Maximum Yield USA December 2021/January 2022 | Page 29

WHAT IS A PLANT VIRUS ?
Plant viruses are extremely small , too small to be seen under a normal microscope , and consist of nucleic acid surrounded by a protein coat . These only infect and multiply within a living host plant where they hijack cells and disrupt growth and functioning . As this is occurring , symptoms may start to show , however , this is not always the case . Viruses have the ability to remain latent inside the plant and only cause symptom expression under certain growing conditions . Some common viruses can be temperature sensitive and only cause symptoms under high or low temperatures , others may be suppressed or masked when the plants are growing vigorously , or displayed when the plants are stressed .
VIRUS TRANSMISSION
Virus-infected plants can randomly show up in the most unexpected places — the middle of an otherwise healthy and thriving crop , in indoor growrooms , and even in fully enclosed cultivation areas . The secret to the success of virus transmission is the multiple methods by which these infectious particles can move from plant to plant . In hydroponic crops , which are usually grown in relatively clean environments , the main vectors are insect pests , new and infected planting material , or human activity . Some viruses are seed borne , however , by only using high-quality seed sources from reputable companies this is less common under protected cultivation . In greenhouses , chewing and sucking insect pests such as aphids , whitefly , leaf hoppers , and thrips can cause a huge amount of damage by simply transmitting viruses , both by carrying in virus from outside the crop and then by spreading it from plant to plant . Prevention of such pests is one of the main methods of virus prevention and control . In a greenhouse or growroom setting , sap-to-sap transmission can rapidly occur during training , pruning and other plant-maintenance procedures carried on with equipment , knives , and grower ’ s hands . Further spread can occur when cuttings or clones are taken from virus-infected plants , particularly where material is harvested from multiple plants without disinfecting propagation knives and tools during the process . Most viruses only survive long term in living plant tissue of certain hosts or briefly within the insects that spread them . However , some viruses such as tobacco mosaic virus can survive for many months or even years in soil , plant debris , dried plant material such as tobacco on tools , in growing substrates , or as seed contaminates . Tobacco mosaic virus can be spread from dried tobacco on the hands of growers and tomato crops , which require regular pruning and training , are particularly susceptible to this .

Most viruses only survive long term in living plant tissue of certain hosts or briefly within the insects that spread them .”

Viruses can look similar to many other plant issues and can be difficult to diagnose .
Mild symptoms of some viruses can make the early signs easy to miss .
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