On the Rust or Mildew. 6S 



No. III. 



ON THE RUST * OK MILDEW. 



It is proposed to discuss this important subject under the following 

 general heads, 1. The nature and appearance of the rust or mildew; 

 2. Its causes ; and, 3. An account of such remedies as have been 

 suggested, either to diminish, or to extirpate the disease. 



1. The Nature and Appearance of the Rust. This disease usual- 

 ly appears in wheat, in the month of June, after the plants have 

 grown to their full length, and before their seeds have ripened. Its 

 first appearence is on the leaves and stems of the plants, in the shape 

 of spots of a dirty white colour. They soon become yellow or 

 brown, and afterwards black ; and they seem to rise, thicken, and 

 grow up in a roundish shape, on the stalk and leaves of the plant. 

 From the time that these spots are found, the vigour and luxuriant 

 growth of the plants evidently decline, and they make no further pro- 

 gress towards maturity. The stalk becomes so brittle, that it breaks 

 under the flail, and emits dust of a disagreeable flavour, affecting the 

 breathing of the workmen f . 



As mildew, whenever it falls on grain crops, arrests the farther 

 growth of the plants, and exhausts the juices that should have ma- 

 tured the grain, it is advisable, to reap the crop whenever the disease 

 appears, and before it extracts the natural juices of the plants. The 

 grain produced by an infected plant is small, poor, and of a pale 

 colour, but as it contains none of the rust, it is not unwholesome 

 food. 



2. Causes of Rust. Several of the accidents enumerated in a pre- 

 ceding section, (No. I. p. 53,) f may contribute to the production of 

 rust ; but the principal causes are, having the laud in too rich a state for 

 corn crops ; a too frequent repetition of so exhausting a crop as wheat, 

 more especially on weak soils, which renders the application of much 

 manure necessary ; or when the crop meets with a check in its pro- 

 gress to maturity, and in that weakened state, is exposed to heavy 

 rains, or variable weather. 



It Jias been well observed, that when crops, intended to ripen their 



* Rust is the proper name, being a literal translation of the French " La 

 Rouillc," and the Latin " Rubigo." The disease has at first a brownish, 

 rusty, appearance, which afterwards becomes black. 



f Sir Joseph Banks's Account of the Cause of the Mildew in Corn. Com- 

 munications to the Board of Agriculture, vol. iv. p. 399. See also the Trans- 

 lation of M. Desmazieres's Paper on the Diseases of Wheat, annexed to " Hints 

 41 on the Agricultural State of the Netherlands," p. 22. The celebrated Tes- 

 sicr was the first naturalist, who directed his particular attention to this sub- 

 ject, in his work entitled, " Traite des Maladies des Grains." 



| Pliny (Lib. 18. c. 28.) attributes the rust to frost, and in this way it 

 may be accounted for. If frosty nights are succeeded by hot gleams, disease 

 is inevitable, unless the frost could be shaken off, before the influence of the 

 sun is felt. It is a singular fact, that plants of wheat under trees escape rust, 

 though the neighbouring crop is infected with it. 



