86 



PLANT GROWTH SUBSTANCES 



pineapples into flower or to increase fruit size. Still other hormones 

 prevent premature flowering of pineapples, and fmally the vegetative 

 propagation of pineapples is facilitated with plant hormones. Thev are 

 rapidly becoming a part of our everyday life, and, as with the telephone 

 and the X-ray, we shall soon wonder how we ever got along without 

 plant hormones. 



Fortunately monocotyledonous species are more resistant than many 

 of the dicotyledonous species. Since corn covers such a vast area of 

 land, it is encouraging to find that at least some types of weeds can be 

 controlled in the field without harming the corn. The results reported 

 are somewhat variable but sufficiently promising to warrant further 

 testing. It may develop that certain varieties are resistant enough to 

 permit sufficient amounts of 2,4-D per acre to kill noxious weeds without 

 affecting corn. Treatment of the soil after planting and before weed 

 seeds have started may be the answer to some of the problems. This 

 pre-emergence treatment applied after the corn is planted appears to 

 control both broad-leaved annuals and weedy grasses. One to five pounds 

 per acre can be appfied as a spray on the ground without preventing 

 corn from germinating and growing. If applied after corn starts growing, 

 care must be taken to hit at the base of the stalk rather than at the 

 tops. When tops are sprayed the corn leaves fail to separate and remain 

 rolled up so that the tassel must push out at the side. Also abnormal 

 flowering and prop roots appear, and the crop may be decreased. How- 

 ever, the results are sufficiently promising to indicate that with selection 

 of proper varieties of corn and improvement of methods controlling 

 weeds in a corn field will be a reality. 



Weeds in sugar cane fields, particularly alligator weed, have been con- 

 trolled by applying 0.2 per cent of 2,4-D at the rate of 100 gallons per 

 acre. Both dusting and spraying were done without noticeable decrease 

 in the sugar production. Weed control in the tropics was demonstrated 

 by van Overbeek and shown to be of tremendous economic importance. 



There are some 10,000 miles of waterwavs in the southern district 

 in and around the state of Louisiana which have become infested with 

 water hyacinth and alligator weed. This constitutes a major problem 

 assigned to the army engineers of the southern district. Navigation, 

 drainage, health of people and wild life are all affected by this problem. 

 There are a number of contact weed killers which are effective on 

 aquatic plants, but they are poisonous to fish and other animals and also 



