RED SPIDER CONTROL 
Last season was one of the best for dahlias. Evidence of this was the greater 
quantity and quality at all shows. DDT, used to control the pests which had previously 
been the greatest despoilers of blooms and foliage, was in a large measure responsible 
for the all-around better performance of gardens. Unfortunately, DDT also was 
indirectly responsible for the serious increase of red spider mite (see "Red Spider’ 
under Cultural Hints in the back of this book). This pest had not previously been 
prevalent on dahlias, and as a result many growers failed to diagnose the trouble when 
it first appeared. As an outcome, the infestation got out-of-hand, causing irreparable 
damage, to plants and in some cases killing them. 
We warned of the likelihood of red spider infestation in our 1946 DAHLIA BLUE 
BOOK, at which time we also recormmended Dowspray-!7 as the best control. Unfor- 
tunately, some of those who followed our recommendation had the misfortune to 
severely ‘burn’ the foliage with this material. However, in our own plantings, we used 
it for the second successive year with highly efficient results and very little foliage 
damage. In view of the unhappy results some had, we conferred with Dr. Neiswander, 
of the Ohio Experiment Station, with the result that we feel more emphasis should be 
placed on the following factors: 
(1) Red spider mite are very hardy little insects and a powerful insecticide is 
necessary in order to have any effect on them. 
(2) All powerful insecticides are dangerous to foliage if not properly prepared 
and applied. 
(3) Dowspray-17 is a contact poison, which means that the insect must be con- 
tacted by the material to be killed by it. 
(4) Red spider are usually on the undersides of the leaves, and especially the 
lower leaves of the plant, hence diligent effort must be made to apply 
the spray where the insects are. 
(5) A fine fog-like spray, lightly and evenly applied, is less likely to cause 
foliage burn than a ''wash'" application, and does the job just as well. 
One application, if carefully applied, should rid the plants of red spider 
for the season. In some cases a second application may be necessary. 
(6) Dowspray-!7 is not soluble in water but when mixed with water it forms a 
suspension’. spray preparation. Since it is a suspension, it is highly impor- 
tant that the material be kept well agitated from the time it is placed in 
the sprayer until used. 
(7) Lasting effect of Dowspray-17 diminishes as the temperature increases, and 
there also seems to be evidence that foliage burn is greater at higher 
temperatures. 
(8) Dowspray-!7 appears to have greater effectiveness in the presence of DDT 
and may be applied in the same spray. 
(9) Care must be used to weigh out very closely the correct amount of material. 
Our recommendation of 34 pound of Dowspray-!7 to 100 gallons of water 
means that only 3/25 of an ounce is required to a gallon of water.  {Pos- 
sibly, the aid of the neighborhood druggest can be enlisted in weighing 
the material for a small sprayer.) Dr. Neiswander has found that a spray 
made at the rate of '/> pound of Dowspray-!7 to 100 gallons is practically 
as effective as the 34 pound preparation, with less danger of foliage burn. 
(10) There is no advantage in spraying batoreutnewincac imate present. 
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