Thursday, December 30, 2010

Fluffy Bums and The Plague

Two pests feature prominently in my garden from December on; Passion vine hoppers and the potato psyllid, known in our garden as fluffy bums and the plague respectively. Passion vine hoppers have been around for a while, and kids everywhere call the juvenile stage 'fluffy bums' as their distinguishing feature is the little cottony looking tuft at the back. They use these to flick down and jump when disturbed, which makes them hard to control. The adult stage looks completely different, more like a miniature delta wing fighter jet and their launching power from a standing start is even more impressive than the fluffy bum stage. They infest a wide range of host plants including most vine crops, citrus, flax, ferns, hydrangea, taro, cannas, palms and cycads.

Both the juvenile and the adult stages of passion vine hoppers suck sap from their host plants and deposit lots of sticky honeydew which leads to sooty mould. Both the sap sucking and the sooty mould can have a seriously damaging effect on the plant and growth can drop off quite quickly. This pest only has one generation per year, overwintering as eggs on thin woody twigs. This can be seen as serration down each side of the twig with eggs laid in each of the serrations. At winter pruning time these twigs should be pruned off, collected up and burnt to reduce the population in the coming summer. With only one generation per year, the key to controlling passion vine hoppers is timing. Depending on the warmth of the season, the juveniles will emerge some time from late October to December. Keep an eye out for them and get an insecticide on while they are still in the juvenile stage, as the adults are much harder to kill. Three sprays about a week apart on any plants that harbour this pest, including around your garden boundary, will get the vast majority of them.

Although only recent arrivals to this country, the Potato psyllid is already a devastating pest for any members of the tomato family and kumara, causing major crop losses for commercial growers and gardeners alike. It is so devastating to these crops that I call it the plague! The adult psyllid looks like a cicada, but about 2mm long, has clear wings tucked against the body and is striped with alternating dark and light bands. The orange-yellow eggs are less than 1mm long, usually found on leaf margins on the end of small stalks. Although similar to lacewing eggs, they are much smaller. The yellowish nymphs look very similar to scale and are mostly found on the undersides of leaves. The nymphs excrete small grains that look like granulated sugar, which settles on lower leaves. This is one of the best ways of identifying that you have this pest. In humid conditions, the sugar leads to sooty mould on the leaves and fruit.

As the pest feeds on the plant juices, they create a virus-like condition known as “psyllid yellows,” which is a result of toxic saliva injected by the insect. This makes the top leaves get a yellow or purple/red tinge to the midribs and edges, the leaves curl upwards and gradually the whole top of the plant will develop these colours. The plants almost stop growing altogether when this happens, and any new leaves that emerge are small, narrow and upright. Once the attack has started, little or no further fruit is set and what is there may not size up. Tamarillos and some tomatoes are very sensitive to this pest and will gradually die after infection.

Potato production also drops off almost completely, and any tubers harvested are mushy and earthy tasting when cooked, and may show brown patches, like zebra stripes. The effect on capsicums is less severe, but still more than any other pest that can affect them. Eggplants are the most resistant, probably due to their hairy leaves, and tomato varieties with very hairy leaves are also more resistant.

Psyllids are a warm weather pest, and populations don’t build up till mid to late summer. A cold winter may decimate the local population, but eventually they will spread from greenhouses or from up north. This does give the possibility of timing crops to try and beat the pest. Growing tomatoes and capsicums to a decent size indoors until the weather is warm enough to plant out may give a reasonable crop before the pest becomes widespread. However you will need to make sure the plants remain psyllid free in the greenhouse.
Some natural control is achieved when there are good ladybird and lacewing populations in the garden, but as only 3 or 4 of these pests is needed on a plant to knock production on the head, total control is preferred. For this, only pesticides will do the job and even these have limited effect on this nasty little beastie. 

The key is frequent sprays, as soon as the pest is seen, to break the life cycle. Spot spray just kumara and members of the tomato family, remember that some weeds such as black nightshade can also harbour these pests. I try to get at least weekly sprays on if this pest is seen, but spraying every 4-5 days is definitely worthwhile until all the psyllids are gone. Make sure you drench the underside of the leaves in particular, as this is where most of the pests will be.

I use a combination of Neem oil and insecticidal soap at about 5ml per litre of each product. These are low toxicity organic sprays that are safe for most beneficial insects and safe for me to use. 
Most garden centres stock a couple of brands which have the active ingredient of potassium fatty acid; usually made from coconut oil. Household detergents (such as sunlight detergent ) can also be used at a rate of 2 to 4 teaspoons per litre of water to make a cheap and effective insecticidal soap.
Some plants are sensitive to soap sprays and may get burnt, Commercial insecticidal soaps are formulated to reduce this risk but it is not eliminated entirely. Always test soap sprays for problems on a small area a day or two before the rest of the garden is treated. If injury does occur, increase the dilution and lengthen the time between sprays.