They're baaaaack! Early Signs of Tomato-Potato Psyllid Infestation

This evening as I looked over my garden, I saw that my bed of tomato plants, which up until now have been looking robust, green and healthy, had one plant that has suddenly developed blight symptoms - yellowing and browning of lower leaves. This called for closer investigation. Is it just blight (a fungal infection), calling for removal of infected leaves, and treating with baking soda and milk, or is it something more insidious?

Last year in January, while weeding a lettuce patch, I glanced over at my potato patch and noticed a blight lesion on a single leaf. Upon further investigation, I discovered the beginnings of what was to be a dreadful infestation of Tomato-Potato Psyllid (TPP) which, despite spraying and other measures, rapidly spread throughout the spud crop, as well as devastating my several beds of tomato plants. This year, both hoping that it might be different, and expecting it wouldn't be, I have chosen to use micro-mesh crop covers on my potatoes, but also planted one bed of tomatoes, partly to see what would happen. Today I spotted the first signs of TPP infestation and infection. I took a few photos to share, so you will know what to look out for.

First, what is TPP? The adult is a 2-3mm long flying insect which was accidentally introduced to NZ in 2005 or 2006, probably by plant smugglers. It has since spread rapidly through out the country, destroying crops. It is easily wind-borne and overwinters on such plants as convolvulus, tamarillos and nightshade. The bugs don't stay still and can be very hard to spot - they become airborne as soon as you disturb the plant. They look much like a teeny cicada, with a white stripe on their backs.

A closer look showed the purpling of leaf veins, a classic sign that TPP have injected the plant with Liberibacter, a bacterium-like illness. In potatoes, it causes "psyllid yellows" - a yellowing of the leaves, eventual collapse of the plant, zebra-chipping of tubers, and often only marble-sized tubers if the infection happens early in the growth cycle. In tomatoes, you may see yellowing or purpling of the leaves, a tendency to have very small tomatoes which don't taste very nice, plant collapse, and in the case of both crops, a big increase in susceptibility to blight, aphids and anything else that can do wrong! Sick plants are weak plants - they cannot fight back.

The leaves shown above had no insects on them, so I kept searching the underside of leaves all over the plant. I found this leaf with some psyllid larvae/nymphs on it - circled in red. The two lower ones are slightly older - more yellow and larger. The top two are younger nymphs, still a translucent green in colour. There were also some eggs on the leaf margin - tiny yellow dots on thin stalk-threads, but far too small for my camera to show.

Tiny, huh? Easy to see why they're easily overlooked and many gardeners don't even realize this is why their plants aren't doing well. Here's another leaf I found which clearly shows several things - curling of the leaf margin, some larger nymphs (yellowish) and lots of opaque "psyllid sugars" - the excreta of the larvae.

The next two photos are from fellow gardener Amber Foster, who discovered she, too has psyllid this week, in her Auckland garden. In the first photo of the underside of a set of leaves, note the eggs on little stems around the leaf margin. You can also clearly see the psyllid nymphs on the leaf, and a couple of young adults are visible too, though a little out of focus.

And this one is what you're most likely to spot when you start looking under leaves - pale green, young psyllid nymphs.

Now you know what to look for, what are the treatment options? Well, there's not a lot of good new there, I'm afraid. Few, if any, sprays are effective against TPP, and even if they are, when the plant is already infected, eliminating the bugs won't change that, necessarily, though the potato industry claims plants can recover in three weeks if all pests are eliminated very early on. Mavrik (by Yates) is one non-organic spray for the home gardener that is supposed to work on TPP. Last year I used a combo of neem oil and pymethrum - it knocked the population right back each time I used it, but they soon reappeared. Koanga Institute sells a product to use against TPP which also includes diatomaceous earth. DE is a useful, natural product, but also harmful to beneficial insects.

On the positive side, by late in the season last year, my tomatoes were covered in ladybirds of several species and their larvae, along with lacewing larvae, all of which were munching on the TPP larvae. Too little, too late last year, but I do have some hope of being able to build the beneficial population enough to be a greater anti-TPP force earlier in the season, one day. Here's a pic of a lace-wing larvae ("aphid-lion") from my plant last year, with a psyllid in it's jaws.

