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Compiled by: Alfredo Martinez,
Extension Plant Pathologist

• 2006 Plant Disease Clinics Annual Summary
• Apple
• Blueberry
• Bunch Grape
• Corn
• Cotton
• Muscadine Grape
• Ornamentals
• Peach
• Peanut
• Pecan
• Soybean
• Strawberry
• Turfgrass
• Vegetables
• Wheat
• Summary of Total Losses Due to Disease Damage and Cost of Control in Georgia - 2006
• ATTENTION! Pesticide Precautions

It is estimated that 2006 plant disease losses, including control costs, amounted to approximately $647.2 million. The value of the crops used in this estimate was approximately $4673.73 million, resulting in a 12.08 percent total disease loss across all crops included in this summary.

The estimated values for most crops used to compute these disease losses are summarized in: Georgia Agricultural Statistics Service, Georgia Farm Report 7, No. 1 and the 2006 Georgia Farm Gate Value Report (AR-07-01). Some estimates for fruits, grapes, ornamentals and turf rely on specialists’ knowledge of the industry and industry sources for information.

2006 Plant Disease Clinics Annual Summary

Extension Plant Pathology maintains two plant disease clinics as educational resources for county extension agricultural faculty to use to aid their clients in diagnosing and correcting disease-related plant problems. There have been some major changes in the past year in regard to the diagnostic clinics. First, the Homeowner IPM plant disease clinic reopened in October, 2006, and is now located in Athens and operated in conjunction with the Athens Plant Disease Clinic by Holly Thornton. The following plant disease samples are now processed at this location: commercial fruit, ornamentals and turf; Christmas trees and forestry; all homeowner samples; legume forages and small grains; urban ornamental landscapes; mushrooms; and wood rots. In addition, there is now a $10 processing fee for all physical homeowner samples submitted to the Plant Diagnostics Clinic in Athens.

In Tifton, the Plant Disease Clinic run by Jason Brock recently moved from the Rural Development Center to the Horticulture Building on the main Tifton Campus, Room 116, 4604 Research Way. Diagnoses of and control recommendations for commercial samples of field crops, grain forages, pecans and vegetables are handled at this location.

Compared to previous years, sample numbers are down. This is due in part to the fact that the Homeowner IPM Clinic was closed for most of 2006, and drought conditions experienced throughout the state were not conducive for most disease organisms.

Diagnoses and educational recommendations are returned to the county faculty. The clinics maintain a computerized data base of samples and their diagnoses through the DDDI system as well as a reference library for use by extension agents, specialists, researchers and students. Monthly homeowner reports are also available via our departmental clinic home page — .

Apple

Apples had very limited disease pressures in 2006. This was due to exceptionally dry conditions from bloom throughout most of the season. Fire blight was not prevalent. As usual, bitter rot was an issue, but dry conditions helped to prevent major losses. There is still a strong need for more efficacious fungicides for control of bitter rot and other summer rot diseases. In addition, though not yet observed, we are concerned that streptomycin antibiotic resistance may yet become an issue; currently, streptomycin is the only effective antibiotic for fire blight. If we lose this antibiotic due to resistance, apply production will be must more difficult. Cost of control included pesticide usage for fire blight, pruning costs, and summer rot control measures.

Blueberry

In 2006, disease losses were minimal in the blueberry crop due to dry conditions. However, a new disease has entered the blueberry market, and it is worth tracking it at this point. The disease is called bacterial scorch, and it is also caused by Xylella fastidiosa. At this point, we are researching means of suppressing this disease, but no control methods are currently being used. To date, disease losses have been minimal, but this is an emerging disease problem, and it may eventually be problematic for the entire blueberry industry.

Bunch Grape

Disease pressure was low to moderate for rot and foliar diseases among bunch grape vineyards in 2006, largely as a result of a dry year. However, downy mildew was prevalent in some locations; this might be a result of fungicide resistance development in the fungal population and, if so, this is very troubling. This will be the topic of future screening efforts.

Also, Pierce’s disease losses were extensive in 2006. North Georgia is on the southern edge of the region where one can effectively grow wine grapes, and this is related to Pierce’s disease, a bacterial disease that is vectored by an insect (the glassy-winged sharpshooter). Cold winter temperatures either kill the insect that transmits the disease, or the temperatures may actually prevent the bacteria from surviving, but the verdict is still out on which is more important. We do know, however, that cold temperatures allow for production of vinifera wine grapes, and we do not recommend that producers plant these at elevations below 1,300 feet. The past two or three winters have been very warm by comparison to average. Whether this is a direct relationship to global warming, or whether this is strictly a random event, remains to be determined. As a result of these warmer winters, however, we have observed substantial increases in vine death even at higher elevations and longitudes. In some cases, producers have gone from losing fewer than 10 vines per year to losses of several hundred vines. Needless to say, we cannot continue in this manner. In order to combat the current trend, we are suggesting that producers incorporate more insecticidal applications to kill the insect vector, and we are conducting experiments with inoculations of closely related bacteria. This is all very experimental at this time, but we are hopeful.

