igii 



BETTER FRUIT 



Page 4S 



plants die at the same time. When the 

 disease spreads from plant to plant, as 

 it does in bush fruits, such as the red 

 raspberr}-, all the plants will be killed in 

 time unless the disease is checked or 

 eradicated. From a casual survey of 

 fields of bush fruits one would naturally 

 conclude that Armillaria mellea is very 

 destructive. A microscopic examination 

 of the plants in such cases has shown 

 that such loss is more commonly due to 

 another form of fitngus, which is under 

 observation at this time, the results of 

 which study are not ready for publication. 



Since the rhizomorphs are so charac- 

 teristic and so large in size, observations 

 on the distribution of the fungus in the 

 soil are quite readily made with much 

 accuracy. The fungus usually occurs 

 where decaying wood may be found. 

 The type of soil has no influence on 

 distribution, except as it may contain a 

 limited or an abundant amount of decay- 

 ing vegetable matter. The more humus 

 the soil contains, and the more decaying 

 vegetable matter in the form of limbs 

 and roots of trees and small plants, the 

 better the conditions for the growth of 

 the fungus. While the fungus does occur 

 sparingly in upland soils, the principal 

 study of its distribution in the soil was 

 made in low land and particularly where 

 it had dune considerable damage to cul- 

 tivated plants. It is very evident that 

 the mycelium occurs in great abundance 

 from three to eighteen inches below the 

 surface of the soil. Strands may be 

 found nearer the surface, and especially 

 when the field has not been cultivated 

 frequently. They may sometimes be 

 found at a depth of three feet. In a 

 field of raspberry canes where all the 

 plants had been killed the rhizomorphs 



l-'iouRE 4— CANE OF RED RASPBERRY WITH VERY FEW 

 RHIZOMORPHS ATTACHED TO IT, BUT WITH A LARGE 

 GROUP OF TOADSTOOLS AT TPIE COLLAR 



were found extending from the dead 

 roots of the plant out through the soil 

 for several feet, forming a complete net- 

 work by very frequently branching and 

 rebranching. 



After the discovery of the rhizomorphs 

 in such abundance on the roots of many 

 dead plants a careful search was made to 

 note the general distribution of the 

 fungus. In removing agricultural drain 

 tile from a soil in which it had been 

 buried not less than six years to a depth 

 of more than two feet numerous rhizo- 

 morphs were found clinging to it. A 

 drain box removed from another portion 

 of the field was covered with a perfect 

 network of the fungus. An excursion 

 through the field revealed it on the 

 decaying roots of stumps and logs of red 

 fir, roots of alder, willow and cotton- 

 wood (a single specimen). On the bot- 

 tom land the roots of live alders were 

 well covered with the strands, while 

 various kinds of decaying wood in a 

 newly cleared but swampy field just 

 being drained were literally filled with 

 the mycelium, largely in the form of 

 rhizomorphs. During the inspection of 

 diseased and dead plants, apple, 

 plum, cherry, prune, gooseberry, 

 currant, blackberry, raspberry 

 and loganberry, in many cases, 

 were found to be badly injured 

 or killed by this fungus. The 

 rhizomorphs of Armillaria mel- 

 lea have been observed in many 

 localities in the Puget Sound 

 region. 



Since other forms of fungi 

 cause root rot disease of the 

 same plants on which Armillaria 

 mellea grows, much difficulty is 

 experienced in many cases in 

 determining the real 

 cause of the disease. 

 In cases where the 

 plants die without 

 the fungus forming 

 a conspicuous myce- 

 lium, rhizomorphs or 

 toadstools, the cause 

 of death can only be 

 determined by the 

 use of a microscope 

 or by the employ- 

 m e n t of cultural 

 methods. In most 

 instances, however, 

 identification may be 

 made by observing 

 the following rules: 

 1. Badly infested 

 plants make little or 

 no growth. Usually 

 those in bearing fail 

 to set or to mature 

 good crops of fruit. 

 The leaves may wilt 

 before or after, be- 

 coming light yellow 

 in color, or drop of¥ 

 before the close of 

 the growing season. 

 In case the infested 

 plant dies during the 

 dormant season the 

 remaining character- 

 istics must be relied 

 on for identification. 



3. The roots and crowns of plants 

 should be carefully examined for the 

 presence of rhizomorphs. They are 

 about the- diameter of the lead in a 

 common pencil, usually nearly round, 

 branched, and may vary considerably in 

 diameter within a length of a few inches. 

 In many fields sorrel is very abundant. 

 The roots of these plants, and especially 

 the dead ones, may be mistaken for 

 rhizomorphs. Rhizomorphs may be 

 easily distinguished, however, if the fol- 

 lowing characteristics are noted. Roll 

 them between the thumb and forefinger. 

 The moist, round body is reduced to a 

 very delicate thread. At the same time 

 the outer dark colored covering is 

 removed as many thin, brown flakes of 

 variable size and shape. There will be 

 a distinct mushroom odor on the fingers. 

 This odor is perhaps the best means of 

 recognizing the rhizomorphs. By pull- 

 ing the rhizomorphs in sections and 

 examining the broken ends very criti- 

 cally by holding the end near the eye 

 and toward a strong light it will appear 

 like a small tube, from the end of which 



Figure 2— CROWN AXD ROOTS OF RASPBERRY WITH 

 NUMEROUS RHIZOMORPHS OF ARMILLARIA MELLEA 



ADHERING TO IT 

 A large number of the rhizomorphs were growing through the 

 ground around the roots of the plant, some of which may be 

 traced, passing across several branch roots. In all cases where 

 rhizomarphs touched the root, strands from the rhizomorphs 

 grew into them. The illustration also shows numerous strands 

 on the base of the canes and on the main roots, which adhere 

 closely to the wood for their entire length. 



