Fruit Pest News

Volume 3, No. 20    August 5, 2002

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.

Fruit Pest News will be produced every two weeks until the end of the growing season.

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: ALERT FOR PIERCE'S DISEASE

    2. Blueberry: New Fungicide Registrations

    3. Plum and Cherry: Black Knot

    4. Apple: Late-season Fungicide Selection

    5. Apple: Mid-summer Insect Pests

    6. Tree Fruit: Pheromone Trap Catches

1. ALERT: Pierce's Disease of Grape

Mid-summer is when Pierce's disease symptoms should begin appearing in grapes. Please watch for it and let us know if you suspect it to be present in your vineyard. We can give you instructions for confirming the disease. Confirmations are needed for your information and to help us track the distribution of the disease. Below is some information on this disease.

Pierce's disease (PD), a potentially destructive disease of grapes, was confirmed for the first time in Tennessee last year. Symptoms of PD had been encountered several times, but it had never been positively identified prior to last year's confirmation on a sample from a diseased vineyard in southeastern Tennessee. A hot-climate disease, PD is creeping northward as our winters continue to be milder than normal. PD is the most formidable obstacle to growing Vinifera grapes in the southern states. Other types of grapes are affected to a lesser degree.

PD is caused by the bacterium Xylella fastidiosa and is spread by certain kinds of leafhoppers. One particularly effective vector, the glassy-winged sharpshooter, has appeared in California and is causing a wine industry-threatening outbreak of PD in that state. X. fastidiosa can infect other types of plants. Many strains have been discovered. Some of these cause diseases of oak, sycamore, and maple (bacterial leaf scorch); plum (scald); peach (phony peach); and alfalfa (alfalfa dwarf).

The severity of PD appears to depend on climate. The bacterium appears to be sensitive to cold winter temperatures, and produces milder symptoms at higher altitudes, farther inland from ocean influences, and at more northern latitudes, even where vectors are plentiful. Please note that the vineyard in southeastern Tennessee had significant damage from PD, and many of the infected vines died.

PD symptoms begin as a drying or "scorching" of leaves http://csatwork.ucdavis.edu/Archives/Graphics/21600 srgb.jpg. The leaves become slightly yellowed along the margins before drying, or the outer leaf may dry suddenly while still green. Typically, the leaf dries progressively over a period of days to weeks, leaving a series of concentric zones of discolored and dead tissue.  About mid-growing season, when foliar scorching begins, some or all of the fruit clusters may wilt and dry up. Leaves drop, but petioles (leaf stems) remain attached to canes for an extended period of time. The bark on infected canes often matures in irregular patches, resulting in "islands" of green surrounded by brown, or the reverse.

Control of PD consists of vector control and roguing (removing) infected plants. More information is needed on where PD now occurs in Tennessee, and where it is likely to occur in the future (and to what degree). (SB)

2. Blueberries: New Fungicide Registrations

The loss of Benlate was not good news to a blueberry industry with a thin arsenal of products for disease control. Recent registrations of fungicides for use on blueberries improve the picture, and should help during the key disease-control period next spring.

Chlorothalonil products such as Bravo and Equus can now be used on blueberries for suppression of mummy berry and anthracnose. Applications begin at budbreak and can be repeated at 10-day intervals until full bloom. Russetting may occur under unfavorable environmental conditions. Refer to the label for restrictions on tank-mix partners. Chlorothalonil was also labeled for asparagus, for control of rust, purple spot, and Cercospora leaf blight.

Elevate 50WDG fungicide has received a supplemental label for control of Botrytis in blueberries and caneberries (raspberries and blackberries). Elevate is applied at 1.5 lb per acre, beginning at 10% bloom and continuing through harvest.

Abound 2SC fungicide received a federal registration for blueberries last winter. The active ingredient in Abound is azoxystrobin, identical to Quadris. For blueberries, the target diseases for Abound are mummy berry, Alternaria fruit rot, Phomopsis twig blight, and anthracnose. The rate is 6.2 to 15.4 fl oz/acre, with a 0-day preharvest interval.  Abound should be used preventatively, up to 3 applications per year, but not more than twice consecutively. (SB)

3. 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 Benlate, 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)

4. 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 undesirable residues on the fruit, but is necessary where fruit rots have become a problem. Captan, thiram, and Topsin M have 0-day PHI's, and would be the products of choice in such cases. In choosing a late-season fungicide, also consider the restricted-entry interval if you have employees. (SB)

Late-Season Apple Fungicides

5. Mid-Summer Insect Pests of Apple

Japanese beetles are primarily leaf feeders. Small fruit trees especially, may need protective sprays if feeding (leaf skeletonizing) occurs in more than the top third of the tree according to West Virginia University's The Orchard Monitor newsletter. Japanese beetle feeding injury has probably peaked in Tennessee. The Japanese beetle and the green June beetle, which mainly damages the fruit, can both be treated with Sevin XLR Plus. After making a representative sample of maturing stone fruit, treat if one percent of the fruit have feeding injury (The Orchard Monitor). Do not treat unless you really need to because spraying can potentially flair up mite populations.

European red mites and twospotted spider mites can build up quickly during these hot, summer days. Trees need to be monitored regularly (each week once they occur) which can vay from mid-May to early July. Within each block, examine 5 leaves from each of 10 trees using a hand lens. Record the number of leaves with one or more mites and then use the table on page 31 of the 2002 Integrated Orchard Management Guide for Commercial Apples in the Southeast to estimate the mite density per leaf. When mite populations reach a density of 5 to 10 mites per leaf (80 to 90 percent infested leaves) a decision should be made as to whether biological control will prevent mites from increasing to higher densities, or if a miticide should be applied. See page 31 of the "Guide" to see the ratio of Stethorus punctum lady beetles and/or Amblyseius fallacis predatory mites that will be needed to control a given pest mite population. In areas where Alternaria blotch is a problem on 'Delicious' apples, biological control is usually not an option. In these cases, mite populations must be maintained at very low levels to avoid high levels of Alternaria and/or premature defoliation.

Peachtree borer and lesser peachtree borer sprays should be made after harvest of stone fruit but not before early to mid-August. Handgun application to the trunk and scaffolds is strongly encouraged since airblast use has resulted in poor control. Use one quart of finished spray for mature, bearing trees and one pint each for young, nonbearing trees. Use Lorsban 4E at 3-6 pints per 100 gallons (3 pints per 100 gallons is normally adequate). If white peach scale are a problem, add 1/2 percent superior oil to the Lorsban for suppression of white peach scale.

Dogwood borer on apples is becoming a problem because they attack burr knots and graft unions. Spray with Lorsban 50W, Lorsban 4E, Thiodan 3EC, Phaser 3EC or Asana XL (I prefer the Lorsban). Treatment in mid to late May is optimal. Lorsban must be applied with a handgun sprayer from no more than 4 feet or with a shielded sprayer to prevent drift onto the foliage or fruit. (FH)

6. Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2002

Biofix for RBLR in Davidson County estimated as March 14

Bradley County Pheromone Trap Catches

Codling moth biofix was April 14

Putnam County Pheromone Trap Catches

Obion County Pheromone Trap Catches

(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, Associate Professor and Extension Entomologist

fahale@ext1.ag.utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211