Plant Doctor Archive

Spider mite on roses - 2

I HAVE grown roses for nine years. The Rose Society newsletter mentioned that Ivomec drench is useful in combating spider mite. I have used this for the past three years but in the last two years the mite infestation has grown. It is back again on the same roses that were hit with spider mite in the previous years, plus more roses are infested. Also infested is my luculia. I have always been very diligent in spraying my roses every two weeks, with a regime of Gild, Shield and Guardall being used. I am very diligent in picking up any diseased leaves and disposing of them in the rubbish, but I seem to be losing the battle. Could the spider mite be in the soil?

THIS really got me thinking. Why would a product used to control parasites in farm animals, like cattle and deer, be suggested for controlling mites on roses? And it sounds from your experience that it's not very effective anyway.

My advice is to only use agricultural or horticultural chemical products for the purposes detailed on the labels. Mites can be difficult to control once they get established, but they don't live in the soil. They tend to survive winter as eggs in the bark of trees or in other dry nooks and crannies, or in mild areas they may continue to feed on weeds or on green house crops. You often find them on indoor plants all year round, too.

So, in spring, your roses are probably being reinfected by mites hatching from eggs laid in the bark, either of the roses themselves or nearby plants, possibly fruit trees.

Of the other three sprays you used only Guardall has much effect on mites. In my experience the best way to control and prevent mite infestation of roses is a programme starting in winter.

As soon as you've finished pruning, give them a thorough spray with a copper fungicide mixed with spraying oil such as Conqueror or Clear White Oil. Make sure to drench the woody bark at the base of the stems completely so the oil smothers the mite eggs and kills them. The copper fungicide kills off disease spores such as rust. You could apply another spray a few weeks later if you wish. Then in spring and summer, follow your two-weekly spray regime using Guardall and Super Shield (not Shield).

Other products you could include are Super Sulphur (which also controls fungal diseases), Mavrik and Mite Killer, but you need to get good coverage under the foliage for them to be really effective. Check the labels for mixing instructions. And you can give your luculia the same treatment.

Mite infestations are generally worse in hot, dry conditions, so try to keep your roses watered in summer drought and apply plenty of mulch to conserve soil moisture.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.