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Trouble from apple powdery ml Idev; was anticipated for Massachusetts growers 

 two years ago* Growers \i;ere warned that it was causing concern in the states to 

 the south and west of us and it would only he a matter of time when it would he 

 trouhlesome in Massachusetts too. Thersfore, it is no surprise to find it start- 

 ing in three Massachusetts orchards this spring. 



The Agricultural Research Service of the United States Department of Agricul- 

 ture states in a recent report, "Apple powdery mildew, spreading rapidly in the 

 past few years, has hecome a troublesome disease in apple orchards east of the 

 Mississippi River", At present it is not serious in Massachusetts hut it may, 

 and prohahly will "be, if growers are not on guard against it, and if they do not 

 take prompt measures to control it when it is found in an orchard, 



Apple Powdery Mildew is Mot Hew 



■le have always had a little powdery mildew in our orchards, and freouently it 

 was brought in on young apple nursery stock when a new orchard was planted. It 

 caused little concern because the mildew was held in check by the sulfur and lime- 

 sulfur which growers were using for control of apnle scab and sulfur is one of the 

 fe'-' fungicides that controls mildew. 



In recent years, grower preference has been for organic fungicides rather 

 than sulfur because they control apnle scab better. As frequently happens, when 

 one changes to new materials to get better control of one disease problem, another 

 is created. The organic fungicides do not control apple powdery mildew and n(yj} 

 this disease is on the increase and promises to be a major problem in fruit grow- 

 ing in Massachusetts. 



How the Fungus Attacks 



The powdery mildew fungus is an obligate parasite - it must have living apple 

 tissue on which to live. It first ap-oears on a tree as a powdery white growth on 

 the leaves and then creeps down onto the soft shoots and twigs and into the buds. 

 If it starts early in the season, there may be corsiderable distortion and stunt- 

 ing of the leaves and shoots. On the fruit it causes a network of russet and, 

 in severe cases, stunting, shriveling, and cracking. The fungus continues to 

 grow and spreads by spores produced on the mildew mat and which are blown about 

 by wind and carried by air currents to other leaves and other trees until raid- 

 summer . 



The powdery mildew overwinters on the twigs and in the buds on infested twigs. 

 The buds are weakened by the invading fungus and are leas resistant to winter cold 

 than healthy buds. They are frequently killed by temperatures 20-30° F. below 

 zero as are also some of the infected twigs. Temperatures slightly below zero do 

 not seem to be effective in wholesale eradication of the fungus. Unless the in- 

 fected overwintering buds are killed by cold, they are the source of infection for 

 new leaves in spring. If the season is early, the mildew may show up between de- 

 layed dormant and pre-pink but this year, since the season is late, it may not show 

 up until pink or later. 



