The two-spotted spider mite, Tetranychus urticae, is one of the most common mite species of agricultural importance. If you see fine spider webs on your house plants, you probably have spider mites. USDA, ELECTRON AND CONFOCAL MICROSCOPY UNIT.
AUTOFLOWERING CANNABIS is a plant, and there is always an insect or disease trying to take any plant out. (They want to live, too.) Be prepared, is the motto, especially when growing a fast-moving plant like Autoflowering Cannabis.
Actually, one of its saving graces is that Autoflower plants grow very fast. Pests can miss their opportunity. And, Autoflowers don’t require specific hours of light to bloom. This means that if you have problems you cannot fix, you can always start over and almost catch up, rather than having to wait for a few seasons to roll around so you have the right photoperiod.
All plants can get attacked by pests, and Autoflowering Cannabis plants are no exception. Fortunately, the inclusion of the scrappy Cannabis ruderalis in their genes gives Autoflowering Cannabis plants some resistance. And, breeders are always working to improve upon their plants’ natural abilities to grow pest-free. These efforts, and fast growth, make it difficult for some enemies to take hold or have an impact when they do.
There are lots and lots of books on plant pests, and as a gardener, you should have at least one as a reference. Still, there are some specific rules you should follow to prevent or minimize pests on Autoflowering Cannabis, and there are some specific critters that merit special note.
The two-spotted spider mite, Tetranychus urticae, is one of the most common mite species of agricultural importance. If you see fine spider webs on your house plants, you probably have spider mites. USDA, ELECTRON AND CONFOCAL MICROSCOPY UNIT.
As a gardener, you already know that prevention is the best route. Keep your grow and grow areas clean, provide adequate air movement, and watch the humidity. Prevent pests.
Here are the major specific pests for which you should be on the lookout. You are probably familiar with most of these as most can attack tomatoes (and other vegetables). Knowing what they look like is important. So is knowing what the proper organic remedy is to prevent or control them.
Spider mites—The two-spotted spider mite has a particular fondness for any Cannabis. These tiny (0.5 mm, 1/50th of an inch long) cell-sucking insects can be the bane of growing Autoflowering Cannabis. Here is where your hand lens will come in handy.
First signs of an infestation of mites are tiny white or orange spots appearing all over leaves, which then turn yellow. If you turn these leaves over, you will see tiny eggs and the characteristic webbing created by spider mites. It is most pronounced at nodes. The buds of badly infected plants will also become covered with the webbing.
Since spider mites thrive under hot and dry conditions, temperatures should be kept below 27°C (80°F), and the humidity should be controlled. Many commercial growers apply a mist every few hours. You might use a spray bottle a few times a day.
Help prevent spider mite infestations by keeping your growing area clean. Don’t bring in other plants. If outdoors, don’t kill beneficials by spraying any generalized insecticides. Keep plants in a constant breeze as this makes it more difficult for the mites to reproduce.
To kill spider mites, use commercially available neem-based products or Spinosad. Read the instructions carefully so you know how long the formula lasts and when to reapply. Mites are tough little critters. They are so tough that you really should toss your soil after the current grow and thoroughly clean everything.
Biological control employs the predator Mesosaeiulus longipes. This is an aggressive mite that works quickly. Phytoseiulus persimilis works well and is also available commercially. Lady bugs and another spider mite destroyer, Stethorus punctillum, are also available to reduce mite populations, though these probably only work indoors. If you use biologicals, you need to be careful as they can impact other wanted predators.
Grow stores will have lots of products from which to choose. Spray the entire grow area, the plants, soil, and containers. An effective home remedy spray for spider mites is a mixture of 9 parts water and 1 part rubbing alcohol.
Russet and broad mites—These tiny (0.5mm, 1/50th of an inch long) insects also suck the juices from leaves and stems. They are almost impossible to see, even with a good hand lens or microscope. Look, however, for first signs of wet or glossy-looking leaves that curl or develop drooping leaf tips. Later the leaves turn yellow and bronze and drop off. If plants are in flower, (alas) these will turn brown and die.
Russet and broad mites are very hard to eradicate as they lay their eggs inside the plant. Neem oil is the first recommendation. The predatory mites Neoseiulus Californians work well and are less harsh on the plants. A fungal remedy is MET52, Metarhizium anisopliae Strain F52, available from grow stores. Aloe products won’t kill them, but mites will avoid aloe and move to treated trap plants such as broad beans.
Heat may help you deal with russet and broad mites. If you can safely heat your grow area to 46–49°C (115–120°F) for an hour, you can do wonders. So will 10 seconds of water at 60°C (140°F) degrees. It is difficult for any mite to survive that. Obviously, you will need to remove your plants first as it is difficult for them to survive the heat, too.
