Waging War on Pests

"Fungus gnats are the bane of all growers," the great Shirley Heller at EuroAmerican Propagators said to me while I was attempting to harden off hundreds of tissue-cultured Echeveria macrophylla seedlings.

Getting the delicate plants from the lab into the greenhouse, and then on to the real world, was a trying task, to say the least. The grow plugs we teased the hyper-sensitive roots into needed to remain moist, and these high moisture levels offered up a prime environment for excessive fungus gnat proliferation. The larval worms would find a tasty root, begin eating it, then head right up the stem, wilting the plant and eventually killing it.

The remedy for the nasty gnats was a combination of preventative tactics using biologically based pesticides, pre-soaking the plugs in a Bacillus thuringiensis solution and redundancy in the environmental control system, in this case a greenhouse in a greenhouse in a greenhouse. A combination of environmental control and careful pesticide use is your best tactic in an organic pest control program, no matter the enemy.

Of the world’s estimated 10-million-plus insect species, only about a thousand are considered agricultural pests. Spider mites, thrips, caterpillars, root aphids and broad mites are some of the top offenders, and if this list doesn’t make your blood start to boil a little, then you are either an unnatural green thumb, or are just really new to the game. Understanding pests’ life cycles is a good place to begin if you want to decimate them completely. As they say, know thy enemy.

Know Thy Enemy

“If you know your enemies and know yourself, you will not be imperiled in a hundred battles...if you do not know your enemies nor yourself, you will be imperiled in every single battle.”

Spider mites are a deplorable bunch. Give them warm, dry conditions and one pregnant female spider mite can create 100 more tiny minions in just one week. Those 100 mites breed like rabbits and soon your garden has an infestation that numbers in the millions. What’s worse are root aphids, which reproduce asexually, scourge plants’ root systems, then sprout wings and fly off to search for new victims.

Broad mites are the invisible killers: being one-twentieth of a millimeter long, you will never see them coming. To beat these abominable arthropods, one must take the time understand how the sapsucking low-liers live. Determining what environmental conditions insect pests like, as well as how they reproduce, their incubation periods and where they live allows you to be more calculated in your ensuing onslaught of pest management tactics.

Knowing the incubation period allows you to apply successive rounds of pesticide treatments in a timely manner. If eggs incubate for five days, you can expect to see more mites six days after a spray. Some pesticides require repeat applications to be effective. The repeat applications need to take into account both the egg incubation time and the entire life cycle of the pest insect.

Thrips, for instance, spend part of their early days protected in the top layer of soil, only to come up top after they mature into hungry adults, ready to feed and breed. A grower must take this stage of life into account to hit the adults, their hatching eggs and every stage in between with deadly effect.

Understanding the pest’s life cycle is paramount in planning an assault. But before the carnage ensues, you must take a moment to reflect on why the garden has been infiltrated in the first place. Where did the unwanted guests come from and what made the garden susceptible in the first place?

Defensive Tactics

“Management of many is the same as management of few. It is a matter of organization.”

Environmental control is key when battling a pest infestation indoors or in a greenhouse. Is the mother stock entirely pest-free? Are they hitch-hiking in on you? Are you using a filter on your intake, or does air flow freely into the room unobstructed? In a commercial operation, houses are netted and intakes are at least screened. Workers wear sanitary coveralls and latex gloves, and step in disinfectant foot baths before entering garden areas. Mother plants, clones and finishing plants are separated. These measures allow for uniform, precise environmental control, proper pesticide application procedures, and detection and isolation of any burgeoning bug explosions.

Once you understand what you are dealing with, you can go about developing your battle plan. The first step is maximizing your garden’s ability to resist bug problems. Indoor gardeners have the benefit of almost total environment control. By keeping temperatures from averaging on the high side, your conditions will be less mite-friendly. If you can control the humidity so the air is able to dry the top layer of soil between waterings, this will help keep fungus gnats from getting too comfortable. Exhausting after applying sprays keeps the room’s humidity low and prevents other disease issues.

This level of control requires mechanical help. Filtered intake and exhaust fans, dehumidifiers, heaters, air conditioners and carbon-dioxide generators need to be synced. Depending on the size of your operation, it can get complicated. The take-home message is: Do what you can to make the growing environment less hospitable to pests. Drape and tie frost cloth around an infested area to prevent the pests from migrating easily, then release a thousand ladybugs and let them go to work.

Beneficial insects can act as your own private army of miniature mercenaries. Ladybugs, green lacewings, pirate bugs and rove beetles are several garden warriors worth getting to know. Some attack a range of pests, while others go after specific prey. When using predatory insects, take the time to learn about them to ensure you get the most out of your valiant insect infantry.

