Scale problems on roses
In May, rose bushes that are more or less defoliated will not benefit from fertiliser. It might force them to sprout, but such new shoots will likely all be blind. Flower bud formation during the growing season cannot happen without leaves making the necessary food and hormones. Roses are not often infested by scale insects but an infestation can be exacerbated by hot, dry conditions.
Types of scale
Scale insects, just like spider mites, bide their time on the lower part of the bushes, puncturing the phloem tubes for food. Female scales can live up to a year. The mother provides a protective scale for the little ones that hatch from the eggs within days and crawl out to do their own puncturing, scale-building and egg-laying. They will even lay over the scale of the mother. Eventually, with no more space available and little food, they move up the stem. The same principle applies to the Australian bug also known as cottony cushion or fluted scale. The female has a large, white fluted egg sac attached which contains many bright red eggs. The young are extremely active tiny crawlers.
How to control scale
• Heavily infected stems that seem to be dying anyway are best cut out of the bush and removed. • Insecticide spray is only effective on the crawlers before they have made their scale or woolly sac. Spray with a horticultural oil such as Ludwig’s Insect Spray or organicide at double the recommended strength. It has a suffocating action that will kill the mothers and unprotected crawlers. • Improve the sap flow by getting more water to the roots. Also, make sure the soil is well aerated so that the roots can become more active.
Since winter pruning time is almost around the corner and many of the infected parts will be cut off in any case, there is no urgency to get on top of this problem right now – unless you are in coastal KZN and expect your roses to keep on flowering.
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