Fruit Pest News
June 11, 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. Apples: What to Do About Fire Blight at this Time
2. Apples: Summer Disease Control Program
3. Tree Fruit: Plant Bugs and Green Stink Bugs
4. Tree Fruit: Insect Trap Counts
1. WHAT TO DO ABOUT FIRE BLIGHT AT THIS TIME
You're stuck with an orchard or block full of fire-blighted trees. What should you do now? It is best to just let the disease run its course. Spread to new shoots is slowing and will end soon, as the shoots stop growing and become resistant to new infections. Dead shoots and branches should be removed in the winter, when pruning does not cause complications. Pruning during the summer can allow bacteria inside the limb to overcome the tree's natural defenses and develop cankers (dark areas) around the cut. These cankers produce bacteria that can spread next year.
If you feel that you must prune out the blighted shoots now, the following technique should help prevent the carryover of the cankers that often form with summer pruning of fire blight shoots: Make the cut into the internode area of a limb that is at least two years old, leaving a stub that extends about four inches beyond the next leaf or branch. During the winter, when it is too cold for the bacteria to form cankers, cut the stub off at the leaf or branch. It is helpful to paint the stubs with a bright-colored paint (such as orange), to make it easier to locate them this winter.
The rationale behind this technique is that the fire blight bacteria have already moved down symptomless limbs internally, sometimes several feet below the blighted tissue. The tree's natural defense system prevents the bacteria from damaging the tissues. By cutting the limb, you allow the bacteria to overcome the tree's defenses and cause a canker to form, setting the stage for spread next year. The "ugly stub" technique provides a means of removing the cankers without sacrificing valuable fruiting wood or structural wood. By pruning the stub back to the next node or branch junction in the winter, no canker forms at the cut, and the internal bacteria never cause a problem.
You may be wondering, "Do I need to dip my pruning shears in a bleach solution between cuts?" With the discovery that the bacteria are usually present inside the shoots and limbs for quite some distance, it is realized that sterilizing the shears does not prevent contamination of shoots; the bacteria are already in them, at varying distances. However, if you engage in normal summer pruning and training of healthy limbs at the same time as fire blight removal, you should sterilize your shears between cuts.
In short, cankers are likely to form around a pruning cut if the cut is made near (or possibly even when far away from) a fire-blighted shoot or cluster, because of the bacteria present inside the limb. By leaving a stub, you are providing a means of removing the cankers from the tree with the loss of only about 4 inches of a naked limb. The alternative would be to make the cuts at nodes or limb junctions, and make a second cut in the winter to remove the cankers that inevitably form. However, such cuts would remove valuable fruiting wood unnecessarily.
The other alternative would be to not do anything at this time, as mentioned above. This is the best idea yet! With this method, you do not induce canker formation in symptomless wood, and the strikes are easy to locate in the winter, when they should be removed. (SB)
2. APPLE: SUMMER DISEASE CONTROL PROGRAM
Your summer disease control program is, no doubt, well underway. The so-called summer diseases take a greater toll on Tennessee apple production than the spring diseases. The summer diseases are fueled by a continuing source of overwintered inoculum, and there are fewer effective fungicides from which to choose. Furthermore, it is more difficult to obtain good spray coverage during the summer than during the spring because of more dense foliage, fruit clustering, and limbs drooping under heavy crop loads.
Your choice of fungicides will depend to some extent on what diseases have historically been a problem in your orchard. If bitter rot has been a problem, captan should be a major component of your summertime spray program. If white rot has been a problem, captan or a benzimidazole (Benlate, Topsin M) should be relied on heavily. For sooty blotch and flyspeck, be sure to include a benzimidazole or a strobilurin (Flint, Sovran). Strobilurins are also a valuable component of a program if scab is still active, as they are very effective against fruit scab. In Golden Delicious blocks, it is a good idea to include ziram or thiram to help protect against necrotic leaf blotch. Mancozeb provides good control of most summer diseases, but cannot be used within 77 days of harvest when used at the 3/4 lb per 100 gallon rate.
Keep in mind the 4-day re-intry interval for captan. Where this is a problem, consider using ziram instead. In such cases, ziram should be mixed with a benzimidazole for improved control of black rot and white rot. Remember that management of diseases with fungicides is improved if cultural practices that reduce inoculum and enhance coverage are used. (SB)
TREE FRUIT: PLANT BUGS AND GREEN STINK BUGS
Plant bugs are
true bugs (Order Hemiptera) in the family Miridae. They have peircing-sucking mouthparts
and their feeding and oviposition can cause damage to fruit or foliage. Tarnished
plant bugs are small (4.9 -5.7 mm), brownish and mottled with shades of yellow and
reddish brown. They feed on a large number of plants including wild mustard and other
flowers, tobacco, cotton, some field crops, vegetables, and tree fruit. In apple,
the overwintered adult bugs move to apple buds around delayed dormant bud stage.
They lay eggs in the blossom buds beginning when the blossoms in the clusters begin
to separate. They continue to feed and lay eggs until the fruit are 1/2 inch in diameter.
