Plant Parasites of Europe

leafminers, galls and fungi

gallers on Pinus

Dichotomous table for gallers on Pinus

by Hans Roskam

1a On above-ground parts => 2

1b Roots of seedlings distinctly shortened, with nodular swellings or proliferations. Bark loose around central cylinder with eelworms in between. Parts above ground shrivelled. P. sylvestris: Unidentified root eelworm

2a On shoots or needles => 4

2b On cones => 3

3a Cones shrivelled, bent, stone hard, not opening, always ± acuminate. Irregular tunnels in scale bases; already dropping 8–10. Usually a single, sometimes 2 or 3 larvae. P. cembra, mugo, nigra, pinea, ponderosa, sylvestris: Pissodes validirostris

3b One-sided curved cones, with resin and frass, containing caterpillars. P. nigra, sylvestris: Cydia conicolana

3c Cone scales inside with elongated wart-like swellings. P. sylvestris, strobus: Kaltenbachiola strobi

3d Blister-like swellings on cone scales caused by spermogonia and aecia of rust. P. densiflora, sylvestris, virginiana: Cronartium quercuum

4a On shoot axial parts => 7

4b On needles => 5

5a Needles swollen at base => 6

5b Needles accumulated terminally on young shoots, development stunted, undulately curved or bent screw-like, not thickened. Pinus spp.: Pineus pini

5c Fungus. Both surfaces of needles with cylindrical projections of aecia, 1–5 mm long; spermogonia present. Pinus spp.: Coleosporium tussilaginis

6a Infestation of developing needles. They are severely shortened, their bases ± fused over a length of 2–3 mm, swollen, sometimes slightly twisted, erect and in autumn often golden-yellow. Larvae 2–3.5 mm long, orange-reddish to red, lacking sternal spatula; one or occasionally more larvae per gall. P. halepensis, mugo & subsp. rotundata, nigra, pinaster, pinea, sylvestris: Thecodiplosis brachyntera

= The pine needle buckling gall midge Contarinia baeri causes needles constricted at base and bend like walking sticks, dropping already in autumn

6b Needles remain linked, with yellowish, bulging thickenings, shortened, often ± twisted screw-like; a basal, expanded, bag-like widening containing a whitish to yellow beetle larva. P. sylvestris, uncinata: Brachonyx pineti

7a On stems, older branches or several year old twig => 10

7b On young shoots => 8

8a Galls caused by animals => 9

8b Bark of young twigs usually with narrow erupting pads on one side 10–30 mm long, with dusting of reddish-yellow spores. Shoots stunted at infestation site, continuing to grow on healthy side and so deflected. Terminal parts become erect subsequently making s-shaped curves. Pinus spp.: Melampsora populnea

9a Axis gaping over a length of about 20–30 mm, ± swollen. Primary bark and resin channels enlarged; secondary bark and wood slightly thickened. Pith cavity containing a large-headed, yellow- to yellow-brown caterpillar. Open gall often covered with resin mass on one side. P. banksiana, mugo, pinaster, sylvestris: Retinia resinella

= The gall midge Cecidomyia sarae has been recorded from resin lumps and wounds caused by R. resinella

= Two more gall midges, Cecidomyia pini and C. harrisi, occur also in resin exudates of shoots and green cones of P. pinaster, sylvestris without causing malformations. The species differ in larval characters, viz., spatula, dorsal lobes on abdomen

9b Caterpillars at first in lower pith of young, stunted shoot tips or buds, sometimes thickened on one side, crooked, later on dehiscing. Pinus spp.: Rhyacionia buoliana

= the larvae of several leafrollers live as borers in the buds and young shoots of pine trees, causing rather similar damage symptoms. Of the more rare species the biology is not known in sufficient detail to enable discrimination, but at least the equally frequent Pseudococcyx turionella should be considered as a potential causer. The larva of Rh. buoliana bores a tunnel from the base of a shoot upwards; this causes the shoot to bend (“posthorn shoot”); when this happens to the main shoot this causes a permanent bend in the trunk later. The larva of P. turionella empties a terminal bud, then burrows for a short distance downwards. Lateral buds around the dead terminal bud then get the opportunity to develop into shoots, causing a splaying or forking of the branch

9c Young shoot curved and distorted, growth stunted. P. peuce, sibirica, strobus, sylvestris: Pineus strobi

10a Stems or branches with nodular swellings or with proliferations, excessive branching or witches’ brooms => 13

10b Bark of thinner plant parts usually swollen on all sides, several cm long, later on with many, pale yellow blister-shaped swellings, about pea-size, from which yellow fungus spores escape after eruption => 11

11a On P. mugo, sylvestris and other pines with paired needles => 12

11b On P. strobus and other 5-needle whorled pines: Cronartium ribicola

12a Fungus host alternating. Aecia conspicuous, often many on 10–20 cm long swellings of twigs. Galls at thickest part sometimes with twice the normal diameter. Fewer on stems and young trees than on branches. Cronartium flaccidum

= Blister-like swellings on bark caused by spermogonia and aecia of rust. P. sylvestris: Cronartium quercuum

12b Fungus not host alternating; it develops haploid aecia in its sori, which are only able to infect Pinus. Galls as for pine blister rust. P.sylvestris: Endocronartium pini

13a Malformation of complete shoots or witches’ brooms => 16

13b Nodule-, tuber- or spindle-shaped malformations => 14

14a Rotund to oblong nodules or tumours => 15

14b Spindle- or club-shaped swelling of a branch or stem part: Viscum album subsp. austriacum

15a Smaller, up to about 15 (30) mm globular, cancer-like compact nodules on the thicker twigs of P. cembra. “Twig tuberculosis”. Cause unknown – ? bacterium

15b On younger, thin twigs oblong to rotund, at first glabrous, later on rugose, up to 20 (25) mm broad and 10 mm high, yellow-brown swellings, permeated by many channels, originating from proliferation of the bark and persisting for several years. P. mugo, nigra, strobus, sylvestris: Trisetacus pini

16a Slightly extended malformation of complete shoots; proliferation and accumulation of buds. “Budding witches’ broom”. P. cembra, mugo: Trisetacus cembrae

16b Usually voluminous, loose, expanded or smaller, almost globular compact witches’ brooms, especially on P. sylvestris, as well as on some cultivated foreign pines: Inducer unknown

Last modified 11.iv.2020