Fungus gnats—These tiny flies breed in the top layer of soil. They mine roots which stunts plant growth, and they are very annoying as they fly around. Fungus gnats are attracted to and thrive in soil that has been overwatered and are normally not a problem if you let the soil surface dry out in between watering.
Aiming a fan on your soil will speed up drying and make it harder for gnats to move around. A physical barrier made by covering the soil with newspaper or a cut paper bag prevents adults from getting into the soil and laying eggs.
Organic solutions again include neem oil. Products containing Bacillus thuringiensis var. israelenisis (Bt) work great as well. They are best when applied while watering. Stratiolaelaps scimitus lives in the soil and will take out larva. You can also spread diatomaceous earth on the soil.
White flies—Tiny white flies lay eggs on the undersides of leaves. After they hatch, the larva suck the juices. Their numbers can become quite large. Often you won’t notice them until the population increases and all of a sudden you see lots of adults flying around. In addition to these annoying swarms, you will note leaves yellowing and a general decline in the health of the infested plant.
Treat white flies with neem oil or Spinosad products. You have to repeat applications as white flies are difficult to fully eradicate. When you spray, cover soil and the growing container. If you are growing indoors, parasitic Trichogramma wasps can be used to control populations.
Powdery mildew—White spots and powder on leaves are the signs of powdery mildew, a fungus that attacks Autoflowering Cannabis and eats leaves. A few fuzzy spots soon spread to other leaves. Infected buds are unusable. If you grow tomatoes, you have probably seen it. It can coat a plant in a matter of days.
Spores of powdery mildew are in the air, but they are encouraged by high humidity as moisture is needed for the fungus to grow. Good air circulation makes it difficult for the fungi to get established so using a fan is a good preventative measure.
If your plants are hit by powdery mildew, reducing humidity to below 45% is a must. It is also imperative that you have a change of air, not just movement. Isolate your plants so they don’t spread the disease.
Early detection is key. Once you find it, immediately use a spray made of any of several home remedies: Baking soda (30mL/3.8 liters or 2 tablespoons/gallon of water), milk (1 to 9 parts water), hydrogen peroxide (mix 5mL of 35% strength hydrogen peroxide to 3.8 liters of water, or 1 teaspoon/gallon). Neem oils as per instructions are some of the best commercial remedies.
Aerated compost tea sprayed on leaves is a good prophylactic move. The microbes in the tea take up space and nutrients that would have been used by pests.
Powdery mildew on leaves. HAROLD FRAZIER, NEW BREED SEED.
Botrytis is another fungus that attacks Autoflowering Cannabis. It causes damping off of seedlings, weakens and destroy stems, and, most heart breaking, can infect and kill flowers. (Ah, the injustice of all that waiting, only to have them cut down in their prime!) It is hard to spot until established with a gray, white, or blue-greenish mold growing on the inside of the flower bud.
Look for signs of Botrytis in flowers. It starts with a drying leaf sticking out from a cola. And keep looking even when the flower has been harvested and is drying. This is a real pest, and if you get it, you will need to clean up to get rid of the spores. The best bet is to prevent it by making sure you have good air circulation.
Slugs and snails—Slugs and snails decimate leaves, starting with characteristic holes. They weaken plants and can destroy flowers. Besides, they leave a slime trail. These are particularly nettlesome when growing Autoflowering Cannabis outdoors.
The use of black felt cloth containers helps keep them from getting to plants. Trapping works great. Put beer or yeast water in shallow containers to attract them away from plants. Place these next to containers or just outside your gardens, not in them. Diatomaceous earth makes a great barrier as neither of these pesky mollusks likes to move over sharp edges.
Other pests—Other pests that may impact your plants include scale, caterpillars, crickets, grasshoppers, leafhoppers, leaf miners, mealy-bugs, thrips, and nematodes, to list a few familiars. There is plenty of information about all of these on the Internet or at your library.
The most important takeaway is to keep your eyes open for pests. Observe and inspect your plants often. Act quickly and follow instructions.
Autoflowering Cannabis plants are no different than other annuals, and the same rules apply when it comes to pests. Inspect your plants every day. It isn’t that difficult. You should be making observations and gathering information about your plant’s growth all the time anyway. Taking pictures with a cell phone is a good practice. That way you can go back, if you do have an infestation, and find and learn to recognize the very early signs.
Second, pests spread, and they spread quickly. Immediately remove any plants that are infected and either destroy them or keep them isolated while you treat them. Some problems will be serious enough or far enough along that you really do need to cut your losses, so to speak. Don’t unnecessarily put your other plants at risk.
And third, always stay organic, starting with biological solutions when applicable. One of these is squishing large insects by hand. You can also try to remove insects with air (either blasting them or using a small hand vacuum cleaner) or use a water spray to knock them down. Resort to chemicals, and just organic ones at that, only when you absolutely have to. Again, make sure to follow directions precisely.
