Resistance Is becoming a common concern. We're 

 finding insects and disease are becoming more 

 resistant to many of the products — fungicides, in- 

 secticides, or herbicides — we use today. Far fewer of 

 these products have been registered In the horticul- 

 tural industry than previously, leaving us with fewer 

 choices or, in many cases, the same or similar com- 

 pounds with new names. Using these same com- 

 pounds over and over can cause the development of 

 resistance. 



We've seen resistance to systemic pesticides 

 (pythium to Subdue, botrytis to thiophanate-methyl) 

 develop most quicidy. Systemic products normally 

 have only one or two methods for controlling the 

 pathogen; contact pesticides, usually more than one. 



Which leads to the idea of rotation. This helps 

 slow down the development of resistance Im- 

 mensely. If only one half of one percent of a certain 

 pest develops resistance to a certain pesticide, 

 within a very short period of time, this percentage 

 can grow to 10%. ..and so on. 



By rotating different classes of pesticides, the 

 chances of the original population surviving is 

 much more limited. Another way to approach this 

 problem Is to use premixes or tank mixes of pesti- 

 cides on many of your applications. This is espe- 

 cially true with crops that we may spray once or 

 twice during Its cycle, if we use only one compound 

 to spray for a pest once a year, we allow that poten- 

 tially resistant population to survive for another. 



Studies on anthracnose control are talcing place 

 at Connecticut's research stations. These are show- 

 ing that anthacnose Is resistant to most of the pes- 

 ticides labelled for use against It; only mixes of 

 compounds are showing any control. 



Growers, using one compound applied many times, 

 expect herbicides to control a whole range of weeds. 

 Rarely will this work well. Premixes and tank mixes 

 are the only ways to achieve reliable control. 



\im Zablocki is Technical Manager, Northern Horlicultural 

 Croup, Scolls Company He can be reached at 603-224-5583. 



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