​Back in 2015, 2 years into growing a large garden at my current property, I wrote a post about the early signs of tomato-potato psyllid infestation, with lots of great photos for easy identification, and info about the pest and how it had affected my garden etc. I'd encourage you to stop and read that article first, then come back here. Unless you know what to look for, most folk don't realise they have a problem until it's way too late. The below pics can be seen more clearly on the above post. 

Since I wrote that article, I have learned a great deal. At the time, overcoming psyllid seemed a very difficult proposition, and the chances of getting decent crops of potatoes, tomatoes, peppers, capsicum, eggplant, tamarillos, cape gooseberries or even kumara (all things affected by TPP) without extreme measures seemed remote. However, armed with a garden diary, good observation skills, some research skills, patience and willingness to experiment, within 3 years I got to the point where TPP was no longer of any real concern to me in my garden. For example, last season, I harvested 30kg of large potatoes from a 3x1 metre plot - using no sprays, covers or treatments of any kind. I harvested 80kg of tomatoes from a 4x1m bed, and more from my greenhouse. And so on.

I will outline the things that I have tried/done, and what has worked for me. Note that these are things that worked for ME - there is no guarantee all the same things will be successful for you, but the following should give you some food for thought and a starting place in figuring out what does work for you. Your garden, your local climate and personal microclimate, financial resources, willingness/ability to use certain measures etc, will all affect the options and outcomes. 

The main point of this article is to give you hope! Having your crops wiped out by psyllid one year does not mean that they are forever doomed! 

In late 2012, I decided to start growing an edible garden here. I set an audacious goal - to grow 1000kg of food within 12 months. I had almost no established gardens, limited resources, lots of hungry mouths, and multiple food allergies in the family - these things were a big part of my motivation, and setting a big goal is how I know I make the most progress. I documented that journey in early blog pages. Part of the "rules" I set to help me make this happen included keeping a detailed garden diary, which I did - including what was planted, when and where, how it did, the weights of all harvests, moon cycles, weather patterns, temperatures, and other observations. I haven't kept quite such a detailed diary since, but the process of doing it taught me a lot, gave me many reference points to refer back to, and my later diaries were very helpful in multiple ways. One of the best things about keeping a diary is that it helps force/focus you to make and record specific observations, and give you records you can look back upon to compare. One of my other rules was to "give anything a go" - if I was given it or could source something free or cheap, I'd have a go at growing or using it, not worrying about the "rules" around how to go about it unduly (as my perfectionist tendencies could otherwise lead to procrastination, and less growing). 

One of the experimental crops I grew in early 2013 was no-dig potatoes. I mowed a patch of lawn, laid down newspaper, spread a little compost, set out the seed potatoes, covered in more compost and mulched thickly with hay. They seemed to grow well, until the early part of the year, when they all suddenly died off very quickly, and the resulting crop was only marble sized spuds. I put this down at the time to the method not working well, but in hindsight later, I realised this crop was very likely infested by TPP, something I didn't hear anything about until over a year later. Sudden yellowing of leaves and only tiny potatoes are a couple of the classic signs of some psyllid-borne disease. I find with psyllid, until folk know what to look for, most don't recognise it (which is why I wrote my post with lots of pics linked above). 

While there are actually lots of different psyllids, with different host plants, many of which have been around for a long time in NZ, tomato-potato psyllid is a relative newcomer, thought to have arrived here in about 2005. It has since spread around the country, feasting on crops from the Solanaceae and Convolvulaceae plant families, and overwintering on cold-hardy types of these and a few selected other species. For the purposes of this article, whenever I refer to psyllid or TPP, I'm referring to tomato-potato psyllid. 

By late 2013 my fledging new garden was well established, and for the 2013-2014 summer I planted several beds in various varieties of tomatoes, keen to grow plenty for preserving as well as eating fresh. They were all doing well, as was the big patch of spuds I had growing nearby, until on the 8th of Jan 2014 I noticed a small lesion on one potato plant...subsequent investigation led me to identify TPP. By March 2014, pretty much all the spuds and tomatoes were a write off. For more see the info and photos later in the article HERE. 

