Herb News


Gardening Articles for week ending  9th December 2006
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Written by Wally Richards.


The question is; do you have a garden invasion happening each evening?
An email from a reader this week stated the following; ?The other evening just on dusk we were out in the garden and heard a low humming noise. My husband thought it was a helicopter or a light plane far in the distance, I thought it was a huge swarm of bees coming, but it turned out to be grass grub on the wing.?   Sounds a bit frightening but that is what maybe happening to many gardens around the country at this time.
       Last year one gardener contacted me and said his citrus trees were being defoliated, so one evening he went outside with a torch to see what was happening. He was amazed to find his citrus trees crawling in grass grub beetles to such an extent, that it was difficult to see the leaves.  Next morning there would not be one to be found only the chewed up leaves that were left.
The poor weather conditions this spring has meant that the beetles have been slow to emerge so likely great numbers of the pests are emerging at the same time when conditions permit.
      The females will lay about a 100 odd eggs each in a 2-3 week period in clusters 20 to 40 about 70 to 200mm deep in the soil. The grubs hatch out 16 to 21 days later and start eating the roots of grasses.
More often than not the female will lay her eggs back in the area that she emerged from unless she is attracted away by light at night. Hence the worst infestations will be localized or near areas that are lit at night. The grubs are not easy to control in the soil until they have reached the base of grass near the soil?s surface which is usually about May to July. By that time there maybe little roots left on the grass and as it is winter then, the grasses often don't show signs of damage until they start to try to grow in the spring. Without sufficient roots to sustain the grasses they tend to fail and brown off.
    Mistakenly gardeners often treat their lawns at that time to no avail as the grubs have returned to the lower depths to pupate. ( I have written extensive information about grass grub control in my recent book, ?Wally?s Down to Earth Gardening Guide.?)
I believe the best way to control the grass grub problem is at this time while they are in the adult beetle stage. Light attracts the beetles around dusk to early evening, just as light attracts moths.
Using this method one can setup a strong light in a window facing out onto a lawn area where the pests are known to be from past problems. Under the window, against the glass you set a trough like a wall papering trough. Fill the trough two thirds full of water and then pour some kerosene onto the water so that there is a film of kerosene over the water. Here is what happens; Mr and Mrs Grass Grub Beetle emerge and see this bright light, they cannot resist the primal urge to fly to the light, so at their fastest flying speed they race to the light. Not realising that a sheet of glass is in the way they bang into it knocking them senseless to fall into the trough below. The kerosene prevents them from crawling out of the water, so there they drown or are stuck till next day, when you can flush them down the toilet or feed them to the chooks. Another very astute gardener uses the same principal to control codlin moths that infest their apple trees. There are other ways this method can be applied where damage is further away from normal light sources, these are explained in my book.
     The beetles can do a lot of damage to the foliage of plants which they eat during the few weeks they are on the wing. Plants such as roses, beans and citrus are affected and you may notice the damaged foliage at this time of the year but no sign of any culprit during daylight hours.
You can reduce the damage by spraying the foliage of the plants with Neem Tree Oil which does not actually kill the beetles but does stop them from eating any more foliage. A spray every 7 days for the next 2-3 weeks would be ideal. You can stop spraying when your light trap stops providing you with a good catch each day.
      What happens to the beetles during the day? Well in most cases they pop back under ground into the holes where they emerged from in your lawn and that is one of the reasons you will see starlings and blackbirds ripping up your lawn to obtain a feed of these beetles.
Grass Grubs are a problem for many so do something about it and show them the light.


Silver leaves on your rhododendrons are the sign that the minute insect pest called thrips have been at work, rasping the skin off the leaves while feeding. The silvering is the scar tissue that is left and like a permanent scar will not become green again but overtime these damaged leaves will be replaced with new foliage. The trick is to stop the damage reoccurring and thus protecting the new foliage.
There are two ways this can be achieved the first is by spraying the foliage with Neem Tree Oil both under and over the leaves just prior to dusk.
      This can be very difficult of a larger rhododendron so the well known rhododendron grower ?Cross Hills? came up with a simple solution a few years back. This involved taking a strip of felt and soaking it in Neem Tree Oil and wrapping the felt around the trunk of the tree. Hold in place with a couple of drawing pins and then covered with food wrap to prevent weathering. The strip would be left on the tree for one month only. The oil will soak into the sap flow and thus be translocated through all the foliage. Thrips rasping on the foliage will then get a dose of Neem in their gut and stop eating, forever. The system has being trialled and used successfully by growers and gardeners.
Only one instance that I have heard off that caused a problem was when it was used on a vireya rhodo, the oiled pad caused a collar rot and the plant was lost. Likely the finer bark of this type means that the best way to treat would be with a spray not a felt pad.
     It is also important the pads not be left on longer than a month as damage can occur otherwise.
Now is the time to treat the rhododendrons with either method as the thrips are now starting to build up their numbers. One treatment per year should be all that is needed but if spraying you would be best to do a couple of sprays about a month apart.
If not treated the damage will be noticed next year when lots of leaves have turned silver.
I have had two gardeners contact me recently about tomatoes that they have purchased.
When cut open these tomatoes have seeds inside that have germinated, having roots and little leaves inside the parent tomato. A very odd occurrence and I can only guess that maybe the tomato has being in cool storage for a time, then when exposed to warmth, the seeds inside have sprouted.
A more sinister aspect could be that chemicals used by some in the tomato industry to ripen green picked tomatoes, are causing the condition. I would be very interested to hear the views of commercial growers.
    One of the gardeners who rang me has carefully removed the seedlings and is now growing them as plants to see how they turn out. I would advise if you come across this aspect, not to eat the sprouted seedlings, the rest of the tomato, presumably is ok.
     Talking about tomatoes you must be careful when removing the laterals not to allow disease to enter the wound.
A spray of Liquid Copper over the wound immediately on removing the side shoot or leaves, will help prevent the loss of a plant through disease.
     I have heard that blight is around in some areas which will also destroy both tomatoes and potato crops. For prevention spray the foliage once a month for two months with Perkfection and if the problem is really bad in your area spray the foliage 2 weekly with Liquid Copper and Raingard.

Problems ring me at 0800 466 464 (Palmerston North 3570606)
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