To a person unfamiliar with the ecology of a New 

 England apple orchard, this list may seem like more 

 than enough options. However, to an IPM grower, the 

 withdrawal of the EBDCs is frightening. The reasons 

 emerge from a closer examination of the remaining 

 materials. 



Benomyl and thiophanate-methyl can interfere 

 with biological mite control by suppressing popula- 

 tions of Amblyseius fallacis, our most important mite 

 predator. Biocontrol of mites in apple trees is essential 

 to second-stage or biointensive IPM. Additionally, in- 

 tensive use of benzimidazoles may lead to earthworm 

 suppression. 



Benzimidazoles are recommended for use only in 

 specific situations, such as to inhibit scab sporulation. 

 Exclusive use of benzimidazoles can lead to resistant 

 strains of Venturia inaequalis, the apple scab fungus. 

 Resistance already precludes use of these compounds 

 in some states. To extend the useful life of these 

 materials, and to avoid stressing mite predators, they 

 must be used sparingly and always in combination 

 with another broad-spectrum fungicide such as captan 

 or the EBDCs. 



Captan has recently been re-registered by EPA, 

 but is still the target of strenuous criticism by food 

 safety advocates. While a very useful fungicide against 

 scab and black rot, it does not control mildew, and is 

 only marginally effective on sooty blotch and fly speck. 

 Specifically, in a year such as 1989, 4 captan applica- 

 tions would have been made for sooty blotch and fly 

 speck, compared to 1 or 2 applications of an appropriate 

 EBDC. 



The gravest difficulty with an attempt to use cap- 

 tan as a complete alternative to EBDCs arises from 

 captan's incompatibility with oil or alkaline materials. 

 The EBDCs do not share this unfortunate characteris- 

 tic. When combined with oil, or even when used within 

 14 days of an oil application, captan can be toxic to plant 

 tissue (phytotoxic). Biological mite control depends on 

 1 or 2 oil applications in the middle of primary scab 

 season. Without the EBDCs, growers are faced with 3 

 options: 



1. Damage to the tree by captan/oil combina- 

 tion. 



2. Oil combined with no fungicide or an infe- 

 rior scab fungicide, resulting in primary sea- 

 son infections and a season-long fungicidal 

 battle against serious crop damage. 



3. No oil before bloom resulting in an expen- 

 sive chemical program against phytophagous 

 mites, without benefit of predator mites. 



No grower will choose the first option, and the other 

 two violate every principle of IPM and will increase 



drastically the total volume of pesticide used in New 

 England apple production. 



Dodine may not be manufactured next season. In 

 any case, though a potent scab eradicant, it can and has 

 produced resistant scab strains. Over-reliance on 

 dodine will shorten its useful life, and already has done 

 so for many growers. Dodine is not effective against 

 apple diseases other than scab, and would generally 

 have to be used in conjunction with other fungicides. 



Ferbam is at best moderately effective against 

 scab and has no post-infection activity, so it must be 

 used as a protectant. While it is fairly effective against 

 rust and summer diseases, ferbam leaves a heavy, 

 black, visible residue for some time, which tends to 

 discourage consumers. 



Fixed coppers are useful in their place, which is a 

 single early-season application. Used after this time, 

 copper will damage leaves and russet fruit. 



Fenarimol, myclobutanil, and triforine . or ergos- 

 terol biosynthesis inhibitors (EBIs), are a relatively 

 new class of fungicides. Though highly effective against 

 scab and (except Funginex) mildew, they do not con- 

 trol other diseases and are expensive. Moreover, they 

 are poor protectants, and their extremely specific mode 

 of action suggest the possibility that they may induce 

 pathogen resistance. Reports from Europe reinforce 

 this suggestion. To prevent this development, and to 

 provide for protectant activity, New England patholo- 

 gists have recommended that EBIs be used with a 

 broad-spectrum fungicide. EBDCs have been the fun- 

 gicide of choice, because they are compatible with oil. 

 Captan is the second choice, but will present the oil 

 phytotoxicity problems discussed earlier. Without the 

 EBDCs, the EBIs may be of marginal utility in New 

 England. 



Thiram has about the same range of activity as 

 captan but is considerably less effective. Many growers 

 consider that its chief value is as a deer repellent. 



Sulfur, while a favorite of organic growers, is 

 barely effective against scab, is toxic to mite predators, 

 and can be phytotoxic. To control scab, growers would 

 normally apply much more sulfur than they would any 

 other fungicide. This application leads to concerns 

 about soil acidification. 



If EBDCs were available, they would be described 

 as follows: 



EBDCs are highly effective against scab and 

 summer diseases, but are useless against powdery 

 mildew. Use at full rates late in the growing season can 

 result in visible residues at harvest. Like captan, 

 EBDCs have virtually no potential to produce patho- 

 gen resistance. The compatibility of EBDCs with oil 

 makes them the mainstay of most New England IPM 

 disease-management programs. Their use incombina- 



20 



Fruit Notes, Winter, 1990 



