Spider Mites Eating Up Your Profits?

Spider Mite Control Treatment Options

In commercial grow operations, plant pests are one of the top causes of decreased profitability contributing to poor plant health, quality, and yields. One such pest that should be at the top of a commercial growers most “unwanted list”, is the spider mite. These tiny arachnids can rapidly infest crops, causing tremendous amounts of damage by extracting plant liquids, and in some cases spreading disease.  

As spider mites multiply quickly in warm and dry conditions typically found in greenhouses, implementing a comprehensive and proactive AG pest control strategy is essential to prevent outbreaks and minimize the use of chemical pesticides. By combining cultural practices, biological controls, and targeted interventions, greenhouse managers can successfully manage spider mite populations and ensure the vitality of their cultivated plants.

The most common spider mite found in a greenhouse is the broad mite, as well as the carmine spider mite, cyclamen mite, the Lewis spider mite, and the two-spotted mite.

The Issue with Spider Mites in Greenhouses 

Spider mites may be small, but they are very worrisome in a greenhouse. These pests spend their time on the undersides of leaves, in new growth, and deep inside flowers. This causes these pests to be very hard to detect and effectively control. Mites have a very quick life cycle meaning that populations can spike rapidly out of control without much warning after mites have infiltrated a greenhouse. Spider mites are not picky in the plants they infest and feed off of due to their wide range of host plants. To make matters even more troublesome, pesticides can be ineffective against them due to resistance. This all contributes to spider mites being placed on the top most unwanted pests in a greenhouse or CEA facility. 

Controlling Spider Mites in a Commercial Grow Operation

Due to mites having a wide host range, they will attack a wide range of different types of commercial plants and crops. These range from African Violets, dahlias, geraniums, chrysanthemums,  cyclamens, hemp, and other flower and vegetable crops. Mites feed on plants using their "mosquito like" mouth to pierce plant tissues. When this occurs some species of mites actually inject a toxin into the plant. The overall feeding damage to the plant varies by both mite and plant species, but the damage will appear on the upper leaf surface as speckles or mottling. 

The temperature and humidity levels in a greenhouse will determine the viability of spider mites depending on the specific species. Typically temperatures between 70-80 degrees F and a lower humidity are ideal for the full life cycle of broad spider mites. For example, female Broad mites will lay between 30-75 eggs on a leaf surface over a week to week and a half span. The larvae then hatch in two to three days. After this point, they will begin to feed on plants. A chart below outlines the general ideal temperature and humidity levels for specific spider mite species. 

Signs of Spider Mites

Spider mites can quickly overtake a growing area due to their fast life cycle and hard to see size. The signs of spider mites include, but are not limited to spotting or mottling on the plant leaves, a sticky dew on plants, black mold on the sticky dew residue, visible webbing for large numbers of mites, and moving mites under leaves and inside buds and flowers. Too high numbers of mites can also cause a loss of vitality in plants.

Control of Spider Mites 

As previously stated, spider mites can be difficult to control due to their size, living areas, and the possibility of pesticide resistance. However, there are ways to control these small pests. There are a number of chemical and organic means to control mites in a greenhouse or CEA facility. Conventional pesticides such as miticides are those that are specific to prevent and control and infestation of mites. Other conventional pesticides that provide great control include bifenazate, pyridaben, and abamectin. It should be noted that due to the habits of mites, several applications may be necessary for full control. 

There are also several biological controls for mites such as the beneficial predatory mite, Phytoseiulus persimilis. Neosililus barkeri have also been shown to be successful across a broad spectrum of mite species. Predatory mites can be obtained from Morr and other commercial biological control suppliers. If these predatory mites are used correctly and under the right circumstances, they provide an effect control that is on par with the chemical approach. Whether or not a grower goes chemical or organic is up to the individual operation’s goals, budget, and overall needs. Special attention should be given to whether the crops grown can withstand chemical or biological controls, and whether the operation is to be organic or not. 

Spider mites are not a death sentence for a growing season if proper control and reaction to their invasion is made quickly and efficiently. Plant quality can also be salvaged if proper care is given to their control. It is important to have an Integrated Pest Management Plan in place, as well as regular checks on plant health in the growing area. It is also suggested that new plants entering a growing facility be placed in quarantine away from other plants in the greenhouse so that the potential spread of mites can be contained.

Additionally, the removal of plants infested with mites and kept away from non-infected plants is also a way to contain the spread. However, if spider mites are spotted in a growing area, it should be assumed that all plants in the growing area are infected. For more information on how to control spider mites, and the best approach for your growing operation, please contact a Morr specialist today who is back with in industry experience! 

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