38 



MISC. PUBLICATION 6 2 6, U. S. DEPT. OF AGRICULTURE 



DELPHINIUM 

 Cyclamen Mite 



The cyclamen mite (Tarsonemus pal- 

 lidus Banks) is chiefly a pest of green- 

 house plants, but at times it seriously 

 injures perennial delphinium, although 

 dahlia, gerbera, geum, and a few other 

 garden plants are attacked. The mites 

 (fig. 62) are too small to be seen without 

 magnification, but their injury, consist- 

 ing of distortion of foliage and flowers, 

 with or without blackening, is usually 

 recognized. On delphinium (fig. 63) 

 the cyclamen mite enters through 

 breaks in the surface layer on injured 

 leaves, breeds within the leaf tissue, and 

 causes gnarling of the tip growth and 

 blackening of the areas fed upon. It 

 also penetrates the crown of delphinium 

 deeply to the base of the leaves. The 

 adult mite is of a caramel color, whereas 

 the younger stages are milky white. 

 The mites travel only short distances 

 but may go to nearby plants if the 

 foliage touches. They may also be 

 spread to other plants by hands, tools, 

 wind, or rain, or carried by other in- 

 sects. The mites pass the winter in the 

 crowns of delphinium and survive be- 

 tween crops on many weeds or other 

 living plant hosts, but not in the soil. 



Treatment. — Since the mites are not 

 exposed on delphinium, spraying or 

 dusting is of little value. The best 

 treatment is to immerse the infested 

 plants in water held at a temperature 



* 



>... 







Figure 62. — Cyclamen mite, in its sev- 

 eral stages, as it occurs in crevices of 

 infested plant parts; 35 times natural 

 size. 



Figure 63. — Terminal growth of del- 

 phinium distorted and blackened by 

 the feeding of cyclamen mites. 



of 110° F. for 15 or 20 minutes, depend- 

 ing upon their size. The best time to 

 do this is when the plants are lifted for 

 division and transplanting. Where 

 enough plants are to be treated they 

 may be placed in a tray provided with 

 suitable handles to facilitate handling 

 during treatment. An even water tem- 

 perature should be maintained by 

 checking frequently with an accurate 

 thermometer, adding more hot water as 

 needed. Stir the water with a paddle 

 to keep it well agitated during the treat- 

 ment. Set the treated plants in a 

 mite-free place. 



Prevention. — Since the mites are 

 easily spread from plant to plant be- 

 cause they cling to the hands or tools, 

 care should be exercised when working 

 with plants known to be infested. 

 Cleanse the hands and tools thoroughly 

 before touching other plants. 



Larkspur Leaf Miner 



Another pest of garden delphinium is 

 the larkspur leaf miner (Phytomyza del- 

 phiniae Frost). Its injury is twofold. 

 The small maggots feed between the 

 leaf surfaces and make an ugly blotch or 

 blisterlike mine similar to that produced 

 by the burdock leaf miner (fig. 48, 

 p. 30). The adult flies puncture the 

 leaves from the under side, and the 

 punctured tissue turns brown and dies. 

 Both summer and early fall growth of 

 larspur is attacked. As many as six or 



