Marijuana Grower's Handbook

by Ed Rosenthal

  CONTROL

  + There is no practical means of controlling deer, in the sense of eradicating them, and this would not be a good option even if there were such a means. The outdoor marijuana gardener should leave the deer’s natural predators (mainly coyotes and wild dogs) alone, as these provide some check on the deer population. However aside from that, prevention is your best choice.

  FUNGUS GNAT

  FUNGUS GNATS

  Fungus gnats are common indoors. They are found outdoors occasionally in moist warm areas.

  Fungus gnats are 1⁄10–1⁄12 inch, (3-4 mm) in size, dark grayish black in color and have a slender build with delicate long legs and long wings. The larvae are clear to creamy-white in color with a shiny black head and can be up to ¼ inch (6 mm) long.

  Adults fly close to the soil level and through the lower region of the plant canopy. Fungus gnat larvae live at the root level, usually from 1 to 3 inches (2.5 to 7.5 cm) below the soil line. In shallow containers the larvae may be found wiggling in the drain tray after watering. Outdoors, adults and larvae live in moist, shady areas.

  Fungus gnats’ larvae weaken the plant by eating roots, root hairs and organic matter growing in planting mix, rock wool, soil and other planting mediums. They are also vectors for disease. Adult gnats do not eat. They live only to reproduce.

  Adult females lay eggs at the surface of moist soil, near the plant stem. The larvae hatch out in four to ten days, depending on temperature, and feed off fungus and plant matter (including plant roots), then pupate in the soil and emerge as adults. The total time from egg to reproductive adult is about four weeks, and females lay several hundred eggs in small batches over their lifetime. Indoors, they breed continuously throughout the year and reproduce very rapidly.

  PREVENTION

  + If plants are outdoors, check the soil for adult gnats or larvae before bringing them indoors.

  + Prevent indoor entry of gnats by keeping screens on all open windows.

  PREDATORY NEMATODE, photo courtesy Nature’s Control

  + Place a barrier over the soil so the gnats have no place to lay their eggs. A piece of cloth, cardboard or a layer of sand, cocomat pot covers and plastic covers for rockwool all work.

  + Fungus gnats need moist soil near the surface to reproduce. Let the soil dry between watering as much as the plants will tolerate (usually to a depth of about 1 inch (2-3 cm). A layer of light, well-draining soil such as vermiculite, perlite, or diatomaceous earth at the top helps with this. This disrupts the larval gnats’ food supply and makes it difficult for an infestation to take hold.

  CONTROL

  + Bacillus thuringiensis (beneficial bacteria.)

  + Barriers (sand, cloth, cardboard, etc.)

  + Cinnamon oil and tea.

  + Diatomaceous earth has sharp points that puncture and desiccate small soft-bodied creatures such as fungus gnat larvae. Diatomaceous earth is composed of fossilized diatom (a type of algae) shells made of 86% silica, 5% sodium, 3% magnesium and 2% iron.

  + Predatory mites (Hypoaspis species): These carnivorous soil dwelling mites seek out any prey they can catch.

  + Predatory nematodes (Heterorhabditis and Steinernema species) are microscopic carnivorous soil-dwelling worms that enter their host and eat it from the inside out. Then they reproduce and burst out of the corpse.

  + Pyrethrum can be used as a spray or can be injected into the plant stem to reach borers.

  + Spinosad

  GOPHERS

  Gophers are a very occasional problem in the garden. They are found mainly in the central and western United States, in Florida, and in Mexico.

  Gophers are medium-sized rodents ranging from about 5 to nearly 14 inches (13 to 36 cm) long (not including tail). Their fur is very fine and ranges in color from nearly black to pale brown. The forepaws have strong claws. The head is small and flattened, with small ears and eyes and very prominent incisor teeth. Gophers tunnel underneath gardens and lawns.

  Gophers feed on plants in three ways: 1) they feed on roots that they encounter when digging their tunnels; 2) they may venture short distances (only a body length or so) from their tunnels to eat vegetation on the surface; and 3) they pull vegetation into their tunnels from below. Gophers may also attract badgers (which eat them), and the badgers may cause considerable damage when digging for their food.

