This invention relates to a method for protecting plants from attack for extended time periods by soilborne plant disease organisms which comprises contacting seeds or plant parts with a systemic plant protectant corresponding to the formula ##STR2## wherein X represents chloro, fluoro or bromo; Z represents trichloromethyl, dichloromethyl or dichlorofluoromethyl and R represents lower alkyl of 1 to 4 carbon atoms or phenyl.
In U.S. Pat. No. 3,244,722, issued Apr. 5, 1966, there are described and claimed, among other related compounds, those corresponding to the formula: ##STR3## wherein R is alkyl of 1 to 18 carbon atoms.
Exemplary compounds listed in this patent include 2-chloro-4-methoxy-6-(trichloromethyl)pyridine, 2-chloro-6-methoxy-4-(trichloromethyl)pyridine, 5-chloro-2-methoxy-4-(trichloromethyl)pyridine and 3-chloro-2-methoxy-4-(trichloromethyl)pyridine. As reported in this patent, various compounds disclosed therein are useful as herbicides; various other compounds are useful in the control of pest fish and aquatic insects; and other compounds are taught to be useful as insecticides and anthelmintic agents for warm-blooded animals.
It has now been found that within the broad genus of pyridine compounds taught in U.S. Pat. No. 3,244,722, the specific compounds having a chlorine, fluorine or bromine atom in the 6-ring position, a dichloromethyl, trichloromethyl or dichlorofluoromethyl group in the Y-ring position and an alkoxy or phenoxy group in the 2-ring position surprisingly and unexpectedly exhibit superior and unique properties in being able to systemically protect plants for extended periods of time from attack by soil-borne plant diseases. This kind of activity is not exhibited by isomers or analogs of compounds employed in the herein disclosed method. The outstanding activity of these specific compounds is particularly unexpected since these compounds are generally not effective at the same application rates against the same organisms outside of the plant itself, i.e., when the compounds are used as a pre-plant soil sterilant or fumigant.
It is an object of the present invention to provide an improved method for systemically protecting plants from attack, for extended periods of time, by soil-borne plant disease organisms.
It is a further object of the present invention to provide a method whereby long-lived activity in plants against soil-borne plant disease organisms is achieved, with toxicants which are generally not effective in controlling these same organisms outside of the plants.
One of the advantages of the present method is that by the mode of action of the active toxicant, plant diseases can be eliminated from infected plants and non-infected plants can be protected from attack.
The present method also offers a practical advantage in that there is no need to employ the additional time and labor required by conventional preplant sterilization with soil fumigants.
A further practical advantage of the present method is that the active compounds are used in amounts which are the equivalent of ounces to several pounds of the active ingredient on a per acre basis as against the conventional soil fertilization practices which require many pounds and hundreds of pounds of active material per acre.