Extension Bulletin E-2996 • New • June 2007 Abiotic Plant Disorders Symptoms, Signs and Solutions A Diagnostic Guide to Problem Solving Robert E. Schutzki Bert Cregg Department of Horticulture Departments of Horticulture and Forestry Michigan State University Michigan State University The term “abiotic disorders” refers to a wide array of plant problems. We use the word “abiotic” to indicate that the symptom is not caused by a biological agent such as an insect, mite or patho- gen. Abiotic disorders are associated with non-living causal factors such as weather, soils, chemicals, mechanical injuries, cultural practices and, in some cases, a genetic predisposition within the plant itself. Abiotic disorders may be caused by a single extreme environ- mental event such as one night of severe cold following a warm spell or by a com- plex of interrelated factors or events. They can also be caused by chronic con- ditions such as a prolonged drought or plant selection inappropriate for the ex- isting site conditions (e.g., planting an acid-loving species in an alkaline soil). Abiotic plant problems are sometimes velop severe leaf yellowing or chlorosis ABIOTIC termed “physiological disorders”. This re- and have reduced rates of photosynthesis. plant disorders flects the fact that the injury or symptom The cumulative and subtle nature of are associated we see, such as reduced growth or crown many physiological disorders can often with non-living causal factors. dieback, is ultimately due to the cumula- make them difficult to diagnose. An ex- tive effects of the causal factors on the treme event such as a severe late freeze or physiological processes needed for plant a misapplied herbicide is an obvious growth and development. When a tree is “smoking gun” to indicate the underly- affected by severe drought, for example, ing cause of injury. More often, however, water stress will result in closure of the diagnosing abiotic problems requires pores, or stomata, on the leaf. This con- careful consideration of plant and site serves water in the leaf but also reduces factors through a process of elimination the rate of photosynthesis and the ability to determine the source and potential of the plant to produce sugars for growth. remedy for the problem. If the drought stress occurs during hot Abiotic disorders are usually classified weather, stomatal closure also limits the by causal factor or symptom. In this cooling effect of transpiration, and leaf bulletin, we will present abiotic disor- scorch may occur. Nutritional imbalances ders whose origins are due to biological/ also limit growth by reducing photosyn- botanical factors, environmental (climate thetic rate and other physiological and and weather) conditions, soil conditions, metabolic processes. Some plants, such as chemical applications, animal damage and pin oak, have a limited ability to take up cultural practice. We will also provide a iron under alkaline soil conditions. Iron is framework for diagnosing problems and essential for synthesis of chlorophyll, so suggest steps to mitigate abiotic injuries pin oaks on alkaline soils frequently de- before or after they occur. For unknown reasons, some of these Biological/Botanical mutant cultivars exhibit a tendency to The genetic makeup of produce shoots that revert to their spe- a species is expressed cies type. Genetic reversions are fairly through its physiological common on dwarf Alberta spruce and and morphological char- Harlequin Norway maple. To maintain acteristics. Whether these the cultivar characteristics, genetic rever- characteristics are per- sions need to be pruned out quickly and ceived as normal or ab- completely when they are observed. normal depends on the individual circumstances Chimeras and location where they Chimeras are botanical abnormalities are found. Understand- that are often confused with nutritional ing the basis for these or chemical disorders. “Chimera” is a characteristics can be use- term used to describe a single plant with ful in determining wheth- two genetically different tissue types. er they need to be Leaf variegation is the most common addressed and can aid in example of chimeras in plant species. outlining a course of ac- The difference in foliage color and the tion. In many cases, these banding of those colors are due to cell characteristics are a fact of mutations in the meristematic tissue nature and simply need to layers. Chimeras can be stable, in that the be appreciated for what genetic differences are consistent and re- they are; in other cases, producible. These chimeras have spawned they can be altered or cor- numerous of our variegated plant culti- rected by simple measures. vars. Chimeras can also be unstable and Here are some common unpredictable, surfacing sporadically on abiotic abnormalities that either shoots or individual leaves. The Genetic reversion on are biological/botanical in Bumald spireas are known for the spo- Harlequin