by Ed Rosenthal
Heavy aphid infestations cause leaf curl, wilt, stunted and delayed growth.
Aphids are vectors for hundreds of diseases and can quickly cause an epidemic. They transfer viruses, bacteria and fungi from plant to plant.
During warm weather each generation takes only 7 to 14 days, and each aphid can produce as many as 100 young, depending on the species. This high reproduction rate lets aphids seem to appear overnight. Indoors, with no predators to keep them in check, they can overrun a garden very quickly.
PREVENTION
+ Air Filtration: Aphids are airborne for part of their life cycle, so a fine dust filter in the air intake prevents aphid entry.
APHIDS, photo courtesy Nature’s Control
+ Monitoring: Check the plants regularly for aphids—at least twice weekly when plants are growing rapidly. Most species of aphids cause the greatest damage when temperatures are warm but not hot (65° to 80° F) (18° to 26° C). They are most prevalent along the upwind edge of the garden, close to outside sources of aphids; check leaf undersides, where many species hang out.
+ Check for ants: when they are present aphids are much more difficult to control, so they must also be eliminated.
+ Catch infestations early. Once their numbers are high and they have begun to distort and curl leaves, aphids are hard to control because the curled leaves shelter them from insecticides or natural enemies.
+ Outdoors, aphids are usually not a problem because of natural enemies such as lady beetles, lacewings and syrphid fly larvae.
CONTROL
Outdoors: Sometimes aphids must be controlled outdoors. This is often accomplished by spraying them off with water. If they remain a problem consider one of the controls listed in the indoor section.
Indoors: Aphids have an easy life indoors and in the greenhouse. They are not threatened by weather, and predators. Without nature's calamities, aphid populations grow exponentially.
+ Aphid Parasites and Predators: Parasites are most effective before an outbreak has reached epic proportions. Predators are recommended for heavy infestations. However, this may just be a prejudice caused by the subtlety of parasites as compared to the aggressive moves of the predators. Predators spend a portion of their life eating and killing aphids and close-up their actions can be as vicious and dramatic as an alligator’s. Parasites inject eggs into aphid larvae. The egg hatches and the parasite larvae feasts inside. It emerges as an adult, “Alien” style, from the mummy. Not quite as dramatic as rampaging predators, except when the newborns crawl out of the corpse, but every bit as effective.
LADYBUG EATING APHIDS, photo Courtesy Nature’s Control
+ Two species of parasitic wasps, (Aphidius matricariae and Aphidius ervi) lay their eggs inside aphid larvae. The parasitized larvae turns brown or black, referred to as a mummy. The generation time of most parasites is quite short when the weather is warm. Once mummies appear on the plants, the aphid population is likely to be reduced substantially within a week or two.
+ Aphidoletes aphidimyza, which are available commercially, are predatory gall midges, that are effective indoors and in greenhouses. They are delicate looking black flies, less than 1⁄8” (3 mm) long, that live for an average of 10 days, feeding on aphid honeydew. They hide beneath leaves during the day and are active at night when the female deposits her eggs in aphid colonies. In two or three days, tiny, bright-orange larvae emerge and begin feeding on the pests for two weeks. Then they pupate in the ground and an adult gall midge emerges 7 to 14 days later. For this reason they cannot be used in conjunction with beneficial nematodes, which eat the pupae.
+ Beauveria bassiana is a beneficial fungus fatal to many insects including aphids.
+ Herbal oil pesticides contain essential oils distilled from plants that are effective and safe for people and pets but not pests. Several brands are available. Zero Tolerance®, made from cinnamon, clove, rosemary and thyme oils is highly effective as are other brands.
+ Herbal teas that include capsaicin, cinnamon oil, cloves, coriander oil, garlic and Italian seasoning are also effective. Mix 1 tablespoon spices per quart of water. If the plant has necrosis from the strength, dilute it. The herbs can be mixed to make your own concoction.
+ Insecticidal soap sprays coat and smother aphids.
+ Neem oil smothers insects but leaves an oily residue.
+ Pyrethrum is a natural plant based pesticide that is widely available.
