DISEASES IN LUCERNE

Press, Volume XCIV, Issue 28104, 20 October 1956, Page 9

DISEASES IN LUCERNE

ALARMING OUTBREAK OF STEM ROT

MID-CANTERBURY AREAS AFFECTED

An alarming outbreak of a stem rot disease has affected a number of lucerne stands in Mid-Canterbury, especially in the Ashburton district. Reports to this effect have been received at Lincoln College where Dr. I. D. Blair, head of the department of microbiology, after examining specimens of the diseased plants, has diagnosed it as a very serious disease commonly referred to under United Kingdom conditions as “clover rot’’ caused by a fungus. Sclerotinia Trifoliorum.

Indicative of the disease, stems of diseased plants are wilted and sapless. A grgyish-white fungus growth is seen at the base of the stem which ultimately is converted into small black lumps of tissue. These little lumps arc about the size of clover tissue and look like rat dirt. They are known as Sclerotia.

An alarming feature of the disease is that ultimately the Sclerotia are returned to the soil and in that form the fungus survives for long periods In mentioning that he had • discussed the position with Mr Peter Whatman.of the Department of Agriculture Ashburton. Dr. Blair told the writer that the salient facts were that the organism builds-up in the soil and affects lucerne and red clover (not white clover). It is likely to be severe only on first-year stands. Recent weather conditions had been particulargely favourable for the development of the disease.

It was important for farmers, once they saw signs of the disease in their stands, to cut them immediately and get the resultant crop off the ground, so as to let the sun dry out the crowns of the plants. Then, if a spell of sunny weather obtained, there was every likelihood of throwing off the effects of the disease. If. however, the lucerne was not cut immediately, the fungus would build up.

“It is definitely a disease which we will have to watch and do some work on.’’ Dr. Blair said. “The black lumps or knobs have probably come in with imported seed. Further, it is known that the fungus is more aggressive on certain strains than others, and, in yiew of the interest now being created in varieties of lucerne, it will be important to sort these out on the basis of their resistance to Sclerotinia rot. Eelworm Disease Also Reported “To add to this tale of woe an eelworm disease has also been reported in lucerne in Mid-Canterbury. This disease occurs very rarely and its widespread development in the Ashburton district is very alarming. The weather has aggravated it and it is here.” Eelworm disease appears to cause a stunting effect on the plants rather than the wilt, and it is at present under investigation by Mr L. Morrison, head of the department of entomology at Lincoln College. Mr Morrison said that there were several strains for races) of stem-and-bulb eelworm which was designated as Ditylenchus dipsaci. The race which attacked lucerne was also specific to that plant. Recent trials in Britain indicated this, except that alsyke clover was also attacked. It was quite likely that this particular form of eelworm disease had been present in New Zealand for years, but had never been identified as such. Farmers and departmental officers in the district would be well advised to keep their eyes open for any signs of the disease in their lucerne stands.

Affected plants, added Mr Morrison, appeared in isolated .punches. They were stunted and showed some dead tissue on the outside. The outstanding symptom was the rosette formation of the crown of the plant. So far there was no known treatment for the disease.