Gardeners’ queries

Press, 9 January 1987, Page 10

Gardeners’ queries

Having grown gerberas for many years with little trouble, it has been a shock to find that many of the leaves on different plants are now blighted. The beds in which they are growing have been built up with horse manure over the years, and maybe this has brought on the trouble? C.D. (Chch). The spotting of the leaves is due to a fungal infection known as white rust. This infection generally shows up on the under side of the gerbera leaves as large white pustules, a distinguishing feature of this disease. Badly infected plants are best destroyed. Where the incidence is slight, all diseased leaves should be removed and plants then thoroughly and regularly sprayed with maneb (or

zineb) at double strength. The horse manure would not be contributory to the incidence of white rust. Gerberas are most responsive to soils which are well endowed with organic matter.

For the last two years my peach tree has formed fruit buds that grow to the size of small marbles and then drop off. Some, as you can see from the enclosed, stay put. The tree does not lack water. J.K. (Ashburton). The samples of immature fruit failed to provide any clues about why they were shed. Very young trees do not produce a lot of fruit initially; there is also a natural drop which occurs several weeks after fruit set. Trees which have suffered badly from leaf

curl will often also prematurely shed their fruit. It Is regretted that more assistance cannot be given regarding this query. Would you comment on the enclosed tomatoes, please? The plants are con-tainer-grown in a prepared soil mix to which a commercial tomato fertiliser has been added; they are healthy looking. The fruit, only just beginning to develop size, has these single black marks on it. About half a gallon of water is applied per plant at each watering, according to given advice. “Puzzled” (Chch). Blossom-end rot is responsible for the blackened, depressed region on each of the tomatoes inspected. This is a

psychological manifestation predominantly associated with insufficient calcium uptake by and in the plant, but also involves inadequate availability of moisture. Once tomatoes begin to flower they should not be subjected to variable conditions such as moisture stress. The soil should not be allowed to dry out, nor should plants be subjected to a constantly wet regime. Damping down of plants in hot weather Is helpful. All this is really an oversimplification of a rather involved matter, but the main thing to keep in mind is to avoid extremes, such as, for example, the half gallon of water you are pouring on at set intervals. Moisture should be applied slowly and according to requirements, not on a prescription basis as it were.