BETTER FRUIT 



An Illustrated Magazine Devoted to the Interests of Modern 

 Progressive Fruit Growing and Marketing 



Entered as second-class matter April 22, 1918, at the Postoffice at Portland, Oregon, under act 



of Congress of March 3, 1879 



Volume XV 



Portland, Oregon, April, 1921 



Number 10 



Controlling Brown Rot of Stone Fruits 



By D. F. Fisher, Pathologist, Fruit Disease Investigations, U. S. Department of Agriculture 



ONE of the most serions menaces 

 to the crop of stone fruits in the 

 humid sections of the Pacific 

 Northwest is the disease called brown 

 rot, and caused by a fungus technically 

 known as Sclerotinia Cinerea (Bon.) 

 Wor. Most orchardists are familiar with 

 its attacks on the ripening fruit, but 

 few appreciate its significance at other 

 seasons, such as the rot of immature 

 fruit, twig and limb cankers, and par- 

 ticularly as a "blossom blight," which 

 prevents the setting of a crop. Fewer 

 still understand important facts in the 

 life history of the fungus which have a 

 bearing on control methods. Since brown 

 rot generally accompanies a period of 

 rainy weather, the manifestation of the 

 disease, both on blossoms and fruit, is 

 frequently regarded as "just rot," or 

 an unavoidable result of climatic condi- 

 tions. Wet weather is essential to the 

 growth and dissemination of the fungus 

 and the spread of the disease, but is not 

 otherwise concerned in the damage, ex- 

 cept as it may hinder control methods, 

 such as early spring cultivation or 

 spraying. 



Life History of the Fungus 



SINCE most people are more familiar 

 with its occurrence on the ripe fruit 

 (fig. 1), this stage will be a convenient 

 one from which to start an account of 

 the life history of the fungus. There is 

 never difficulty in finding plenty of 

 fruit destroyed by brown rot during the 

 ripening season of cherries, prunes, and 

 other stone fruits in the humid sections 

 west of the Cascades, and if there hap- 

 pens to be a rainy period at this time a 

 large proportion of the crop may be de- 

 stroyed. One rotten prune or cherry car- 

 ries enough spores, or "seeds" of the 

 fungus (a parasitic plant) which causes 

 the disease, to infect the whole orchard 

 or neighborhood. These spores are mi- 

 croscopic in size and are produced by 

 myriads in the ashy gray tufts which 

 cover the rotted fruits. The spores are 

 wafted about by the wind or carried by 

 insects, and if one is deposited upon a 

 sound fruit and there be moisture pres- 

 ent it will germinate the same as any 



other seed. But the germ tube in this 

 case penetrates the skin of the fruit and 

 destroys or "rots" the tissues. Within a 

 short time spore-tufts break the skin of 

 this fruit and a new crop of "seeds" 

 is ready for dissemination. If rainy 



Fig. 1. Brown rot on maturing Italian prunes. 

 The small tufts scattered over the rotted prunes 

 are composed of millions of spores, each one of 

 which is capable of infecting a sound fruit if it 

 finds suitable lodgement on it. The disease also 

 spreads by contact as shown in the illustration, 

 having first started on the dried up prunes and 

 spread progressively through the cluster. 



weather continues the disease spreads 

 like wild-fire, and fruit that is sound at 

 night will show rotted spots in the morn- 

 ing. Brown rot is omnipresent in all 

 orchards of this section and it is due to 

 this fact that long distance shipment 



of the ripe fruit is impracticable. It is 

 never known whether fruit is infected or 

 or not, or whether in the humid atmos- 

 phere of a refrigerator car it will "stand 

 up" in transit. Fortunately the district 

 is well supplied with canneries and dry- 

 ers which furnish a profitable way to 

 handle the crop, and fresh-fruit ship- 

 ment is not essential. But even with the 

 canned and dried fruit outlet serious 

 difficulty is frequently met in saving 

 the crop long enough to process in rainy 

 seasons. 



THE rotted fruits either cling to the 

 tree over winter as "mummies" and 

 shed more of the same kind of spores 

 in the spring to infect the blossoms, or, 

 as is more generally the case in the Pa- 

 cific Northwest, at least, they fall to 

 the ground where the fungus undergoes 

 a certain change of development. Under 

 these conditions it forms hard or stony 

 "sclerotia" or resting bodies in the tis- 

 sues of the rotted fruit. By this means 

 it is carried over into another growing 

 season. Whether it rests one or two 

 years is a mooted point with different 

 investigators, but evidence collected by 

 the writer indicates that it may be either 

 one or two years. 



These "mummies" become covered 

 with soil or refuse, or are kept moist by 

 close contact with the soil, and about 

 the time the buds are swelling in the 

 spring they also resume activity. From 

 the sclerotia in these mummies a stalk- 

 like body appears, growing toward the 

 surface of the ground. The length of 

 the stalk varies with the depth the 

 mummy is buried, the writer having 

 collected some as long as five inches. 

 Reaching the surface, there is unfolded 

 from the top of the stalk a cup-shaped 

 structure that soon flattens and some- 

 times becomes inverted like an umbrella. 

 (See fig. 2). This is similar to an ordi- 

 nary mushroom or "toad-stool" and is 

 technically called an "apothecium." It 

 carries myriads of spores of another 

 type than those produced on the ripe 

 fruit. They arc contained in tiny sacs 

 which are closely packed together on the 

 inside of the cup — or outside of the um- 



