Any Questions?   Pests and Diseases

Q. We have a strawberry tree (arbutus unedo) which we planted about 7 years ago. The tree has grown to about 18 feet, with abundant healthy foliage on the new growth. However, the leaves seem to rapidly develop black spots and die back, leaving only the most recent growth healthy and intact. Any regrowth that occurs along the stem also seems to rapidly suffer the same fate.

The supplier of the plant says that only the outermost layer of leaves will remain in a normal specimen, but I think that the tree is not entirely healthy, as indicated by the blackening of the leaves. Any ideas what we can do?

The tree is in a sunny position, on slightly acid, clay soils. The site is not waterlogged, as the tree is at the top of a bank, adjacent to a pond.

A. I'd agree with you. Strawberry trees are susceptible to "leaf spot" and it sounds quite clearly that some infectious agent is responsible for what is happening. I know of no case where plants lose leaves in the manner that you describe by any normal means of dropping mature leaves.

I'd guess that the cause is bacterial similar to what happens to roses with "black spot". The cure is not easy to administer and the disease is quite resilient. The bacteria are usually spread by water-borne rain-splash or insects. Not watering will help if this is a contributory cause.

Remove all affected leaves and spray with Bordeaux mixture, remove fallen diseased leaves from beneath the tree and dispose of by burning or other means, but NOT on the compost heap. You may need to repeat this treatment several times to eradiate the disease.

The other alternative is that the spots are fungal in origin, in this case the spots appear to be concentric circles, close inspection may show pin-prick sized fruiting bodies. The treatment is the same but spray with benomyl or a copper-based fungicide.

Feedback  - I didn't have enough Bordeaux mixture to treat the tree when I looked in the shed, so I used a modern systemic treatment that targets black spot. I used it at a fairly high concentrations & drenched the entire tree, including all the lower branches that had no leaves.. Within three or four days a large number of 'budlets' have formed, even in those areas which looked dead. So, I am going to repeat the treatment every two weeks, which is the maximum rate that they recommend, although I might reduce the concentration from now on.

I had almost given up hope, it looks like there may be a chance, yet ( our gardener was full of doom about the prognosis! ). Thanks for the help.... will keep you informed on progress.

Feedback 2 - I thought that I would give you an update on our Strawberry Tree. Evidently, it is an Andrachnoides, not Unedo, as I told you ( or so our gardener tells me ). Well, it was on the point of expiring, when I contacted you. You suggested spraying with Bordeaux mixture, but I didn't have enough - so I used Systhane from the Bio company. I have sprayed at quite a high concentration, every three weeks. The results have been really excellent. It seems to have stopped the fungus, are whatever, in its tracks & the tree is shooting new, undamaged, leaves throughout the branches. It really has been rescued 'in the nick of time'. Thanks to your help, and a bit of serendipity, it looks like it will be restored to full health...

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Q. I have an Acer palmatum. I found what I think to be scale mites on it.

I have taken them and their eggs off. the leaves are shrunken and wilting. can I do anything else to help it? its in a pot.

A. First of all, the chances are that you've missed some of the scale insects or their eggs (they're crafty little critters), so buy some Malathion or pirimiphos-methyl insecticide as any eggs will be hatching about now. I would also spray any adjacent plants too in case the infection is there too.

Secondly, you can help build up the health of the plant in general. Does it need re-potting? If it's not quite ready for this, but has been in the pot for some time, how about removing the top 2" or so of compost, taking care not to damage the roots and replacing this. I'd also give it a dose of slow acting fertilizer such as bonemeal and also a quick blast of a liquid fertilizer.

Q. I have recently moved to Thetford, and my lawn has been attacked by a white caterpillar looking bug which my neighbors say are "Chafer Beetle" larvae and that they eat the grass roots. Apparently, they like the light, sandy, Breckland soil. The only suggested remedy is to lift the grass in turves and remove the larvae from the soil and roots. I did this over an area of about 4 sq m and found hundreds of larvae. This, of course, effectively destroyed the affected area of grass.

A. What you've probably got are the larvae of Chafer beetles, usually either cockchafers or garden chafers. As you have discovered, they feed on grass roots.

