





















CHRYSANTHEMUM Gloechne cUTT I NGS 
Dna We SAG mg/h ConbGE | ‘ 
VIRUSES 
The word 'virus"' is being referred to by the medical profession as well as by the florists and a short 
explanation of virus should prove of interest. 
Viruses of the chrysanthemum are considered to be infectious; that is they can be transmitted to a — 
healthy plant only by contact with an infected plant. They are not carried in the soil, water or air as are 
other diseases caused by fungi and bacteria. 3 | aa 
The virus particles cannot be seen by the most powerful microscopes. Most of them will pass through 
bacterial filters. They respond like living organisms. They are always present in the sap of diseased 
plants and can be transmitted to a healthy, plant through wounds or by mechanical means. The = 
chrysanthemum is known to be affected with three viruses, namely yellows, mosaic and stunt. Stunt 
is the only one that has caused much concern. It has been found that aphids as well as mechanical 
handling will cause stunt to spread. hes 
Once a plant is infected with a virus it usually always remains affected. To define a virus the follow- = 
ing is.as good as any: A virus is a protein which requires the presence of living cells for multiplication 
and it causes changes in the structure and functions of living cells. zs Ota 
STUNT 
SYMPTOMS. Young foliage may be paler than normal and has a tendency to more upright growth — 
rather than growing at a wide angle with the stem. Diseased plants show stunting in growth 
after they have been in the soil a few weeks, and at maturity they may in some cases be less — 
than half as tall as normal. Buds may form and blossoms open a week or 10 days ahead of 
those on healthy plants, although on some varieties stunted plants will bloom after the normal = 
plants. Varieties possessing red pigment (the bronzes, pinks and reds} the red component of the 
color is badly bleached. With most varieties the blossoms are greatly reduced in size. ee 
CONTROL. Knowing that stunt is a virus and that it can be spread by insects as well as manual — 
operations the following recommendations for its control are necessary. (1) Select only the health- = 
iest plants in June or July for stock purposes. (2) Use a sterile knife when removing cuttings or — 
pinching the plants. (3) Keep all insects from these plants by isolation and use of good insec- 
ticides. (4) Rogue out all plants from time to time that look the least bit weaker. (5) Be careful  —> 
not to bruise or handle the plants. (6) Use single plant selection procedure and keep case his- | 
tory on each clon. (7) Do not attempt to increase population until mother block of stock plants 
is entirely free from diseased plants for at least two generations. 7 oT 
Realizing that such a procedure to keep stock clean from stunt is very expensive and that all growers — 
cannot carry out these control measures it is therefore, necessary for the propagators of chrysanthe- 
mum cuttings to carry out this extreme control measure. 
DODDER 
SYMPTOMS. Dodder is a parasitic twiner, tear 
clusters of small flowers. They are leafless annua 
with very slender yellow, white or red stems, w 
become attached to the plant by means of root 
suckers. Dodder is occasionally found on ch 
anthemums and will cause a complete loss of ¢ 
CONTROL. Dodder is common in low, wee 
places and may be carried into the greenhouse 
the soil or manure. Soil sterilization is the only pr 
vention. After dodder is attached to the pla 
remove the affected plants and burn. ig 

Stunt in Harvester 
