Some more pests and disease around the botanic gardens

1. Leaf miner

There are a number of different insects whose larvae feed inside the leaves. They can be referred to as "leafminers." Adults may be beetles, wasps, sawflies, moths or flies. They lay their eggs on or in the leaf. Each species always produces the same shape and size "mine." Some look like blisters, some as in this case, look like meandering lines. A wide range of plants are attacked. Control is by removing affected leaves promptly.

2. Case moths (order Lepidoptera)

The larvae of these moths make bag-like structures to protect themselves while they feed on foliage. Different species will have different ways of covering these cases - some have no coverings at all. Below is an example of a case moth larvae which has covered its case with pieces of twig and leaf. It is very well camouflaged. The case increases in size as the larva grows. When fully fed, pupation occurs inside the case. Female moths are wingless and lay eggs inside the case. The larvae that emerge will disperse and make their own cases.

A wide range of plants are affected by different species of case moth. Control is by hand removal of the cases.

3. Leaf Spot - Iris x germanica

Below is an example of this disease which is caused by a fungus which attacks plants in their dormancy. It first shows up as tiny brown spots, each with a watersoaked area around it. As these spots enlarge they turn grey and develop brown to red margins. The spots eventually coalesce to form large dead areas and the leaves are killed. Ongoing spread can weaken plants and hinder flower production.

Worse in warm, wet weather. Fungal spores are spread about by the wind and by water splash. Irises grown from rhizomes commonly have this disease. Irises grown from bulbs are less affected.

Control is by removing affected foliage and destroying. In severe infections, a copper oxychloride spray can be used. A suitable wetting agent can help the spray stick better to leaf surface. It may be necessary to repeat treatment every 10-14 days in ongoing humid, wet weather.

4. White rust - Capsella bursa-pastoris

This fungal disease affects plants in the Brassicaceae family. It is not related to the group of disease generally referred to as rusts. Usually it is characterised by small raised yellowish-green spots on upper surface of leaves with corresponding white soft-looking spore masses on the undersurface. These spores are carried to other plants by the wind or by insects. Badly affected leaves are misshapen. It is most serious in cool, moist conditions.

Control of weeds is important - Capsella bursa-pastoris (shepherd's purse), Coronopus didymus (bittercress), Raphanus raphanistrum (wild radish) are part of the Brassicaceae family. Crop hygiene is important - crop rotation and destroying diseased plant material. Spraying is not effective.

Ref : What Garden Pest or Disease is That? Judy McMaugh