Gardening Articles for week ending 20th AUGUST 2016


About a month ago I wrote about spud time as it is a good time to buy the new seasons seed potatoes and start sprouting them for planting out.

The time for planting out is mostly governed by frosts and the damage they can do to a early crop.

Now days we face an even bigger danger and that is the potato psyllid, which is causing total loss of crops in many areas.

One key factor of prevention is a very early crop of fairly quick manuring potatoes which will suffer only minor damage in most gardens. Later in the season when the pest numbers increase,  there is a noticeable increase in damage and crop failure..

Potato crops planted say in November or December will need a lot of protection to produce good spuds for storage.

In the worst affected areas of New Zealand plantings in October will also need ample protection.

MAF New Zealand has  a web page on their web site and forwarded the same information to garden centres through out NZ.

Here is part of that information:
What does the tomato/potato psyllid look like?

The adult tomato/potato psyllid is about the size of an adult aphid but looks like a tiny cicada under magnification. The female lays yellow eggs that are attached by stalks to plant leaves, usually to the leaf edges. Psyllid nymphs hatch from these eggs and after five moults (instars)become adults.

The nymphs are flat scale-like insects which are mostly inactive but move when disturbed.

Nymphs and adults feed by sucking plant juices, which is how they are thought to spread a substance called  Liberibacter. (The toxin that does the damage)

Nymphs and adults secrete plant sap as white granules called ‘psyllid sugars’ which can be seen on the leaves.  In humid conditions and where there are large numbers of psyllids, black sooty mould fungi can grow on the sugars. Dense sooty mould on leaves may reduce photosynthesis, but this is rarely
a problem on outdoor plants as the psyllid sugars are usually removed by wind and rain.

How will the tomato/potato psyllid/Liberibacter affect my plants?

On tomato the symptoms of psyllid yellows are the yellowing and stunting of the growing tip and a cupping or curling of the leaves. Many flowers may fall off the trusses of infected plants and fruit may be small and mis-shaped.

On potato, psyllid yellows disease causes a stunting and yellowing of the growing tip, and the edges of the curled leaves often have a pink blush.

The stem may have swollen nodes and show a browning of the vascular tissue.

After a while, infected potatoes develop a scorched appearance and plants collapse prematurely. Potato plants that are infected at an early stage develop numerous small tubers.

The tomato/potato psyllid breeds mainly on plants in the Solanaceae (potato and tomato family), but can also attack some species of Convolvulaceae (kumara and bindweed family).

Other host plants of the tomato/potato psyllid include Apple of Peru, capsicum, chilli, egg plant, kumara, poroporo, tamarillo, pepino and thornapple.

Why is the tomato/potato psyllid a problem? Tomato/potato psyllid adults and nymphs cause damage to host plants through feeding on leaves and by transmitting a bacterial pathogen, Liberibacter, that lives in plants. The bacterium is believed to cause diseases such as ‘psyllid yellows’ in tomatoes and potatoes, and ‘zebra chip’ symptoms in potato tubers.

These diseases can drastically reduce the quality and yield of your crop. End

So the problem is greater than just protecting your tomatoes and potatoes as you are likely to have other plants and weeds growing that will also host the pests which means they can re-infest your crops which will require continued protection.

A number of gardeners will likely have convolvulus growing on their land or nearby and this common weed is also a host.

For potatoes as mentioned an early crop can in some area be grown and harvested before the psyllid's population get growing for the season.

Crops already in and well on the way will likely be ready to harvest about Labour Weekend.

One gardener found last year that the crop was very good when they lifted a few mature plants.

Unfortunately they left the rest of the crop in the ground with the tops on and found when they harvested again that the potatoes had the dark rings inside and as a result tasted horrible and had to be thrown out. A good warning for others if you leave the mature potatoes in the ground cut the tops off and cover the stubble.

Last week we wrote about the Silicon Cell Strengthening kit which you can use to make it difficult for the psyllids to feed and thus safely reduce damage. (Copy is on the site)

With later plantings of potatoes besides using Wallys Neem Tree Granules and Super Neem Tree Oilthere is quarantine cloth that can be put over hoops above the foliage to prevent the psyllids from getting on the potato crop.

The winged adult psyllid has been reported to be able to fly for 1524 miles so re-infestation from other gardens nearby will be a ongoing problem.

The female laying 510 eggs in a 21 day period is another reason for good controls.

The yellow sticky cards available to home gardeners should be employed near the tops of growing plants and in doorways and ventilation entrances of glasshouses.

The cards catch adults flying into a crop and that also helps to keep population levels low.

It has been found with tomatoes that if an effected plant is cleared of he pest then new fruits will be normal. This is a little late for potatoes that have formed when plant is infected.

The psyllid is a very big problem for the home gardener.

Problems ring me at 0800 466464 (Palmerston North 3570606)
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Replies to This Discussion

Thank you Wally. So good to be forewarned.


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