  When gophers are suspected, the first task is to make sure that they aren’t moles instead. Moles cause little direct damage to gardens, and as a result they’re seldom worth the trouble to eradicate. It is rare to see either one on the surface, so the best ways to distinguish them are the signs they leave behind.

  First, check their diggings: a molehill tends to be a rough cone with a hole or an earthen “plug” near the center. A gopher mound is more fan-shaped, with the hole or plug near one edge. Next, look for damage. Moles generally cause very little damage. Gophers may chew the plants’ roots, causing them to wilt and making it possible to pull them up with just a slight tug. If plants are chewed off completely at the soil line, or completely gone, roots and all, then chances are good that there is a gopher problem.

  Reproduction rate and life cycle: Gophers mate once a year, in the spring, and produce a litter of up to five young in late spring to early summer. They live for up to 12 years.

  Containers, indoor gardening, and hydroponic systems offer complete protection against gophers. If you are planting directly in the soil, minimize weeds; line the planting hole on the bottom and sides with hardware cloth. A border of oleander plants around your garden may repel gophers. Commercial gopher repellents (most include castor oil, garlic, or capsaicin) placed in the mouth of the mound may drive them off.

  CONTROL

  + In general, it is best to try repellents first, as they are by far the easiest way to deal with gophers. However sometimes the only solution is to eliminate them.

  + The simplest means of exterminating gophers is fumigation. Commercial fumigants are generally paper or cardboard cartridges filled with charcoal and potassium nitrate. They’re ignited and dropped into the tunnel openings, and the gasses they produce as they burn kill the gophers. Watch for wisps of smoke rising from the ground—these may mark other exits from the gopher’s tunnel. Seal the exits with packed earth or heavy rocks, so the gopher cannot flee. Carbon dioxide (CO2) is a fumigant. Use a CO2 tank by placing the delivery hose in the tunnel opening or drop 8 to 16 ounces (225 to 450 grams) of dry ice into the tunnel. If fumigation is not effective, try trapping them. Traps are available at garden shops.

  LEAF MINERS

  Leaf miners are not common in indoor marijuana gardens. Outdoors leaves are occasionally attacked, but they are not usually a threat to the plant or yield.

  Leaf miners are usually the larval form of various fly species although a few species of moths and beetles also produce leaf-mining larvae. These larvae are very small maggots, seldom more than 1/10 in (3 mm) long and range in color from white to pale green. The adult flies resemble tiny houseflies, about 1/12 in (2 mm) long.

  Leaf miners are found under the surface and in the tissue of leaves

  The leaves look like someone carved scribble lines into them. At the same time they plant their eggs deep inside, and they keep multiplying. When they hatch, the larvae feed off of the leaves until they get big enough to pupate. Pupation occurs within the leaf or in the soil beneath the plant. Once they emerge they repeat this cycle and cause a bigger infestation.

  Leaf miners leave the plants open to pathogens and fungi. Leaf damage causes low yields. When the females dig to lay eggs, plants secrete a sap that attracts ants and flies, thus inviting more infestations and problems.

  There are many species of leaf miners, and an expert can distinguish between species by the characteristic appearance of the tunnels which evolved to provide them more protection than the surface of leaves.

  LEAF MINER DAMAGE

  Females implant one egg at a time close together. Species vary in fecundity. Some produce up to
350 eggs each. Eggs hatch in two to six days, and larvae begin tunneling. Eventually they become pupae, either dropping to the ground or remaining in the leaf, depending on species) The pupae develop into adults and the cycle repeats. Expect two to six generations per year outdoors, but indoors a single generation can take as little as a month, and they reproduce year-round.

  PREVENTION

  + Outdoors, plant deterrants such as lambsquarter, columbine, and velvetleaf.

  CONTROL

  + If only a few leaves are affected, remove and discard them.

  + Naturally occurring parasitic wasps usually help control the population.

  + Beauveria bassiana (beneficial fungi)

  + Capsaicin

  + Herbal teas

  + Herbal oil based pesticides, such as Ed Rosenthal's Zero Tolerance®

  + Horticultural oil

  + Neem oil

  + Parasitoid Wasps

  + Pyrethrum

  + Spinosad

  MEALYBUGS AND SCALE

  Mealybugs and scale occasionally attack Cannabis. They are more often a problem with long-lived mother plants.

