Leaf drop

Other forms of visible injury are related to various physiological alterations. Air pollution injury can cause early senescence or leaf drop. Stems and leaf structure may be elongated or misshapen. Ornamentals and fruit trees can also show visible injury to the blooms of the fruit, which can result in decreased yield. 

Injury any physical or biological response to pollutants, such as a change in metabolism, reduced photosynthesis, leaf necrosis, premature leaf drop, or chlorosis. 

Foliage Deterioration, Chronic Leaf Drop, Dieback... 

Foliage deterioration, chronic leaf drop, and dieback are caused by numerous fungi, acting in semiparasitic fashion Gloeosporium cingulatum S. and V.S. = Cal-letotrichum coffeanum Noack, Phoma sp., and others. 

Bacterial leaf spot causes small, angular black spots on leaves. Leaves may turn yellow and drop early. Spray lime-sulfur every 10-21 days until leaf drop if weather is wet or humid, or if the spots are spreading. 

Poplar, yellow 0.30 8/day, 5 days/week. 13 weeks 82. leaf drop 0. height 233... 

Thompson, C. R., and O. C. Taylor. Effects of air pollutants on growth, leaf drop, fruit drop, and yield of citrus trees. Environ. Sci. Technol. 3 934-940. 1%9. 

In summary, oxidant stress reduced water use and photosynthesis, increased leaf drop and fruit drop, and resulted in a severe reduction in yield of marketable fruit. All these effects occurred without the development of plainly visible leaf symptoms. 

Several inferences can be drawn from these data that may suggest the impacts to be expected at the consumer and decomposer levels. Accelerated leaf drop may influence the development of pests—namely, aphids, scale insects, and red citrus mites. Pest populations might be increased if injured leaves had higher concentrations of amino acids or free sugars before abscission (see Chapter 11) or diminished if leaves fell too rapidly. Leaf and fruit drop would provide a larger substrate for populations of decomposer organisms at the soil surface. 

If a soap is added to a lead hydrogen arsenate-hydrated ferric oxide mixture considerable damage and leaf drop is caused, especially if the soap contains a strong base, as in the case of commercial potash fish-oil soap or potassium oleate. Laboratory tests show that more soluble arsenic is formed than with a soap of a weak base such as triethanolamine oleate.7 The addition of cryolite to an arsenate inhibits the formation of soluble arsenic 8 fluosilicates cause decomposition. These fluorine... 

Johnson EL and Emcho SD (1994) Variation in alkaloid content in Erythroxylum coca leaves from leaf bud to leaf drop. Ann Bot 73, 645-650. 

Extremely high dosages of N02 or chlorine for a few minutes may stimulate rapid leaf drop with no identifiable chlorosis or necrosis. Under field conditions, accidental spillage of chlorine has been observed to cause almost complete defoliation of eucalyptus and elm trees within a few hours, even though the exposure lasted only a few minutes. In controlled experiments, N02 caused excessive defoliation of citrus, peppers, and other deciduous plants when they were exposed briefly to very high concentrations (250 ppm). Ozone-induced leaf drop may result from brief exposure to high concentrations, but more often it results from longterm or repeated exposures and probably should be considered a symptom of chronic injury. 

The trees should finish shoot production as early as possible, to ensure that the leaf-drop period is uniform and short. The longer this period lasts, the greater is the possibility of infection. 

If there is infection, the tree should be treated with copper after the harvest, at the start of leaf drop, during leaf drop and after pruning, when a period of rain is forecast. 

Wood and bark diseases gummosis, sunken bark, etc. visual not determined cut out visible sites of infection. Control at budburst or at leaf drop... 

Leaf surfaces pale powdery orange spots beneath. Cause Rust. Hollyhock s most common disease also deforms leaves and stems and causes early leaf drop. Its orange spots release fungal spores that spread via wind and rain. Grow resistant cultivars keep leaves dry and encourage good air circulation. In problem areas, apply wettable sulfur several weeks before rust normally appears. Remove and destroy infected plant parts. 

Leaves pale and mottled. Cause Lace bugs. These /s - A", dark-colored bugs have lacy wings. They feed on the undersides of leaves and deposit small black spots of excrement. Severe infestations can cause early leaf drop. Control by spraying leaves with superior oil or insecticidal soap. 

Leaves yellow and drop. Cause Rust. Whitish blisters on the undersides of the leaves followed by yellowing and leaf drop indicates rust. Prune out and destroy infected branch tips. To reduce the spread of mild infections, spray with sulfur, repeating 2 or 3 times at weekly intervals. 

Drought, or too little water, can cause wilting, along with leaf scoreh (browned leaf edges), early fruit or leaf drop, stem dieback, and plant death. 

Symptoms Leaves show yellow patches that later turn brown or black these blotches may enlarge to cover whole leaves, causing early leaf drop. Symptoms start near the bottom of plants and work upward. Infected shoots are stunted, and flowers may be deformed. 

High concentrations of ozone in the atmosphere may cause early fall color and leaf drop. This damage can be difficult to diagnose because symptoms mimic many other disease conditions. Check for similar damage on other ozone-susceptible plants growing in the same area. 

Symptoms Because waterlogging inhibits root function, it causes essentially the same symptoms as droughty conditions do—wilting. Other common symptoms include yellowed leaves and sudden leaf drop. 

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