winds were frequently high. 



As shown in Table 1, the delayed 10-day SI 

 program was very effective in controlling primary 

 scab in orchards with low or moderate scab inocu- 

 lum. The amount of scab inoculum in most orchards 

 was estimated the previous season using quick vis- 

 ual evaluations of foliage and observing scab at pack 

 out. If scab was obvious in the block, or exceeded 2%, 

 then the orchard was considered to have high inocu- 

 lum. Otherwise, inoculum was judged to be low. 



/ have heard that if I wait 7 days 

 on either side of an oil application, I 

 can apply captan. Will that work 

 with the SI program? 



Unfortunately, there are no good rules for inter- 

 vals between captan and oil applications. Try to 

 maximize the interval between oil and captan by 

 making somewhat earlier oil applications, and using 

 other fungicides early in the season. For example, 

 use Cyprex or SI alone early around oil, and save 

 captan for later. If you have a real need to use 

 captan, a 7-day or even 14-day interval may or may 

 not be enough. There are no hard data. The ad- 

 vantages of captan have to be weighed against un- 

 certain risks of phytotoxicity. 



If I want to use an SI program, do I 

 have to use captan or some other 

 protectant with it? 



Use SI alone only if necessary to avoid the 

 captan/oil problem. It is most important to use 

 captan around bloom and early fruit set as a protec- 

 tant against fruit scab. So use SI alone earlier rather 

 than later. Use higher rates or 

 closer intervals when you do. 



/ had a lot of fruit scab 



last year 



using the Sis. Given that, 



and 



their expense, why 



should I use them? 



egy, these problems generally could be traced to 

 application mistakes. 



Application problems which lead to scab are 

 caused by too little SI being absorbed into tissue. 

 There are several potential reasons for an inade- 

 quate application, at least on parts of a tree: 



* Trees too thick or too tall, so coverage is inade- 

 quate in some parts; 



■^Alternate row sprays resulting in too low a 

 rate per acre; 



*Low volume applications made in poor condi- 

 tions, such as wind, rapid drying, and poor 

 calibration; 



*Rain within 2 hours of the application washing 

 off material; 



^Continuous rain, making mid-season applica- 

 tions impossible; and 



* Exceeding the 10-day interval, with a major 

 infection at the end of the interval, and not ap- 

 plying 2 sprays 7 days apart. 



With large trees, or where spray coverage is not 

 even or complete, the Sis may be a poor choice. If you 

 are not comfortable with and knowledgeable about 

 the differences between Sis and standard fungi- 

 cides, you may want to avoid them. However, the 10- 

 day interval and the initial delay offer schedule flexi- 

 bility, and when used well these materials are very 

 effective. Cost and fruit scab must be kept in mind, 

 but both can be controlled. While there was fruit 

 scab in many orchards last year, it was not limited to 

 orchards using Sis. In many other cases, Sis on a de- 

 layed 10-day schedule produced a very clean crop in 

 a very tough scab year. 



In general, we felt that the 

 Sis on the delayed 10-day sched- 

 ule performed very well. How- 

 ever, as shown in Table 1, some 

 growers did exceed acceptable 

 levels of scab. Rather than find- 

 ing problems with the basic strat- 



22 



Fruit Notes, Spring, 1991 



