Providing an optimum environment that favors healthy plant growth and discourages pests is a critical tactic of IPM. Many growers underestimate the role that temperature, humidity, and airflow have on pests and their ability to attack and thrive.
CBD Hemp is a high light-intensity plant. Having appropriate light is essential to growing healthy plants. Growers typically target photosynthetically active radiation (PAR) between 800-1000 umol/m2/s2 at the plant level to get vigorous plant growth. Light deficiency weakens the plant defense system and makes the plant more susceptible to pests.
Maintaining an appropriate range of temperature during the plant cycle is important to avoid plant stress and increased plant susceptibility to pests. Generally, air temperatures of 78° F to 85° F in the vegetative and flowering stages are best during the day, while temperatures of 68° to 75° F are best during the night.
Soil temperatures of 72° F to 75° F are best for healthy rooting clones. Temperatures that are too high or too low will reduce photosynthesis, which will decrease growth and productivity as well as make plants less able to tolerate pests. Some arthropod species such as the two-spotted spider mite (Tetranychus urticae), which is a typical pest of CBD Hemp in controlled environments, is known to increase its reproductive rate under hot conditions. If plants are also drought-stressed, this pest will further thrive and potentially damage growth irreversibly.
Carefully controlled humidity is fundamental to preventing plant diseases. Plants transpire significantly, especially toward the end of the growing cycle. Maintaining balanced humidity in the room can help prevent disease from growing in damp environments. For example, high humidity within the plant canopy can promote spores of powdery mildew to germinate and grow on the leaf. University researchers suggest the optimal temperature and humidity ranges which encourage powdery mildew outbreaks are 68° F to 77° F and >55% RH. In general, disease-causing fungal pathogens are more active and cause greater damage as humidity increases.
Constant airflow, especially within the plant canopy, affects many critical aspects of plant growth. Airflow around the leaf increases transpiration rates, nutrient uptake, humidity and carbon dioxide levels at the leaf surface. Airflow modeling, adequate fans, and proper plant spacing are critical to provide good, uniform airflow when growing thousands of plants side by side in greenhouses and indoors.
CO2 enrichment is a common practice in commercial production that is used to increase plant photosynthesis. As a result, plants show increased dry weight, plant height, number of leaves and lateral branching. The optimal CO2 concentration for growth and yield seems to lie between 800 and 1000 ppm during the vegetative stage and between 1000 and 1200 ppm during flowering. To be effective, CO2 enrichment must be appropriately coupled with light, fertility and irrigation. The majority of growers use bottled CO2 for purity and consistency, but some use CO2 generators that burn fuel to produce the gas. If the air/fuel mixture is off, it can create contaminants (i.e. ethylene) that can cause strange symptoms in the crop and potentially significant damage.
Consult with your Hawthorne Gardening Company technical services representative for further information, tips and recommended products.
Disclaimer: When using this guide for recommendations on treating plant pest issues, you must always verify and follow any and all product label directions for use as required by federal and state laws.