124 
and weeds around greenhouses are badly infested with thrips in 
summer, when the greenhouses are not in use, and on these plants 
it continues to breed until fall, when the seed heads of such plants 
as pigweed (Auiavantus rctroflcxus), wild sunflower (Hcliantlius 
retroflcxus), and foxtail grass (Chcetochloa viridis) are filled with 
w'inged thrips ready to migrate into the houses. It is very im- 
portant, consequently, that all weeds should at least be kept down 
by cutting, tho it is much better to cultivate the land several times 
during the summer to prevent weeds and grasses from coming up. 
Cold frames to be used in starting young plants should not be 
placed near an infested onion field, nor where vegetation is allowed 
to grow wild. 
Spraying and fumigation with tobacco extracts (pages 154 and 
159) thruout the fall and winter will hold the thrips in check. The 
gardener should not wait until his plants are visibly injured, but 
should continually look for the insect, and as soon as the first 
thrips is found, should begin operations. 
Hydrocyanic acid gas has been used by some with apparent 
success. In a small greenhouse containing 4.500 cubic feet of space, 
we were successful in killing 99 percent of the thrips, without 
injury to the cucumber plants, by using the gas at a strength of 
one ounce of cyanide of potassium to 2,000 cubic feet. The maxi- 
mum and minimum temperatures thruout the period of fumiga- 
tion, which lasted all night, were 74° and 65° F. respectively. 
Kerosene and soap emulsions (page 153) are effective against 
the thrips before the plants have made much foliage, but at a later 
period it is impossible to spray thoroly under the surface of all the 
leaves, and as these emulsions kill by contact it is of the greatest 
importance to reach all the insects. 
Dipping the leaves of small plants in a soap solution just before 
transplanting them to the greenhouses has been found useful when 
plants become infested in cold frames. 
The Red Spider 
Tctrauyclnis biiiiaciilafiis Harvey 
( Tctrauyclnis Iclavins) 
This common pest is a tiny mite rather than a true spider. It 
has been a source of trouble to the indoor cucumber-grower for 
years, and altho it can usually be kept in check by careful and 
thoro cultural and spraying methods, it is a veritable pest w^hen 
it once obtains a foothold. It is a general feeder, and among the 
outdoor vegetables which it often injures are celery and eggplant. 
This mite (Fig. 17 and 18) is so familiar to growers that a 
brief description will suffice. It is about one-fiftieth of an inch 
