DISEASES OF CULTIVATED PLANTS 569 



to weed instead of producing fruit. When this is the case the vegeta- 

 tive function of the plant is carried on too rapidly to allow fruiting. 

 Fortunately, this condition is under our control. In the first place, 

 we should use a fertilizer that is not too one-sided in ammonia con- 

 tent ; but we must reckon with the fact that a fertilizer which would 

 prove to be the very best during a dry year would prove to be too 

 high in ammonia during a year when the amount of moisture was 

 normal or above the normal. Where the bloom buds are shed on 

 account of too rapid growth of the vine, this condition may be 

 checked almost immediately by cutting out the growth buds at the 

 terminals of the plants. Care should be taken to leave at least two 

 "hands" of bloom buds. This makes the process of disbudding a 

 little more tedious, but if all the bloom buds are removed the plants 

 will not be able to set any fruit. In disbudding rapidly-growing 

 plants to make them set fruit, care must be taken not to carry this 

 operation to an extreme; otherwise, we introduce a disease which is 

 known as leaf curl, or roll leaf, and is described in subsequent pages. 



A third cause for the dropping of many blooms is due to the 

 presence of a minute greenish insect very similar to the suck-fly of 

 the tobacco, which has a pernicious habit of spending most of its 

 time on the bloom buds of the tomato plant. By means of its slen- 

 der beak it pierces the stems of the fruiting hands, and in this way 

 injures them to such an extent as to cause the shedding of buds, and 

 even, in severe cases, to cause the droppings of newly set fruit. The 

 insect is rather shy, and not readily discovered, especially if the 

 tomato plant is brushed against or moved. If, however, the observa- 

 tions are made very quietly, there is no difficulty in finding one or 

 more of these small flies engaged in its disastrous work. 



The life history of this insect has not been carefully studied 

 out so far as the writer knows, but the mature insect may be killed 

 by spraying with a nicotine solution, and by some of the other con- 

 tact insecticides. It is, however, a rather difficult matter to get the 

 insecticide on the pest, because at the least disturbance of the vines 

 it flies away and gets out of danger by hiding under a leaf. 



Leaf Curl, or Roll Leaf, The appearance of the plant when 

 affected by this disease is so striking that all tomato growers are 

 familiar with it. There are a number of causes which lead up to 

 this difficulty. The most important one in Florida is the presence 

 of too much moisture in the soil. Another very prolific cause of 

 this disease is the too severe pruning of the tomato plants. Where 

 this is carried on rather drastically, it is almost certain to produce 

 the disease. As disbudding is practiced by many of our growers, and 

 staking of tomatoes is also customary over a large area, we find this 

 disease not at all uncommon. The bad effects of it, however, are as 

 a rule not recognized, since the leaves usually remain green and the 

 plant continues to grow. A plant, however, that has been pruned or 

 disbudded to the extent of producing leaf curl is less productive 

 than one that has not been pruned to such a decree. 



Where leaf curl is due to too much moisture in the noil, caro 

 should be taken to plow the field in such a way as to relieve it of tho 



