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Pest Guide – Whiteflies

Pest Guide: Whiteflies

Whiteflies are insects in the Aleyrodidae family. These common agricultural pests may be small, but they can also be quite destructive, and unfortunately, they love marijuana plants. This article will offer insights into everything growers need to know to identify and combat whitefly infestations.

What Are Whiteflies?

Whiteflies are soft-bodied winged insects. They look like tiny moths, but they’re actually more closely related to aphids and mealybugs, and they behave more like spider mites. There are actually over 1500 different species of Aleyrodidae and they can be found in just about any region, but growers don’t need to be able to tell the difference between them. The key is learning how to identify the their general characteristics to make it easier to identify infestations early.

These insects have white wings and yellow bodies and are about 1/12 of an inch long when fully grown. Some growers describe whitefly infestations as looking like a cloud of winged dust because these insects typically cluster on the undersides of leaves and often emerge en masse when the leaves move.

To populate, whiteflies lay their eggs on the undersides of leaves. The eggs can be gray or yellow depending on the species, but they’re almost always conical. Each adult whitefly can lay as many as 400 eggs, which require only a week to hatch. Needless to say, it’s important for growers to identify and eradicate these pests quickly to prevent any problems from getting out of hand.

After hatching, eggs develop into flattened nymphs, sometimes referred to as crawlers. As nymphs, whiteflies typically feed on the lowest leaves of marijuana plants. They’re tiny, though, so most growers don’t notice the nymphs themselves, only the damage they cause to plants. An important tip is to consider that whitefly nymphs spend about four weeks feeding on the lower leaves of the plant before developing into adult whiteflies, which tend to congregate and feed higher up. Checking your lowest leaves regularly can help to stop an infestation before it kills your plant medicine.

Unlike most insect pests, whiteflies are diurnal, meaning they’re active during the day. Infestations are most common from mid- to late-summer, but these pests can survive winter in warm climates and they’re known to infest not just outdoor crops, but also within greenhouses.

Signs of Whitefly Damage

The easiest way to tell if adult whiteflies are infesting a crop is to shake the stem of the plant gently. The insects will emerge, often in a small cloud, and at this life stage they will be visible to the naked eye. Look at the undersides of the leaves, as well. Since adult whiteflies produce so many eggs, just killing the adults won’t do growers much good.

Growers may see signs of whitefly damage before the first insects even reach maturity. Look for white spots on the topsides of lower leaves, slow plant growth, yellowing leaves, and dry outer leaf margins. If the whiteflies have already caused serious damage, the leaves may become brittle and fall off.

The damage caused by whiteflies can happen fast. Before growers even see them, the nymphs can weaken the lower leaves of the plant, causing them to wilt and fail to carry out photosynthesis. When this happens, the plant’s growth will be stunted even if growers manage to control the infestation.

As the whitefly season progresses, the damage will move up the plants. Remember, the adults congregate at the top, while the nymphs prefer to feed lower on the plants.

How Do Whiteflies Cause Plant Damage?

Whiteflies cause plant damage by feeding on the leaves. They feed by puncturing the leaves and sucking the nutrients out. This is what creates the white spots on the leaf tops.

As they feed, whiteflies leave behind excrement in the form of a nutrient-dense, sticky-sweet substance often referred to as honeydew. This causes growers even more problems, as honeydew creates a perfect medium for mold, which further inhibits marijuana plants’ abilities to photosynthesis and grow. The honeydew also attracts ants. These ants don’t feed on whiteflies, but depending on the climate, they may feed on these pests’ predators, further exacerbating the problem.

How to Prevent Whiteflies

The best way for growers to deal with whiteflies is to take preventative action against them instead of waiting until the infestation has gotten out of control. These insidious insects are pesticide-resistant, which makes them particularly difficult to eradicate in large numbers. Thankfully, there are a few relatively easy steps that growers can take to prevent infestations from occurring in the first place.

Quality Seeds

Healthy plants grown from high-quality seeds will be better able to resist whitefly infestations. It’s important to buy seeds from a reputable seed bank and pay careful attention to water, nutrients, and light levels throughout the growth cycle. It won’t just make infestations less likely, but will also produce a heavier, higher quality crop.