In the process of trying to stop the psyllid that year, I tried:

• Removing and burning leaves with any bugs on them. The larvae don't move fast, but the adults are tiny, airbourne and leap about very quickly. The eggs are also minute and you only have to miss a couple.....so while this helped slow them slightly, it was pretty much a losing battle from the get-go. 
• Remove and destroy leaves with signs of disease. The TPP are sucking insects, which can weaken a plant, but their biggest threat is that they carry certain infections which are injected into the plants by their sucking mouthpieces, quickly spreading throughout the plant and making it sick. Removing some leaves will not change the systemic disease. 
• Spray with Maverick - the only spray at the time claiming to be effective against psyllid. This knocked back the population following each spray, but they soon recovered. I would have had to spray every 2 weeks throughout the season - and since my aim was to grow organic food, as free of chemicals and sprays etc as possible, this didn't fit with my whole reason for growing my own, so I stopped doing it. Others use different sprays - but the situation is the same - you have to keep doing it. 
• Use neem granules and sprays and/or pyrethrum and/or diatomaceous earth - like the synthetic sprays, the effect was temporary. And with some research, I am not convinced that these products are wise to use on edible crops - neem comes with warning labels not to do so. They are also harmful to beneficial organisms. So I stopped using those too. 
• Encouraging predatory insects - by avoiding sprays, growing lots of flowers etc etc. Both lacewings and ladybugs moved in and did feed on the larvae, though it was later in the process by the time their numbers built up, and the plants were already too sick to be really saved. It gave me new respect for the role of beneficial insects in the garden though, which I carried through to subsequent garden seasons, with very positive results not just against TPP but other pests as well. 
• I read about Wondermesh, a type of fine quarantine cloth intended to protect crops from TPP (among other things), and ordered some to try using on subsequent crops, though obviously it was too late for these crops. Once the plants are infested by either the bugs or the diseases they bring, covering them would only create a nice haven for the bugs to flourish in, and speed the demise of your plants. Mesh needs to be used to exclude them from ever reaching the plant in the first place. More on that below. 

In early 2015, I had a different bed in my garden planted with some tomatoes, mostly to see what would happen. Sure enough, they got TPP as well - which led to the article I wrote documenting them. I ended up initially removing the worst affected plant, and trying to control it manually on the others, to see what would happen. The outcomes for these plants weren't good, and I ended up removing all of them. 

However, of more interest, at the same time I happened to be doing an experiment in my glasshouse, growing 25 tomatoes plants in buckets (to see what growing medium was best). I took no measures against TPP to protect those plants, and yet NONE of them ever got TPP. Just outside the glasshouse were other potted plants of capsicum, kumara etc, all of which got TPP. The glasshouse is home-made from recycled windows, and all summer I kept the doors and windows open to prevent overheating. Yet no plants insider the glasshouse ever got TPP. I did a little research and concluded that the high temps in the glasshouse (despite the open windows) were sufficient to either make it a place they didn't want to venture in the first place, or to disrupt their breeding cycle. I did have other pests in the greenhouse - especially green looper caterpillars - but observed the predatory insects that were moving in and controlling them, so made a point of also planting in there to encourage such friends - providing them with food, water, shelter etc etc. Predatory wasps, praying mantis, ladybugs, lacewings, harvestmen, hoverflies and more all did a great job of controlling various bugs in my greenhouse. 

I've grown tomatoes and related crops in my glasshouse every year since, and never, ever had a psyllid problem on any of them. 

​Meanwhile, out in the garden I decided to plant potatoes in half-barrels - again I was experimenting with different varieties etc - and to cover the barrels in Wondermesh to keep out TPP.  Unfortunately, as the plants grew taller and taller, the mesh was harder to anchor down, and our high winds lifted it a number of times - ultimately those plants did get psyllid, though later in the season. I had ok-ish harvests from them, but nothing to write home about. 