Going on the Offence

“What is essential in war is victory, not prolonged operations.”

On to the slaughter. Which of the myriad tonics out there do you use on those crusty curmudgeons plaguing your plants? There are a number of effective synthetic options, but they often have health and safety concerns associated with them. In an organic system, the focus is on growing stronger plants that are naturally resistant to pests and diseases, and supplemented with a regular rotation of preventative sprays of agricultural oils, microbial inoculants and compost teas. While these practices will keep you ahead of the bugs to a certain extent, realistically, you will get bugs at some point.

Spinosad is a natural chemical found in many organic horticultural insecticides produced by the bacteria Saccharopolyspora spinosa. This bacterium was first discovered growing in an old sugar pile at an abandoned rum distillery. The yellowish-pink hyphae that were protruding from the ground caught the eye of an astute scientist and a new insecticide was discovered. Spinosad induces seizures in pests, killing them.

It affects the adults of some species and the larvae of others. Take this into account when establishing your spray plan by rotating to another microbial assassin to continue the war. Rotating your sprays reduces the chances of bugs developing a resistance to any one pesticide.

Fungus gnats got you down? Get back at them with Bacillus thuringiensis, whose spores have a crystalline structure that breaks off in the larvae’s stomach and then burns its way through the guts, melting the worm from the inside out. Or use the nematode Steinernema feltiae, which worms its way into any available orifices on the larvae, infecting it with bacteria that sicken and kill the little wiggly fiends.

Root aphids and a host of other bugs can be controlled with the fungus Beauvaria bassiana. This helpful fungus rots bugs from the inside out. Sprayed onto foliage or drenched into the soil, spores attach to the exoskeletons of passing insects. The spores germinate and their hyphae start to grow into the insect’s body, slowly digesting the doomed pest. It takes several days for the insect to succumb to the fungal infiltration, and when it does, more fungal spores are released into the environment, securing the area against future infestations.

Pyrethrums are organic compounds produced by chrysanthemum flowers that have deadly insecticidal properties. These natural compounds overwhelm and shut down the nervous systems of insects. There are synthetic pyrethrums called pyrethroids, which are based on the natural version and effective, though they cannot be used in organic agriculture.

Another plant-derived pesticide is neem oil. Azadirachtin, the active component in neem oil, comes from the neem trees of India and Africa and is effective on about 250 different insect species. With several modes of action, neem affects both larvae and adults, either disrupting hormonal systems or inhibiting normal feeding behavior. A combination of neem oil and pyrethrums is a solid one-two punch.

Enzymatically based pesticides are growing in popularity due to their ability to annihilate insect infestations. Enzymes work by degrading the chitin and soft tissues. The two main enzymes used in agriculture are protease and chitinase. Protease breaks the bonds between amino acids, melting soft tissues attached to and underneath the exoskeleton, while chitinase breaks the bonds between the glucose-like molecules that make up the chitin-based exoskeleton. Both are safe to use and with proper application, rates will not affect beneficial insects. Keep your eyes out for more of these products hitting store shelves in the future.

Building Stronger Subjects

“Victorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win.”

To prevent insect infestations from happening in the first place, keep your plants strong with proper fertilization and compost teas. Do not let plants wilt, as the sap of a wilted leaf has a higher sugar concentration, making it a tasty treat for an opportunistic insect. Too much nitrogen will cause weak tissues as well. Crops fed organic rather than synthetic fertilizers showed a decrease in aphid infestations, which researchers believe is due to a higher nitrogen availability in plant tissues from synthetic fertilizers.

A great way to keep plants strong is fertilizing with silica. Silica is not necessary for plant growth, but it is recognized by the USDA as a plant fertilizer because it has shown major disease-suppression abilities. One simple source of silica is diatomaceous earth (DE), which is composed of tiny glass shells from ancient plankton deposits. DE desiccates, or dries out, insects by absorbing oils and fats from the exoskeleton and soft tissues. The silica particles are sharp and cut into insect tissues, expediting the desiccation. Do not water immediately after applying DE, as the environment needs to be dry for it to work. Beyond the physical destruction of insects, silica also helps plants grow stronger cell walls, which helps keep pests at bay.

All growers must deal with pests. Good growers learn how to manage pests; great growers learn how to prevent them. Take the time to understand the situation, get to know your target pest, control your environment, read product labels and keep your plants strong from the inside out by staying on top of irrigation and fertilizer regimens. Integrating your pest management systems will maximize your yields for years to come.