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Pest identification and control

This paper shows how to identify the eight pests that cause the most damage to cannabis, and how to keep their numbers small. It gives the life cycle of each pest, how to monitor it, and the biological controls and treatments that you can apply. Use it with the IPM decision procedure.

Plant health8 figures8 sources~18 min to read

In this paper

01 Purpose and scope 02 Definitions 03 Evidence and limitations 04 Pests that remove sap from leaves: spider mites, thrips, aphids, and whiteflies 05 Pests that you do not see: russet and broad mites, fungus gnats, root aphids, and caterpillars 06 Pest monitoring and scouting each week 07 Biological controls and treatments for each pest 08 Troubleshooting 09 Expected results and limitations 10 References

Start here

Purpose and scope

Jurisdiction

The biocontrol agents and the rates in this paper are examples only. Make sure that the regulations in your area let you use each agent, and that a supplier has it. If you are in NZ, examine the regulations of HSNO and MPI before you release an agent.

This paper is for a new grower. It shows how to identify the eight groups of pests that most frequently cause damage to cannabis, and how to keep their numbers small. The groups are: spider mites, russet and broad mites, thrips, fungus gnats, aphids and root aphids, whitefly, and caterpillars.

For each pest, the paper shows how it looks, how quickly its population increases, and how to monitor it. The paper also shows how to apply a treatment to each pest, with biological controls (organisms) and with sprays.

Use this paper with the IPM SOP. The IPM SOP is a different paper with the decision procedure. It tells you when to apply a treatment and which treatment to use. Read this paper to identify the pests. Read the IPM SOP to operate the program.

The paper names 8 pest groups. For each group, it gives the signs, the life cycle, the monitoring, the biocontrol, and the treatment
The paper is for a new grower. Each term has a definition where the term first occurs
Use this paper with the IPM SOP (the decision procedure). This paper is the reference for identification
Prevention and detection at the start are the most important tasks, because each pest increases in number more quickly than you can spray

Short information on each pest. The cycle times are the fastest times in warm rooms. They become shorter when the temperature increases.^[1]
Pest	Where it eats	Sign of the pest	Fastest cycle	Primary biocontrol
Spider mites	Bottom surface of the leaf	Thin webbing and pale stippling (30x loupe)	Approximately 3 days	Phytoseiulus persimilis
Russet mites and broad mites	Growing tips	New growth that is cupped, glossy, and twisted (60-100x necessary)	Approximately 1 week	Amblyseius swirskii
Thrips	Leaf surface	Silver streaks and black frass dots	Approximately 1-2 weeks	Amblyseius cucumeris
Fungus gnats	Roots / wet media	Dark flies above the medium and larvae in the soil	Approximately 2-3 weeks	Steinernema feltiae
Aphids	New growth	Soft groups of aphids, white molted skins, and honeydew	Approximately 1 week	Aphidius parasitoid wasps
Root aphids	Crown / roots	Yellow leaves, and you see no pest in the canopy	Approximately 1-2 weeks	Beneficial nematodes
Whitefly	Bottom surface of the leaf	A large group of white flies in the air when you move the plant	Approximately 2-3 weeks	Encarsia / Eretmocerus
Caterpillars	Flowers / buds	Frass and holes. They cause bud rot.	Approximately 2-3 weeks	Bacillus thuringiensis (Btk)

Figure 1. The eight pest groups, where to look, the signs to look for, and the first biocontrol agent to use.

Terms

Definitions

This section gives the terms that occur many times in this paper and in the IPM SOP. It is not necessary to know the terms at this time, because each term occurs again.

IPM (Integrated Pest Management)A method with layers: prevention, monitoring, biological controls, and sprays for one specified pest. IPM does not use a calendar to apply sprays.

Biocontrol / beneficialAn organism that you release to eat or infect the pest. It can be a predator (for example, a predatory mite), a parasitoid wasp, or a microbe (a fungus or a bacterium).

Preventative and curativePreventative agents are in the room before the pests come. They keep the pest population small. Curative agents decrease an outbreak that is in progress.

