74 
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 ex- 
planation 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 dis- 
eases caused by fungi and bacteria. 
The virus particles cannot be seen by the most pow- 
erful microscopes. Most of them wil 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 5 viruses, namely yellows, 
Aspermy, rosette, 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. 
Material 
100 gallons 
DuPont Spreader Sticker 
Parzate 
Deenate 50W 
*Vapotone 
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 cheese- 
cloth 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. 
Dodder te. 
SYMPTOMS. Dodder is a parasitic twiner, bearing 
clusters of 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. 
*Parathion, 15% wettable powder may be substituted for 
Vapatone and used at the same rate as Parzate, I'/. pounds 
per 100 gallons; 5 ounces per 20 gallons and 2 tablespoonsful 
per 3 gallons, 
20 gallons 
Once a plant is infected with a virus, it usually al- 
ways remains affected. To define a virus, the follow- 
ing is as good as any: A virus is a protein which re- 
quires the presence of living cells for multiplication and 
it causes changes in the structure and functions of liv- 
ing cells. 
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: 
Amount to Make 
3 gallons 
2 tablesp. 1 teasp. 
5 ounces 2 tablesp. 
V4 lb. I'/> tablesp. 
3'/y tablesp. I'/> teasp. 
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 prevention. 
After dodder is attached to the plants, remove the 
affected plants and burn. 
Stunt in Variety Harvester 
