Plant disorders may be either due to nutritional deficiencies or unsuitable growing storage conditions. In appropriate temperature atmospheric or erratic water or food supply, poor light, unsatisfactory atmospheric conditions may also cause deficiencies of the mineral salts that are essential for healthy plant growth.
The normal flowering shoot on a greenhouse rose possesses fully expanded sepals, petals, and reproductive parts. The failure to develop a flower on the apical end of the stem is a common occurrence-such shoots are termed blind. The sepals and petals are present, but the reproductive parts are absent or aborted. Blind wood is generally short and thin, but it may attain considerable length and thickness when it develops at the top of the plant. This may be caused by insufficient light, chemical residues, insect, pests, fungal diseases and other factors.
Bull heads or malformed flowers
The center petals of the bud remain only partly developed and the bud appears flat. They are common on very vigorous shoots, particularly bottom breaks, and it is possible that there is a lack of carbohydrates to develop the petals. The cause of bull heading is as yet unknown, how ever, thrips infestation will also cause malformed flowers.
Off- coloured flowers present a problem with some yellow varieties in that the petals may be green or a dirty white instead of a clear yellow. Raising the night temperature several degrees will reduce the number of off-coloured flowers. Occasionally the pink or red varieties develop bluish-coloured flowers. This is very often associated with use of organic phosphate and various other kinds of insecticides.
The area of the stem just below the flower “wilts” and will not support the head. Sometimes this is due to insufficient water absorption; cutting off the lower 1 to 2 inches of stem and placing the cut stem in water at 37°C will revive the flower.
Blackening of rose petals
This is caused by low temperature and high anthocyanin content. GA3 treatment causes accumulation of anthocyanin in petals of Baccara roses. This effect was more pronounced at low temperature (20°C at day and 4°C at night) than in higher temperature (30°C at day and 20°C at night).
Iron deficiencies can cause pale foliage. Adjusting the pH of the soil may solve this problem
Splitting of calyx
The calyx may split down either half or completely. The petals are deprived of their support, which results into bending down of petals. Thus, the regularity of shape and structure of the flower destroyed. Splitting is associated with weather, particularly where light and temperature fluctuate. Some reduction in splitting can be obtained by keeping the night temperature at 5°F. High plant density per unit area caused more calyx splitting. Increasing doses of N reduced the number of split calyces while increase in potassium rates enhanced it. Varieties tolerant to calyx splitting are Epson, palmir etc.
This disorder affects the growing tips which curl and become distorted. Tips of the young shoots fail to separate and continuation of growth results in a characteristic curvature. Poor light and other adverse conditions are thought to be the causes of the disorder. Water stress and potassium deficiency are suspected causes for a physiological curly tip and die-back of carnation flowers.
It occurs when the night temperature is too low and the days are short at the time when flower buds are forming. A rosetted type of growth is indicative of this difficulty. Center petals that fail to develop can be due to excessive heat; or in dark weather some varieties apparently lack enough food to open the flower. Chlorosis, or yellowing of the upper foliage, is generally associated with over watering, excessive fertilizer in the soil, or insects or diseases attacking the root system. Continued growth of shoots and failure to form flower buds when short days are started the mean night temperature was too low. Sunscald is prevalent on standards in flower in very warm weather. The petals turn brown and dry up.
An abnormality characterized by numerous leaves, short petioles and small laminae, which gives some cultivars of gerbera a bushy appearance known as bushiness. Nodes are not clearly distinguished and no internode elongation is seen.
It is common post harvest disorder in cut gerberas. This is mainly caused by water imbalances. It could be ethylene controlled and associated with early senescence associated with water stress.
Yellowing and purple margin
Nitrogen deficiency causes yellowing and early senescence of leaves. Phosphorus deficiency causes pale yellow colour with purple margin. Increase in levels of nitrogen and phosphorus were found to promote development of suckers and improve flowering in gerbera.
Leaves appear bleached in the centers and may have brown tips. To control this problem, shade should be given so as to reduce the light level to 1800-2500 foot-candles.
Leaf scorch of gladioli due to the presence of fluorine compounds in the atmosphere which accumulated on the tips of leaves. The injury is associated with heavy application of super phosphate.