70 
Pests and. Their Control 
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. 
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 aftecied 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. 
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. 
The following viruses have been found in chrysanthemums: 
Stunt Blanche Mosaic or Virus Q 
Aster Yellows Nightingale Mosaic 
Spotted Wilt Ivory Sea Gull or Crinkle 
COMBINATION SPRAYS 
At times it is more economical and convenient to mix two or more sprays and apply them in one 
operation. Before such mixtures are prepared, the grower should be sure no reaction harmful to the 
plants will occur, and that the efficiency of the separate ingredients is not reduced. Consult your State 
Entomologist or Plant Pathologist for information on combination sprays for specific crops. 
A good combination spray for chrysanthemums which will control most diseases and insect pests, 
can be made with Parzate, DDT and Vapotone. Details on dilutions are as follows: 
Material Amount to Make 
Water 100 gallons 20 gallons 3 gallons 
DuPont Spreader Sticker 6 oz. 2 tablesp. | teasp. 
Parzate I'/> Ibs. 5 ounces 2 tablesp. 
Deenate 50W Palles. V/4. |b. I'/> tablesp. 
*Vapotone V/> pt. 31/5 tablesp. I1!/5 teasp. 
To prepare: (1) Measure out spreader and dilute in small amount of water. (2) Fill tank with 
required water and add the diluted spreader and stir. (3) Take out a small amount in jar, add the 
proper amount of the Parzate and shake vigorously until all the powder is thoroughly wetted. (4) 
Pour this mixture back into the tank, preferably through a fine screen or cheesecloth and stir. (5) 
Measure out Vapatone and dilute in small amount of water and add to the tank. Keep stirring or 
keep agitator running while adding the materials. 
* Parathion, 15% wettable powder may be substituted for Vapatone and used at the same rate as 
Parzate, |!/5 lbs. per 100 gal.; 5 ounces per 20 gal. and 2 teasp. per 3 gal. 
DODDER 
SYMPTOMS, Dodder is a parasitic twiner, bearing 
clusters ot small flowers. They are leafless annuals, 
with very slender yellow, white or red stems, which 
become attached to the plant by means of root-like 
suckers. Dodder is occasionally found on chrys- 
anthemums and will cause a complete loss of crop. 
CONTROL. Dodder is common in low, weedy 
places and may be carried into the greenhouse in 
the soil or manure. Soil sterilization is the only pre- 
vention. After dodder is attached to the plants 
remove the affected plants and burn. 
Stunt in Variety Harvester 