Life cycle / generation timeThe time from the egg to the adult that makes eggs. In warm, dry rooms, this time is less than one week for mites. As a result, a small area of mites becomes a problem in all the crop quickly.

Loupe / scopeA hand loupe with 30x magnification shows spider mites. Russet mites and broad mites are smaller than one millimeter. 60-100x magnification is necessary to see them. Before you apply a treatment, use 60–100× to make sure that you identify the pest correctly. The symptoms are the same as the symptoms of heat stress (leaf curl) and tipburn.

Frass, honeydew, stipplingFrass is the waste of the pest. Honeydew is a sticky liquid with sugar that sap-suckers make as waste. Stippling is the group of thin, pale marks that pests make on a leaf when they eat.

Action thresholdThe number of pests at which you stop to monitor and start to apply a treatment. Each facility sets the action threshold for the facility, and it is not the same for all facilities. Refer to the IPM SOP.

Figure 2. A preventative biocontrol agent in the room at the start keeps the population low and stable. If you wait until the threshold, the population is large when you apply the treatment, and it increases quickly.^[5]

Terms in the facility Nano Banana 2

Quality of the information

Evidence and limitations

Three types of information

We want each paper to be correct. Thus we examine each paper for information that is not solid. This information comes from the view of one grower, from a small number of sources, or from grower methods that have no controlled test. We identify this information, and we do not show it as solid.

Frequently there is no paper for the decision that you must make. Then we use the reports of other growers and the methods that work in the rooms that we know. This information can help you, but it is not the result of a laboratory test. Use the methods that work for your plants, for your room and for your meters. If a table does not agree with your crop, use the data from your crop and record the difference.

Solid

Tests of plants, specifications or many sources that agree show that the information is correct

Before you apply a treatment, use a loupe or microscope to identify the pest. Different pests can be almost the same visually.
If you know the life cycle of the pest, you can select the correct time for each control.

Grower method

Many growers use this method in their rooms. Start with it, then change it for your room.

The signs of frequent cannabis pests on plants, and the biocontrol agent for each pest where you can use it.

Weak

The view of one grower, a small number of sources, one test, or a method that works in one room

Very short life-cycle times (for example, a life cycle of 3 days) as typical times. These times occur only in conditions that are very hot and dry.
Estimates for the density of sticky traps as the best values that tests show.

If you find an error, make a report. We will correct it. Make the report on GitHub, with the name of the paper and the information that is incorrect. If you have a source, include it: Make a report of an accuracy problem. The regulations, labels and licenses of your area always override each procedure in these papers. The label weak in a paper shows the points where the risk of an error is highest.

The primary pests, part 1

Pests that remove sap from leaves: spider mites, thrips, aphids, and whiteflies

These four pests are sap-suckers. They make holes in the cells of leaves and stems, and they remove sap. As a result, they cause the same damage: pale stippling, changes of shape, and weak growth.^[2] The secondary signs of each pest are different. Use these signs to identify each pest.

Spider mites: stippling on the bottom of the leaf and thin webbing. In hot, dry conditions, the time from egg to adult is frequently approximately one week (in some conditions, less than two weeks). A female frequently makes approximately 100 eggs in its life. The correct times change with the temperature and the host.
Thrips: silver streaks, and frass dots that are small and black. The thrips fall to the medium and become pupae there. Thus sprays on the leaves do not touch one full stage of their life.
Aphids: soft groups on new growth, white molted skins, and honeydew. Black sooty mold starts on the honeydew. Adult aphids can make new aphids, and not eggs. As a result, the population increases very quickly.
Whitefly: small white adults. Their shape is almost the same as the shape of a moth. When you move the plant, a large group of the adults moves into the air. The leaves become equally yellow, and the bottom of the canopy becomes weak.

The cannabis aphid (Phorodon cannabis) is the aphid that is most related to cannabis. At this time, growers know it as a pest in North America.^[3] The same cause applies to all four pests: the environment. Warm and dry conditions make each life cycle shorter. Thus the first method is climate control, and not the spray.

Spider mites

Webbing and thin, pale stippling on the bottom of the leaves. Use a 30x loupe to identify the pest correctly.

Thrips

Silver streaks with black frass dots. The pupae are in the growing medium.

