News & Updates:

For over a hundred years copper fungicides afforded the best means of control of black spot. We advanced from Bordeaux mixture to Bordinette, and then to Cuprox, and we applied them after winter pruning, the spring blooming, and the summer trimming. By doing so, we decreased the infestation greatly, but recently TMTD has been made available and it excels and supersedes all copper sprays. There are several proprietary preparations of it-for example, Thiotox. By applying it to the under-surfaces of the foliage every ten to fourteen days we can almost banish black spot and all other fungus diseases from our roses. The introduction of TMTD and the practice of frequent spraying mark a tremendous advance in efficient growing of roses. The health and vigour of the plants is amazing; they retain their leaves, and so are able to manufacture vast additional quantities of food.

rose wilt (Plate 43)

Rose wilt is due to infection with a filterable virus, quite unrelated to those causing wilt in other plants. Inoculation of filtered sap from affected roses into healthy roses will reproduce the disease. Budding from affected plants can be a source of transmission.

In most years wilt in any type of plant is only endemic, but rises from time to time to epidemic proportions. This increase is frequent in the forms affecting Iceland poppies, stocks, antirrhinums, tomatoes, and other plants. We know of no explanation of this sudden increase in virulence and incidence of such diseases in plants and animals.

Rose wilt is peculiar to Australia and New Zealand, and was recorded first in 1908. A somewhat similar disease occurs in Italy. Our first epidemic occurred in 1915, and there was a very serious recrudescence in 1927-9. We have had no widespread epidemic since that time. The disease is most common in the spring, and early stages may easily escape notice. The first obvious symptom is a recurving of the leaflets at the tips of young shoots. If touched they fall off and are noticeably brittle. Defoliation spreads down the shoot, with the leaves becoming light in colour, or even yellow, before falling. Very soon the stem-tips lose colour, become almost translucent and die; they are then black. Later the base of the shoot turns yellowish-green and soon becomes dark-brown. The inter-vening part of the stem remains green for a while, but gradually the whole shoot dies. Older wood may be affected later.

An infected rose may produce apparently healthy growth after losing some stems. The new shoots may repeat the symptoms in the following spring, or the whole plant may appear to recover for even a year or two. All varieties seem to be susceptible.

Probably the virus of rose wilt is transmitted from plant to plant by aphis or secateurs. Very infectious and absolutely incurable, it is the most dreaded of all rose diseases. One infected plant can ruin a whole garden within a very few years. Dead wood does not seem to be infectious.

Control of aphis and quick recognition of early symptoms are extremely important. No time should be lost in digging out and burning an infected plant. At least two or three barrow-loads of soil from round its roots must be removed from the garden. Leave the hole open to sunlight for a week or more, lightly sprinkle it with lime, and refill it with a mixture of one part of old cow manure or compost and six parts of virgin top-soil, to which a little bone-meal has been added. Usually this treatment will be given in November. Allow the soil to rest until the following planting season, for it seems possible that the disease can be transmitted through infected soil.

There are advocates of sterilization of secateurs as one moves from plant to plant in the everyday gathering of rose-blooms, or removal of faded flowers. Such a procedure makes rose-growing very tedious. The early symptoms of rose wilt appear before any blooms are ready to cut, and any plant that comes under suspicion should be watched carefully, for one desires neither to dig out an unaffected plant nor to allow the disease to spread to other plants by delaying unduly the burning of a plant with rose wilt. During this period of suspicion it is easy and safe simply to avoid that plant. If you fear that other members of your household may be less careful, mark the plant by tying a large, easily seen cloth on a stake driven in beside it.