PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Non-living agents (contd)
ENVIRONMENT.
Fig. 222. Cold weather injury to
carnations. Twisted leaves on carnation
caused by unseasonable cold weather.
PhotoNSW Dept. of Industry and Investment.
Fig. 223. Flowers of many
plant species are more
sensitive to frost than the
leaves, eg chrysanthemum.
Fig. 224. Etiolation.
Left: Healthy seedling
Right: Spindly growth
due to insufficient light.
Fig. 225. Oedema on umbrella (Schefflera actinophylla) leaf. Oedema occurs when plants
absorb more water through the roots than they can transpire through the leaves, so the surface
cells of the plant burst. Small masses of tissue may expand and break out on the surface of the
leaf (or other plant part) causing watery swellings, small galls or rings which later becomes
corky brown or gray and scabby. Oedema often appears on the under surface of leaves near
the ground, eg camellia, geranium. Restricting water supplies during cloudy weather may
lessen the problem but control is not really necessary. PhotoCIT, Canberra (P.W.Unger).
Fig. 226. Enlarged lenticels on a potato
tuber due to the excessive soil moisture before
harvest. Photo NSW Dept. of Industry and Investment.
Fig. 227. Leafrolling may be due to a range of environmental causes.
Left: Tightly rolled rhododendron leaves. PhotoCIT, Canberra (P.W.Unger).
Right: Rolled tomato leaves due to high soil moisture or excessive
pruning. Plants absorb more moisture through their roots than they can
transpire through their leaves. Rolling usually begins on the mature foliage
at the base of the plant; affected leaves are leathery, firm and thickened. In
most cases yield is not affected. Leaf rolling on potato is caused by the
potato leaf roll virus. PhotoNSW Dept. of Industry and Investment.
Non-parasitic pests and diseases 393