CATERPILLARS (CUTWORMS, CABBAGE WORMS, LEAF-EATERS, CORN BORERS)
In spring and summer caterpillars are common outdoors, but rare indoors.
Caterpillars are the larval stage of butterflies and moths. They have soft, segmented bodies with a head, thorax and abdomen. The thorax contains three pairs of jointed legs that have hooks and the abdomen has five pairs of stumpy legs. Caterpillars are often the same color as the leaves so they are hard to spot. In addition to this general outline, here are some specifics on the types of caterpillars that commonly infest Cannabis:
Cutworms: The adults are grey to dark brown moths with wingspans of 1.25-1.75 inches (3-4.5 cm).The caterpillars grow to 1 to 1.5 inches (2.5 to 3.75 cm) long. Colors include brown, green, gray and black. Eggs vary widely by species but are usually laid on the stems or the upper sides of leaves.
Cabbage worms: Also called cabbage loopers. The adult moths are off-white with one or two black spots on each wing. They have a wingspan of about 1.5-2 inches (3.75-5 cm). The caterpillars are green, usually with narrow white stripes along the body, and may grow up to 1.5 inches (3.75 cm) long. Cabbage worms move by arching their backs to bring their hind legs forward, then extending their bodies. Eggs are ridged and dome-shaped and usually laid singly on the undersides of leaves.
Leaf-eaters: Many different species. The adults are usually moths, varying widely in color and with wingspans ranging from 1 to 1.75 inches (3 to 4.5 cm). The caterpillars are usually green, but range from gray to brown, and up to 1.5 inches (3.75 cm) long. Some leaf-eaters are “wooly bear” caterpillars, their bodies are covered with long hairs that look much like fur. The eggs may be found anywhere on the plant, depending on the species.
CATERPILLARS
Corn Borers: The adults are yellow or tan-colored nocturnal moths with wingspans of about 1 inch (2.5 cm). The caterpillars are about 1 inch long, light brown in color with a brown head and spots on each segment. Eggs are white to pale yellow in color, laid in clusters of 20 to 30 on the undersides of leaves.
Some caterpillars eat leaves. Others bore into the stem and eat the pith, the stem’s soft inner tissue. Cutworms feed at night, and spend the day in shallow burrows near the plants. Corn borers attack mature plants - they need a stem large enough to hold their bodies. After the eggs laid on the leaves hatch, the young larvae eat the leaves around the eggs for two weeks to a month, leaving close clusters of tiny holes. To catch borers early, look for these small holes. Later in the season look for small holes in the plant stalks, possibly covered with thin silky webbing. After borers have been at work for a while they sometimes cause the stalk to develop “fusiform galls.” These are bulges in the plants’ stalks that widen in the middle and taper at both ends. The borers may leave visible trails on the stalks leading to the galls.
Caterpillars eat both leaves and the soft stems. Borers pierce the stem and eat the soft inner tissue. The branches and leaves above the caterpillar wilt, since they receive no water or nutrients. If it is a main stem the whole plant dies. If it is a side stem, only that branch succumbs. In addition to the direct damage they cause, caterpillars leave behind damaged tissues that are vulnerable to infection.
Caterpillars are voracious eating machines and can savage plants very quickly. They chew continuously to support their high growth rate. They can destroy a tray of seedlings overnight.
Leaf-eaters leave large holes as calling cards in the leaves they dine on. Cabbage worms and other caterpillars also infest buds. A bud that turns brown and wilts “for no reason” may house a cabbage worm consuming
it from within.
Cutworms are perhaps the most obvious of all caterpillars: plants damaged by cutworms are literally chewed through at the soil line, causing the plant to topple. Seedlings and young plants are completely consumed.
Moths usually lay one to two batches of eggs each year, though some species produce up to six generations per year in warm climates. Each female lays several hundred eggs. The adults mate in spring to early summer, and the caterpillars emerge in the early summer to fall. The caterpillars feed until they are ready to enter the pupal stage. Then they spin cocoons or dig burrows and hibernate until they emerge as adult moths. The generation that emerges in late summer and fall often overwinter as caterpillars, emerging in early spring to begin feeding again. This is especially common with cutworm species.
