Gardeners’ Queries...

Press, Volume C, Issue 29505, 5 May 1961, Page 7

Gardeners’ Queries...

I am sending you a specimen of my chrysanthemum plants. These were raised from clean cuttings and have been well grown, with ample attention. They have also been sprayed with D.D.T. emulsion according to the maker’s instructions, probably 10 times all told. Would you say the trouble is chrysanthemum gall midge? I am burning all diseased plants. (Brougham Street. Christchurch.) Your diagnosis is quite correct—your plants are suffering with a quite severe attack of gall midge. Your specimen shows the typical symptoms of tills trouble—small galls abou* the size of the lead in a lead pencil, scattered over the stem leaves and occasionally on th* 1 flower buds. This trouble was only introduced to New Zealand in 1953. and was first recorded in Christchurch in 1957 It 4 s causing chrysanthemum growers to carry out quite extensive spray programmes, par- ■ . in warm districts, where quite a number of generations are produced each year In cooler districts it is [less serious since there are fewer generations. The stunted growth which results gives poo” plants and flowers. As you have found. DD T. is not too effective a spray against this pert. BH C. is better, whilst the best sprav Is parathion. This material is. however, only available to commercial growers owing to its highly poisonous nature. With these sprays it is possible to keep the peat under control, so that the destruction of your stock should be unnecessary. Spray in the morning, when the midges are most active, and at weekly intervals to clean up your stock Use sprays at manufacturers’ recommended strengths. I am hbaving trouble with leaf “burn” with some of my plants, especially phlox, paennv, aid Foliage of some of the plants tends to shrivel and curt, whilst adjacent plants are quite satisfactory. Soil is about a foot deep, and holds moisture well, but is

sandy beneath, whilst the position is rather open, and very exposed to north-east winds. Rainfall is about ’0 inches a year. Have yon any suggestions on the cause’ (TixaU, Kaiapoi.)

From your letter and specimens I am strongly of the opinion that exposure to wind, coupled with too free a drainage, Is tile fundamental cause of your trouble. The leaves showed no trace of fungal or pest attack that would directly contribute towards your “leafbum.” The presence of leafbum on Some plants and not on others is I think, purely due to better established or better sheltered plants and/or slightly better soil in the areas w*here defoliation does not occur. You could prove—or disprove—nny diagnosis next year by keeping tie hose trickling at the foot of one of the plants which has shown leaf bum this year