Edward Sikora, Jim Pitts, and Bobby Boozer

Anyone who has ever stopped by a roadside stand where peaches are sold has appreciated the beauty of a basket of peaches. From their fragrance to their color, no other fruit is as lovely as a peach.

Growing this beautiful fruit is another story. Although growers must constantly battle a variety of diseases, an assortment of fungicides are available for use in disease control spray programs. In selecting the fungicide to use, Alabama peach producers usually consider both the effectiveness and the cost. Along with these factors, growers also need to choose a program that addresses the development of disease resistance. If a fungicide is overused, fungal strains that are resistant to that fungicide and to other fungicides in the same chemical class can develop.

An effective disease resistant management program relies on reducing the number of applications of a fungicide class during the season, using tank-mixes of compounds when appropriate, and /or alternating different classes of fungicides within the spray program during the season. If growers don’t follow these practices, then fungal strains that are resistant to the overused fungicides can develop.

During the cover period (after bloom and just before harvest), peach producers in Alabama commonly use sulfur as part of their fungicide spray program. It is a relatively inexpensive material and is moderately effective in controlling peach scab, a common fungal disease that often results in infected fruit being covered with lesions. Sulfur, however, it is not considered as effective as Captan, a more expensive material, for controlling scab when used in cover sprays during the season.

In the preharvest period, peach growers usually apply two or three sprays of the fungicide Orbit. This is mainly due to its relatively low cost and its overall effectiveness in controlling brown rot, a common fungal fruit rot of peaches in the Southeast. Continued use of Orbit in this manner could potentially lead to the development of resistant strains of brown rot to this fungicide and other fungicides in its class, such as Indar, Elite, and Funginex, effectively removing them from the growers’ dwindling arsenal of fungicides available to control this economically important disease.

In an AAES study, researchers compared six fungicide spray programs (treatments) on the cultivar ‘Monroe.’ The experiments were conducted at the Chilton County Horticultural Station near Clanton. Treatments were replicated four times with four trees per replication in a randomized complete block design.

The spray program consisted of seven applications of sulfur or Captan through the cover period. The sulfur or Captan cover spray programs were coupled with various preharvest fungicide sprays. Preharvest applications were applied at seven days and one day before harvest. Preharvest treatments consisted of one of the following spray schedules: Captan then Orbit, Rovral then Orbit, or two sprays of Orbit (the industry standard). The fungicide Bravo Ultrex was applied during the bloom period (shuck split and at petal fall) in all of the programs evaluated.

Rhizopus rot on post-harvest peaches.

A total of 40 fruit were picked from the center two trees of each treatment/replication. Percent of fruit with peach scab and percent marketable fruit were determined at harvest. Incidence of brown rot and Rhizopus rot was determined seven days after harvest following storage of fruit at 77oF degrees.

Peach scab was observed on the majority of fruit in all treatments, with the most severe damage in the unsprayed control. Spray programs that used Captan during the cover period always produced more scab-free fruit and more marketable fruit than programs that used sulfur (Table 1). On average, the percent of fruit exhibiting scab lesions was 58.9% with Captan programs compared to 78.6% with sulfur programs. The average marketable fruit (fruit with no scab lesions or only a few lesions) was 84.6% with Captan programs compared to 58.5% with sulfur programs.

Table 1. Effect of Fungicide Spray Programs on Incidence of Peach Scab and Production of Marketable Fruit, 1997-1999
Fungicide program1				% Fruit with scab			% Marketable fruit
B2	C	H1	H2	1997	1998	1999	1997	1998	1999
U	U	U	U	100	100	92.5	37.0	6.2	37.5
B	C	O	O	94.4	69.3	31.2	90.0	76.8	95.6
B	S	O	O	100	86.2	52.5	40.2	42.0	75.0
B	C	C	O	74.0	64.3	31.2	89.0	74.3	88.7
B	S	C	O	96.9	82.5	40.6	61.2	55.0	86.2
B	C	R	O	68.4	68.1	30.0	89.0	71.8	86.8
B	S	R	O	100	92.5	56.2	53.6	46.8	66.2
1 B = bloom sprays (petal fall, shuck split), C = cover sprays, H1 = first preharvest spray, H2 = second preharvest spray, U= Unsprayed, C = Captan 50WP (5 lb/acre), O = Orbit (4oz/acre), S = sulfur 80% (9 lb/acre), R = Rovral 50WP (2 lb/acre).
2 In 1997, sulfur was applied for bloom sprays for all programs in which sulfur was used during the cover period, and Captan was used for all programs in which Captan was used during the cover period.

A cover spray program consisting of seven applications of Captan 50WP at five pounds per acre would cost a grower approximately $95 an acre. The same program using sulfur 80% at nine pounds per acre would cost about $13 an acre, which is $82 less than the Captan program. However, the Captan program has the potential to increase the production of marketable fruit by 25%, which based on the wholesale value of peaches in 1999, would come to an increase of about $300 per acre, or a net increase of $218 after considering the extra cost for Captan.

There were no significant differences among spray programs with regards to brown rot or Rhizopus rot, though all programs typically had less disease than the unsprayed control (Table 2). Programs that alternated between classes of fungicides (Rovral/Orbit or Captan/Orbit) in the preharvest spray period controlled brown rot as well as the program that used two consecutive Orbit sprays. The replacement of one Orbit spray with a fungicide of another fungicide class such as Rovral or Captan would constitute an effective disease resistant management program for brown rot.

Table 2. Effect of Fungicide Spray Programs on Incidence of Brown Rot and Rhizopus Rot, 1997-1999
Fungicide program1				% Brown Rot			% Rhizopus Rot
B2	C	H1	H2	1997	1998	1999	1997	1998	1999
U	U	U	U	18.5	2.5	30.0	7.4	25.0	6.2
B	C	O	O	10.0	3.7	11.2	2.2	18.1	15.0
B	S	O	O	4.3	15.6	9.2	3.2	26.2	16.8
B	C	C	O	5.5	6.8	5.6	0.0	18.7	15.6
B	C	R	O	5.4	5.0	3.1	0.0	15.0	3.1
B	S	C	O	6.1	11.8	16.8	1.0	33.1	16.8
B	S	R	O	2.1	17.5	11.2	1.0	26.8	11.2
1 B = bloom sprays (petal fall, shuck split), C = cover sprays, H1 = first preharvest spray, H2 = second preharvest spray, U= Unsprayed, C = Captan 50WP (5 lb/acre), O = Orbit (4oz/acre), S = sulfur 80% (9 lb/acre), R = Rovral 50WP (2 lb/acre).
2 In 1997, sulfur was applied for bloom sprays for all programs in which sulfur was used during the cover period, and Captan was used for all programs in which Captan was used during the cover period.

Though Rovral is a relatively expensive product compared to Orbit ($41 per application versus $12.50 for Orbit), Captan is a reasonably priced alternative ($13.65 per application). The slight increase in cost is a small price to pay for an effective disease resistance management program.