Caterpillars reproduce slowly compared to many pests, but they have large appetites and each one can cause a lot of damage.
PREVENTION
Caterpillars vary widely in their habits, so preventative methods must be adapted to the pest.
+ Planting indoors all but eliminates caterpillar predation of young plants. Keep seedlings indoors as long as possible before transplanting.
+ Clear the garden of weeds, grasses, and plant debris throughout the year, but especially at the end of the growing season. Use electric “bug zappers” with blue or ultraviolet light to attract and destroy nocturnal moths.
+ Garlic: repels egg-laying moths.
Cutworms: Plant seedlings as large as possible. Turn the soil two weeks before planting and destroy any larvae you find. Put a “cutworm barrier” around each seedling. Use a cutworm barrier that is at least 1 inch (2.5 cm) into the soil and 4 inches (10 cm) above the soil and is laced with Tanglefoot.
+ Cabbage worms: Use row covers in spring, when the adult moths breed, to prevent them from laying eggs on the plants.
+ Leaf-eaters: Use row covers to block egg-laying adults. Wrap stems with aluminum foil above and below major branches and apply a layer of Tanglefoot or similar stickum to the foil. Turn the soil before planting, especially in the spring, and destroy overwintering larvae and pupae.
+ Corn Borers: Destroy stalks and other plant debris after harvest.
CONTROL
+ If you have only a few plants and you spot cutworm damage you can usually find the caterpillars within about 10 inches (25 cm) of the damaged plants. Other caterpillars can be shaken off plants or handpicked.
+ Water sprays wash away and drown caterpillars, a vacuum cleaner can remove them as well.
+ BT, Bacillus thuringiensis, is a living bacterium that the caterpillars ingest. They sicken the caterpillars so they stop eating and die within a short time. When they die they release new generations of bacteria that are hungry for caterpillars. They are harmless to humans and pets. The insecticide should be used at the first sign of caterpillars.
+ Cinnamon: brew a cinnamon tea using about an ounce of cinnamon to a gallon of very hot water. Let it cool, then strain and spray. Direct hits are best.
+ Insecticidal soap works best when sprayed directly on the pests.
+ Neem oil: diluted neem oil can be sprayed on plants every 10 days. It makes them unappetizing to caterpillars. Direct hits are toxic to the leaf-eaters. The oil leaves a residue on the leaves.
+ Pyrethrum is a natural plant derived pesticide harmless to humans and other warm-blooded animals.
+ Spinosad: Spinosad’s active ingredient is derived from a soil-dwelling bacterium, Saccharopolyspora spinosa. The bacterium produces a variety of insecticidal compounds when cultured in fermentation tanks. Spinosad must be ingested, so it has no effect on sucking insects and predators but is deadly to chewers such as caterpillars. Once they ingest the substance insects sicken and die. It is nontoxic to wildlife, pets, and humans with minimal impact on the plants. However use Spinosad with caution around honeybees.
+ Trichogramma: Several species of tiny stingless wasps that attack and destroy caterpillar eggs before they hatch. They must be released at the earliest sign of infestation, and cannot be used with most insecticides (BT and Spinosad are exceptions). Consult the supplier for recommended species and coverage rates.
+ Special note on stem borers: If you do not control stem borers quickly, your yield will be greatly decreased or even non-existent. Before they bore into the stalk they can be eliminated using the same techniques as for caterpillars. It is a different story once they are situated in the stem’s enclosure. Sometimes you can yank the borers right out of the holes they’ve chewed. Another method is to bore a hole in the stem above the borer and inject one of the recommended caterpillar insecticides into the stem using either a syringe or an eyedropper.
DEER
Deer populations vary widely, both geographically and by habitat. Deer favor light forest and grasslands near forested areas, as they dislike getting more than a few hundred yards from cover. Gardens in suburban areas built near suitable forestland may have problems with grazing deer. Garden plots set up in wild or rural areas are very likely to be visited by deer if the habitat supports them.
What does the pest look like?
