Problems With Aucuba

Scale Insects

• Japanese aucuba shrubs sometimes attract various armored scale insect species, including greedy scales (Hemiberlesia rapax) and oleander scales (Aspidiotus nerii). These tiny pests look more like bumps on the bark than actual insects. That's because newly hatched crawlers quickly find a suitable feeding spot where they remain for the rest of their lives. Scales feed by piercing plant tissue and withdrawing fluids. Although small numbers rarely cause visible damage, heavy scale populations can make leaves wilt, turn yellow and prematurely drop from the shrub. Infested bark might develop cracks and ooze a sticky substance.

Controlling Scales

• Prune off scale-infested foliage to help reduce pest populations. Like other armored scale species, adult oleander and greedy scales have hard, platelike coverings that protect them from chemicals, but using a 1 to 3 percent horticultural oil solution can often help control scale pests if you time your application to coincide with egg hatching.

  Following the specific instructions on the product's label, mix 5 to 7 1/2 tablespoons of horticultural oil for each 1 gallon of water. Spray the plant to thoroughly cover the bark, twigs and leaves for the best results. Avoid using horticultural oil sprays when it's foggy, rainy or more than 90 degrees Fahrenheit outside.

Leaf Spot Diseases

• Various fungal pathogens attack Japanese aucuba shrubs during overly wet weather conditions. As the name suggests, leaf spot fungi cause large, irregularly shaped spots to form on infected leaves. Severely affected shrubs might drop all their leaves, but the fungi rarely cause any lasting damage. Because of this, leaf spot diseases rarely require chemical treatments. Instead, prune off diseased plant parts as soon as you notice the problem. Rake up and destroy any fallen plant material from under your shrubs. Avoid watering from overhead because standing water and wet leaves promote fungal germination.

Nematodes

• Several nematode species feed on Japanese aucubas, but the root knot nematode (Meloidogyne spp.) typically causes the worst damage. These soilborne, microscopic roundworms feed on plant roots, causing bumpy swellings, called galls, to develop on the thick tissues. The galls interfere with the shrub's ability to absorb water and nutrients, which can result in stunted growth, discolored foliage, leaf loss and stem dieback. Infested aucubas suffer from reduced vigor and the root damage eventually leads to the shrub's death.

Preventing Nematodes

• Chemicals aren't generally effective for root knot nematodes, and you can't remove the swellings from the roots without permanently damaging the tissue. Help prevent nematode infestations by buying only certified stock from reputable nurseries and avoid planting shrubs in soils that have hosted nematode populations in the past. You can minimize the impact of root knot nematodes by taking proper care of your Japanese aucuba plants.

Proper Care

• Japanese aucubus prefer moist, fertile soil and need well-draining sites. These plants thrive in partially shady to fully shady areas. Shrubs planted in sunny areas often develop black blotches on the leaves. Reduce the risk of fungal diseases by promoting air circulation around your plants. Space Japanese aucubas 24 to 36 inches away from other plants and buildings to allow for ample air flow.