Companion Planting

Companion planting is a great way to stop whiteflies from infesting a garden. Marigolds, nasturtiums, and basil will all repel whiteflies, so plant them around the perimeter of the garden so they’ll get plenty of sun. Just make sure they won’t be competing for nutrients with the marijuana plants.

Other plants are great at hiding the scent of marijuana from whiteflies, making it harder for them to find the garden, to begin with. Try planting bee balm, pineapple sage, hummingbird bush, or mint nearby.

Predatory Insects

Whiteflies have a few natural predators, and most of them will be more than happy to help control populations before they explode into a full-blown infestation. Ladybugs, lacewings, and predatory mites are all present in most natural ecosystems, and they all feed on whiteflies in various stages of their development. Hummingbirds also consume whiteflies in prodigious quantities, so try creating a habitat around the garden that attracts these birds, if possible.

Reflective Mulch

Some vegetable gardeners swear by applying aluminum reflective mulch early in the season to repel whiteflies, and cannabis growers can use this same technique. This reflective mulch deters not just whiteflies, but also other harmful insects, by making it more difficult for them to locate the host plants. It won’t do much good to apply the mulch once an infestation is already underway, so growers who want to avoid unnecessary crop losses should mulch early in the season.

Whitefly Traps

Whitefly traps won’t usually catch enough of these tiny pests to control an active infestation, but setting them out in advance can alert growers to the problem early enough that they can save their plants. Don’t bother buying expensive traps. Just set out a few yellow index cards covered with petroleum jelly near the plants. The yellow color will attract them to the index cards, which will look like new plant growth, where they’ll get stuck and die. Monitor these traps each day to see if the population is growing.

Controlling Active Infestations

Already have an active whitefly infestation and want to curb it early before it destroys the crop? Don’t despair. While whiteflies are resistant to chemical insecticides, there are a few all-natural methods for getting rid of them.

Spray Them Off the Plants

Growers should start any whitefly control regimen with hosing the adults, nymphs, and eggs off of the plants. Whitefly eggs are notoriously hard to remove, but excessive water pressure can damage the plants, too, so don’t go overboard. If there are still eggs clinging to the bottom of the leaves after they’ve been hosed down, it may be necessary to add some extra control measures.

Prune Heavily Damaged Leaves

If the leaves have already been severely damaged, they won’t be able to photosynthesize efficiently. It’s better for the plant’s health to prune them off. Plus, removing damaged leaves comes with the added benefit of getting rid of any whitefly eggs hanging onto the bottom. Just dispose of them far from the garden to prevent re-infestation and treat the remaining plant with oils as described below.

Apply Oils

Essential oils and horticultural oils are great for controlling whiteflies. Not only are they effective, but they’re also natural, so they won’t cause harm to predatory insects that would otherwise be helping to keep the population under control.

Try neem oil first, applying it using a mister to the bottoms of the leaves. If neem oil doesn’t work, try garlic oil. Just make sure to keep both these solutions away from developing buds, as they can both alter the taste and aroma profiles of growers’ yields.

Some growers forgo the neem oil and garlic oil completely and just apply a vegetable oil mixture to their plants. Mix two tablespoons of regular, food-grade vegetable oil into a full gallon of water. Spray it on the entire plant, paying special attention to the bottoms of the leaves. It won’t be as likely to alter the taste and flavor profile of the buds, but growers should still avoid spraying them as much as possible.

Using oils to control whiteflies is effective, but it takes some time. Growers should apply their essential oils, horticultural oils, or, yes, cooking oils, to the plants twice a week. Keep at it until all the whiteflies are gone.

The Bottom Line

Whiteflies are an insidious garden pest that love not just vegetables, but also one of nature’s medicine plants,  marijuana. They’re notoriously difficult to get rid of, so most growers take preventative measures in the beginning of the season to avoid infestations right from the start. If there’s already an active infestation, take action immediately to prevent it from spreading by following the advice above.