  These pests are closely related to one another, but take their names from their appearance. Mealybugs are named for the white, “mealy” wax that covers their bodies. On plants they look like tiny puffs of cotton, usually in crevices and joints between branches. The adult female insects beneath the wax are 0.1 to 0.2 inch (2-4 mm) long, with flat, oval, segmented bodies. Males are tiny flies that do not have the females’ waxy covers.

  SCALE

  Scale derive their name from the hard shells that adult females produce, which look like bumps or "scale" on the stems and leaves of the plants. Scale vary widely within this general model: from round to oval in shape, from white to dark brown in color, and from 0.1 to 0.5 inch (3 to 15 mm) in diameter. As with mealybugs, adult male scale resemble tiny flies.

  Female mealybugs plunk themselves at the nodes close to their hatching site. Scale are found on leaf surfaces, especially the undersides and on stems and in crevices. Occasionally scale or mealybugs colonize the stem right at the soil level, where the stem joins the roots.

  Female scale and mealybugs feed on plant sap. They live only long enough to fertilize the females.

  Some species have developed a symbiotic relationship with ants, similar to that of aphids. Ants protect and herd them to collect the “honeydew,” concentrated sugars that they exude as waste. If there are no ants to eat it, it’s quickly colonized by sooty mold.

  The plant is weakened by the insects’ leech-like action on their vital juices and the honeydew droppings create mold infections on the stems and leaves. Scale and mealybugs are often vectors for plant diseases.

  Mealybugs are considered a specialized scale. Both are in the same order as aphids and whiteflies, and are true bugs in the biological sense: they have specialized probing and sucking mouthparts that they use to drain plant juices.

  Female scale and mealybugs tend not to move much as adults. They attach themselves to the plant and produce a protective layer to ward off predators while they suck the plant juices. Mealybugs cover themselves with a web of cottony wax that some potential predators avoid. Scale produce hard shells as armor against their enemies.

  Reproduction rate and life cycle: The overall life cycle is the same for both mealybugs and scale. The females produce 200 to 1000 tiny eggs that they shelter either on or beneath their bodies. When the eggs hatch (in 1 to 4 weeks) the very small (less than 1 mm) nymphs spread out over the plant and begin to feed. In a few weeks they develop into either winged males or stationary females. The entire generation takes 1 to 2 months, and depending on the species they produce anywhere from one to six generations in a year.

  CONTROL

  + Mealybugs are relatively easy to eliminate on marijuana plants because the plant’s structure does not offer easy places for them to hide and protect themselves.

  + Hand-wipe with a sponge or a Q-Tip: Mealybugs tend to locate in plant crevices and other hard to get to spots. A Q-tip moistened with isopropyl alcohol is an ideal tool for reaching them.

  + Alcohol Spray

  + Limonene products kill mealybugs and scale on contact.

  + Herbal sprays such as Ed Rosenthal's Zero Tolerance® which contains cinnamon, clove or other insect repellant herbal oils are effective exterminants. They kill both on contact and by their evaporates, especially in the protected areas mealybugs choose as habitats.

  + Pyrethrum

  + Neem oil

  + Parasitoid wasps that are specific to various species of mealybugs and scale are available. Some wasp species include Leptomastix dactylopii, Anagyrus pseudcocci, and Metaphycus helvolus.

  + Mealybug destroyer: Cryptolaemus montouzieri is a ladybug that preys on many species of mealybugs.

  + The minute pirate bug (Orius species) eats mealybugs and scale, among other pests.

  + The lady beetle Ryzobius lophanthae is a voracious soft scale predator. It is opportunistic and also eats aphids and mealybugs when it encounters them. However, it is most effective on scale.

  + Horticultural Oil, especially sesame oil products.

  + Insecticidal Soaps

  MOLES

  Moles are common in temperate rural areas, less so in cities and suburbs. They may gravitate to outdoor hemp fields because cultivation loosens the soil and makes it more hospitable to the insects that moles eat.

