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Chart of Pests on Leaves

WHAT'S BUGGING YOU? - MORE LEAVES
by Nanette Londeree, Master Rosarian

Spring is in the air, and roses are bursting with new life, cloaked in succulent new foliage. Undamaged and unblemished, this tender young growth has an appeal all its own. Sporting vibrant shades of green and red, from buffy olive to jade green, and Bordeaux red to pansy purple, it changes daily as the delicate leaves unfurl and grow. As the season progresses, besides the proverbial May flowers, your pristine foliage may exhibit some other, unexpected attributes – a speckled rusty orange-splattered, black-spotted or yellow marbled look, or twisted and deformed, thin and spindly forms. So what’s bugging your leaves now?

Plants, whether cultivated or wild, generally grow best when the soil provides them with adequate nutrients and moisture, sufficient light reaches their leaves, and the temperature stays within a "normal" range. However, like people and pets, plants can get sick, and the agents similar to those that cause disease in people can do the same to plants. A broad definition of plant disease is anything that damages plant health. Infectious disease is produced by living organisms - most commonly bacteria, fungi, nematodes, viruses and protozoa. Disease resulting from one of these causal agents or pathogens is termed a biotic disease. The major diseases that plague roses are caused by fungi and the three common ones that affect roses (and many other types of plants) during periods of rainy weather are anthracnose, blackspot and rust.

A great number of plant maladies aren’t caused by any type of living creature, but instead by non-living factors, and are described as “physiological disorders” or abiotic diseases or disorders. Abiotic disorders may be a result of a single extreme environmental event like one of our scorching, triple-digit summer days, or an ongoing condition like lack of water. The major causes of abiotic disorders are:

  • Nutrient deficiencies and excesses - the absence or unavailability of an essential nutrient to a plant (think chlorosis from lack of available iron) or too much of a particular nutrient or mineral (leaf tip dieback from over fertilizing).

  • Temperature extremes - air temperatures that are either too high or low.

  • Water extremes - too little water can result in wilting, discoloration of leaves and premature leaf drop; too much water deprives roots of oxygen - the plant may show signs of chlorosis or have small, thin or dying foliage.

  • Light extremes - excess light can fade the color of blooms, while too little can result in spindly growth as plants “stretch” for available light.

  • Herbicide damage - Exposure to herbicides produces cupped, curled, or chlorotic leaves, small leaves, or necrosis of the entire plant. The herbicide type and the dosage to the plant determine which symptoms appear and their severity.

  • Mechanical damage - Plants can be torn, cut, crushed, chewed, sliced or punctured from wind, animals, lawn mowers and weed whackers, the errant gardener or a myriad of other possibilities. The nature and magnitude of the damage is relative to both the type of plant and the cause of the damage.

    As you savor the beauty of your new spring foliage, be on the lookout for damage so that you can take any needed action early.


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    Last Modified: 08/06/2013