Plant Doctor Archive

Woolly growth on fruit tree

I HAVE a dwarf apple tree that appears to have some sort of fungus growing on it in patches. Should I spray it with a fungicide?

FROM the photos you sent the problem looks more like woolly aphids than a fungus disease. These aphids usually feed on the root system of susceptible plants, particularly apples and relatives such as crabapples, pyracanthas, cotoneasters and sometimes pears. But they also move above ground and you can find them on new shoots, on the calyx end of fruit or among cracks in the bark.

If you pull the woolly threads apart you should find purplish-brown aphids sheltering inside and you may also find them wandering around outside their woolly haven, especially on new growth. They feed by sucking sap, which damages buds, and badly affected trees can end up looking quite twisted and deformed. They also secrete honeydew which encourages the growth of sooty mould on leaves.

Generally, woolly aphids prefer moist conditions so tend to be more of a problem in cool, shady gardens than in hot, sunny areas. In autumn they tend to move down to the roots, especially in cold parts of the country.

There are a lot of contact sprays you can use to control woolly aphids above ground, such as pyrethrum, mineral oils (such as Eco Oil, Super Spraying Oil) and Nature's Way Insect Spray, but you need to make sure to get thorough coverage so the spray actually penetrates the woolly protective coat and gets to the aphids. Alternatively, you could use a systemic spray such as Rogor 100, Target or Confidor, or a combination product like Fruit Tree Spray which controls a wide range of pests and diseases.

To control them on the root system you could use Soil Insect Killer or Diazinon. Make sure to follow all spray label recommendations carefully.

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