The feeding punctures cause tiny indentations and distortions of the fruit. There
is a complex of plant bugs that can attack apples. These include the apple redbug,
green apple bug, dark apple redbug and the mullein leaf bug. Some cause a conicle
indentation in the fruit without russeting or corky tissue, such as the tarnished
plant bug. Others produce corky indentaions or even long corky scars due to repeated
feeding tracks. Since the feeding or oviposition damage is done early in the fruit
development, there is nothing that can be done to reverse the damage. Fortunately,
much of the feeding daqmage , especially the indentations without russeting or corky
tissue, is overlooked when grading the fruit.
The tarnished plant bug is
the major pest of peaches although the oak plant bug, the hickory plant bug and the
green stink bug (Pentatomidae) can be damaging. The general injury categories are
blossom injury and fruit drop, cat-facing injury, scarred injury, water-soaked injury
and gummosis. Blosson injury, fruit drop and cat-facing are the most damaging. Blosom
injury and fruit drop include feeding damage causing blossom drop and feeding damage
between petal-fall and shuck- off causing fruit drop. About one third of blossom
drop can be caused by tarnished plant bug.
Cat-facing deformities are caused
by feeding between the shuck-split stage and 20 mm diameter fruit. Cat-facing damage
consists of depressions that are covered with brown, corky tissue, predominately
free of fuzz. There is usually a mass of gum at the center of the injured area. The
fruit attacked early usually drop while that injured later (diameter greater than
20 mm) will be scarred but remain on tree.
Typical scarred injury consists
of small (1-2 mm) brown, corky, fuzz free areas sometimes with a red pigment in the
skin around the edge of the scars. Numerous of these small scars can can blend to
form 9 by 25 mm scarred areas.
Water-soaked injury consists of small dark
green areas that appear water-soaked. They are round and 2-3 mm in diameter. Gummosis
is the oozing of clear gum from insect feeding punctures.
Monitor for plant
bugs by hanging reflecting, white rectangular sticky traps 3 feet from the ground.
Hang the traps along the edge of a block preferably near wooded areas. Hang 3 traps
per block or one trap for every 3-5 acres. Start monitoring at Pink and continue
until mid-summer. The threshold for peach is one plant bug per trap.
The
green stink bug causes sunken areas or pits that can badly deform the fruit. Much
of the damage occurs late in the summer as shallow, water-soaked depressions. You
can monitor for green stink bugs by jarring the branches over a ground cloth (sheet)
or beating tray. I referred to "Common Tree Fruit Pests" by Angus H. Howitt
for much of the information on plant bugs and green stink bugs. (FAH)
TREE FRUIT: INSECT TRAP COUNTS
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 |
| 5-4 | 2 | 0 | 0 |
| 5-11 | 0 | 0 | 1 |
| 5-23 | 1 | 0 | 3 |
| 5-28 | 0 | 0 | 9 |
| 6-1 | 0 | 0 | 6 |
| 6-11 | 0 | 0 | 13 |
| 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 |
| 5-3 | 35 | 0 | 1 | 17 |
| 5-4 | 3 | 0 | 0 | 8 |
| 5-7 | 12 | 0 | 0 | 10 |
| 5-8 | 6 | 0 | 0 | 2 |
| 5-11 | 12 | 0 | 0 | 7 |
| 5-14 | 2 | 0 | 1 | 0 |
| 5-16 | 7 | 0 | 5 | 1 |
| 5-21 | 11 | 0 | 17 | 11 |
| 5-22 | 3 | 0 | 6 | 11 |
| 5-25 | 3 | 0 | 14 | 2 |
| 5-29 | 5 | 0 | 8 | 3 |
| 6-1 | 6 | 0 | 9 | 2 |
| 6-4 | 0 | 0 | 4 | 1 |
| 6-8 | 3 | 0 | 11 | 3 |
| 6-11 | 4 | 0 | 2 | 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 |
| 4-30 | 0 | 0 | 0 |
| 5-2 | 0 | 0 | 0 |
| 5-4 | 1 | 1 | 0 |
| 5-7 | 22 | 0 | 0 |
| 5-9 | 7 | 0 | 0 |
| 5-11 | 8 | 0 | 0 |
| 5-14 | 2 | 0 | 0 |
| 5-16 | 1 | 0 | 6 |
| 5-18 | 3 | 0 | 20 |
| 5-21 | 1 | 0 | 14 |
| 5-23 | 0 | 0 | 8 |
| 5-25 | 2 | 0 | 3 |
| 5-28 | 10 | 0 | 28 |
| 5-30 | 3 | 0 | 8 |
| 6-1 | 2 | 0 | 2 |
| 6-4 | 0 | 0 | 6 |
| 6-6 | 1 | 0 | 12 |
| 6-8 | 2 | 0 | 8 |
| 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 |
| 5-1 | 0 | 5 | 0 |
| 5-4 | 3 | 4 | 0 |
| 5-6 | 0 | 6 | 0 |
(FAH)
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
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