The Symptoms of Chestnut Tree Blight 



By F. D, 



This article is written with the hope that it will sup- 

 ply some desired facts and assist in correcting false 

 notions. Investigations on the dissemination and life- 

 history of the blight fungus are in progress at the 

 present time and new facts are constantly being de- 

 termined. Our knowledge being far from complete, it 

 is only ad\isable to present the facts which appear to 

 be fairly well established. 



SVMPTCIM.S .\ND EFFECTS. 



Young infections i:)f chestnut blight on smnnth- 

 liarked vigorous shoots (two to six or more years old) 

 can be easily recognized by the presence of yellowish 

 or yellowish-brown patches, slightly raised, and stand- 

 ing (lut in marked contrast to the (ili\e-green healthy 

 bark. The area invaded by the fungus may be fairly 

 regular or very irregular in outline, the latter showing 

 what has been designated as the amoeboid type. In 

 young infections of this type there are no fruiting pus- 

 tules, but these make their appearance later. If the 

 external l)rown layer of cork cells is removed from the 

 ad\ancing edge of the in\aded area, the whitish or 

 buff-colored mycelium, or vegetative body, of the 

 blight fungus is exposed. Infections of this tyjie may 

 spread until the shoot is cumijletely encircled, and 

 fruiting pustules will lie furmed later. 



Young infecti<in> <>n slow-gn iwing twigs or on the 

 smooth Ijark uf older l)ranchcs <ir trunks are not as 

 evident, but they generally show as somewhat discol- 

 ored, dead areas, sometimes slightly depressed, and oc- 

 casionally with a raised margin. The area invaded 

 may l)e nearly circular, giving a so-called "target" in- 

 fection, but it is more frequently elongated in the di- 

 rection (if the lung axis of the shoot nr liranch. The 

 invaded area gradually enlarges until the shoot or 

 branch is comjileteK' encircled. A small shoot may be 

 cnnipletely encircled liefore the appearance of fruiting 

 pustules, but on larger limbs or on the main trunk the 

 fruiting pustules begin to make their appearance long- 

 before complete girdling has taken place. These fruit- 

 ing l)odies show as small yellow, orange or reddish 

 l)rown pustules (1/16 inch or slightly more in diam- 

 eter) which i)reak through the bark some distance liack 

 fmni the advancing edge of the lesion. 



The interior tissue (inner bark invaded by the fun- 

 gus) is changed V> a yellowish brown color, which is 

 in marked contrast to the bright, fresh color of the 

 normal healthy tissue, and a careful examination by 

 cutting away the i)ark will show the butf-colored fans 

 of the fungus, wdiich may have ])enetrated as deep as 

 the cambium layer. 



During damp weather following rains, or in moist 

 situations, long, irregularly twisted threads varying in 

 color from buff to bright yellow may be extruded from 

 some of the pustules. These are masses of conidia or 

 summer spores, and have been designated as "spore- 

 horns" or tendrils. The spore-horns when first formed 

 are suft and sticky, but when dry they become haril 

 and brittle and are frecpienth' darker in cnlnr. 



\'oinig infections on old trunks or large limbs with 

 thick fissured bark cause little change in the appear- 

 ance of the bark itself, and the fungus may have gained 

 considerable headway before there is any external evi- 

 dence of its presence. Sometimes the first indication 

 of an infecti(5n on large limbs or trunks is the appear- 

 ance of abnormal longitudinal splits or fissures. The 

 orange or yellow fruiting ])ustules appear in the dee]) 

 crevices or cracks, and sporc-hnrns ni;iy be dexclnpcd 



Heald. 



from these under favorable conditions of moisture and 

 temperature. In case of doubt as to whether a given 

 discoloration is caused by the blight fungus the follow- 

 ing test may be used : Place the twig or piece of bark 

 in a closed \-essel so it is supplied with plenty of mois- 

 ture and will be retained in a moist atmosphere. In 

 all cases if the fungus is present and is alive, bright 

 vellow or orange, cottony tufts will make their appear- 

 ance upon the surface, and in many cases spore-horns 

 will also be developed. 



.\n infection with the blight fungus is sometimes 

 the cause of a pronounced enlargement, or hyper- 

 troi)h\-. This enlargement may involve the entire in- 

 vaded portion or it may be more pronounced at the 

 upper end of the lesion. Enlarged lesions are appar- 

 ently the most frequent on vigorous shoots. Longi- 

 tudinal splits or fissyres in the bark are very character- 

 istic of hypertrophied lesions. In many instances the 

 lesion may show a marked sunken area due to the kill- 

 ing of the invaded bark, while the surrounding tissues 

 have continued to grow at the normal rate. This dead 

 tissue may be more or less cracked or fissured and a 

 tvpical canker ileveloped. In the old lesions which have 

 compIetel>- girdled a limb or liranch the bark becomes 

 cracked and fissured and begins to peel away. The 

 branch referred to had been killed by this lesion and 

 had been dead for a year. On old rough-barked trunks 

 or branches the bark over old lesions will give a hollow- 

 sound when tapped, due to the fact that the inner bark 

 has been destroved by the fungus. The bark may be 

 readih- peeled awa\ and the fibrous portion is niore or 

 less shredded. 



Aside from the discovery of the actual lesions there 

 are various other symptoms which indicate the pres- 

 ence of blight. Dead leaves hanging in characteristic 

 drooping clusters are an indication of blight-killed 

 twigs or branches. If the twigs or branches are not 

 killed until late spring or summer, that is, prior to the 

 first of September, the leaves reach normal size, and 

 these clusters of dead leaves will generally remain 

 clinging to the tree during the winter period after the 

 normal leaves have fallen. This aiTords one means 

 of detecting blight-killed branches in the winter. In 

 blight-alTected branches there is an indirect efifect upon 

 the size and persistence of the burs. If the girdling 

 is completed early in the growth of the burs, they are 

 likely to remain small and undersized, but with later 

 completion of girdling they may attain ftdl size. These 

 l)urs of blight-killeil branches commonly remain hang- 

 ing upon the tree during the winter, constituting an- 

 other evident symiJtom for the detection of blight 

 during the leafless period. 



In case the girdling of a branch is not comjileted 

 until late fall, the normal shedding of the leaves occurs. 

 In the spring, howexer, the leaves from these branches 

 remain undersized and assume a yellowish or pale 

 Color, and soon wither and die. If girdling is com- 

 pleted later in the spring or not until midsummer, the 

 leaves of the afi^ected branches develop to full size, 

 but later turn yellowish or assume a characteristic 

 reddish l)rown color. Later when the leaves die they 

 assume more of a brownish tinge, and some fall from 

 the tree while ni;iny remain hanging for a considerable 

 time. 



The dex'elopment of sprouts or "suckers" is an- 

 other e\-ident syni])toni of blight which can be n ited 

 at an\ period in the \ ear. As so ui as a br,-inch or the 



