Fruit Pest News
Volume 3, No. 12 May 27, 2002
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. Registration of New BASF Fungicide (Cabrio) Delayed
2. Nemacur Cancellation
3. Effect of Rain on Fungicide Wash-Off
4. Peach Scab
5. Apples: Trauma Blight Fire Blight
6. Tomatoes: Fusarium Wilt
1. Registration of New BASF Fungicide (Cabrio) Delayed
You may have heard about the new strobilurin fungicide from BASF Corporation for which registration was expected this spring. Pyraclostrobin, the active ingredient, has the trade names of Cabrio (fruits and vegetables), Headline (row crops and potatoes) and Insignia (turf). Much university work has been conducted with this material under the code name F500. The registration process was delayed, and BASF currently estimates registration by the fall of 2002. Cabrio, like other strobilurin-type fungicides (e.g.., Quadris, Flint, Sovran), has broad-spectrum disease control properties, and registration is expected to include many crops. (SB)
2. Cancellation of Nemacur
All domestic uses of fenamiphos (Nemacur) nematicide will cease as of May 31, 2005. Bayer has voluntarily cancelled the registration, citing escalating costs of defending the material relative to limited sales. During the three-year phaseout, Bayer will continue to produce and sell Nemacur.
Nemacur has little usage in Tennessee, but is relied upon in the coastal plains areas for post-plant nematode control in peaches. No other post-plant nematicide is available for use in peaches, and the loss of Nemacur will increase the importance of a knowledge of the presence of root-knot nematodes in the soil before planting trees. Proactive measures would consist of fumigation or the use of a root-knot resistant root stock. (SB)
3. Effect of Rain on Fungicide Wash-Off
If rain if forecast on or around the day you plan to make a fungicide application, it is best to spray before the rain, rather than after. Disease-control products work best in a preventive mode. They need to be in place, working to protect the plant tissues while they are wet. But that begs the question, "Just how durable are those protective covers? How soon do I need to re-apply a fungicide after a rain?" The following article was written for apple growers by Dr. Jim Travis, Pennsylvania State University plant pathologist. The guidelines he provides should apply to all crops, although the example products may not apply. (SB)
If you are using protectant fungicides, you need to consider the effect of rain on wash-off of the materials. The strobilurin (Sovran, Flint) and sterol inhibitor (Nova, Procure, Rubigan) fungicides are absorbed into the leaf and fruit tissue after application (once the residue has dried) and are not affected by rain wash-off. The protectant (Dithane, Manzate, Penncozeb, Captan, Ziram, Thiram, Carbamate) fungicide residues can be affected by rain. A general rule-of-thumb for the effect of rain on washing off protectant fungicides follows.
This rule has been used for many years to provide growers with general guidance. Newer protectant fungicide materials may be less subject to wash-off, but information is limited.
4. Peach Scab
I have not yet seen peach scab symptoms, which usually begin appearing around this time. Peach scab has a 40-day latent period, which means that symptoms do not appear for 40 days after infection. Control is not needed on varieties that are within 40 days of harvest, since any infections that occur will not have time to develop before harvest. This does not mean that early-maturing varieties will not have scab if it is not showing at this time (a 40-day latent period could be in progress). It just means that a spray at this time would not reduce scab on an early-maturing variety. Be sure to begin your brown rot sprays within 3 weeks of harvest for each variety. (SB)
5. "Trauma Blight" Fire Blight
Last week's
frosts remind us of the bad things that can happen to trees to cause"trauma blight." This
is fire blight that results from infections
associated with injuries due to late frosts, hail, or high winds. Expect trauma type fire blight to be most severe when the bacterial
population is high. While free water on the surfaces of leaves is likely during a
frost or with hail, infections do occur in the absence of rain under high wind conditions
that tatter the foliage. Even here, rain increases the severity.
Action to
take: If a trauma event occurs, a streptomycin application should be made within
24 hours if fire blight symptoms are present in the orchard. The application
should be made even if the foliage is still wet. If you think the fire
blight bacterial population is high (the block has a history of fire blight
and the weather has been constantly warm),
apply the streptomycin even though no symptoms are present. Note: It is only
after a trauma event that we recommend the use of streptomycin after bloom.
It is not recommended for routine control of shoot blight. This is because
it is not effective for control of shoot blight, and repeated use of this valuable
product can cause resistance to it to develop in the fire blight bacterium.
(SB
6. Tomatoes: Fusarium Wilt
Editor's note: I know, tomatoes are not a fruit. But we will occasionally include some vegetable pest news in this newsletter, because many fruit growers also grow vegetables. Please guide us by giving us ideas on what you would like us to include.
There has been an alarming increase in fusarium wilt cases in commercial tomatoes in Tennessee the last couple of years. Be on the lookout for bright yellow leaves when the plants load up with fruit. The yellow leaves may appear on one side of the plant, and progress to a brown color and die. The internal vascular tissue is brown, rather than the normal light green to cream color. Fusarium wilt may occur in varieties that are resistant to races 1 and 2 fusarium wilt, because these varieties are not resistant to race 3, which is increasing in the state.
Control options are limited. The best control is to prevent the introduction of infested soil into your field. Once a field is infested, the best control is to plant a resistant variety. Few acceptable varieties have resistance to race 3. Floralina is the only resistant variety that has been tested in Tennessee. For varieties that are not resistant to race 3, soil fumigation with methyl bromide helps to delay and reduce the disease, but does not eliminate it. Cultural practices (e.g. maintaining a soil pH of 6.5 to 7.0; controlling root-knot nematode) help mitigate the disease, but do not provide an adequate level of control by themselves. Crop rotation is of little value, because the causal fungus is so long-lived in the soil. As you can see, fusarium wilt is a "bad boy." If you find suspect plants, contact your agent about getting a confirmation, so that you can take remedial actions next year. (SB)
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