I have neighbours who are professional gardeners, and who grows a lot of their own food, and has done so for decades. He told me many times that it was "impossible" to grow good potatoes in our soils, and given the space they take up etc, I was becoming disinclined to put much time or effort into growing spuds for a while. However, in my quest to overcome TPP in other crops, I did keep researching for options. 

​One day I stumbled across a research article looking at the effects of TPP-related bacterial infection on the growing of commercial potato crops. (Unfortunately I can't find the original article to link it here at this time). The point I noticed in the report was that when a potato crop has been infected by the Liberibacter disease which psyllid carry, and then potatoes from that crop are then replanted to grow subsequent crops, that these future crops are found (by testing) to have traces of the bacterium in them, but about 90% of the resulting potatoes will be asymptomatic - meaning that there will be little to no evidence of yellowing leaves, poor crops or zebra-striping (the horrible browning in the spuds that makes them look and taste awful) etc. It's as if the plant is immune. Hmmm....if 90% of potatoes were unaffected, then that would mean just throwing out about 1 spud in 10. Ah-hah! I felt an experiment coming on.....

So, I started with some bought potatoes (as I didn't have any saved spuds) as well as some Māori potatoes my neighbour gave me. I grew these in the garden, without protection, starting them earlier in the season to allow some (hopefully) reasonable growth before TPP hit, which it inevitably did. After the crop died off, I harvested spuds and replanted them. Every year since, I have kept these crops going - harvesting and replanting my own potatoes, and the results have been fascinating! What I have observed is:

• Subsequent crops have grown well. In the first couple of seasons, I noted some mild infestations with TPP - but they would be there one day, and gone a couple of days later - instead of a rapidly building population of the bugs, I would notice a few on a leaf or two, and then they would simply vanish, and the plants would continue to flourish. The last few years I haven't been able to find any bugs on the plants at all. 
• One year, a tomato plant popped up in the middle of the spud patch - likely from a seed in the homemade compost I had spread. I left it there to see what would happen. The plant got quite big, but then got completely hammered by TPP while the spuds all around it sailed on, unaffected. 
• The longer I grow spuds in the SAME location, the better they do. Each season I replant the BEST potatoes after harvesting the crop, burying them in the ground and covering with compost and my usual mix of dolomite (for strong cell walls), organic blood and bone, and sulfate of potash. During the season I mulch/cover with lawn clippings. Watering helps too - you get bigger spuds if they are well watered (or there is plenty of rain). I expanded some extra spuds to a new bed this season, and they're not looking anywhere near as grand - though this will improve in time. I grow 5 varieties - as these are the ones I particularly like or do particularly well for me - no longer bothering with others. 
• Meanwhile, my neighbour, once I taught him what TPP was, realised his garden has been infested annually, and has busily sprayed his crops every year, and every year complained about how badly they do. When I dug up 30kg of beautiful big spuds this year from a 3x1m plot and showed him, he finally decided he'd try things my way - I've given him some of my left over seed potato to plant and look forward to seeing how he does with them. 
• I acknowledge that, if my plants are still carrying traces of the bacterium (no way of knowing without scientific testing), then they can potentially be a source of that bacterium to be picked up by any TPP that visit my plants and then move on to other crops. But after considering this and weighing it up, I decided that I can live with that - TPP is all around us (I live in a small town) - and the bugs will get it from other sources; my plants may or may not still have any absorbable bacteria in them, but seem to be ignored by the TPP anyway now. Plus I can actually grow potatoes to eat. 

So, I grow potatoes without any protective measures, from saved/replanted spuds from my own crops, and they are effectively immune to TPP. 

​Another often recommended tip is to grow crops as early as possible in the season, to avoid the peak psyllid times (they only really proliferate once temps get higher, which in my garden is January onwards). However, where I am, it's too cold to plant out tomatoes etc until late November at the earliest, and so this has not been an effective strategy for me, for the most part. If you're in other parts of the country, however, it's worth bearing in mind. Growing tomatoes and related plants early or late in the season may be a way to avoid the worst effects of psyllid. 