maple. origin. radic appearance of unstable leaf chimeras. The stability of the chimera depends on Genetic mutations and the tissue layer where the mutation oc- reversions curs. If you discover variegation on an Genetic anomalies are prevalent in individual stem and not over the entire the plant world and often garner much plant, it is possible that it is a chimera and attention. For example, not an abiotic disorder related to plant seedling growers often nutrition or chemical injury. find mutants in their nursery beds. Albino seedlings are common seedling mutants. Be- cause they lack chloro- phyll, these seedlings quickly die off once they exhaust energy reserves from the seed. However, many mutants are stable and sustain growth. These stable mutants can Chimera on Anthony Waterer spirea. exhibit unique form, foli- age, flower, stem and other characteristics that Leaf abscission and retention warrant their develop- Leaves emerge in the spring, func- Genetic reversion on ment and introduction tion during the growing season, turn dwarf Alberta spruce. into the trade. colors and drop in the fall. Leaf drop occurs whether the plant is deciduous systems, signs of graft incompatibility or evergreen; it just happens with dif- may be visible as an uncharacteristic in- ferent aged leaves. There are times tensity of the fall color. Disruption of when leaf drop or retention is normal translocation leads to a buildup of sugars and times when it may be related to a during leaf senescence that intensifies fall plant problem. foliage color. This is especially the case Leaf abscission or drop is triggered in on Acer rubrum cultivars with known in- the fall by seasonal changes in day- compatibility problems. Graft incompat- length. Chlorophyll degrades, and the ibility issues on these Acer rubrum plant hormones abscisic acid and ethyl- cultivars led to production on their own ene cause an abscission layer to be roots. Graft incompatibility remains a formed at the base of the petiole. In concern in fruit tree production. Incom- evergreen species, needles usually func- patibility is not easily detected and can tion for 2 to 3 years, depending on the surface at various times in a plant's life. species. Normal leaf yellowing and ab- Unfortunately, for many it surfaces when scission occur on the insides of the stem the trees are mature and affected by on 2- or 3-year-old wood. Yellowing or wind or some other environmental con- browning of needles on the shoot tips is dition. Graft incompatibility can result a sign of problems. If a stem or leaf is in semimature trees snapping off at the injured or dies before seasonal changes base in wind storms. Failure of the tis- occur, abscission layers will not form and sue union is visible at the trunk/root col- leaves will remain on the stem. Leaves lar. On plant species with known remaining on isolated stems in the fall or problems, check on the budding or graft- winter are signs of stem or leaf problems. ing practices during production. Anoth- Stems may be girdled by an insect borer er form of incompatibility occurs when or mechanical injury, causing a break in there are differences in growth rates be- Leaf retention vascular connections resulting in stem tween the scion and the understock. on oak. death and leaf retention. An early kill- These differences can lead to dispropor- ing frost prior to the formation of the tional growth at the junction of the two abscission layer may cause dead leaves to tissues. be retained throughout the winter. In some deciduous plant species, leaf Galls and burls retention is a normal characteristic. Galls and burls are ab- Marcescent leaves are the dead leaves normal growths on retained by some plant species. Typical woody plants. They can examples of genera exhibiting marces- occur on branches, trunks cent leaves are oaks and beeches. Species and, in some cases, on within these genera do not complete the roots of woody plants. formation of the abscission layer until Galls may be caused by the following spring. Leaves will fall an insect or disease; how- when bud break occurs and stems resume ever, the origin or causal Proliferation of trunk sprouts growth. If leaf retention is a concern, factors for burls and other leads to callus buildup. identify the plant species, check for evi- callus outgrowths are dence of stem injury, and review recent unknown. Abnormal weather conditions. growths form through a proliferation of cells. Graft incompatibility These cells continue to Graft incompatibility is due to the fail- develop and do not dif- ure of the bud or graft union between a ferentiate into normal tis- scion and an understock. For unknown sue types. In some cases, reasons, the tissues of the two plant parts the outgrowth results do not form a stable union. Failure of the from a cluster of shoots. Callus knob formed from union disrupts translocation in both the Each year, new shoots are reoccurring trunk sprouts.