Damaged turf will lift away as the roots have been eaten and no longer hold the turf in the ground. Small mammals such as birds, badgers and foxes can cause further damage as they lift turf looking for the grubs to feed on. The grubs are soft bodied, cream in color with tan or brown heads.

Control used to be with Carbaryl though this is now no longer an option as this is now a restricted chemical - prescription only, used for killing head lice!

Fortunately there is a now a  biological control available to eradicate these pests. This is pet, child and environmentally friendly in a way that any chemical solution cannot be.

Go for a co-coordinated approach and apply an spring or autumn lawn feed as well to help the grass recover. The beetles emerge in the late spring to early summer and this is when they lay their eggs for next years crop of larvae.

Don't expect a quick fix, particularly if they're endemic to the area. They may have built up in numbers for some reason over a period of time, you say you've just moved to the area - was the garden neglected? If you keep addressing the problem little and often (after the first onslaught!) then it should get under control.

Q. I have a problem with my japonica. I planted it last spring and was delighted with it's progress until it got about 3 foot high and then dusty mould spots appeared on the lower leaves and the infection worked its way up until there were no leaves left! I did try to treat it with Nimrod T but perhaps this wasn't the thing to use. Anyway I persevered and cut it back in autumn to about 6 inches and 'nurtured' it through the winter and lo and behold it survived and again was doing very well. Now it's got to about 3 foot high again and I've noticed the dusty mould spots are back!!!!

A. It sounds like "black spot" similar to the disease that roses can get. Despite appearances this is caused by a bacterium and not a fungus, (Nimrod T is a fungicide) you need to use a systemic chemical and spray with that. You also need to be very hygienic around infected plants, fallen leaves hold the spores and will re-infect by rain splash, so you need to clean up all debris and throw it in the bin (not on the compost heap).

Alternatively, it may be a fungal disease and the Nimrod T wasn't shaken up properly. It tends to settle out in the bottle with the active ingredients sinking to the bottom, give it a good shake before mixing it. I did the same thing myself with it once - I thought it was old and had gone off, but tried again, this time shaking it and lo and behold it worked.

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1/ spray with a systemic insecticide such as Murphy's "Tumblebug" to kill the aphids.

 

2/ Kill the ants nest if possible (more difficult) with ant traps.

Q. My greenhouse tomato crop is being attacked by beetles. They are 3 or 4 mm long, shiny black, with 4 yellow spots on their backs. Do you have any idea what they are, and is there any way to control them without making the fruit inedible?

A. They sound like ladybugs to me, and won't harm your tomatoes in any way. They come in a variety of background and spot colors and numbers other than the traditional 2 black spots on red. If your crop is being noticeably attacked then it will be by something that the ladybugs are feeding on, look for aphids or the like. It might just be that the ladybugs have got "stuck" in your greenhouse, by wind / weather conditions and need to be allowed to leave again. What symptoms of attack are your tomatoes showing?

Q addendum. I definitely don't think these are ladybugs (picture attached)  - would that they were! They are slimmer in shape - more the shape of a lily beetle, though a different color, and smaller. They don't jump, so I don't think they are flea beetles. I thought at first I had blossom-end rot, but it's actually holes in the fruit, some quite large, not always at the base of the fruit, and some of which contain the said beetles. Even some of the green fruits are showing evidence of attack. I have looked carefully and there is no sign of any aphid infestation at all. I would say that the adults have laid their eggs inside the fruit and the larvae have been eating the fruit from the inside, then are emerging as adults. I have searched the web over the weekend and can't find any pictures or any descriptions of garden pests which match this. Meanwhile, I have some soft soap which I'm going to use to try and kill the adults and hopefully break the breeding cycle and try and save the rest of my crop!

A. addendum.  According to my guide to the Insects of Europe, your beetles are probably Anthocomus fasciatus - no common name that I know of. It is not a well known pest of anything at all really. You originally mentioned blossom end rot, my guess is that you may have had this initially which is what helped the beetles to get established and then when they started to emerge from the damaged tomatoes in any numbers, there was more dinner sitting in front of them!