It should go without saying that a gardener should never spray Autoflowering Cannabis flowers with even organic pesticides unless growing for seed. Some go one step further and never spray any part of the plant when a plant is in flower. To do so risks having spray drift onto flowers, and that can impact the quality of the harvest.
If directions allow, always repeat applications, even though you cannot see any more pests. Pests hide. And, vary the remedies as well, if possible. Autoflowering plant pests quickly develop resistance if you constantly apply the same remedy.
One of my favorite tricks to deal with insect pests, specifically spider mites, whiteflies, and thrips, is using broad beans as trap plants. A couple of plants grown in a separate pot and placed among Autoflowering Cannabis plants will act like a magnet to attract pests away from your crop.
Broad beans, Vicia faba, will at least serve as monitors of any potential problems and, because of the short life of Autoflowering Cannabis, may actually keep things in check. (Plus, you may even get some green beans.) One side benefit is that broad beans are legumes, and the plants will put nitrogen into the soil.
Finally, a certain number of pests is okay. This is because of the speed at which Autoflowering Cannabis develops. The pests just don’t have enough time to multiply to sufficient numbers to destroy your crop. Still, you will not want to carry over these pests to future grows. Cleaning up after each harvest is extremely important to meet this goal.
Autoflowering Cannabis plants grown in good soil may not need supplemental nutrients. There is nothing unusual here; your plants will only falter if there is something missing in the soil mix. This is why I stress buying soil from a local grow store to start, based upon the recommendation given there.
Autoflower showing calcium deficiency (at top of photo). FULL DUPLEX.
Gardeners don’t like to hear that you cannot really tell what nutrient may be lacking just by looking at leaves. A lack of any one of three major nutrients can cause yellowing of leaves, for example.
Still, leaf signs tell you something is going on. Just exactly what is an educated guess. Leaf changes are where to start looking. (If you want more information about this subject see Teaming with Nutrients, Timber Press, 2013.)
Lack of iron starts with yellowing of new growth. So does a lack of nitrogen and zinc, but this plant probably has iron deficiency. DIYANA DIMITROVA OF DEPOSIT PHOTOS.
Boron deficiency—Boron is needed for cell wall development and for development of flowers, among other things. The tips of plants that are experiencing boron deficiency exhibit yellowing of leaves. They then turn brown and eventually gray. This is the key tip (pardon the pun). Since very little boron is needed by plants, a deficiency is a rare occurrence.
Calcium deficiency—Calcium is needed for building cell walls and it helps plants absorb potassium. There are two key plant signals for this deficiency. A lack of calcium results in weak branches that fall off. Leaves display dead patches that get larger as time passes.
Chlorine deficiency—Chlorine is needed for the proper operation of stomata and is needed to break the bonds of water during photosynthesis. It is rarely in short supply because it is in our water; but, when it is, leaves turn bronze.
Copper deficiency—Copper is used in the production of sugars and proteins. Signs of a deficiency are seen in new leaves, which will display dead leaf tips and leaf margins. The leaves will take on a darker blueish color. They curl and die.
Iron deficiency—Iron is needed to pass around electrons during key metabolic processes needed for nitrogen fixation, and is also used in making chlorophyll. Plants that are lacking in iron display yellow leaves, starting with new growth and upper leaves. The leaf veins will remain green. Leaves start to fall off.
Magnesium deficiency—Magnesium is in the center of the chlorophyll molecule, so it is absolutely critical for photosynthesis. When lacking, the plant’s lowest leaves turn yellow and die. The signs move up the plant as younger leaves also begin to die.
Autoflowering Cannabis showing signs of nitrogen deficiency. Note the green veined leaves on the left. This is the early sign and distinguishes this yellowing from that caused by other problems. CANNABIS UNIVERSITY.
Autoflowering Cannabis leaves showing progression of phosphorus deficiency. FULL DUPLEX.
Manganese deficiency—This is a key nutrient, as it frees oxygen during photosynthesis. If it is in short supply, new leaves develop dead spots and then turn yellow.
Molybdenum deficiency—This nutrient is needed for plants to use nitrogen properly. Leaves in the middle of the plant turn yellow. New growth curls and twists, and sometimes the leaves turn a maroon or crimson color.
Nitrogen deficiency—Nitrogen is used for the production of proteins and enzymes, among other things. If a plant is deficient, it will turn yellow. This usually starts with the older leaves which give up nitrogen for new growth.
Phosphorus deficiency—This is the key element in ATP, the energy currency of plant cells. The symptoms of phosphorus deficiency start with the darkening of foliage. Growth slows and leaves turn purple and brown and curl upward.
Potassium deficiency—Potassium is used to control stomata, in photosynthesis, and for water transport throughout the plant. Deficiency results in lower leaves turning brown and dying. This is often preceded by faster growth, which is pretty hard to notice in Auto-flowering Cannabis. Stems can take on a reddish color.