Aphids

New growth with leaf curl, groups of aphids, white molted skins, and sticky honeydew.

Whitefly

Yellow leaves, and white flies that move into the air from the bottom of the leaf when you move the plant.

Figure 3. Four sap-suckers, four different signs of damage. All four pests eat with the same method. Use the secondary signs to identify each pest.

Figure 4. When the room is hotter and drier, the spider mite cycle is faster. The cycle is approximately 3 days in a hot, dry room and almost 3 weeks in a cold room.^[1]

The primary pests, part 2

Pests that you do not see: russet and broad mites, fungus gnats, root aphids, and caterpillars

This group is dangerous because the damage shows before you see the pest. Russet mites (Aculops cannabicola, less than 1 mm, 80-100x necessary) and broad mites (approximately 60x necessary) are too small to see without magnification. They cause cupped, glossy, or ‘wet-looking’ new growth, twisted tops, and growth that stops. Growers frequently think incorrectly that these symptoms show nutrient stress or heat stress.^[6]

Russet mites and broad mites: New growth that is cupped, glossy, and twisted. The mites are smaller than one millimeter, and 60-100x magnification is necessary. Growers easily think that the problem is a nutrient problem.
Fungus gnats: The larvae eat root hairs in wet media. The adults are weak, dark flies above the medium. The larvae let root-rot pathogens go into the roots.
Root aphids: The aphids eat at the crown and at the roots. They cause yellow leaves and growth that stops, and you see no pest in the canopy. Examine the root zone and the bottom of the pot.
Caterpillars and budworms: frass and holes in the flowers. They cause bud rot quickly. Do the scouting at the end of the day, when the larvae eat.

Fungus gnat larvae make plants weaker and cause wounds on roots. The damage and the diseases from the soil have an effect on each other. As a result, a gnat problem in wet media frequently becomes a root-rot problem.^[7] Tests show that cannabis is also a host of the rice root aphid. This aphid is below the ground, and scouting of the canopy does not find it.^[4]

Risk of an incorrect diagnosis

Before you change the feed, use a loupe or scope and examine the roots. Twisted, glossy tops look the same as the symptoms of nutrient burn or heat stress. More feed does not remove mites.

Figure 5. Examine the plant in the position of each pest. If you look only at the middle of the canopy, you do not find these four pests.

Find the pests at the start

Pest monitoring and scouting each week

You cannot keep the population of a pest small if you do not measure it. The most important method that you have is to find the pests at the start. Do a scouting walk each week on the same day. Examine the bottom of the leaves, the growing tips, the flowers, and the root zone. When the rooms become hotter, increase this to two times each week.

Hang yellow sticky cards at the height of the canopy for thrips, whitefly, and fungus gnat adults. As a start point, use a density of approximately one card for each 100 m² (approximately 1,076 ft²). More cards give a better signal. Put the cards for fungus gnats low, near the surface of the medium, where the adults move in the air. Each week, record the number on each card. Then you know the trend and not only one reading.

Do the scouting each week on the same day. When the temperature and the speed of the life cycle increase, examine the plants two times each week
Yellow sticky cards: a minimum of approximately 1 for each 93 m² (1,000 ft²). Put the cards low at the medium for fungus gnats. Put the cards at the height of the canopy for thrips and whitefly
Record the number on each card each week. A trend that increases (not one number) is the alarm
Use a 30x loupe for spider mites and a 60-100x scope for russet mites and broad mites. Examine the bottom of the leaves, the tips, the flowers, and also the roots
Each facility sets the action threshold for the facility. For example, one grower accepts 10-15 thrips/card/week. A different grower, with viruses in the previous crops, accepts less than 5

Figure 6. When you record the number each week, the sticky cards give a trend curve. The slope of the curve, and not one reading, shows when to start the IPM SOP.

Figure 7. A scouting walk with five steps that you can do again. Do the same each time: the same day, the same plants, and the same cards, each week.