Another thing I did, though it was mostly accidental to start with, was grow bush tomatoes in the garden, under Wondermesh. This started because I had all that mesh I'd bought, and wanted to put it to use. I set up a garden bed one spring with metal hoops over it, covered in mesh, and planted brassicas and beetroot under it, figuring it would give them a little protection from late frosts that would slow their growth and would also prevent white butterflies once they started up. Turned out that it created a most wonderful microclimate which those plants thrived in, and I started harvesting good sized heads of brassicas within 6-8 weeks! 

More to the point for the focus of this article, I happened to have planted a couple of Russian Silvery Fir bush tomatoes at one end under the mesh. I'd been trying to grow these for several years  - every year they'd start off great then turn their toes up for no apparent reason quite suddenly. I'd tried them in the greenhouse, in buckets, in the ground, outside etc. They are a pretty plant with very fine fern-like leaves compared to other tomatoes, and I concluded they were prima donnas. I was giving them one last shot that year before tossing the rest of the seed out, and happened to have some space at the end of the row under the mesh, so bunged a couple of plants in. Well, they LOVED it! They grew and flourished and I was picking bowl after bowl of large, juicy fruit from them. 

Growing vining (indeterminate) varieties of tomatoes under mesh is a bit tricky - unless one manages to build an entire, mesh covered, walk-in structure (believe me, I've wanted to!), then there are issues for vining tomatoes of needing a set up where the plants can be regularly accessed for training and pruning as well as harvest, having the height for their stakes/trellis or whatever, and not lifting the mesh often for access, potentially allowing TPP in. Yes, you can potentially just grow them on the ground, with mesh over, and let them do their thing, but I find slugs and snails are very grateful for all the juicy fruit lying about, and I'm not keen on that. So, I was sticking to growing vining tomatoes in my greenhouse. 

However, bush type (determinate) tomatoes, only grow to a certain height, don't need pruning and training (though do need some support for heavier fruit types) etc - so they are perfect to grow under mesh. 

Every year since the above, I've grown Silvery Fir bush tomatoes under mesh in my garden. The last 2 seasons I harvested 94kg from 14 plants and 80kg from 12 plants respectively (each in a bed 1.25m wide by about 3m long). I've developed a set up where I have horizontal steel mesh they can grow up and through, so that once the fruit form, the weight of the plants lays them down over the mesh but keeps the fruit off the ground, with the whole lot under steel hoops about a metre or so high, covered in mesh which is weighted down on the sides and ends. I only need to lift the lower part in sections a couple of times to pull weeds from around the base of the plants, and then uncover later in the season when I begin harvesting (and recover between pickings). 

I will continue to grow bush type tomatoes under mesh covered hoops in my garden - where they flourish in the microclimate and are protected from both pests and birds. The one caveat on that is this - if aphids or whitefly get in under the mesh, then they can quickly get out of control since their predators can't reach them. I don't usually find this a problem on the tomatoes, but it is for brassicas. Anyway, I've started adding a few sticky yellow cards hung from the top rails under the mesh to the beds to catch any small pests flying about before they become a problem. 

After discovering TPP in my garden in late 2013, I had about 3 really bad years where it seemed no matter what I did, everything (related) was wiped out by these voracious pests. But then it seemed as if they were no longer a problem. For a bit I imagined they'd just moved on from my garden, but that didn't make sense since my neighbour had lots of them, and other gardeners around town were becoming familiar with and identifying the pest everywhere. It took me a while to realise it was because of the cumulative effect of the changes I was making that tomato-potato psyllid were simply not a big deal for me anymore. Yes, they're still there, and yes, if I set out vulnerable crops in the garden without any measures of protection, it's likely to be an issue. But I don't do that, and am no longer particularly concerned by them. What I do do (and plan to do) is:

• ​Continue to grow potatoes from my own saved spuds each year - as they are immune. If I want to introduce a new variety, I will do so, accepting that the first year's crop will be "sacrificial" and that I will then build up healthy crops in subsequent seasons. 
• Continue to grow bush tomatoes under mesh in my garden, producing enough for our preserving needs. Because bush tomatoes produce more or less all at once, rather than slowly over the season, this also means only needing to do several harvests over a few weeks rather than daily for a prolonged time, which would be inconvenient under the mesh. 
• Grow vining tomatoes for fresh picking/eating in the glasshouse. 
• Grow capsicums, eggplants, pepino etc in the glasshouse. I may also plant some in the garden, under mesh, though probably not until next year, as life mean I'm doing limited gardening this season. 
• I grow kumara in containers outdoors and don't protect them - while TPP will target them, they seem to do limited damage with this crop, so it's not worth fussing about. 
• Diligently remove nightshades and other weeds that host TPP and survive winter frosts in my garden. 
• Continue to plant herbs and flowers and provide habitat etc that supports and attracts beneficial organisms. 
• Continue to feed my garden beds with compost, mulches, and selected natural additives, while limiting digging, to enhance and protect soil and microbes and therefore plant health and resistance to pests and diseases. 
• Avoid spraying, as this is harmful to beneficials as well as pests. The only spray I use is a natural biological agent against codling moth in early summer. 
• Continue to spend time observing and experimenting - so that I can note what works and repeat it, and what doesn't and change it. 

Tomato-potato psyllid are a major pest for gardeners. However, by learning to understand this pest (know thy enemy!) and modifying some of your gardening techniques and choices, it, like any other major pest, can be overcome - or at least controlled to where it's no longer causing you despair, without resorting to lots of chemicals or other drastic options. Observation and applying what works are two important tools in the garden - and the goal should be to make life easier, not harder, for yourself, while producing lots of yummy, healthy food. 

TPP does not have to wreck your garden or your sanity! So hang in there, try some new ideas, and see how it goes. As I have found, there is hope after TPP!

Whenever gardeners ask what's eating their brassicas*, the inevitable answer is, white butterfly caterpillars. But it might actually be something else..... (*brassicas include cabbages, brussel sprouts, cauliflowers, broccoli, radishes, kale, turnips, mustard greens and so on). 

Most people are familiar with the sight of white butterflies flitting around their gardens in summer, and if they grow vegetables, will soon learn these dastardly critters like to lay their eggs only on brassicas, and their resulting larvae (green caterpillars) can munch a LOT of holes in the plants very quickly, devestating young plants, and hiding within the heads of more mature ones - is there anything more frustrating than trying to remove those green caterpillars from amongs the florets of your precious broccoli? 

However, there is another flying pest which also lays eggs only on brassicas, and whose green caterpillars also eat the plants...that is, the diamondback moth. Much smaller and more inconspicuous than the white butterfly, and of course, nocturnal, many gardeners seem to be unaware of this alternative source of pesky caterpillars. Why does it matter which one is giving you problems? Because measures taken against white butterflies won't necessarily keep out diamondback moths, and the moths also will be active at times when white butterflies may not. 

​So, first, let's check out some pictures of both species side by side...note that these are not to scale - pics to show you how small the diamondback is lower down...

The diamondback moth is much tinier than the white butterfly, but the caterpillars are not dreadfully dissimilar. The most obvious evidence that your culprit is the diamondback is the presence of the loosely spun silk mesh cocoons on the undersides of the leaves, where the caterpillars pupate. 

I also have noticed that in my garden, white butterflies are conspicously absent so far this season - I've seen one fly through - but there are holes in my brassicas, and upon closer inspection, evidence of the diamondback's offspring. The diamondback moth is active in cooler conditions than the white butterfly, so may begin damaging your crops much earlier.