Silicon deficiency—This element is used to protect plants from insects, among other things, so symptoms of deficiency can include more attacks than usual. In addition, since it helps with photosynthesis, plants that lack it become weak and spindly.
Sulphur deficiency—Sulphur is needed for the production of chlorophyll. If a plant lacks adequate supplies, new growth turns yellow. Growth slows and becomes stunted.
Zinc deficiency—Zinc is a key component of many enzymes and in the production of auxin, a key growth hormone. Without enough zinc, plants leaves become twisted. Veins on older leaves turn yellow.
Yellow leaves with or without dark veins, wilting, leaf curl, dark and dead spots… all of these can be caused by nutrient deficiencies. Autoflowering Cannabis plants show many of the same symptoms as do tomatoes. You can find them depicted by searching the Internet.
As with pests, preventing nutrient deficiencies is much better than having to correct the nutrient balance in your soil, especially while trying to grow a plant in it. Corrections take time, depending on the nutrient, and you may not have enough time to be effective with these fast-growing plants. For this reason, it is important to use the absolute best soil you can find. Either it should be already tested, or you should test it yourself to make sure it is not deficient in any of the essential nutrients.
A great thing about growing Autoflowering Cannabis is that it doesn’t take much soil mix. This means you can afford to buy the best, or you can make your own best mix. It also means you should toss it into your compost pile or into your gardens when you finish a crop, as you can afford to start over with new, fresh, fully nutrient-filled soil.
Remember that soil pH is important when it comes to nutrient availability. Ideally it should be between 5.5 and 6.5. If you buy your soil, chances are this is the range it is in. In particular, if the pH is too high, iron, zinc, copper, boron, and manganese become locked up. If the pH is too low, it is phosphorus, calcium, and magnesium that are unavailable. Testing soil pH is easy and inexpensive.
Finally, the use of cover crops can help keep the soil food web functioning and add nutrients, especially nitrogen, to your soils. Some will also fight off or trap pests. My favorite is white sweet clover. Most other common cover crops are too big for Autoflowering Cannabis. It is best to start these plants early so they are established when you plant your Autoflowering seedlings.
In addition to pests and nutrient deficiencies, there are a few other common problems you should be aware of when growing Autoflowering Cannabis. These are the same problems you encounter growing tomatoes and vegetables, so they shouldn’t come as a surprise to the experienced gardener. Still, it doesn’t hurt to give you a reminder.
This is particularly a problem with seedlings. Too much water literally suffocates the roots. Too little and the plant cannot take up nutrients and may not be able to maintain turgor (or stiffness), causing it to wilt before it dies. Keep the soil surface slightly moist until the second or third set of leaves appears. Then let the plant tell you what it needs.
Autoflowering Cannabis is negatively impacted by both too high and too low humidity and temperature. Plants become stressed and stop growing. THC production is lowered.
The ideal temperature for growing Autoflowers is 26°C (78°F). You can vary this a bit, but once you hit 32°C (90°F) and above, plants slow and stop growing. At the other end of the spectrum, Autoflowering Cannabis can survive at temperatures around 7°C (45°F), but they may change color at lower temperatures, taking on a dark reddish hue. They also won’t grow very well.
Autoflowering Cannabis seedlings will stretch and elongate unnaturally when the light is not strong enough. This is a natural response for any plant, but these grow so fast, it is accentuated. When branches develop, they are hard to support on skinny stems. It is important to give your plants as high a quality of light as you can.
Sometimes Autoflowering Cannabis seeds won’t germinate. And when they do, sometimes, when they are sold as feminized, they produce male plants instead of just females. These seeds are expensive. If either of these problems happens, try to retrieve your money from the vendor who sold them. For failed germination, also try soaking them in a 4-to-1 water to regular 3% hydrogen peroxide mix. Some believe this will break the seed hull, while others contend it works because it kills harmful bacteria that prevent germination.
When males appear from a packet of feminized seed, there isn’t anything you can do to change things. Let the supplier know and consider trying to breed your own plants using the male pollen. There is no guarantee the progeny will carry the autoflowering gene, but it might be fun to try your hand at breeding since you have some male pollen.
No plant likes its roots to sit in water. If your soil won’t drain, your plant will slow and eventually die. Increase air circulation. By the same token, soil can drain too fast and plants won’t get nutrients. Consider carefully removing the plant without disturbing its roots and placing it into better soil.
If you are an experienced gardener, there is really nothing new to learn when it comes to pests and protecting your plants. For the most part, you will already know what to do. And, with any luck, you won’t be tested.
Finally, if something goes wrong with your plant, it is not worth risking your health trying to fix things. This is a plant that you probably plan to ingest. There is no place for dangerous chemicals. If you can’t fix things safely using organics, then toss the plant. It goes without saying that this is a hobby. Keep it a safe one.
