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www.landscapeirrigation.com Landscape and Irrigation May/June 2017 33 ALL PHOTOS PROVIDED BY RAINBOW TREECARE SCIENTIFIC ADVANCEMENTS profuse flowering), dead tissues (such as dieback, necrotic leaves, and wilting), and anything else that is an alteration of the plant's normal appearance (such as usual color of leaves, spots on leaves, or uncharacteristic patterns on leaves). All of these diagnostic symptoms require at least a passing knowledge of the common shrubs and their cultivars in your area, of course. Shrubs are commonly propagated for unusual traits — such as colored leaves, stunted sizes, or even contorted growth — that do not occur commonly in nature. With a little experience it should be pretty straightforward to know a weeping shrub from a wilting shrub. If you are still unsure, there are many online resources available to assist with diagnostics. Abiotic issues Shrub health issues that are not directly the result of an invading insect or pathogen are often classified as "abiotic" issues, but, really, they could be called "site condition issues," as poor growing conditions for the shrub are almost always the cause. Common issues include things such as lack of water causing drought stress, too much water caused by drainage problems, pollution/soil contamination, nutrient deficiencies, and herbicide damage. There can also be biotic issues that result from abiotic conditions. Examples of this would be things such as fungi causing leaf spots while the leaves keep getting wet from the sprinkler system. You can treat the leaf spots with a fungicide, but the issue will continue to persist until the sprinkler system is adjusted. Just like the insect and disease issues discussed previously, scouting for symptoms that may indicate an abiotic issue should be a regular part of walking a property. Contorted or stunted growth may be the result of herbicide damage. Off-color foliage, including interveinal chlorosis, can suggest a nutrient deficiency and possibly root system issues related to watering. Dead tissues can also indicate hydration irregularities. Depending on where in the country you are, dead tissues on leaves and twigs can also be symptoms of frost damage. Growth control While growth regulators have been around for many years, it has only been recently that they have become a standard operating practice for many landscape maintenance professionals. A big part of their rise in popularity has been the development of products that offer predictable and consistent growth control results. Plant growth regulators (PGRs) are utilized by property managers to reduce the amount that a shrub grows following a trimming event. The growth of treated shrubs is typically reduced 30 to 70 percent, and holds them for 8 to 12 weeks at a time (sometimes longer, depending on the species). This is beneficial to the property managers as PGRs allow them to focus labor toward the project areas most visible to the client rather than allocating them toward tasks such as maintaining a perimeter hedge or trimming parking lot shrubs. Beyond the operation advantages PGRs provide, there are health benefits to the plant as well. First, just reducing the number of pruning events a shrub is subjected to has positives from a health standpoint. Pruning puts a plant into a growth "mindset," meaning it is focusing its energy toward growth, often at the expense of allocating energy toward things such as root growth, defense compounds, or storage compounds. Second, modern plant growth regulators, such as paclobutrazol, help stimulate a plant into allocating growth away from vegetative growth and into these other categories such as root growth or defense compounds, making them more resistant to certain abiotic and biotic health threats. There is also research suggesting treated shrubs are more resistant to acute drought than untreated plants due to thicker leaves, increased root systems, and higher levels of absicic acid. This plant hormone is know as the "stress hormone," and allows plants to quickly open and close their leaf stomata throughout the day in hot and dry conditions. Thus they can better balance the need to have them open to get carbon dioxide for photosynthesis with the detriment of having them open and losing water. Application methods and timing Whether we are talking about insects and disease, abiotic issues, or growth control, eventually the discussion needs to come around to applications. Shrubs have some unique challenges for application techniques that are not shared by other living Cosmetic issues are serious health issues for shrubs.