In fact, the diamondback moth does not have a pupal resting stage during winter - it's lifecycles continue all year long, but at a speed determined by climate conditions. So over the colder months, the life cyle may take 80 or so days, whereas in summer it will only take 30-35 days to complete a cycle from egg to mature moth. The time spent as larvae is greatly influenced by temperature, varying from 2-7 weeks. It will complete 6-7 life cycles in a year.

White butterflies on the other hand, are more effected by colder weather - they may complete as many as 5-6 lifecycles in the far north per year, but only about 3 in the lower North Island/upper South and 2 in the deep south. The cooler weather of autumn triggers their pupa to go into diapause, and they remain their chyralis stage for 3-5 months.

If one hasn't actually seen a diamondback moth and identified it, it is hard to appreciate just how tiny these never-the-less potentially devestating pests are. So here are some pics of one I caught in a jar to show you - they are only around 6mm long, and at rest have their wings folded down along their bodies, leaving a very streamlined shape that about the size of a small darning needle. Bear that in mind when considering mesh to exclude pests from your crops....

A common organic method of keeping white butterflies off brassicas is to use nets. And it works well - so long as the mesh is small enough to exclude BOTH white butterflies and their much smaller counterpart, the diamondback. That's the main reason I've written this post really - so you can know your enemies and aren't fooled into excluding one but admitting the other. Exclusion by netting is THE best protection - just make sure the barrier is well anchored down on all sides, as well as being of fine enough material - I've known white butterflies to squeeze through the most unlikely gaps! Also, choose netting that will minimally block light, or your plants will become leggy and weaker. You need fine mesh to keep out the diamondbacks - see more on mesh below.

B.t and pyrethrins are other organic control methods that can be effective. 

Parasitic and predatory wasps, praying mantises, lacewings, ladybugs, spider and birds are all natural predators of diamondback moth larvae, and in some cases, the adult moth. White butterfly caterpillars have a trick up their sleeve though - they accumulate mustard oils from their host brassica plants in their bodies, making them unpalatable to most predators, though some insectavorous birds will still eat them. 

Encourage natural predators by growing a variety of flowering plants in your garden, and by providing natural habitats. 

Nasturtiums are often planted as a trap crop - they lure white butterflies away from the brassicas. Nasturtiums are the only non-brassica plant on which white butterflies will lay their eggs. The plants can then be removed and composted (or given to chickens to pick through), eggs, caterpillars and all. 

Learn to recognise the pupal stage of both species - and if you spot any at any time of the year, destroy them. The diamondback pupa will be on the brassicas - but the white butterflies seem to form their crysalises elsewhere; at least, I've never seen them on my broccoli, no matter how much they've munched the leaves! 

In the 2016/2017 summer, I grew a bed full of broccoli in my garden, with no covers or protection. I planted them on the 5th of January, and was able to harvest yummy broccoli off those plants from late February right through until September, as they continued to grow abundant side shoots after the main heads were harvested. By September my June planted crops were producing more than we could eat, so I left those ones to flower and seed.

The numbers of caterpillars did build up a bit in late Feb/early March to the point of exercising some digital control a couple of times (literally twice - that's all), but otherwise they were kept in check by the predatory beneficials to the point where they were of no major concern. Now, it was a colder, wetter summer than usual, so the white butterflies in particular were slower to get going, but the same principals of predation apply at any time of the year where the critters concerned are reproducing.

So which beneficial keep my cabbage pests under control? Primarily: praying mantises, predatory and parasitic wasps, harvestmen, spiders. Maybe birds, but I've not caught them in action to be sure. How does one encourage such critters in the garden? In the same way as all critters you want: provide food, water, shelter and breeding habitat. 

