Fungus Gnats Can Cause Damage
Infestations of large numbers of fungus gnats will produce an exponential increase in numbers of larvae , resulting in root damage that then causes yellowing leaves , loss of plant vigor , and often substantially reduced production . The larvae can also be carriers of disease , which is then introduced to all infested plants , and in some cases , results in a complete loss of crop . Though fungus gnats are generally more of an annoyance than a threat , their presence should be taken seriously and measures to control and eliminate this pest should be initiated as soon as possible .
Management & Control
Once you have confirmed your crop has fungus gnats , there are a few considerations and practices you can employ to prevent and correct the situation . Knowing what attracts these gnats and how they grow and damage your plants is the first step . Overly moist soil is the first consideration . Surface soil that is wet most of the time not only attracts fungus gnats , but does not help your plants . Root systems need oxygen as well as water and nutrition . Oxygen
“ Surface is essential for the plant ’ s respiration process , which is responsible for converting sugars into energy . Without this energy , your plants are not going to produce much . Because of this , the objective for proper watering is to allow the surface ( top three inches ) to dry before applying water again . Allowing the lower section of the root zone to go dry is also not good , so deep , infrequent water is a good idea . You will need to sample moisture levels throughout the root zone and adjust watering schedules to achieve this . Different soil compositions will require different watering schedules , so remember : one schedule doesn ’ t fit every situation . If you are using a grow media like cocoa mulch or potting soil , there are lots of organic materials in your media . This not only tends to hold water longer but is the primary source of food for fungus gnats . Organics may be what the plant wants for a living soil , but these gnats are not welcome to that party . One practice that can still provide a great organic soil structure while discouraging gnats is topping off the grow media with a half-inch of fine sand or silt . This material drains rapidly and dries quickly , and the dry surface discourages the adult gnat from laying eggs . The soil beneath the sand will remain adequately moist , however , you will still need to establish the best watering cycle to allow oxygen to penetrate deeper into the soil . Once fungus gnats have infested the grow media of your crop , prevention
soil that is wet most of the time not only attracts fungus gnats , but does not help your plants .” is no longer going to do the job . Some type of biological or chemical control will likely be needed . As the objective is to attack the larval stage of this pest , focus on soil treatment . With ornamental plants , chemical control is often the preferred choice . Go to the strongest , most reliable killer as soon as possible . Cyflurthrin is very effective for gnat control . Simply add to the water when irrigating once every three to six months and fungus gnats will not be a problem . With edible crops , most growers want to start with an organic biological control agent . Bacillus thuringiensis ( BT ) is a spore-forming bacterium that produces crystal proteins toxic to many species of insects and will usually eliminate fungus gnat larvae . Bacillus thuringiensis is organic and not toxic to humans or animals , though it does kill worms . Again , mixing the recommended amount of BT into the water periodically and drenching into the entire root zone is the best technique . Note that spraying the leaves will not affect the larvae living in the soil . To rid yourself of the annoying fungus gnat adults , you will find the simple pest strip is the safest , yet most effective technique used to eliminate fungus gnats . Once your soil treatment has become effective , the adults will disappear and you can take down the strips .
Make your gardening more pleasant and productive by preventing these pests from infesting your garden .
Frank Rauscher is a certified horticulturist and consultant for the hydroponic and landscape industry with a background in product development . Frank is a member of the Southern Nevada Landscape Association and active in the Southern California green industry , where his focus is drought-tolerant xeriscapes . He specializes in discovering the “ root-cause ” of plant stress .
Maximum Yield USA | February 2017 103