Fruit Pest News
Volume 4, No. 19 August 18, 2003
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. Strawberries and Blackberries: Virus-Indexed Plants Now Available at Nurseries
2. Grape Downy Mildew
3. Apple: Phytophthora Crown Rot and Collar Rot
4. Apple: Identifying Fruit Rots
1. Virus-Indexed Small Fruit from NCSU Now Available at Nurseries
The North Carolina Crop Improvement Association operates a certification program for many crops including strawberries and sweetpotatoes. In the past year it has established a certification program with brambles. Currently, there are five strawberry nurseries and one bramble nursery that sell certified plants. Virus indexed plants are produced by the NCSU Micropropagation Unit (Dr. Zvezdana Pesic-VanEsbroeck, 919-515-7781) and are sold by the NC Foundation Seed Producers, Inc. (Dr. Myron Fountain, 919-513-3444) to certified nurseries. Here is a list of nurseries that are certified by the NC Crop Improvement Association:
STRAWBERRIES
B&H Nursery (Jeff Hartzog, Keith Barlow)
298 Peak Creek Church Rd., Laurel Springs, NC 28644
phone: 336-982-8155 or 336-982-9585, email: jdhfarmer@hotmail.com
McNeill Farms (Steve McNeill),
1621 Kentyre Farm Rd., Sanford, NC 27330
phone and fax: 919-499-9706, cell: 919-775-9428, email: skmcneill@alltell.com
McConnell Farms (Danny McConnell)
117 Old Dana Rd., Hendersonville, NC 28792
phone and fax: 828-692-2819, email: mcconnell@brinet.com
Shingleton Farms (Tommy Shingleton)
P.O. Box 357, Stantonsburg, NC 27883
phone and fax: 252-238-2155, cell: 252-236-5187, email: T.shingleton@cocentral.com
BLACKBERRIES
Jones Farm NC (Barbara Jones)
7094 Honeysuckle Lane, Bailey, NC 27807
phone: 252-235-3248, fax: 252-235-0155, cell: 252-399-9844, email: jonesfamsnc@aol.com
Source: Gina Fernandez and Zvezdana Pesic-VanEsbroeck (NC State University) and Myron Fountain (NC Crop Improvement Association)
2. Grape Downy Mildew
Downy mildew often becomes very noticeable in vineyards in late summer and fall. This disease causes direct yield losses by affecting flower and fruit clusters. Indirect losses can result from premature defoliation of vines due to leaf infections. Be wary of premature defoliation of vines after harvest, because this predisposes the vines to winter injury.
Summer spay programs are needed even where a conscientious program was followed during the spring. You can't rest! Springtime symptoms of this disease often go unnoticed. Furthermore, spores of this fungus are capable of riding on air currents for some distance, so they can enter a vineyard during the summer.
Leaf symptoms can vary depending on the age of the leaf when infected, and the temperature. Leaf spots can be large and yellow, with indistinct margins, or small, angular, yellow to necrotic, and limited by the veins. In late summer and fall, most leaf infections appear as the latter. Older leaves become infected first, and the disease spreads towards the leaves at the ends of the canes. Leaves eventually become dry and brown and fall from the cane. Such defoliation reduces sugar accumulation in fruit and decreases hardiness of overwintering buds.
Shoot tips, tendrils, and blossom clusters may also be infected. Young berries are very susceptible, appearing grayish when infected and covered with a downy felt of fungus sporulation. Although berries become less susceptible as they mature, infection of the rachis (the main cluster stem) can spread into older berries. Berries infected at this time generally do not soften or show a downy growth; instead, they become brown and shatter easily.
The downy mildew fungus overwinters primarily in fallen leaves. Survival is best on the soil surface and is enhanced by wet winters. The overwintering spores germinate in water in the spring to produce a spore that disperses to plant tissue by splashing rain.