How to do that is not so much about focussing on these particular species, but by providing a beneficial-friendly-overall garden environment which leads to an increase in all sorts of beneficials, including these ones. Here are some of the ways I do this:

• Use NO sprays or poisons - even "natural" ones are generally harmful to beneficial as well as pest critters
• Plant a wide variety of flowers and flowering plants - the more the merrier. I major on edibles, but include others as well. My list is very long and I will post it elsewhere, but as a "sampler" I include phacelia, borage, rosemary, lavendar, buckwheat, calendula, marigolds, cosmos, zinnias, nasturtiums, lots of herbs like oregano and thyme, flowering fruit and vegetable plants etc. 
• Provide water - shallow bowls with stones in them for bees and others to land on, and fresh water
• Leave some areas of the garden "wild"- abundant in thick and varied growth, which provides habitat and shelter
• Observe where your beneficials tend to overwinter, and provide and leave plants for this purpose. Eg ladybugs seem to particularly like to overwinter on spent corn stalks and under large silverbeet leaves. 
• Learn about breeding needs - eg drone flys, excellent pollinators, breed in water heavy in organic matter - so a bucket full of manure and water let sitting in a corner, with stalky material draped over the side to make an easy exit ramp for the rat-tailled maggots, encourages their breeding. On the other hand, I do draw the line at paper and German or commons wasps having nests in my garden - those I will kill. The odd wasp flying in and eating my bugs I'm good with, but too many where I'm working, wanting to protect their nests, is not ok for me - I'm allergic to the stings. 
• Be willing to let some *pests* live in your garden - without those pests as food, the predators won't come. It takes a full and abundant ecosystem to properly support all things in balance. 
• Never deliberately kill a species until you have identified it - learn to recognise the goodies and the baddies. And make informed choices. Eg, I know that the South African praying mantis is displacing NZ native mantises, and some would say to kill them. However, they are a major provider of pest control in my garden, and I've never seen a native here anyway. So I am happy to have them. 

Paper wasps (left), common wasps (centre) and German wasps (right) are all common in NZ, and predate on caterpillars of all kinds, as well as a number of other foods. However, they have their downsides. I don't let them have nests in my garden, but am happy for them to eat the catepillars.

If you aren't willing to put up with ANY holes and caterpillars in your brassicas, then suitable mesh is the way to go. Old net curtains are a popular choice. A finer grade bird netting may keep out white butterflies, but it won't keep out diamondbacks who are very small. Any netting needs to be secured so that the leaves don't touch it - these determined pests will happily lay eggs through netting, even dropping their eggs a short way onto leaves. 

For completely keeping the pests away from your brassicas, the best choice is Wondermesh or a similar quarantine mesh. I bought a good amount of it from Lincoln's BHU, where they have done extensive trials using it to exclude psyllid from tomatoes and potatoes, and found it to also reduce incidence of blight and increase harvest size. With a 10 year life span, and allowing water and light to reach the plants, I find this fine mesh very useful in a number of applications in my garden. In the 2017/2018 summer, I am overhauling a large segment of my garden, and in the process am aware of the fact I am temporarily reducing plants and habitat that attracts beneficials. Therefore, this summer's brassica crop is under Wondermesh. Care needs to be taken to secure the mesh flat to the ground on all sides with no gaps, or the sneaky white butterflies will crawl in anyway (diamondbacks, despite their smaller size, seem to be less sneaky). Here's a couple of pics of my cabbages, cauli, broccoli, and kohl rabi under the mesh - interplanted with beetroot, and a couple of tomatoes at one end. 

Another way to (theoretically) avoid pests in the brassicas, is the timing of your planting. However, to reap the rewards of ready-to-eat brassicas for winter, one has to plant them out in about Feb/March in most areas, when the pests are at their peak. One can plant seedlings in Sept/Oct and eat the results before the numbers of white butterflies increase in about January, however diamondbacks are active over a longer season as they can cope with cooler conditions. 

So, yes, these pests are not active in winter, but that is when the plants also grow their slowest or enter near dormancy (brassicas are essentially dormant when temps are below 10C). So to get good results at that time of year, one really needs to grow them in a greenhouse. See post on effect of winter temps on brassicas HERE.

Otherwise, some kind of protection from pests is needed - it's the gardener's choice what it will be. I prefer a combination of encouraging beneficials, timing some crops to avoid peak pest seasons, and using mesh covers as necessary.