These will vary depending on your climate, the pests and diseases I will mention here can cause problems for growers in southeast Queensland. Always try a spray you have not used before on one plant to see if there are any adverse effects before spray them all. Some sprays can burn the leaves or sometimes defoliate the plant. Always mix the spray to the makers recommended strength.

Holes in the leaves. Grubs, loopers, grass hoppers, these can be picked off and killed or a spray of pyrethrum or carbaryl used.

Leaves discoloured, a fine spider web underneath the leaf, tiny red or orange insects under the web. Red spider or two-spotted mite. If this is on plants in the garden try removing badly affected leaves and spraying the plant with the garden hose especially under the leaves. Plants in the shade house remove badly affected leaves and spray with dicofol [Kelthane] or red spider spray.

Brown marks at the center of the leaf where the stem joins on rhizomatous types. This problem can have several different causes. Water or foliar fertilizers lying on the leaf can cause it. Water or spray earlier in the day so the leaves will dry. It can also be caused by thrips. These can be controlled with a spray of maldison [Malathion or Malathon].

Brown marks on the leaves, usually on the older ones. This can have several causes; it could be bacterial leaf spot. This usually occurs on older leaves or leaves damaged in some way sometimes by leaves rubbing or old flowers lying on the leaves. A fungus can also be the cause. The affected leaves could be removed or parts of the leaf cut off. Do not water the leaves. A spray of copper oxychloride may help.

The leaf stems rot off next to the rhizome starting at back end of the rhizome and moving forward. This is caused by pythium or damping off fungus. Poor drainage in the potting mix and or over watering will encourage this problem. Isolate the affected plants; do not water the plants until the potting soil has dried out, repot into fresh potting mix if the plants recover. A preventive soil spray of furalaxyl [Fongarid] may help.

The leaves have a white powdery coating; on cane types, they fall off except the top two or three and stems also have a white powdery coating. This is caused by powdery mildew, it usually occurs in the winter months. There are a few things you can try, increase the air circulation in your shade house, remove badly affected leaves, and spray your plants with a fish emulsion fertilizer, a silica spray or triforine every two weeks.

Flowers and leaves covered with grey mould. This is caused by botrytis fungus. Try improving the air circulation; do not water your plants with an overhead spray, try a spray of mancozeb.

Sprays that can defoliate some begonias dimethoate [Rogor] , lime sulphur, white oil.