Integrated Management of Summer Disease of Apple

 

Illinois Apple Industry. There are more than 350 commercial apple growers, with approximately 6,000 acres of orchards, in Illinois.

 

Need for IPM of Apple. The economic survival of commercial apple growers in Illinois is threatened by crisis over pesticide use. Apple is among the most pesticide-intensive crops. FQPA restrictions impact pest management most critically during mid-to-late season period because: 1) there is no measurable resistance in apple cultivars to summer diseases, 2) pesticides applied during this period are more likely than springtime sprays to leave residues on apples at harvest, 3) the most widely used pesticides during this period are in EPA Group One, the highest priority for FQPA action, and 4) registered alternatives to conventional pesticides are fewer in mid- to late-season than in the spring.

 

Summer Diseases.  Most common summer diseases in apple orchards in Illinois are sooty blotch, flyspeck, bitter rot, black rot, and white rot.

 

 

IPM VS. Standard Method. The standard procedure to control summer diseases of apple is to spray the trees with fungicides at petal fall, then at 10- to 14-day intervals until approximately two weeks before harvest. The sprays are called petal-fall, 1^st cover, 2^nd cover, 3^rd cover, ....cover spray. Usually 6 to 8 cover sprays are needed to control summer diseases of apples. According to a weather-based disease-warning system (IPM), the 2^nd cover spray is applied when 175 hours of wetness have accumulated after the 1^st cover spray. The performance of the “Standard Method” and the “IPM” approach were compared in 6 apple orchards (Champaign, Peoria, Sidney, Sullivan, Urbana, Villa Grove) in Illinois in 2001 and 2002 (Fig.1).

 

Results. The weather-based system (IPM) predicted for the second cover spray later than the conventional spray schedule at all locations (Table 1). The disease prediction system saved the growers from two to eight sprays (25 to 100%) on a two-week spray schedule. There was no significant difference in disease incidence between standard and IPM treatments (Table 2).

Fig. 1.Locations of the experimental orchards.

Fig. 2. Accumulated leaf wetness hours in the orchards during May 13 and September 9.

 

 

 

Table 1. Dates of the first and second cover sprays, and number of sprays saved using the weather-based disease-warning system (IPM). Standard = trees were sprayed at 10- to 14-day intervals after the first cover spray; IPM = trees were sprayed at 10- to 14-day intervals after accumulation of 175 wetness hours after the first cover spray.              

 

 

 

Table 2. The incidence of summer diseases in the orchards. Standard = trees were sprayed at 10- to 14-day intervals after the first cover spray; IPM = trees were sprayed at 10- to 14-day intervals after accumulation of 175 wetness hours after the first cover spray.