Seedsman Blog

Pest control: How to identify and eliminate thrips

Growing in soil or organically has lots of benefits and is of course the most natural way to produce cannabis. But as with all natural gardening there’s always a risk of pests and insects that can become a problem if not treated properly. 

Thrips are small crawling invertebrates that love to suck the sugary juices from your cannabis plant mainly through the leaves but also on the stems. The healthier your plants and environment is, the happier the thrips are going to be too. You might think seeing a few flecks of damage will be ok and choose to neglect this symptom, but if not monitored and controlled early and regularly this pest can get out of hand quickly and leave your crop in a really bad state. 

Growing cannabis indoors creates the perfect year round environment for thrips to thrive and create an endless breeding cycle without any natural predators to come and keep things in balance and under control as would be the case outside. 

How do I know if I’ve got thrips? 

The first sign of thrips is small dead or yellow spots appearing on the lower leaves. They can also leave a sheen like sticky trail on the top of the leaves. 

If you turn the leaf over you will find small little crawlers about 1-2mm in length, light in colour and moving around pretty quickly for the little thing that it is.

How did I get thrips in the first place? 

There are a number of ways thrips could have got into your environment. They could have come in through the soil you bought, the rainwater you used, from your clothing after you went for a walk or just brushing past a plant in your garden and then falling off when you went in to check your plants. It could have been from a cutting you took off a friend – but don’t be mad, just let them know and you can tackle the problem together! Team work makes the dream work.

If you regularly walk the dog or are in an outdoor setting with plants, consider changing your clothes before you go into the grow room. Many professional facilities now require staff to shower and put on PPE before they go into the plant rooms.

To get rid of thrips we need to understand their life cycle. 

The life cycle of the thrip is fast, which means they have an ability to quickly multiply before you have a chance to even think about doing something about it. If you have seen some signs, they’re already well under way getting jiggy with it on your plants. 

They have five growth stages, egg, larva, prepupal, pupal and adult. Females when they reach adult size will live for up to 30 days but in that time they will lay 2-10 eggs per day, which means they have a multiplication rate of 60-300x per every one female. 

Each egg takes between around 19 days at 20 degrees, just 13 days at 25 degrees, to transition into an adult. This adult transition phase takes place on the substrate of your pot as the pupal fall to the ground and burrow down slightly when they reach this stage. When they have finished development they find their way back to the food source by climbing up the stem or anything that goes up towards the juicy leafy greens. This is also where they are likely to quickly find a mate and start the whole cycle again, growing larger in numbers every time. 

300 eggs hatching, 50% being female could lead to you having 45,000 thrips munching on your plants in no time and thinking about laying eggs in just a couple of weeks!

Now we understand just how explosive the growth rate of these little thrips are. You can understand the need to act fast AND be persistent with the treatment to ensure breaking the whole cycle. Being complacent and slacking off early could result in the whole cycle restarting from eggs you didn’t think about hatching and it will all happen again and you could be well into flower before you notice just how bad it has got. 

Every bite they take on your plant leaves damage that your plant has to try and repair. All the time it is doing this it is taking energy away from its main purpose of producing beautiful buds that are covered in sticky trichome glands. The plant can’t do both! And if your plant is looking like this….I’m sorry to say, you’ve left it way too late! In the time it will take to properly recover you may as well have cleaned down your grow space and planted some new seeds. 

Natural Predators

The first thing you might want to think about if you are growing completely organically is fighting fire with fire, an eye for an eye and employing the old mother hubbard approach – that is to find another insect that likes eating these insects. But don’t worry, you won’t have to keep finding something bigger to come along and eat the bugs you’ve introduced to treat the thrips! You’ll find that when they can’t find any more thrips to munch on they will just either move on or die off – sorry little helper buddies, that’s nature but we thank you for your sacrifice so we can have some super healthy and fine herbs! 

Three of the most popular natural predators recommended for thrips are the Orius Laevigatus, Amblyseius Cucumeris & Amblyseius Swirskii. Using them in combination will increase their effectiveness and speed. 

Orius will voraciously attack adults and hatchlings on the plants. They are great in veg as they require a long day period in order to be effective or they can’t reproduce, and need replacing more frequently in flower cycles but also, they get stuck to the resin! 

Swirskii & Cucumeris are soil born predators that hunt out the thrips as they try to find a home in the soil to transform from pupa to adult. Cucumeris wait for any pupae making their way down from the plants and stop them finding a space to transform by eating them. This action prevents any further thrips from entering the garden and making their way up to the plants.

Prevention and disruption tactics

The price of predator mites can be expensive and they may not always be available. There are some products on the market that are effective but also many that have chemicals and pesticides in them that are not meant for consumable plants (just ornamental ones). The cannabis grow product market is not strictly regulated and there have been regular occurrences of products containing banned pesticides in them that are neurotoxins to humans, bees and aquatic life. What you put in your body is up to you, but if you’re producing for patients, you really need to avoid these products as they are systemic, meaning they remain in the plant indefinitely and can even permanently contaminate your grow space. 

Saccharopolyspora spinosa is a beneficial bacteria that has a toxic effect on some insects. Two extracts from it Spinosyn A and Spinosyn D are combined to make Spinosad and it is considered organic. This is considered generally safe for consumable plants and is widely used in the agriculture of peppers. It is advised to only use this in veg stages and very early flowering and this is a rule we would advise sticking to for any product. Spinosad causes neurotoxicity to the thrips which makes them have a kind of seizure and then die. Multiple applications are needed in a short space to ensure the breeding cycle is broken.

You cannot use products like spinosad if you  are using natural predators – it will kill them!

If a grow shop sells something under the counter it’s probably best not to use them on your plants for a good reason. 

If you want to keep it as natural as it can get…

A recipe that we’ve used for a while now during the veg stage of growing has been a homemade recipe that you can make for under £5.

Ingredients

  • 3 Hot Chilis, Fresh chopped or dried flakes
  • 3 Fresh Garlic cloves
  • Aloe Vera leaf or gel
  • Lemon Juice
  • Neem Oil (you can buy this locally in afro hair supply shops)
  • Washing up liquid (use an ecologically friendly one so you don’t kill your good bacteria)
  • 1l of water

Method

  1. Take your chilis and garlic and chop them up. 
  1. Take a cup of water from your litre and boil it. Steep your chili and garlic like tea until cool, then strain. 
  1. Squeeze your lemon.
  1. Slice your aloe vera leaf and remove the gel inside. 
  1. Add the aloe, the lemon juice, the lemon and garlic water and add to a blender and blend thoroughly. 
  1. Add a spoon of neem oil and a couple of drops of washing up liquid. 
  1. Add to the rest of the litre. 

We would couple this with adding a fine layer of diatomaceous earth over the tops of your growing substrate. This is microscopically jagged sand that shreds insects like thrips as they break out of or try and cross the soil surface. This is relatively cheap online. 

If you can not acquire any, get some sharp sand and wash it thoroughly to remove any salts that are on there you do not want, then add an inch layer over the top of each pot to prevent the thrips from being able to break through. 

Seedsman

Seedsman

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