Q. How do I get rid of ants (red) and ant hills from my lawn

A. There's not really any quick and easy way to this apart from digging up the nest and removing the queen. Presumably this is not really an option in a lawn. The easiest way is probably to pour boiling water down into the nest, this has the effect of killing lots quickly but rarely gets to the heart of the nest first time, likewise ant powders and sprays have an impressive superficial effect rarely sorting the problem first time. Ant "traps" are effective but take time, they consist of a covered plastic dish about 10cm in diameter with a central reservoir that you fill with the supplied poison. The idea is that the ants enter and think its food and take it back to the nest to feed to the other ants - seems a bit sneaky to me. Any poisons should be laid when the ants are active so that it affects the maximum number of them.

One way to help reduce the amount of ants in the lawn is to mow at regular intervals, if the hills get regularly flattened than the ants often give up and move somewhere else or are unable to build a large colony. Although they can give you a very itchy bite, red ant bites in Britain are harmless and the ants themselves don't harm your plants unlike the black variety that frequently run aphid "farms" for the sticky honeydew that aphids produce.

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Q. My garden is infested with leatherjackets, which is the best way to deal with them at this time of year? (spring)

A. At this time of the year, the best way to deal with leatherjackets is to soak the grass with water (requires no effort if your weather's like ours!) and then lay sacking or black plastic weighted down onto the grass. This will bring them to the surface.

Either you go and pick them up and remove them, or do something like throw bits of bread high in the air to attract the birds who will come and do the job for you.

Q. How can I get rid of red mite in my greenhouse please?.

A. Red spider mite are an excellently adapted pest and therefore difficult to remove (!).

1/ Raise the humidity level if appropriate by spraying the plants with water, this slows them down.

2/ Before applying pesticides remove any visible webs, a feather duster is good for this, the webs protect them from fine droplets of spray.

3/ Spray with peremethrin, derris, dimethoate or Malathion, this may be necessary at 10-14 day intervals until they have been removed. Bear in mind though that there are a number of resistant strains of red spider mite.

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Q. We planted a mixed beech hedge, purple and green in Autumn 2000. This year we have noticed what appear to be blue aphids of a downy consistency on the undersides of the leaves and a sticky residue. They first appeared on four new saplings only planted in Autumn 2001 but have now spread to all the plants. What could this be? Are there blue aphids and if so how should this be treated? (Geneva France)

A. I'm not going to guess at what your insects are, aphids come in all kinds of colors, I've never seen blue ones, but I'm prepared to believe that they exist!

The cure is more straightforward, you need to buy some systemic insecticide and use some kind of sprayer to apply it. In the UK I'd recommend Murphy's Tumblebug, in France - who knows - but I'm sure there will be an equivalent. Systemic means that it is taken up by the leaves and then passed around the plant internally so the bugs then suck up the poison with the plant juices. If they're downy, this will usually make it more difficult for contact insecticides to have an effect, systemics don't have the same problem.

Q. Hello, and help I have an old hedgerow at the end of my garden it's been there gods knows how long, it has the usual plants that you find in hedgerows allover Ireland Hawthorn, Honey suckle, Elder. My Problem is the Elder tree is covered with small black flies the leaves are falling and the tree has developed a scruffy appearance what can I do to remedy this as I really love the hedge and so do the birds. Can you help.

A. It sounds like your elder has a bad attack of blackfly. Elder are susceptible to this but some years are worse than others. You could spray with a systemic insecticide though I would advise against a chemical spray as it is part of a hedgerow with associated wildlife.

You could spray an organic remedy on it based on natural soaps (should be available commercially down the garden centre) though I haven't found these of much use myself. I'd approach it in one of two ways:

1/ It's a part of natures cycle and may die or will survive and next year won't be as bad (or it will die then).

2/ Cut off the worst affected parts with insects attached and destroy them or remove down the tip, a sort of modified version of "1" above.

We expect our gardens to be full of healthy plants with no signs of nature. Blackfly and elder are as much a part of nature as are the birds that enjoy your hedgerow, they're both native species - depends on how you see your local ecosystem.

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