Deer are grazers with graceful bodies, thin legs, and long necks. They vary greatly in size depending on species, age, and sex, but usually fall between 4 ft. and 6 ft. (1.2 and 1.8 m) long and weigh 80 to 220 lbs (35 to 100 kg). Usually the heavier races are found in the north and the smaller lighter ones in the south. The males carry antlers beginning in late summer, and usually shed them in very late winter or spring.
Deer emerge from forest cover at night to browse on plants, but flee quickly when approached. They have excellent senses so most of the time the gardener knows them only by their tracks and the damage they leave. Some deer have become accustomed to humans and don’t flee on sight.
Deer prefer fresh leaves, fruit, and other rich plant matter. In the marijuana garden they tear up and eat entire small plants, strip plants of leaves and trample them. Marijuana evolved cannabinoids in part as protection against herbivores. Most mammals find the leaves and flowers unpleasant. Deer are among the few exceptions. This means that in areas that have large deer populations they may be attracted to your garden simply because it’s a food supply that most other herbivores leave alone. Even so they prefer young, tender plants. As marijuana plants mature and cannabinoid levels increase, they become less palatable to deer.
Deer lack upper incisor teeth. They do not bite plants the way a rabbit or similar animal might. Instead the deer takes hold of leaves with its lips and lower teeth, then tears them off. This makes for ragged browse damage, very different from the neatly clipped leaves left by rodents. Look also for deer tracks and droppings near the garden.
Reproduction rate and life cycle: Deer follow a normal mammalian life cycle. Adults mate in the late fall through mid-winter, and the female gives birth to one or occasionally two fawns in late spring to early summer. Deer usually mature in one to two years, and live for 10-20 years if not killed by predators or disease.
PREVENTION
+ Deer pose little threat to plants grown indoors. However, all outdoor gardens near deer habitats are vulnerable.
+ To prevent deer damage they must be kept away from the plants. There are two main ways of doing this: repellents and fences. Repellents are less expensive, and may be the only option if discretion is important. But fencing is more certain when it is practical.
+ Deer find the odors of garlic, capsaicin, and rotten eggs offensive, and several brands of commercial repellents containing these ingredients are available. Other materials also repel deer by smell:
+ Anything that carries a human’s scent, such as worn clothing or human urine.
+ Urine or scat from dogs or other predators. Predator urine is available commercially. Scat is sometimes available from your local zoo.
+ Scented bar soap, suspended in a net bag near the plants.
+ If you are not certain that a repellent is safe for use on food plants, then surround the marijuana plants with oth
er plants that you don’t plan to inhale or ingest. Replace the repellent according the manufacturer’s instructions, or every few days for the other scent repellents listed above.
+ Anything that startles or frightens deer is effective. Buy several home motion detectors at a hardware store and set them up in a perimeter around the grow site. Depending on the resources at the site, motion detectors can be rigged to trigger high-pressure water sprinklers (these are sold as “scarecrow sprinklers”), bright lights, battery-powered radios or ultrasonic noise when a deer approaches. Remember to set up lights to point away from the plants, and if discretion is important then shield the lights or lower the radio volume so the deer can detect them but nearby watchers cannot. Deer can become accustomed to most sounds, sights, or smells. Once they realize that the repellent isn’t harming them they’ll learn to ignore it. This means that you need to change your repellent from time to time, and not just from one brand to another, but from one ingredient or method to another. Combining methods is also useful. For example, setting up an odor repellent and a scarecrow sprinkler together.
+ Fencing must be constructed with the abilities and habits of deer in mind. A deer can jump any fence less than 8 ft. (2.5 m) high, if it can get close enough. Fences must also be built tight to the ground, or deer can slip under them. One alternative to an 8 ft (2.5 m) fence is an electrified fence. Deer prefer to slip through a barrier rather than jump over it if that looks possible. A standard electric fence built from 2 or 3 strands of 20-gauge smooth wire on insulated posts often deters them. Once they try to slip between the strands and get shocked they generally keep several feet away from the fence - too far for them to jump it. A variant called a “Minnesota fence” actually uses an attractive bait such as peanut butter to get the deer to lick the fence or a foil tag attached to the fence. The deer get a mild shock and avoid the fence completely after that.