4 MASS. EXPERIMENT STATION BULLETIN 361 



WATERING PRACTICES 



The method of watering tomatoes under glass has a bearing on the conditions 

 which contribute to the prevalence of leaf mold. The time of day and the charac- 

 ter of the weather prevailing when water is applied are also very important. 



Sprinkler systems wet the foliage and produce moisture conditions on the leaves 

 conducive to the best general development of the disease. The open hose method 

 is most generally used, but it causes the water striking the ground to splash on 

 the foliage and offers the temptation of watering from the walks. Simple and 

 inexpensive watering nozzles or shovels can be attached to the hose to confine 

 the water to the bottom of the plants and these implements are used by many 

 growers who have recognized the importance of keeping the foliage dry. 



Small (42, 45) demonstrated with a few plants that the wetting of the foliage 

 had no appreciable effect on the prevalence of tomato leaf mold. Newhall (29) 

 asserted that a planting carefully bottom-watered is as subject to attack as one 

 sprinkled overhead. In the writer's experiments, however, which simulated 

 commercial greenhouse conditions, evidence of the effect of wetting the foliage 

 on the incidence of the disease was clearly demonstrated. Two greenhouses 

 were each divided into two equal areas. In one area the watering was done with 

 a sprinkler system and the foliage was thoroughly wetted during each watering. 

 The watering was done in the morning and occasionally in the afternoon. In 

 the other area the plants were bottom-watered with a watering shovel. Leaflets 

 from the prunings during the growing season were counted for a tabulation of 

 the amount of infection. There were totals of 26.2 and 13.8 percent more infected 

 leaflets in those areas where the plants were sprinkled (Table 1). The different 

 disease conditions associated with the two different methods of watering are more 

 clearly shown in Figure 3. These differences, while not significant under the two 

 sets of conditions in the same greenhouse, would have been much greater if each 

 treatment had been made in a separate greenhouse, because of attendant difi"er- 

 ences in the humidity of the air about the foliage. 



Table 1. — Comparison of Overhead .\nd Bottom Watering in Relation 

 TO THE Prevalence of Tomato Leaf Mold 



Fall Cropping Season 1931. 



Percentage of Diseased Leaflets 



Date of 

 Foliage Counts 



October 29, 1931 



December 2, 1931 



January 4, 1932 



January 13, 1932 



Total 95.2 92.7 69.0 78.9 



The wetting of the foliage contributes to the development of the disease es- 

 pecially if the watering is done late in the day. The experiment also showed 

 clearly the suppressive effect on growth of sprinkling the foliage with cold water. 



