Fruit Pest News
April 30, 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 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 Crop Situation
2. Strawberry Diseases Appear
3. Watch for Orange Rust in Blackberries
4. New Crown Gall Control
5. Tree
fruit: Insect Update
1. CURRENT CROP SITUATION
Light frosts during each of the last two weeks continued to harass fruit growers in Tennessee. There have been some loss of strawberry blossoms where frost protection was not used. Some of the peaches at the Plant and Pest Diagnostic Center aborted at the shuck fall stage of growth. Mother Nature has thinned those fruit nicely, to the point at which no more thinning will be needed. Harvest is beginning in some plasticulture strawberry fields. The weather has been dry. (SB)
2. STRAWBERRY DISEASES APPEAR
Despite the dry weather, some dreaded strawberry diseases were reported last week. Two cases of anthracnose were called in, and one case each of Phytophthora crown rot and angular leaf spot were confirmed in the Plant and Pest Diagnostic lab. Frost protection efforts may have contributed to some of these, but the cases were mostly light to this point. These situations bear watching. (SB)
3. 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.
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 fungicide Nova 40W can now be used for control of orange rust. Nova helps
prevent leaf infections. It will not cure a systemically-infected plant. (SB)
4. NEW CROWN GALL CONTROL
Crown gall can be a problem on fruit trees, especially stone fruits, and is caused by the soil-borne bacterium Agrobacterium tumefaciens. The only available prevention for crown gall in the past has been pre-plant root dips with a biological control composed of the competitive bacterium Agrobacterium radiobacter strain 84. This product has been available commercially as Galltrol (agar plates) and Norbac K84 (gel suspension). Norbac K84 has been removed from the market, although the Galltrol version should still be available. Norbac K84 is being replaced with NOGALL 1026, which has been modified to prevent resistance in the crown gall bacterium from occurring. This has been a problem in some areas of the world.
NOGALL 1026 will come as a live bacterial culture on a finely ground peat medium. It has a much better shelf life than the gel formulation, but should still be refrigerated. A 100 gram packet should be mixed with one gallon of water and the tree roots can be dipped or sprayed.
Crown gall can also be a problem in grapes, but is caused by a different strain of the bacterium than that which affects stone fruits. As a result, the biocontrols mentioned above will not control crown gall of grape.
NOGALL 1026 will probably have to be ordered. The company's address is New BioProducts, Inc., 2166 NW Fritz Place, Corvallis, OR 97330. The phone number is 541-752-2045. (Adapted from an article by Gary Thornton and Alan Jones, Michigan State University.)
5. TREE FRUIT: INSECT UPDATE
The following is an overview of how the
degree-day (DD) clculations are made. We start counting DD when the biofix occurs
(first sustained catch of the target moth in the pheromone traps). In Davidson County
this was April 4 for the codling moth (CM) and April 9 for the Oriental fruit moth
(OFM). Let us look at the OFM as an example. We recorded the maximum temperature
of the day and the minimum temperature. On April 9 that was 83F and 67F, respectively.
You add those two numbers to get 150 which you then devide by 2 to get the average
temperature for the day of 75F. We know that with insects if the temperature drops
below a certain point, called the lower threshold, no development occurs. In the
case of the CM the lower threhold is 50F while it is 45F for OFM. In our example,
75F minus the lower threhold of 45 gives us 30 DD accumulated that day. On the next
day, April 10, the high was 86F, the low 66F so we accumulated 31 DD more. The insects
to continue to develop when it is warm enough and the more the DD the more they develop.
Note that there is an upper threhold where it can get to warm (the upper base is
an average of 88F for CM and 91F for OFM). Since we accumulated 30 DD on April 9
and 31DD more on the 10th the cumulative DD for those two days was 30 plus 31 equals
61DD. As reported in last weeks newsletter we had 282.8DD accumulated for the Davidson
County site as of April 23 for OFM. The 2001 Southern Peach, Nectarine and Plum
Pest Management and Culture Guide states that for first generation OFM, for moderate
to high density OFM orchards (caught more than 10 moths /trap/week) that two insecticide
applications should be made 14 days apart, the first at 500DD after biofix. We have
319.3 DD through April 26 and with the warm weekend we will soon be at 500DD.
(FH)
Obion
Co. (traps put out April 9)
| Date | OFM | CM | RBLR |
| 4-13 | 0 | 21 | 28 |
| 4-20 | 6 | 0 | 3 |
| 4-27 | 0 | 0 | 0 |
| Davidson Co. | ||||
| Date | OFM | CM | RBLR | OBLR |
| 3-26 | -- | -- | 8 | -- |
| 3-28 | -- | -- | 0 | 0 |
| 3-30 | -- | -- | 8 | 0 |
| 4-2 | -- | -- | 10 | 0 |
| 4-4 | 0 | 12 | 13 | 0 |
| 4-6 | 0 | 1 | 13 | 0 |
| 4-12 | 23 | 5 | 53 | 0 |
| 4-16 | 11 | 1 | 12 | 0 |
| 4-19 | 0 | 0 | 0 | 0 |
| 4-20 | 0 | 0 | 0 | 0 |
| 4-23 | 12 | 2 | 0 | 0 |
| 4-25 | 5 | 0 | 0 | 0 |
| 4-26 | 0 | 0 | 0 | 0 |
| 4-27 | 2 | 0 | 0 | 0 |
| 4-30 | 6 | 0 | 0 | 1 |
| Putnam Co. | |||
| Date | OFM | CM | RBLR |
| 4-6 | 4 | 0 | 15 |
| 4-9 | 15 | 1 | 9 |
| 4-11 | 12 | 0 | 67 |
| 4-13 | 3 | 0 | 37 |
| 4-16 | 0 | 0 | 14 |
| 4-18 | 1 | 0 | 1 |
| 4-20 | 1 | 0 | 8 |
| 4-23 | 0 | 0 | 11 |
| 4-24 | 2 | 0 | 1 |
| 4-27 | 0 | 0 | 0 |
| Bradley Co. | |||
| Date | OFM | CM | RBLR |
| 3-15 | 2 | 0 | 0 |
| 3-23 | 1 | 0 | 5 |
| 4-5 | 0 | 0 | 2 |
| 4-7 | 0 | 0 | 1 |
| 4-9 | 1 | 0 | 0 |
| 4-12 | 3 | 0 | 0 |
| 4-13 | 2 | 0 | 0 |
| 4-15 | 3 | 0 | 7 |
| 4-22 | 0 | 2 | 2 |
| 4-24 | 0 | 5 | 0 |
| 4-25 | 0 | 4 | 0 |
| 4-28 | 2 | 8 | 0 |
| 4-29 | 0 | 10 | 1 |
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Associate 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