Fruit Pest News

Volume 5, No. 19  August 10, 2004

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.

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. Grapes: Pierce's Disease and California Wine Grapes

    2. Grapes: Multicolored Asian Lady Beetles and Wine Grapes

    3. Plum and Cherry: Black Knot

    4. Apples: Late-Season Fungicide Selection

    5. General: Japanese Beetle Update

    6. General: Pheromone Trap Catches

1. Pierce's Disease and California Wine Grapes

I just returned from a tour of some of the fruit-growing regions of California, and got the low-down on Pierce's disease (PD) and its most important vector, the glassy-winged sharpshooter. The disease and the sharpshooter are thoroughly established in the Temekulah Valley wine region of southern California, between San Diego and Los Angeles. The Napa Valley wine region of northern California has been spared so far. Glassy-winged sharpshooter outbreaks have occurred in garden centers along the coast, probably resulting from the importation of nursery stock from southern California. However, these outbreaks of the insect have been eradicated in each case by the California Department of Agriculture. The behavior of the glassy-winged sharpshooter in California makes it easy to spot. Its feeding on trees produces much honeydew and causes a white-colored sap flow from the tree twigs.

On a related subject, the current thought is that the efficiency of the glassy-winged sharpshooter in transmitting the Pierce's disease organism is due to its ability to feed on older plant tissues. Theoretically, this placement of the bacterium provides it with better winter protection than would be found in younger shoots, thus allowing survival in colder climates.

Please watch for PD and let us know if you suspect it to be present in your vineyard. 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).

Symptoms. PD symptoms begin as a drying or "scorching" of leaves. 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. (SB)

2. Multicolored Asian Lady Beetles and Wine Grapes

The multicolored Asian lady beetle is an introduced insect that has become widespread in Tennessee and most all of the eastern U.S. since the early 1990's. While it feeds on aphids and is an excellent predator, it also can congregate around houses and other building in October and spend the winter within the walls, crawl space, attic etc., which has made this insect a major nuisance pest.

While reading the Purdue University online fruit newsletter entitled "Facts for Fancy Fruit," this lady beetle was mentioned as an indirect pest of wine grapes in central and northern Indiana and other wine grape growing areas in the Great Lakes region. This insect has become a problem on late August and September harvested wine grapes. The beetles congregate within the clusters and are harvested and crushed during crush and pressing. Unfortunately, the beetles can excrete a yellow, smelly defensive chemical (methoxypryazine) into the juice giving it an objectionable smell and taste.

Please be on the lookout for these insects in grape clusters and let us know if these lady beetles are a problem in Tennessee wine production. It would also help to know what varieties of grapes are attracting these beetles. (FH)

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 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 visible 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. Japanese Beetle Update

The first Japanese beetle adult that I saw this spring in Nashville was on May 28. This pest has been moving into Middle Tennessee from the east for 8-9 years or so. Populations have increased dramatically in the area and the amount of feeding damage (skeletonized leaves) has caught many people by surprise. While ornamental tree and shrub defoliation gets most of the attention, grapes, blackberries, blueberries and other fruit and vegetable crops can be fed upon by this pest. While they are primarily foliage feeders, they can also feed on ripe blueberries or brambles.

Japanese beetle adult activity is essentially over in many areas of the state. Most of the insects have fed, mated and the females have deposited their eggs in the moist turfgrass soil. The good soil moisture across most of the state should allow for higher than normal egg survival so expect as many or more next year.

I was at the Plateau Experiment Station last week for the Steak and Potatoes Field Day. Japanese beetles were still found to be feeding, aggregating and mating. Young plantings of grapes and blackberries were especially fed upon. Excessive foliar feeding should be prevented on these young plants to promote adequate growth by periodically using an insecticide such as Sevin.

The adult beetles on the Cumberland Plateau and those in other milder areas of the state should finish up their egg laying soon. The larvae (white grubs) will remain in the soil and feed on grass roots until next spring, after which they will pupate prior to emergence as adults. (FH)

6. General: Pheromone Trap Catches

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, Professor and Extension Entomologist

fahale@utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211