In this next photo, again from my garden last summer, you can see one of the ladybirds, along with a ladybug larvae. The red arrow is pointing to a psyllid nymph.

By far the best option is physical barriers that prevent the psyllid getting to the plant in the first place. Lincoln University's Biological Husbandry Unit have been conducting trials with Wondermesh here, and sell it in various quantities. I'm using it over my potatoes this year - and so far, so good.

I have a feeling I may need to build a walk-in, mesh covered tomato cage to grow them in the future! As a bonus, or maybe just another good reason to use mesh, in clinical trials it was shown to substantially reduce or prevent blight on crops too!

FAQ's & Further Info

Since I posted this information on the NZ Vege Gardeners Facebook page I'm part of, there has been a number of questions and further discussion. I'll try to add the most pertinent parts here for further information.

What happened to your tomato plants last year? Did you still get tomatoes off them?

Once the tomato plants became infested with TPP in early January, deterioration was fairly rapid. At the time I first identified TPP, I had planted four beds with tomato plants. One bed had been in a while and had well developed plants of Silvery Fir Tree, Moneymaker and Cocktail, all covered in good sized but still green fruits. Two of the other beds were planted with Roma for bottling, and the fourth was half in Tiny Tims plus one each of Sweet 100 Russian Red, and the other half of the bed planted with Silverbeet/Rainbow Chard. The Tiny Tims, Sweet 100 and Russian Red all had fruits on them, but the Roma were just starting to flower.

Within a very short time of identifying TPP, all the plants got blight. In the case of one Roma bed, it was literally overnight - one day the plants were looking good, and the next they looked awful! I pulled that entire bed out right away.

Meanwhile, I wanted to persevere with the bed of Moneymakers etc, hoping to at least have the existing fruit ripen and be able to be used, and decided to keep on with the other two beds of tomatoes too. I sprayed them all with a combination of neem and pyrethrum weekly as recommended, removed blight affected leaves, and also sprayed with a milk solution for the blight. Really, it seemed to make little difference. In the end, I did get fruit off the Tiny Tim and Moneymaker bed plants, and a few from the Roma bed, but none of them tasted the same, and in hindsight it was mostly a waste of time and effort. Here are some photos - taken on 7th January, 12th February and 27th March 2014, of the bed with the Moneymakers, Cocktail and Silvery Fir Tree plants (you can see the young Romas in the bed behind in the Jan pic, looking good). You can see how the plants collapsed - in Jan they were healthy (pic taken the day before I identified TPP in my potato bed), by Feb, the Silvery Firs have collapsed and died, and the only healthy-ish green leaves remaining on most of the other plants were close to the top of the plant. By March they were pretty much in full collapse, held up only by the stakes so I could take off the remaining fruit.

Are there any varieties that are resistant to TPP?

Not yet! Selecting and breeding for TPP-resistance is really in the hands of the home gardeners. Why would big corporations bother, when they can make lots of money selling sprays to kill the bugs? Some of us growing tomatoes in high-TPP areas are looking out for plants that resist, or at least hang in there longer than the others, and saving seed from them, and growing from those the following year, to see if we can develop resistant strains. I had one Moneymaker plant that stayed strong for a bit longer than the others, and a Russian Red didn't do too badly. Even more interesting, I had one self-sown Tigerella come up in a dis-used chicken run, from tomatoes fed to the chickens the previous year. That plant got no attention from me, and didn't get either TPP or blight. I've saved seeds from it! Time will tell.....

What else can we do?

Do everything you can to encourage beneficial insects in your garden, as they may be the best means of controlling TPP - plant lots of flowers, allow some of your vegetables to flower and go to seed (bonus, you can save seeds for yourself!), provide a shallow dish of drinking water or a small pond, and have a corner of your garden which is allowed to be fairly "wild" - lots of vegetation and minimal interference from you; these kinds of areas harbour over-wintering ladybugs for example. Learn about the species that show up in your garden, and how to encourage them. Avoid using sprays (including natural ones) that are harmful to beneficials.

Consider ways to avoid the peak of the TPP season (warm summer months) by growing early crops if possible. However, that may not work in more southern areas, especially in less friendly spring seasons. I'm 2 hours north of Wellington - this season I sowed seeds of Sub Arctic Plenty, supposedly the world's earliest tomato at 50 days to fruiting, in the first week of August in the greenhouse, and as I write this in early January, the plants have fruits, but only the very first one has ripened on any of the plants.

