ANNUAL REPORT, 1947-48 33 



Control of Cranberry Bog Weeds. (C. E. Cross.) Since grasses, sedges, and 

 rushes continue to be the chief weed problems of cranberry growers, efforts have 

 been made to extend the season in which oils can be used selectively in the treat- 

 ment of these weeds. The first two weeks of May continue to be the safest time 

 for the treatment of weeds with both kerosene and Stoddard Solvent. Frost 

 flooding of the bogs and rainy weather during these two weeks usually prevent 

 the accomplishment of all the oil work projected on weedy bogs. 



It is unsafe to spray Stoddard Solvent, even at the rate of 200 gallons per acre, 

 after the terminal buds of cranberry vines have opened. Weather conditions at 

 the time of spraying do not affect the results of spraying late in May — any new 

 growth touched with this oil is seriously injured, though last year's leaves and 

 stems may not be hurt. Any work in late May or early June with Stoddard 

 Solvent must be done as an individual weed treatment, the oil being applied to 

 the base ot the weed only and kept from contact with any new growth on the 

 cranberry vines. 



Stoddard Solvent at 200 gallons per acre will kill asters, white violets, several 

 species of Panicum, and numerous sedges and rushes. Experiments on a great 

 variety of weeds are being continued. 



Studies of the weather in relation to kerosene spraying have been made and 

 lead to the following conclusions: 



1. It is far more important that the bog be dry prior to oil treatment than 

 that it remain dry afterward. Many grasses, sedges, and rushes die readily if 

 dry when sprayed, even though rain falls immediately after treatment. The same 

 types of weeds die after kerosene treatment even if the bog is flooded four hours 

 afterward. 



2. If cranberry vines have made some new growth, kerosene sprays can ap- 

 parently still be used without vine injury if the shelter air temperature is 60°F. 

 or lower. In some instances no injury occurred from kerosene spraying on vines 

 with one inch of new growth when the temperature was 70°F. Too little is still 

 known of the effect of humidity, sunshine, and wind velocity on the toxicity of 

 oil sprays; but at present cool, cloudy, and windy days appear preferable to 

 warm, bright, and calm days for late kerosene treatments. 



Paradichlorobenzene was dissolved in kerosene and sprayed on cranberry 

 vines and weeds. The addition of PDB does not add appreciably to the weed- 

 killing properties of kerosene, the material dissolves only after excessive agitation, 

 and the solution is very harmful to new growth on cranberry vines. 



Further trials with paradichlorobenzene applied to cranberry bogs under one 

 inch of sand indicate that the kill of small bramble (Rubus) and three-square 

 grass (Scirpus) is inadequate to warrant the treatment. However, both spring 

 and fall treatments using T^ pounds of PDB per square rod under one inch of 

 sand when wild bean is dormant appear to give nearly complete control of this 

 weed. 



When PDB is used under sand in new plantings, the cranberry vines develop 

 so slowly that this treatment is not recommended. 



Exhaustive tests of isopropyl phenyl carbamate failed to show any use for 

 this material in cranberry weed control. 



Winterkilling Studies. (C. E. Cross.) Experiments during the last two winters 

 have shown that a single layer of 8-ounce burlap is sufficient to prevent the winter- 

 killing of cranberry vines. The same is true of rough cotton cloth such as is 

 used in the making of 100-pound sacks. Two thicknesses of tobacco netting did 

 not give adequate protection to the cranberry vines. Substantially more cran- 

 berries were harvested from areas covered with cotton and burlap than from 

 unprotected areas. 



