)
4. Bacterial Leaf Spot of Brassica Leafy Greens
Some serious cases of bacterial leaf spot, caused by Pseudomonas syringae pv maculicola, have occurred in commercial mustard and collard in West Tennessee. This disease can be highly destructive and has been a problem on leafy greens in California, Oklahoma, Ohio, and South Carolina in the last 10 years, although it has occurred on heading type brassica crops for many years. This bacterial spot is favored by cool, wet weather and will be difficult to control as long as the weather remains in that mode. Fixed copper sprays are the only registered control products, but spray programs utilizing these materials in other states have not been successful in control.
The bacteria can enter the field from wild cruciferous weeds on running water, blowing leaves, wind-blown rain, or insects. It can also be seed-borne. Crop rotation should provide at least one year between susceptible crops, which include all cruciferous crops (brassicas). Crop debris should be disked under soon after harvest is complete. (SB)
5. Dogwood Borer
Dogwood borers tend to lay their eggs on rough areas of the bark
of apple such as burr knots and graft unions. Treat the bark of apple trees with
Lorsban 50 W or 4E (28 day preharvest interval [PHI]), Thiodan 3EC (21 day PHI),
or Asana XL (21 day PHI) in mid to late May for optimal results. Use a handgun sprayer
and for Lorsban, spray from no more than four feet or with a shielded sprayer to
prevent drift onto foliage or fruit. (FH)
Woolly Apple Aphids
These aphids
feed on both roots and on twigs and pruning cuts above ground. Above-ground infestations
are of greatest concern on younger trees. Target woolly apple aphids when seen with
Dimethoate 4EC/400 or Diazinon 50W. (FH)
Pheromone Trap Catches and Biofixes
Nashville
(Davidson County) Pheromone Trap Catches for 2006
Oriental fruit moth (OFM), redbanded
leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry
moth (GBM), variegated leafroller (VLR), black cutworm (BCW), diamondback moth (DBM)
| OFM | RBLR | OBLR | CM | GBM | VLR | BCW | DBM | |
| 3-1 (put out RBLR, OFM, VLR traps) | -- | 0 | -- | -- | -- | -- | -- | -- |
| 3-2 | -- | 3* | -- | -- | -- | -- | -- | -- |
| 3-9 | -- | 15 | -- | -- | -- | 0 | -- | -- |
| 3-13 | 0 | 50 | 0 | -- | -- | 0 | -- | -- |
| 3-21 | 0 | 71 | 0 | -- | -- | 0 | -- | -- |
| 3-28 | 0 | 15 | 0 | -- | -- | 0 | -- | -- |
| 3-29 (put out GBM, BCW, & DBM traps) | 0 | 5 | 0 | -- | -- | 0 | -- | -- |
| 3-30 | 0 | 4 | 0 | -- | 0 | 0 | 0 | 2** |
| 4-4 | 24*** | 34 | 0 | -- | 0 | 0 | 0 | 2 |
| 4-6 | 5 | 14 | 0 | 0 | 1 | 0 | 0 | 1 |
| 4-7 | 14 | 4 | 0 | 0 | 3**** | 0 | 0 | 0 |
| 4-11 | 12 | 10 | 0 | 0 | 1 | 0 | 0 | 1 |
| 4-17 | 39 | 9 | 0 | 0 | 23 | 0 | 0 | 4 |
| 4-18 | 6 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 4-24 | 49 | 0 | 14^ | 0 | 2 | 0 | 0 | 3 |
| 4-27 | 9 | 0 | 15 | 0 | 0 | 0 | 0 | 4 |
| 5-3 | 13 | 0 | 25 | 0 | 0 | 0 | 0 | 1 |
| 5-9 | 10 | 1 | 22 | 0 | 0 | 0 | 0 | 0 |
| 5-19 | 5 | 10 | 27 | 0 | 0 | 0 | 0 | 0 |
* Biofix for RBLR in Davidson County was March 2.
**Biofix for DBM in Davidson
County was March 30.