Consider investing in micromesh to cover your crops - which in the case of tomatoes may take some modification of the way you usually stake or cage them.

Alternatively, grow your nightshade plants in a greenhouse where the temp reaches at least 35-37C for 2-3 hours most days - this will destroy psyllid eggs and prevent the crops from becoming infested. (See below update on infested plants this year)

The mesh seems really expensive - is it worth it?

Two years ago, it was very difficult for the NZ home gardener to get the micromesh at all, and what was available was about $17 per metre. Now that Lincoln's BHU is importing and selling it, prices are down quite a bit - it cost me $186 for 20 metres including courier (price will vary a bit by meterage ordered and where you are located) - which works out at $9.30/m all up for me. The fabric is 3.6m wide, so gives good coverage. Yes, still an investment, but on the plus side it will last 10 years, has shown evidence of keeping out blight as well as TPP, and will keep out most other flying pests too, so can also be used on other crops such as brassicas and carrots when not in use on your toms and spuds.

I live in a high-wind area. Will the mesh survive?

So do I! Winds of 120--150kmh for months of the year are common here. This is my first year using the mesh, but despite my somewhat haphazard way of weighing down the sides around my spud barrels with miscellaneous pieces of wood, the mesh hasn't even lifted off at all, and has had no damage - and this spring was basically one big blow! The mesh looks flimsy in the photos - makes you think of something like fine net curtains. But it's not like that at all - it's more like a fine version of the mesh used in flyscreen doors - lighter and somewhat more flexible, but strong.

So what are you planning to do about the infested plants this year?

Since the plants in my garden are different varieties than what I grew last year (Sub Arctic Plenty, Box Car Willie, a grafted tomato, and Gardener's Delight) I've decided to remove the worst affected plant, remove infested leaves from other plants, and wait and see what happens. The Sub Arctic Plenty have fruit on them that should ripen fairly soon. The others I don't really mind either way. It's all an experiment! Meanwhile, I do still have my 25 plants in buckets in the greenhouse, which are currently ripening, so will get some toms this year (they now have blight, but no TPP so far). If any of those in the garden show resistance, I will, of course, save seed from them.

Update: While my garden was infested with TPP that season, including chilli plants and kumara right outside the greenhouse, my 25 tomato plants inside the greenhouse were untouched, DESPITE THE UNSCREENED DOORS AND WINDOWS BEING OPEN ALL SUMMER! It turns out that temps of 35-37C for 2-3 hours a day will severely knock back or even destroy psyllid eggs, and so they were never able to establish themselves on those plants since my greenhouse got at least that hot more days than not.

What's the plan for next year at this stage?

Next season I have decided to grow continuously sown Tiny Tims under mesh (they don't need pruning or staking, and produce well, only growing 30ish cm high), and also some Sub Arctic Plenty under mesh, using wooden X-frames to support them off the ground (I don't know the proper name, but can see the design in my mind's eye, from an old fashioned book I have somewhere....). At the same time, I will grow some of whatever seems the most resistant plants in the open, uncovered, to see what happens.

Meanwhile, of course, I will continue to encourage beneficial populations, reduced convolulus and nightshade weeds as much as possible, and look out for new ideas and information.

Update: I ended up growing tomatoes and potatoes deliberately only in the greenhouse in the 2015/2016 summer (because I knew the temps would protect them from TPP - see above). There were some self-sown specimens of each in the garden, however, that I left to grow to see what would happen. For some reason, though, we had NO TPP that season here, despite heavy infestation the previous 3 seasons! Other local gardeners noticed a great reduction in populations too, though most still did have the bugs, though later in the season than usual. Why? I don't really know - but I'm putting it down to a much colder and longer than usual spring, and not very warm summer. Which was not good news for those of us wanting to grow pumpkins and other long-growing warmth lovers, but from a TPP point of view, it was great! Or maybe we've all become more diligent about removing winter hosts such as nightshade and convolvulus weeds. Or something. Either way, it was good; will be interesting to see what happens in the summer of 2016/2017!