Agents to release and sprays to apply

Biological controls and treatments for each pest

Select the correct tool for each pest, and for preventative use or curative use. For spider mites, the specialist predator Phytoseiulus persimilis is the fast curative agent. But the humidity must be more than approximately 60% relative humidity (RH) for this predator. You can use Neoseiulus californicus or Amblyseius swirskii as preventative agents. For thrips, use Amblyseius cucumeris or swirskii at approximately 100-300 mites for each square meter. You usually see the effect after approximately 3 weeks.^[5]

For aphids, use parasitoid wasps of the correct species (Aphidius colemani for green peach aphid and Aphidius matricariae for cannabis aphid) and the fungus Beauveria bassiana, which kills insects. For whitefly, use Encarsia wasps or Eretmocerus wasps, and swirskii. For fungus gnats, apply a drench in the medium with Steinernema feltiae nematodes and the bacterium Bti, approximately each 2 weeks. For caterpillars, use Bacillus thuringiensis kurstaki (Btk). Btk kills only larvae that eat it. Tests on cannabis pests include some of these biopesticides.^[8]

No sulfur in flowering

Do not apply sulfur in flowering. It can cause residue, a bad aroma or flavor, and phytotoxicity on the buds. Predatory mites and micronized sulfur decrease the number of russet mites and broad mites.

Table to select the biocontrol agent. The rates at which you release the agents, and the conditions, are start points. Adjust them for your facility and your supplier.
Pest	Preventative	Curative	Microbial / spray	Important condition
Spider mites	N. californicus / swirskii	P. persimilis	Insecticidal soap, oils	P. persimilis: more than 60% RH is necessary
Russet mites and broad mites	A. swirskii	Predatory mites	Micronized sulfur	No sulfur in flowering
Thrips	cucumeris / swirskii (100-300/m2)	Soil predators for pupae	Beauveria bassiana	Apply to the canopy and also to the medium
Fungus gnats	S. feltiae nematodes	Bti drench (each approximately 2 weeks)	Bti / Gnatrol	Apply the treatment to the wet medium
Aphids	Aphidius wasps	Use the wasp of the correct species	Beauveria bassiana	colemani and matricariae
Root aphids	Beneficial nematodes	Soil drench	Beauveria bassiana	The pest is below the ground. Apply a drench to the roots
Whitefly	Encarsia / Eretmocerus	Add swirskii	Insecticidal soap	The pest continues to occur. Start before the population increases.
Caterpillars	Scouting and Btk at the start	Btk spray	Bacillus thuringiensis (Btk)	The larva must eat it

Figure 8. Select the agent for the pest, and for preventative use or curative use. The time at which you release the agents is more important than the dose. Biocontrol agents increase more quickly than the pests only if you release them before the pests start.

Frequent errors of growers

Troubleshooting

Most large pest problems have their cause in incorrect diagnosis and an incorrect time of treatment, and not in the products. The same errors occur in many facilities. A scope and a calendar prevent all of them.

Symptom	Usual cause	Make sure and correct
Twisted, glossy new growth	Russet mites or broad mites (not nutrients)	Make sure of the cause at 60-100x before you change the feed
Thrips or gnats increase again after you spray	The spray does not touch the pupae or larvae in the soil	Apply the treatment to the medium and also to the canopy, and not only to the leaves
You released biocontrol agents, but the pest population continues to increase	You released the agents after the correct time, when the pest population increased very quickly	Release the agents before the pests come (preventative). Predators cannot increase as quickly as the pest population.
The population of P. persimilis decreases, and the pest mites stay	The room has less than approximately 60% RH. This humidity is incorrect for the agent	Increase the RH, or select a predator for drier air
Residue, or a bad aroma or flavor, at harvest	You used sulfur or strong oils in flowering	Stop the sulfur and the strong oils before bloom starts
The new crop has pests from the first day	You did not do a quarantine of the clones and mother plants	Isolate and examine each plant that comes into the facility

If a treatment has no effect

There are three possible causes. The identification of the pest is incorrect. The treatment did not touch each stage of the life cycle (the stage in the soil also). The environment is not correct for the agent. Most biocontrol that has no effect has one of these three causes.

Figure 9. Do not apply a treatment if you are not sure of the cause. The step to make sure of the cause is between the symptom and the treatment. This step prevents most sprays that are not necessary.

