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HOME + GROW INFORMATION + PLANT PESTS & DISEASE FAQ

FAQ: PLANT PESTS & DISEASE

I want to use an insecticide to kill the bugs on my plants. What are my natural alternatives?
Why are there webs appearing on my plants?
What kind of predator mite should I use in my garden? How many do I need?
What are these little black flies flying around the base of my plants?
I think I have aphids. Now what?
How do I get rid of whiteflies?
What the best way to keep spider mites from coming back?
Do you have any suggested rates for using Azatrol in a recirculating system?
 

I have a bug problem and I want to get rid of it immediately. What are my alternatives to the pesticides I see at the hardware store?
If you are concerned about environmental health or safety, you will first want to take a look at botanical options. Botanicals are pesticides which are derived from plants. They quickly degrade and are considered to be safer than common synthetic chemicals. However it is important to use them properly, just like any insecticide. Two common botanicals that you might look into are Neem and pyrethrins

Neem is widely used in Asia and India for a number of things including brushing teeth! It contains a bitter chemical that bugs don't like to eat, and it also acts as a growth regulator that interferes with insect reproduction. It is effective on a wide range of insects. Plus, it has very low toxicity to mammals.

Pyrethrins come from a chrysanthemum species, Dendranthema grandi-flora found in Kenya and Ecuador. Pyrethrins kill insects by interrupting their nerve impulses.

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There are some sort of webby-looking things appearing on my plants. I’ve also noticed that my plants have polka-dotted discoloration in some areas. What is this and how do I fix it?
It sounds like you have spider mites. Spider mites are often found on indoor plants, and in the right temperature and humidity, their population can quickly explode out of control. If you look closely you will see tiny spider-like creatures running over the webs. The damage spider mites do looks like needle puncture marks where the mites have sucked the sap from the leaf. This damage may at first appear silver in color, or yellow, but eventually it will sink in and turn brown.

There are several alternatives to dealing with mites, and the choice you make is up to you and the number of plants you are dealing with. If you have only a few plants, you can control the mites by rinsing the plant in water, paying extra attention to the undersides of the leaves, where mites accumulate. The webs can also be broken up with blasts of water.

You may choose to use a miticide, and we carry several natural ones. Pyrethrum is an old standby and is effective against numerous pests. Another good choice is Pest Out which is 100% certified organic and is effective against spider mites, thrips and aphids. Use caution when spraying any solution on your plants; it is best to use a low dosage on a single plant first to test for any ill side effects.

To maintain control after knocking down a heavy infestation, we suggest introducing beneficial insects to your garden. As a balance of beneficals is achieved within a grow area, there is less fluctuations of pest populations. Beneficals can be released two days after the use of insecticidal soaps and horticultural oils, however residual pesticides can stick around for up to a month and will kill beneficials as well as pests.

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What kind of predator mite should I use in my garden? How many do I need?
There are generally three kinds of Predatory Mites that are available. Each is specific for use against a certain kind of mite and a certain temperature and humidity. We find the most effective control is found using the Triple Threat mix of all three species. To wipe out an infestation, we recommend blasting them with 1000 predators to 50 square feet.

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There are lots of tiny black flies around the base of my plants. What are these? Are they harmful?
Those little black critters are known as fungus gnats. The term refers to a large group of insects, most of which have not been extensively studied. They reproduce in moist, shaded areas in decaying organic matter like leaves and algae. The life cycle is about four weeks, with continuous reproduction when warm temperatures are maintained. Larvae not only feed on fungi and decaying organic matter, but on living plant tissue, particularly root hairs and small feeder roots. Usually, there are very few ill effects from these flies, but control is advised. After the roots have been injured, root rot may attack the plant. Entire crops have been lost in this manner. The plant symptoms may appear as sudden wilting, loss of vigor, poor growth, yellowing, and foliage loss.

Fungus gnats can be easily controlled with a pyrethrin spray. They can also be physically captured with yellow sticky cards. A Cooperative Extension pamphlet written by A.L. Antonelli of Washington State University suggests that since fungus gnats are attracted to sprouted wheat grain, that a pot of sprouted wheat could be used as a trap crop. Antonelli recommends setting the pot in the problem area and leaving it for a few days. Female gnats will lay their eggs on this moist material and then the pot can be submerged in boiling water to kill the eggs and larvae. Alternatively the contents of this pot could be discarded outdoors. This procedure would need to be repeated every two weeks until the flies are no longer a problem.