***Biofix for OFM in Davidson County is estimated to be April
3.
****Biofix for GBM in Davidson County was April 7.
^Biofix for OBLR in Davidson
County was April 24.
Bradley County Pheromone Trap Catches for 2006
| OFM | CM | |
| 3-29 | 3* | 0 |
| 4-3 | 26 | 0 |
| 4-5 | 0 | 1 |
| 4-10 | 16 | 0 |
| 4-17 | 19 | 5** |
| 4-24 | 17 | 17 |
| 5-1 | 17 | 2 |
| 5-8 | 15 | 1 |
*Biofix for OFM in Bradley County on March 29.
**Biofix for CM in Bradley County
on April 13.
Putnam County Pheromone trap Catches for 2006
| OFM | RBLR | OBLR | CM | VLR | |
| 3-21 (put out RBLR & OFM) | -- | -- | -- | -- | -- |
| 3-24 | 0 | 0 | -- | -- | -- |
| 3-27 | 0 | 0 | 0 | 0 | 0 |
| 3-31 | 2** | 12* | 0 | 2*** | 0 |
| 4-2 | 1 | 3 | 0 | 0 | 0 |
| 4-7 | 6 | 23 | 1 | 1 | 0 |
| 4-10 | 1 | 16 | 0 | 0 | 0 |
| 4-15 | 9 | 60 | 6 | 0 | 1 |
| 4-17 | 0 | 13 | 1 | 0 | 1 |
| 4-21 | 3 | 14 | 0 | 0 | 0 |
| 4-28 | 10 | 3 | 2 | 1 | 0 |
| 5-7 | 0 | 0 | 2 | 0 | 3 |
| 5-12 | 0 | 0 | 0 | 0 | 0 |
*Biofix for RBLR in Putnam County estimated as March 3 (trap not out early enough).
**Biofix
for OFM in Putnam county March 31.
***Waiting to verify biofix for CM, catch probably
too early.
Obion County Pheromone Trap Catches for 2006
| OFM | RBLR | OBLR | CM | VLR | |
| 3-13 | 1 | 49* | 0 | -- | 2*** |
| 3-21 | 0 | 40 | 0 | 0 | 0 |
| 3-27 | 1 | 2 | 0 | 0 | 0 |
| 4-3 | 2** | 13 | 0 | 2**** | 0 |
| 4-17 | 1 | 18 | 3^ | 1 | 5 |
| 4-25 | 7 | 0 | 0 | 0 | 4 |
| 5-1 | 4 | 0 | 3 | 0 | 4 |
| 5-15 | 0 | 0 | 1 | 0 | 0 |
*Biofix for RBLR in Obion County estimated to be on March 3 (trap not out early
enough).
**Biofix for OFM in Obion County on April 3.
***Waiting to verify
biofix for VLR in Obion County, catch probably too early.
****Waiting to verify
biofix for CM in Obion County, catch probably too early.
^Biofix for OBLR in Obion
County.
Additional Pheromone Trap Catches in Davidson County for 2006
Sod
Webworms (SWW), Armyworm (AW)
| SWW | AW | |
| 4-18 | 3* | 0 |
| 4-24 | 15 | 4** |
| 4-27 | 15 | 1 |
| 5-3 | 16 | 0 |
| 5-9 | 52 | 3 |
| 5-19 | 41 | 0 |
*Biofix for SWW in Davidson County for 2006.
**Biofix for AW in Davidson County
for 2006.
Knox County Pheromone Trap Catches for 2006
Tufted Apple Budmoth
(TABM)
| OFM | RBLR | OBLR | CM | VLR | TABM | |
| 5-1 | 40 | 15 | 2 | 5 | 0 | 17 |
| 5-10 | 3 | 1 | 3 | 2 | 1 | 8 |
| 5-15 | 10 | 1 | 0 | 3 | 3 | 3 |
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Professor and Extension Entomologist
Both authors available at:
615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211
Copyright 2006 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.