Corn

In 2006, corn was harvested from 269,144 acres in Georgia with an average yield of 131 bu/A. The 2006 crop was valued at $102,543,111. Southern corn leaf blight was of minor importance in 2006. Southern rust, which was very important in 2003, was inconsequential in 2004, 2005 and 2006. Rainfall was less abundant during the 2005 and 2006 growing seasons than in 2003 and 2004, so aflatoxin levels increased slightly for the 2005 and 2006 crops. The true importance of damage from nematodes, e.g. sting, stubby root and southern root-knot nematodes, is becoming more apparent as growers and county agents become more familiar with the symptoms.

Cotton

In 2006, it was reported that cotton was harvested from an estimated 1.40 million acres. The average lint yield was 844 lb/A. The crop was valued at $745,462,412.

Losses to seedling disease, primarily Rhizoctonia seedling blight or “soreshin,” were low due to ideal growing conditions at planting time. Losses to nematodes, primarily southern root-knot nematodes, continue to be one of the most important problems for cotton growers in Georgia. Mid-season drought during 2006 increased losses associated with damage from nematodes. Until growers are able to practice effective crop rotation and increase the number of years between cotton crops in a field, the losses and damage from parasitic nematodes will continue to increase unless growers use nematicides effectively. Ascochyta blight was of particular concern among growers in the southwestern region of Georgia in 2006; however, it appears that losses to this disease were minimal.

Muscadine Grape

Minimal disease pressure was observed in most muscadine vineyards. When rots were observed, Macrophoma rot was the predominant disease observed. Black rot was observed on leaves, but this did not translate to fruit rots. Moisture levels were low, and disease losses were minimal.

Ornamentals

The 2006 farm gate value for ornamental horticulture (excluding turf) was estimated at $597.63 million. Landscape, re-wholesale and retail (i.e. service) industries are estimated to account for an additional $1.8 billion, for a total ornamental industry value-added estimate of $2.39 billion. Disease loss estimates were generated for only ornamental production and excludes the value-added service industries as true value, disease loss, and cost of control are not documented and vary greatly within the industry. This change was initiated in 2005 and is a major change from disease loss estimates in previous years, as only farm-gate value is reported and figured into the loss estimate.

Root rot diseases still account for the largest percentage of disease loss in commercial ornamental production. Downy mildew, rust diseases and needle blight on Leyland cypress continue to increase in occurrence and cost of control due to additional fungicide inputs and labor costs.

Peach

Due to exceptionally dry conditions observed throughout much of the season in the major production regions, peach production in 2006 experienced very limited disease pressure. Brown rot pressure was extremely low due to dry weather during most of the harvest. Scab, though present, was also minimal. The same was true of bacterial spot. Problems with Armillaria root rot and phony peach were observed. Armillaria continues to be a major, expanding problem in replant peach production. Bacterial canker was observed in a couple of locations, but it was very sporadic — only worthy of mention since it is somewhat rare.

Peanut

In 2006, peanut was harvested from approximately 592,000 acres. Yields in 2006 averaged 2,888 lb/A for a total production valued at $321,334,435. Growing conditions were favorable for peanut production early in the season; however, hotter and drier conditions were common during the second half of the season over much of the Coastal Plain.

The 2006 season was fairly mild for tomato spotted wilt. Severity of this disease was much lower than in 2005. Warm soil conditions during the second half of the 2006 season favored the development of white mold, which was the most important peanut disease for Georgia last year. Early and late leaf spot diseases were a problem for some growers; however, dry conditions slowed the spread of these diseases. Leaf spot diseases are often more severe in fields where peanuts are planted on a short rotation. Dry weather helped reduce the overall severity of leaf spot diseases in 2006.

Pecan

The 2006 pecan season was relatively dry, resulting in conditions unfavorable for disease development. Loss potential was variable, ranging from 1 to 40 percent.¹

Soybean

The recurrence of soybean rust, Phakopsora pachyrhizi, in Georgia was the most important disease issue for soybean producers in 2006. Asian soybean rust was found to successfully survive the winter of 2005-2006 on protected patches of kudzu in southern Georgia, in Miller, Grady, Thomas and Brooks counties for example. The disease, however, was not detected on sentinel plots in the state until mid-July (first in extreme southwestern Georgia). The most important spread of Asian soybean rust into commercial areas occurred in late August and early September. It is estimated that at least 45 percent of the growers in Georgia applied at least one fungicide spray for the management of this disease. In fungicide trials, significant yield losses were attributed to rust. In one trial, yields were improved by more than 20 bu/A where fungicides were applied

In 2006, soybean was harvested from an estimated 156,268 acres with an average yield of 28 bu/A. The total soybean production for Georgia in 2006 was valued at $26,272,081.

Frogeye leaf spot was fairly common but was relatively unimportant for most growers. Nematodes remain an important problem of soybean in Georgia, especially in fields rotated with corn or cotton.