Maneb, mancozeb, Ridomil Gold Copper, and Ridomil Gold MZ are excellent downy mildew fungicides, but have 66-day preharvest intervals. Among the fungicides used during the summer on grapes, captan, Abound, fixed copper, and ziram have the best activity against downy mildew. A 10 to 14-day spray interval should be followed until the harvest restriction is reached. Susceptible varieties should be sprayed after harvest also, so as not to incur the vine-weakening effects of defoliation by downy mildew. (SB)
3. Phytophthora Crown Rot and Collar
Rot of Apple
Crown rot, collar rot, and root rot in apple trees are caused
by Phytophthora species (root rots can also be caused by other types of fungi). These
three diseases can occur on one tree and can be caused by a single infection, but
are given different names to designate the part of the tree affected. Collar rot
occurs in the scion part of the tree. This disease has decreased due to changing
variety preferences and to the practice of raising graft unions above the soil line
at planting. Crown rot is a disease of the rootstock portion of the tree. It has
become more important because of the increased use of susceptible rootstocks such
as MM106 and M26. Phytophthora root rot is a disease of the root system away from
the crown region. It may occur along with crown rot or may occur by itself.
In
the spring, symptoms of Phytophthora include delayed bud break, leaf discoloration,
and poor growth. Foliage is sparse, yellowish, and may develop an early purple discoloration
in autumn. In dry weather, infected trees are the first to exhibit symptoms of water
deficit.
The most obvious symptom is a partial or complete girdling of the
trunk with reddish-brown, water-soaked areas of dead tissue at the base of roots
where they attach to the trunk. The entire underground portion of the trunk is usually
water-soaked and
brown with the dead area extending upward to the graft union.
The fire
blight bacterium can cause rootstock cankers on M26 and M9 that are almost indistinguishable
from crown rot. Fire blight cankers form in July and August following early season
blossom and/or shoot infections. Rapid decline of trees on these rootstocks in late
summer may be caused by fire blight cankers below the graft union.
Avoid planting
fruit trees in poorly drained locations, and do not allow depressions to form around
the base of trees. Where drainage is questionable, use the less susceptible rootstocks
such as seedling and M9. Moderately susceptible rootstocks are M7, M26, and MM111.
Ridomil
and Aliette fungicides are helpful in control, but should not be solely relied upon.
They should be used in conjunction with cultural practices. Because Phytophthora
diseases occur sporadically, it is usually not economical to treat entire orchards
on a regular, preventative basis. Rather, use them in problem areas. Also note that
these fungicides seldom are effective in reviving trees once the crown has become
infected and moderate symptoms of decline have appeared. Ridomil can be used in the
fall and spring only, applied as a soil spray. Dipping the roots of nursery-grown
trees into a solution of Aliette prior to planting may reduce, but not eliminate,
Phytophthora inoculum on roots. Aliette can be used as a foliar spray to nonbearing
trees. (SB)
4. Apple Fruit Rot Diseases
Fruit are entering their period of highest susceptibility to rot diseases. It may be worthwhile to review the major rot diseases of apple fruit, so that your spray program can be adjusted accordingly, if needed.
Black rot of fruit is characterized by dark, firm rots that are not sunken. As the lesions enlarge, they may produce a series of concentric rings alternating from black to brown. Fruit infection can occur early in the season, as soon as the bud scales begin to loosen. This early infection usually involves the sepal, and results in blossom-end rot later in the season. The black rot fungus also causes frogeye leaf spot and limb cankers.
White rot, sometimes called Bot rot, can be destructive on certain varieties such as Golden Delicious, on which small, tan, developing lesions are often surrounded by a red halo. When fruit rot under warm conditions, as they usually do, the rot is tan to light brown, soft, and watery. Under cooler conditions, rotted areas are usually firmer and deeper tan, and resemble black rot. White rot fruit lesions extend in a cylindrical pattern to the core of the fruit.
Bitter rot fruit infections are circular, sunken, and brown in color. When developing lesions reach about the size of a quarter, concentric rings of spores are produced around the center of the lesion. Under moist, humid conditions, the spore masses appear creamy to pink to orange in color. Decay lesions extend in a cone-shaped pattern toward the core, as opposed to the cylindrical shape of white rot lesions. Numerous infections can occur and losses can be extensive in warm, wet weather.
Apple fruit rots are managed by good pruning practices to improve spray coverage and drying time. Either remove the prunings from the orchard or mow them with a flail mower. (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
