LEAF-CAST OF CONIFERS 
Species of the genera Pinus, Abies, Picea and Larix frequently suffer 
from needle-diseases known in common by the general name leaf-cast or 
needle-cast. ‘These diseases have been much more abundant in Europe 
than in this country. Frequently they have been epiphytotic on certain 
hosts in Europe. Although all leaf-cast diseases of conifers are very similar, 
they have various specific characteristics. The one considered in this 
outline is common on yellow pine (Pinus ponderosa Douglas) in the 
northwestern part of the United States. 
SYMPTOMS 
General symptoms. The leaves of certain branches turn brown at 
any time during the growing-season. In young trees, the leaves of the tips 
of all of the branches may be attacked while in older trees only the lower 
branches on the windward side usually show diseased needles. Witches’- 
brooms of large size are produced on older trees. Often the brooms are 
heavy enough’ to cause them to hang pendant from a larger limb. The 
recent growth of affected young trees is much deformed, due to the forcing 
of growth back of the tips of the twigs which are killed. (See Jour. Agr. 
Res. 6 : 277-288, pl. XXXII.) 
On the needles. The needles may be infected at any time during the 
growing-season. They show variable symptoms according to the time 
of year at which infection takes place and the point on the leaf where infec- 
tion was initiated. In the material provided, NoTE:— 
1. The brown tips of certain needles. This is the first evidence 
of the disease when the needle becomes infected near the tip. 
2. In some cases the entire needle may gradually become straw- 
yellow in color and then turn brown later in the season. — 
3. The long rows of black, shiny fruit-bodies of the pathogene 
on the dead needles. On which surface of the needle do they occur, dorsal 
or ventral? DRAW. 
On the twigs. The mycelium grows from the affected needles into the 
twig and produces hypertrophy. Later the affected twigs die. The branch 
bearing affected twigs becomes gnarled and enlarged. Adventitious buds 
are forced and a witches’-broom is developed. In the specimens provided, 
OBSERVE :— 
4. The hypertrophied twigs and branches. 
5. The character of the brooms produced on the older trees. 
(See Jour. Agr. Res. 6, pl. XXXII.) 
DRAW showing the effect on the woody parts of the tree. 
ETIOLOGY 
The leaf-cast of yellow pine is caused hy Hypoderma deformans Weir. 
Hypoderma is a genus of the Ascomycetes in which apothecia with valve- 
like coverings are formed. These valves open, exposing the hymenium 
when abundant moisture is present. They close again during dry periods. 
: Life-history. The life-history of this pathogene has only recently been 
investigated by Wier. (Jour. Agr. Res. 6 : 277-288.) Other closely 
related species causing leaf-cast of other conifers have been studied for 
years and the life-histories of all these species are similar. Where pycnidial 
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