Good results

Expected results and limitations

Usually, you do not remove all the pests. You keep the pest population less than the action threshold, for a long time. Biological control is slow. You usually see the effect on thrips approximately 3 weeks after you release the agents. To stop a cycle of fungus gnats, use traps for the adults and kill the larvae. The time that is necessary is usually 4-8 weeks.^[7]

Prevention is the treatment with the lowest cost. Put each clone that comes into the facility in quarantine and examine it. Keep the mother plants clean (a mother plant with pests makes cuttings with pests). Control the humidity and the airflow. Sanitize the tools and the rooms. Do the scouting each week, and do not stop.

A facility that prevents pests and finds them at the start has much lower costs for curative agents and much less crop loss. A facility that waits for outbreaks and then applies treatments has higher costs and more crop loss.

Usual results

The correct result is a pest population less than the threshold, and not zero pests. Prevention gives clean crops, and sprays that you apply in an emergency do not.
Biological controls are slow, but they continue for a long time. For thrips, you see the effect after approximately 3 weeks. To stop a cycle of fungus gnats, approximately 4-8 weeks are necessary.
Prevention steps: put clones in quarantine, keep mother plants clean, control RH and airflow, sanitize, and do the scouting each week.
A mother plant with pests always gives clones with pests. The mother room is the most important point to examine.

Figure 10. The cost of prevention is stable and small. The cost of curative agents and crop loss is much larger when you wait for outbreaks and then apply treatments.

Compare your results with the thresholds in the IPM SOP. Then you know if the program works correctly. Use good airflow design. It removes the warm areas with high humidity and no air movement where pests are.

References

Ahmed, M. Z., McKenzie, C. L., & Osborne, L. S. (2024). Arthropod and mollusk pests of hemp, Cannabis sativa (Rosales: Cannabaceae), and their indoor management plan in Florida. Journal of Integrated Pest Management, 15(1), 1. https://doi.org/10.1093/jipm/pmad028
Pulkoski, M. A., & Burrack, H. J. (2023). Assessing the impact of piercing-sucking pests on greenhouse-grown industrial hemp (Cannabis sativa L.). Environmental Entomology, 53(1), 1-10. https://doi.org/10.1093/ee/nvad044
Cranshaw, W., Halbert, S. E., Favret, C., Britt, K., & Miller, G. L. (2018). Phorodon cannabis Passerini (Hemiptera: Aphididae), a newly recognized pest in North America found on industrial hemp. Insecta Mundi, 0662, 1-12. https://digitalcommons.unl.edu/insectamundi/1162/
Cranshaw, W., & Wainwright-Evans, S. (2020). Cannabis sativa as a host of rice root aphid (Hemiptera: Aphididae) in North America. Journal of Integrated Pest Management, 11(1), 15. https://doi.org/10.1093/jipm/pmaa008
Lopez, L. (2023). Meet Amblyseius swirskii (Acari: Phytoseiidae): a commonly used predatory mite in vegetable crops. Journal of Integrated Pest Management, 14(1), 20. https://doi.org/10.1093/jipm/pmad018
van Maanen, R., Vila, E., Sabelis, M. W., & Janssen, A. (2010). Biological control of broad mites (Polyphagotarsonemus latus) with the generalist predator Amblyseius swirskii. Experimental and Applied Acarology, 52(1), 29-34. https://doi.org/10.1007/s10493-010-9343-2
Cloyd, R. A. (2015). Ecology of fungus gnats (Bradysia spp.) in greenhouse production systems associated with disease-interactions and alternative management strategies. Insects, 6(2), 325-332. https://doi.org/10.3390/insects6020325
Effects of Selected Biopesticides on Two Arthropod Pests of Cannabis sativa L. in Northeastern Oregon. (2024). Crops, 4(4), 19. https://doi.org/10.3390/crops4040019

Each citation in the paper, for example [1], refers to an item in this list. Each item is a primary source or an instruction from an authority, unless the item shows a different type. The results of cannabis tissue culture change much with the genotype. Before you use the dilutions, hormone doses and local regulations, make sure that they agree with the primary sources.