DON'T TAICE A CHANCE WITH APPLE SCAB IN 1958 



Dry weather in the spring of 1957 made it an easy year for scab control 

 and most growers had little or no scab on fruit at harvest. Continued dry 

 weather in summer and fall did not favor build-up of leaf scab so that for 

 1958 the carryover is light. 



The question in the mind of nearly every grov^er is, "With a very light 

 carryover, is it necessary for me to follov/ a strict protective scab control 

 program or can I take it easy?" Unfortunately, there is no unconditional 

 answer, and, regardless who gives the answer, at best, it can be only a guess. 

 But the chances are tliat it will be a better guess if there are a few facts 

 on which to base it. 



Suppose we start with one scab spot on one leaf on one tree and the leaf 

 drops to the ground. The fungus grovjs and winters in the leaf but no winter 

 spore cases v^ill develop and produce primary scab spores because the fungus is 

 self-incompatible. But suppose we start with two scab spots on one leaf. The 

 fungus from each grows through the leaf tissue and as the threads from one spot 

 reach those from the other there is union and formation of winter spore cases 

 because threads from different spots are compatible. Winter spore cases can be 

 formed also when two leaves v^ith only one scab spot each are overlapping or in 

 contact with each other oii the ground so that fungus threads can grow from one 

 leaf into the other. 



It is possible for 250 winter spore cases to be formed on one square inch 

 of one scabby leaf on the ground and it has been calculated that from one 

 square inch of such a leaf more than 33,000 primary spores can be discharged 

 in 45 minutes of wetting. If even a few of these spores land on unprotected 

 leaf tissue or flower clusters, each will produce a scab spot in 12 to 15 days 

 with many spores capable of causing secondary infections and, what is more, 

 each scab spot will continue to produce and scatter spores with each rain the 

 rest of the season unless it is "burned out". And each secondary scab spot will 

 produce more spores in 10 or 12 days. All this from just one discharge and 

 in one primary infection rain. When this is multiplied by several discharges 

 during infection rains, it is obvious that a grower can have a rather heavy 

 scab population going on in his orchard in 20 or 30 days if he neglects his 

 scab control program. 



Several years ago Dr. A. B. Burrell of New York, in a talk at the Annual 

 Meeting of the M. F. G. A. reported that it cost more for scab control if there 

 were scab infections on spur leaves or early in the season. He advised early 

 scab control and a strict protectant program through the primary infection 

 period. This is still good advice for Massachusetts growers for 1958 even 

 though there is a light scab carryover. 



The fungicides listed in the spray chart will give satisfactory scab 

 control if applied on time and thoroughly. Grov/ers should read about apple 

 powdery mildew on the last page and decide v/hether to include mildew protection 

 in the early scab sprays or to wait until milde\-; is found in the orchard. 



C. J. Gilgut 



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