Perhaps the most important weapon you have against fungus gnats (and all pests) is good grow room sanitation. Don’t allow decaying plant material to buildup. Always remove fallen leaves, algae, or any sort of organic material that collects around the base of plants. This material is a breeding ground for pests and diseases

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I think I have aphids. Now what?
There are so many aphid species that just about every plant has at least one species that likes it. The first thing you might notice when you have aphids is that the plants aren’t thriving or are even wilting. If you look at the growing tips of your plants or underneath young leaves, you’ll see dense colonies of tiny (I - 3 mm) soft-bodied, pear-shaped insects. Aphids feed by inserting their piercing-sucking mouthparts into the vascular system (phloem) of the plant and sucking out the sap. This causes discoloration, curling, crinkling and wilting of leaves, and malformation and distortion of buds and shoots, leading to plant stunting and deformities and reducing the vigor of the plant. The worst thing about aphids, though, are the viruses they often transmit . The cotton aphid is known to transmit over 50 plant viruses, and the green peach aphid over 100 (Kennedy et al. 1962). They also secrete honeydew which is like a Petri dish for growing potentially fatal, sooty black mold.

Aphids reach adulthood in only a week, and they can quickly multiply into a giant problem. One adult can produce 50 to 250 young during her lifetime, depending on the host plant and its nutritional status. The nymphs can mature and begin reproducing in 7 to 10 days. The life expectancy of the adult can be from 7 to 21 days, making possible more that 30 generations per year in the greenhouse.

Aphids can be washed off with water, or sprayed with horticultural soaps and oils. Two great organic alternatives are Neem Oil and Pest Out. Pyrethrins are also highly effective. After knocking down a pest population, it is often a good idea to introduce beneficial insects or predators into the growing environment. Green Lacewings are a great choice as are aphid predators. You may want to use yellow sticky traps as a monitoring device for future infestations, although you may find that you catch more beneficials than aphids!

Kennedy, J. S., M. F. Day, V. F. Eastop. 1962. A Conspectus of Aphids as Vectors of Plant Viruses. -- Commonwealth Institute of Entomology. London, 114 pp.

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How do I get rid of whiteflies?
Whiteflies can be difficult to get rid of, as they are highly prolific reproducers . The species is usually parthenogenetic, meaning that the birth of young can occur without mating. The adult females lay 200 to 400 eggs on the undersides of leaves, and these young mature within 18-25 days.

You may choose to handle your infestation in several ways, and they will all work so long as you are persistent. There are several products on the market that are all organic and safe for humans. Safer's Insecticide soap will do the trick, as will Neem Oil. A Pyrethrum-based insecticide would work as well. All of the above products are organic and can be applied up to the day of harvest. The most important thing to remember is that the treatment is a contact killer so it needs to be done once a week for three to five weeks, otherwise new bugs will hatch out and the problem returns. By applying the insecticide 3 to 5 weeks it will break the entire life cycle of the pests.

For maximum effectiveness, attack your infestation in three stages

  1. Use a vacuum to suck up adults early in the morning (as soon as the lights go on). Low temperatures make them slow moving and easy to catch.
  2. Use an insecticidal soap or oil in areas where the populations are very high.
  3. Order Encarsia Formosa (Whitefly Parasites), releasing one to five per plant or one for every 10 square yards of plant area. You should aim for no more than one adult whitefly per leaf at time of parasite release.
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Once a spider mite infestation has been controlled, how does one keep them from coming back? How and where do they come from and can they be eradicated before hitting our plants?
First of all, after control has been established over an indoor insect population the best thing to do is be vigilant, inspect your plants daily so that any eggs that were missed can be dealt with as soon as they hatch. Your plants will love you for it.

Spider mites can come with plants or cuttings that you bring to your indoor garden. Spider mites can travel on your clothes, on your shoes, on your pets, and with air currents! In order to thrive spider mites like warm, dry conditions - which generally can be found indoors. If you can lower your temperature to 70-72 degrees and/or add humidity (up to 65% depending on the type of plant) to your growing environment, pests such as spider mites may remain inactive - which means that you might see them on your plants but they won't be doing any damage.

Greenhouse workers have been known to change their clothes and step into shallow pans of bleach water before entering a greenhouse in order to keep bugs out. Also if you have any vent openings in your indoor garden that lead to the outside, they should be screened to prevent insects from entering.

You can use the sticky substance "Tanglefoot" around the base of plants to prevent spider mites and crawling insects from moving from one plant to the next. Depending on the type of mite infestation you have, you can purchase and introduce predator mites (carnivorous mites) that will eat the spider mites that are harming your plants.

Spraying your plants with an oil-based spray (turn your lights off or raise them very high up until the plants are dry), will help protect the plant against an insect infestation. Weekly sprayings with Azatrol or Einstein Oil (sometimes every 2-3 days) can help control an insect infestation if one happens to gain a footing on the plants.

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Do you have any suggested rates for azatrol in a recirculating float system for lettuce?
Yes.  We run Azatrol now at ½ the bottle rate. 1 oz. (6tsp/or 30mL) per 20 gallons.
The manufacturer’s suggested rate is 1oz per 10 Gallons.  We find this to be way too strong.