  Moles are burrowing mammals about 5 to 7 inches (13-17cm) long, weighing 3 to 4 ounces (85-115 g). They have soft dark fur, very small eyes, pointed snouts, and strong digging claws on their front feet. Moles seldom appear on the surface, though. The gardener usually notices their burrows instead.

  Moles build tunnel complexes in rich soil. They eat insects and earthworms, and therefore favor moist soils with a lot of soil-dwelling insect life.

  Moles seldom damage plants directly. However their tunnels and mounds may allow plant roots to become dry, or create a hazard for careless walkers.

  Generally the most important consideration in dealing with moles is distinguishing them from gophers, which are much more destructive. The marijuana farmer has little to worry about from moles. The clearest distinction between them is the shape of their diggings: a molehill tends to be a rough cone with a hole or an earthen “plug” near the center. A gopher mound is more fan-shaped, with the hole or plug near the narrow end.

  Reproduction rate and life cycle: Moles generally have one litter of two to five pups per year, in mid to late spring. Except for the spring breeding period they tend to be solitary and highly territorial. They fight other moles even to the death if one invades another’s tunnel system.

  PREVENTION

  + If you are planting directly in the soil, line the planting hole on the bottom and sides with hardware cloth. Repellents may work in outdoor gardens. The best-attested repellent is castor oil, sold in various brand-name formulations. Odor repellents such as predator urine also work.

  CONTROLS

  + If moles aren’t causing root damage then there is really no need to get rid of them. However if it is necessary to rid the garden of moles then the methods are the same as for gophers: fumigation or trapping. The commercial fumigant cartridges sold for gophers also work against moles, as does carbon dioxide from dry ice or a tank. Garden supply shops sell many kinds of mole traps, both the live-trap and lethal kind.

  RATS

  Rats are not common pests in marijuana gardens, but may sometimes kill plants by gnawing or digging. They are an environment-specific problem, as they view cannabis as a target of opportunity. Rats are rodents ranging from 10 to 16 inches (25 to 40 cm) in length, not including their long tails. They weigh 6 to 12 ounces (170 to 340 grams), and have dark fur ranging from brown to black. Their heads are long and taper to a snout with long whiskers, and their ears are rounded and prominent.

  Rats are common wherever humans live, although they are not always visible. Some rats live in the wild, feasting on insects, other smal
l animals, nuts, fruits, and nature’s detritus. They lair in burrows, walls, piles of trash, dense brush, attics, wherever they can build a secure nest.

  Marijuana is not a primary food source for rats, but they like to chew the woody stalks of plants. This cuts the plants down. Rat teeth grow constantly and gnawing behavior is instinctive. Cannabis is chewing gum for rats.

  Rats are a problem for the marijuana garden only when the grow site is close to something that they like to eat. Gardens near cornfields, orchards, food warehouses, areas with nuts or berries growing wild, and other similar places are at risk. Food at campsites draws rats close to the garden, so secure all food and destroy or remove all food scraps.

  Rats are prolific breeders. They breed year-round if they have sufficient food and a warm place to keep their young. A female produces four to nine litters a year. Litters average 8 pups so a fecund female can produce 12 to 60 a year. They adjust their population automatically to the local food supply.

  PREVENTION

  Rats do their damage in a matter of minutes, and a single rat can destroy several plants in one night. By the time you know you have a rat problem it is often too late.

  + Eliminate tasty rat-food and nest sites in the area. Clear away brush and trash. Cannabis isn’t a primary food for rats so they won’t try as hard to get it as they would if they actually liked to eat it.

  + Plant as far as you can from attractions such as fruit trees or berry bushes, and other food sources.

  + If there are stray cats in the neighborhood of your garden, put out food to attract them. Rats avoid areas that smell of cats.

  + The most effective prevention is a physical barrier to keep the rats away from the plants. It needs to be at least 18 inches (45 cm) high and have no opening larger than 0.5 inch (12.5 mm). A simple way to meet these requirements is to wrap a tomato cage in chicken wire or hardware cloth and put one of these around each of the plants when you set them out. Another is to buy coarse steel wool (sold in bulk at hardware stores) and wrap it around the stalk of each plant, securing it with twist ties.