508 



THE FARMERS HAXDBOOK. 



are hard to kill, requiring about two hours' soaking in a solution of 1 part 

 formalin in 200 parts water, or a solution of 1 part corrosive sublimate 

 in 1,000 parts water. According to some Departmental experiments, even a 

 l-in-300 solution of formalin is apparently injurious to any young shoots 

 developing from the eyes at the time of dipping, and in such circumstances 

 a solution of 1 part formalin in 500 parts of water can be used. 



Recent experiments have shown that hot formalin controls Rhizoctonia 

 scab effectively. A solution of 1 pari of commercial formalin (40 per cent. 

 formaldehyde) in 120 parts of water is made and heated to 122 deg. Fab.. 

 The potatoes are immersed for two minutes in the solution, placed on a 

 draining hoard and covered with a (doth that has been soaked in the ho1 

 solution and wrung oul slightly. The tubers are left covered for one hour 

 and then laid out till air-dry. This method requires care, as the temperature 

 of the solution has to be noted with a thermometer and must be maintain! 

 at L22 deg. Fah. while the seed is being treated. 



Scab due to Eelworm (Heterodera radicicola), — This disease, which is 

 also known as Root Knot or Root Gall, appears to be spreading very much in 

 New South Wales. Such plants as the following are attacked: — Field crop-: 



Potato attacked by Eelworms (IJeterodera radicicola). 

 [See further illustrations on page 492^. 



lucerne, some cowpeas, soy beans, pumpkins, melons, tobacco. Vegetables: 

 all kind-, as cabbage, cauliflower, spinach, lettuce, beans, peas, tomato, potato, 

 carrot, and parsnip; many flowers and trees. About 500 different kinds of 

 plants are known to be attacked. The cause of the injury is a tiny round 

 worm — Heierodera radicicola, often called an eelworm, and also (from the 

 effects of its attack) a gall worm. It belongs to a group of worms known 

 as nematodes, many of which are injurious to plant-, while others attack 

 animals. The disease.. is readily seen on examining the roots. Irregular 

 enlargements, either scattered or so (dose that the whole root system is 

 abnormally thickened, will be seen. These enlargements interfere with the 

 functions of the roots, and often the first indication of attack is the wilting 

 and failure of the plant. In the potato plant, the tubers themselves are 

 usually attacked. Blister-like lumps are formed, and often the surface of 

 these break, thus producing a very scabby appearance. 



